Ebola: The Evolving Catastrophe

The Reston virus differs markedly from the others because it is maintained in an animal reservoir in the Philippines and has not been found in Africa. Serologic studies have shown that a small percentage of Philippine pig farmers have IgG antibodies against the agent without ever developing severe symptoms, providing additional evidence that the Ebola Reston virus is able to cause mild or asymptomatic infection in humans.

This is the most recent species to be named and was isolated from Angolan free-tailed bats in Sierra Leone (STAT, 2018). Bombali ebolavirus has the capacity to infect human cells, although it had not yet been shown to be pathogenic.

The natural reservoir for Ebola has yet to be confirmed; however, bats are considered to be the most likely candidate species. Three types of fruit bats (Hypsignathus monstrous, Epomops franqueti, and Myonycteris torquata) were found to possibly carry the virus without getting sick. As of 2013, whether other animals are involved in its spread is not known. Plants, arthropods, rodents, and birds have also been considered possible viral reservoirs (WHO, 2018).

Person-to-person transmission is associated with direct contact with the body fluids of individuals who are ill with EVD or have died from the infection in the absence of personal protective equipment (PPE). Those who provide hands-on medical care or prepare a cadaver for burial are at greatest risk. Examples:

• In a meta-analysis of Ebola virus transmission among household contacts that included nine studies, the secondary attack rates for those providing nursing care was 47.9%, compared with 2.1% for those household members who had direct physical contact but did not provide nursing care (Dean et al., 2016).
• The ritual washing of Ebola victims at funerals has played a significant role in the spread of infection in past outbreaks and contributed to the epidemic in West Africa. As an example, a single funeral ceremony in late 2014 in Guinea was linked to 85 subsequent cases of EVD (Victory et al., 2015).

The likelihood of infection depends, in part, upon the type of body fluid to which an individual is exposed and the amount of virus it contains. Transmission is most likely to occur through direct contact of broken skin or unprotected mucous membranes with virus-containing body fluids from a person who has developed signs and symptoms of illness (CDC, nd b).

Acute infection

According to the World Health Organization (WHO), the most infectious body fluids are blood, feces, and vomitus. Infectious virus has also been detected in urine, semen, saliva, aqueous humor, vaginal fluid, and breast milk (Varkey et al., 2015). Reverse-transcription polymerase chain reaction (RT-PCR) testing has also identified viral RNA in tears and sweat, suggesting that infectious virus may be present.

Ebola virus can also be spread through direct contact with the skin of a patient, but the risk of developing infection from this type of exposure is thought to be lower than from exposure to blood or body fluids (CDC, nd b). Virus present on the skin surface might result either from viral replication in dermal and epidermal structures, contamination with blood or other body fluids, or both.

The risk of Ebola transmission also depends upon the quantity of virus in the fluid. During the early phase of illness, the amount of virus in the blood may be quite low, but levels then increase rapidly and may exceed 108 RNA copies/mL of serum in severely ill and moribund patients (CDC, nd b). Epidemiologic studies have found that family members were at greatest risk of infection if they had physical contact with sick relatives (or their body fluids) during the later stages of illness or helped to prepare a corpse for burial (Glynn et al., 2018).

Convalescent period

Infectious virus or viral RNA can persist in some body fluids of patients recovering from EVD even after it is no longer detected in blood. For example:

• Follow-up studies of approximately 40 survivors in the 1995 outbreak in Kikwit, Democratic Republic of the Congo found that viral RNA sequences could be detected by RT-PCR in the semen of male patients for up to three months, and infectious virus was recovered from the semen of one individual 82 days after disease onset.
• A study of patient samples collected during the outbreak of Ebola Sudan virus disease in Gulu, Uganda in 2000 detected the virus in the breast milk of a patient even after the virus was no longer detectable in the bloodstream. Two children who were breastfed by infected mothers died of the disease.
• During the 2014 - 2016 outbreak in West Africa, infectious virus or viral RNA has been detected from several sites. These include:
  • Urine
  • Ebola virus was cultured from a patient’s urine 26 days after the onset of symptoms, which was 9 days after the plasma RNA level became negative
  • Semen
• In a sample of 93 men who were discharged from an Ebola treatment center, the virus was detected in semen up to nine months after discharge (Deen et al., 2015). However, the percentage of patients with persistent virus and the level of virus detected in semen decreased over time. In a patient treated in the United States, the concentration of viral RNA in semen during early recovery was 4 logs higher than in blood during peak infection (Barnes et al., 2017). A modeling study from the 2014 - 2016 outbreak suggests the median time to semen RT-PCR negativity is 47 days after symptom onset, and the probability of shedding at 18 months is <1% (Subtil et al., 2017).
• Although transmission from persistent virus at these sites is possible, the risk of transmission is not well established (CDC, nd c). As an example, a patient in West Africa who had viral RNA in his semen at least 199 days after symptom onset transmitted the Ebola virus to one, but not another, of his sexual contacts (Christie et al., 2015). The transmission occurred approximately five months after his blood tested negative for the Ebola virus.

Aqueous humor

Ebola virus RNA was detected, and the infectious virus was isolated from the aqueous humor of a patient with uveitis 14 weeks after the onset of Ebola symptoms and 9 weeks after viremia had resolved (Varkey et al., 2015).

Cerebrospinal fluid

A patient who had recovered from EVD developed meningitis approximately 10 months after her initial diagnosis, and an infectious virus was recovered from the cerebrospinal fluid (CDC, nd e).

Ebola virus may be transmitted through contact with contaminated surfaces and objects. The US Centers for Disease Control and Prevention (CDC) indicates that virus on surfaces may remain infectious from hours to days (CDC, nd e). There are no high-quality data to confirm transmission through exposure to contaminated surfaces, but it is clear that the potential risk can be greatly reduced or eliminated by proper environmental cleaning (WHO, 2014).

There are no reported cases of Ebola virus being spread from person to person by the respiratory route (Dickerson et al., 20108). However, laboratory experiments have shown that Ebola virus released as a small-particle aerosol is infectious for rodents and nonhuman primates (Mattia et al., 2016). Healthcare workers may therefore be at risk of EVD if exposed to aerosols generated during medical procedures.

Transmission to healthcare workers may occur when appropriate PPE is not available or is not properly used, especially when caring for a severely ill patient who is not recognized as having EVD.

During the epidemic in West Africa, a large number of doctors and nurses became infected with Ebola virus. In Sierra Leone, the incidence of confirmed cases over a seven-month period was approximately 100-fold higher in healthcare workers than in the general population. Several factors accounted for these infections, including:

• Delayed laboratory diagnosis
• Inadequate training about safe management of contaminated waste and burial of corpses
• Incorrect triage and/or failure to recognize patients and corpses with EVD
• Limited availability of appropriate PPE and hand washing facilities

Medical procedures played a major role in some past Ebola epidemics by amplifying the spread of infection. For example:

• An iatrogenic point-source outbreak occurred in 1976 when an individual infected with Ebola virus was among the patients treated in a small missionary hospital in Yambuku, Zaire. At this hospital, the medical staff routinely injected all febrile patients with antimalarial medications, employing syringes that were rinsed in the same pan of water, then reused. Virus from the index case was transmitted simultaneously to nearly 100 people, all of whom developed EVD and died (Breman et al., 1978). Infection then spread to family caregivers, hospital staff, and those who prepared bodies for burial.
• A different type of iatrogenic amplification occurred in 1995 in Kikwit, Democratic Republic of the Congo, when a patient was hospitalized with abdominal pain and underwent exploratory laparotomy. The entire surgical team became infected, probably through unprotected respiratory exposure to aerosolized blood. Once those persons were hospitalized, the disease spread to hospital staff, patients, and family members through direct physical contact.

Despite these dramatic episodes of nosocomial transmission, other hospital-based experiences have demonstrated a much lower incidence of secondary spread. For example:

• A patient with unrecognized EVD was treated in a South African hospital in 1998. Only one person became infected among 300 potentially exposed healthcare workers (Chertow et al., 2014).
• A similar observation was made when a patient with an unrecognized infection with Marburgvirus, a closely related filovirus, was treated in a South African hospital in 1975, resulting in the spread of infection to only two people with close physical contact.

Assistance from the international medical community has played an important role in controlling large epidemics in Africa. In the past, intervention strategies focused largely on helping local healthcare workers to identify Ebola patients, transfer them to isolation facilities, provide basic supportive care, monitor all persons who had been in direct contact with cases, and rigorously enforce infection control practices. During the West African epidemic, the massive international response made it possible to supplement isolation procedures with more effective supportive care.

• Contact with infected animals
  • Human infection with Ebola virus can occur through contact with wild animals (e.g., hunting, butchering, and preparing meat from infected animals) (CDC, nd f). In Mayibou, Gabon in 1996, for example, a dead chimpanzee found in the forest was butchered and eaten by 19 people, all of whom became severely ill over a short interval. Since that time, several similar episodes have resulted from human contact with infected gorillas or chimpanzees through hunting. To help prevent infection, food products should be properly cooked since the Ebola virus is inactivated through cooking. In addition, basic hygiene measures (e.g., hand washing and changing clothes and boots after touching the animals) should be followed. Some public health messages in West Africa regarding the consumption of "bush meat" have contained incorrect information and may have been counterproductive (Bonwitt et al., 2018).
• Exposure to bats
  • Direct transmission of Ebola virus infection from bats to wild primates or humans has not been proven. However, Ebola RNA sequences and antibodies to Ebola virus have been detected in bats captured in Central Africa. Bats have been identified as a direct source of human infection with Marburg virus.

Other potential routes of transmission include the following:

• Accidental infection of workers in any Biosafety-Level-4 (BSL-4) facility where filoviruses are being studied.
• Use of filoviruses as biological weapons.

To date, there is no evidence that Ebola virus can be transferred from person to person by mosquitoes or other biting arthropods. Past epidemics of EVD in Central Africa would certainly have been larger and more difficult to control if the virus were transmitted by these mechanisms.

After entering the body through mucous membranes, breaks in the skin, or parenterally, Ebola virus infects many different cell types. Macrophages and dendritic cells are probably the first to be infected. Filoviruses replicate readily within these ubiquitous "sentinel" cells, causing their necrosis and releasing large numbers of new viral particles into extracellular fluid.

Rapid systemic spread is aided by virus-induced suppression of type I interferon responses (Basler, 2017). Dissemination to regional lymph nodes results in further rounds of replication, followed by spread through the bloodstream to dendritic cells and fixed and mobile macrophages in the liver, spleen, thymus, and other lymphoid tissues. Necropsies of infected animals have shown that many cell types may be infected, including endothelial cells, fibroblasts, hepatocytes, adrenal cortical cells, and epithelial cells. Lymphocytes and neurons are the only major cell types that remain uninfected. Fatal disease is characterized by multifocal necrosis in tissues such as the liver and spleen.

Patients with EVD commonly suffer from vomiting and diarrhea, which can result in acute volume depletion, hypotension, and shock. It is not clear if such dysfunction in EVD is the result of viral infection of the gastrointestinal tract, or if it is induced by circulating cytokines, or both.

In addition to causing extensive tissue damage, Ebola virus also produces a systemic inflammatory syndrome by causing the release of cytokines, chemokines, and other proinflammatory mediators from macrophages and other cells.

Infected macrophages produce tumor necrosis factor (TNF)-alpha, interleukin (IL)-1beta, IL-6, macrophage chemotactic protein (MCP)-1, and nitric oxide (NO). These and other substances have also been identified in blood samples from Ebola-infected macaques and from acutely ill patients in Africa. Breakdown products of necrotic cells also stimulate the release of the same mediators.

This systemic inflammatory response may play a role in inducing gastrointestinal dysfunction, as well as, the diffuse vascular leak and multiorgan failure that are seen later in the disease course.

The coagulation defects seen in EVD appear to be induced indirectly, through the host inflammatory response. Virus-infected macrophages synthesize cell-surface tissue factor (TF), triggering the extrinsic coagulation pathway. Proinflammatory cytokines also induce macrophages to produce TF. The simultaneous occurrence of these two stimuli helps to explain the rapid development and severity of the coagulopathy in Ebola virus infection.

Additional factors may also play a role in the coagulation defects that are seen with EVD. For example, blood samples from Ebola-infected monkeys contain D-dimers within 24 hours after virus challenge, and D-dimers are also present in the plasma of humans with EVD. In Ebola virus-infected macaques, activated protein C is decreased on day two, but the platelet count does not begin to fall until days three or four after virus challenge, suggesting that activated platelets are adhering to endothelial cells. As the disease progresses, hepatic injury may also cause a decline in plasma levels of certain coagulation factors.

Failure of adaptive immunity through impaired dendritic cell function and lymphocyte apoptosis helps to explain how filoviruses are able to cause a severe, frequently fatal illness. Ebola virus acts both directly and indirectly to disable antigen-specific immune responses. Dendritic cells, which have primary responsibility for the initiation of adaptive immune responses, are a major site of filoviral replication. In vitro studies have shown that infected cells fail to undergo maturation and are unable to present antigens to naive lymphocytes, potentially explaining why patients dying from EVD may not develop antibodies to the virus.

Adaptive immunity is also impaired by the loss of lymphocytes that accompanies lethal Ebola virus infection. Although these cells appear to remain uninfected, they undergo "bystander" apoptosis, presumably induced by inflammatory mediators and/or the loss of support signals from dendritic cells. A similar phenomenon is observed in septic shock. However, one study has shown that, at least in Ebola-infected mice, virus-specific lymphocyte proliferation still occurs despite the surrounding massive apoptosis, but it arrives too late to prevent a fatal outcome. Discovering ways to accelerate and strengthen such responses may prove to be a fruitful area of research.

Patients with EVD typically have an abrupt onset of symptoms 6 to 12 days after exposure (range 2 to 21 days) (Deen et al., 2015). There is no evidence that infected persons who have not yet developed signs of illness are infectious to others. However, all symptomatic individuals should be assumed to have the virus in the blood and other body fluids, and appropriate safety precautions should be taken.

Initial syndrome

• Most cases of EVD begin with the abrupt onset of fever and chills, but low-grade fever and malaise may also precede the development of more severe symptoms (Uyeki et al., 2016).
• Common signs and symptoms reported from the West African outbreak include:
  • Diarrhea
  • Fatigue
  • Fever
  • Headache
  • Loss of appetite
  • Vomiting
  • Reports have also described:
    • Weakness
    • Myalgias
    • A high fever accompanied by relative bradycardia as seen in typhoid fever

Rash

• A diffuse erythematous, nonpruritic maculopapular rash may develop by day 5 to 7 of illness.
• The rash usually involves the face, neck, trunk, and arms, and can desquamate.
• It is generally easier to see in light-skinned persons.
• During the outbreak in Sierra Leone, rash was reported as rare. It was, however, clearly described in case reports of infected health care workers.

Gastrointestinal

• Gastrointestinal signs and symptoms are common and usually develop within the first few days of illness. These include:
  • Abdominal pain
  • Nausea
  • Vomiting
  • Watery diarrhea (up to 10 liters per day)
• During the 2014 - 2016 West African outbreak, vomiting and diarrhea resulted in severe fluid loss, potentially leading to dehydration, hypotension, and shock.

Hemorrhage

• Case series from the West African epidemic indicate that many patients develop some degree of bleeding during their illness, most commonly manifested as:
  • Blood in the stool (about 6%)
  • Ecchymoses
  • Mucosal bleeding
  • Oozing from venipuncture sites
  • Petechiae
• Clinically significant hemorrhage may be seen in the terminal phase of illness and in pregnancy.

Neurologic

• Patients occasionally develop meningoencephalitis, with findings such as:
  • Altered level of consciousness
  • Gait instability
  • Hyperreflexia
  • Myopathy
  • Seizures
  • Stiff neck
• These clinical manifestations typically develop around days 8 to 10 of illness.

Cardiac

• Pulse-temperature dissociation with relative bradycardia may be observed during acute illness.
• In addition, retrosternal chest pain attributed to pericarditis has been reported.
• Myocarditis has also been described.

Respiratory

• Tachypnea and shortness of breath may represent hypoxia or hypoventilation due to respiratory muscle fatigue, contributing to impending respiratory failure. This phenomenon was observed in nearly one-third of patients treated in Europe and the United States in the setting of intravenous fluid resuscitation.

Ocular

• Patients may develop conjunctival injection and/or signs and symptoms of uveitis (e.g., blurred vision, photophobia, blindness) during the acute phase of illness.
• In addition, uveitis has been documented during convalescence.

Patients with EVD typically develop leukopenia, thrombocytopenia, and serum transaminase elevations, as well as, renal and coagulation abnormalities. Other laboratory findings include a marked decrease in serum albumin, hypoglycemia, and elevated amylase levels (see Table 1 above).

Leukopenia

• Leukopenia usually presents as lymphopenia, followed by an elevated neutrophil count (Mulangu et al., 2018). Immature granulocytes and abnormal lymphocytes, including plasmacytoid cells and immunoblasts, may be seen in blood smears.

Thrombocytopenia

• Platelet counts decrease during the acute phase of illness, but generally do not fall below 50,000 to 100,000/microL (CDC, nd g). Platelet counts typically reach a nadir around day 6 to 8 of illness.

Abnormal hematocrit

• Patients with EVD may present with an increased or decreased hematocrit. As an example, in one cohort study that evaluated 100 patients, 15 had an increased hematocrit upon presentation and 36 were anemic.

Transaminase elevations

• Because Ebola virus can cause multifocal hepatic necrosis, blood chemistry tests usually demonstrate elevated serum aspartate aminotransferase (AST) and alanine aminotransferase (ALT) levels.

Coagulation abnormalities

• Prothrombin (PT) and partial thromboplastin times (PTT) can be prolonged and fibrin degradation products elevated, consistent with disseminated intravascular coagulation (DIC). These changes are most prominent in severe and fatal cases.

Renal abnormalities

• Proteinuria is a common finding, and renal insufficiency with elevated BUN and creatinine can be seen in both the early and late stages of disease.
• Acute kidney injury is exacerbated by excessive fluid loss from diarrhea and vomiting without adequate volume replacement, but may also develop as a result of direct viral-mediated tissue injury in the absence of severe volume loss.

Electrolyte abnormalities

• Patients may develop significant electrolyte disturbances (e.g., hyponatremia, hypokalemia, hyperkalemia, hypomagnesemia, and hypocalcemia) secondary to the gastrointestinal manifestations of the disease. Such individuals may require frequent repletion of electrolytes to prevent cardiac arrhythmias.

Patients who survive EVD typically begin to improve during the second week of illness (CDC, nd g). Fatal disease has been characterized by more severe clinical signs and symptoms early during infection, with progression to multiorgan failure with death typically occurring in the second week.

Some patients develop secondary complications related to their disease and/or the treatments they receive (Wolf et al., 2015). These include bacterial sepsis, respiratory failure associated with aggressive fluid resuscitation, and/or lung and kidney injury.

The convalescent period of EVD is prolonged and can persist for more than two years. Patients may suffer from weakness, fatigue, insomnia, headache, and failure to regain weight that was lost during illness, resulting in significant disability. Other clinical manifestations include:

• Acute arthralgias, which may result from the formation of antigen-antibody complexes during recovery.
• Extensive sloughing of skin and hair loss, which may result from virus-induced necrosis of infected sweat glands and other dermal structures.
• Retro-orbital pain, uveitis, and hearing loss (Jagadesh et al., 2018).

Symptoms can be severe, and in one report of Ebola survivors after the outbreak in Uganda, many patients were unable to resume their previous work activities (Mattia et al., 2016). It has been postulated that a higher Ebola viral load at the time of clinical presentation is associated with the development of symptoms during convalescence, but this awaits confirmation (Mattia et al., 2016).

Some patients develop clinical manifestations soon after recovery from their initial infection. In a study of 277 Ebola survivors from the West African epidemic who were evaluated after discharge from a treatment center. 76% had arthralgias, 60% had new ocular symptoms (e.g., blurry vision, light sensitivity, itchy eye), 24% had auditory symptoms (e.g., tinnitus, hearing loss), and 18% had uveitis (Mattia et al., 2016). The median time from discharge to onset of clinical manifestations was one to two weeks.

However, others appear to develop late complications of EVD, with manifestations developing months after they have recovered from their initial illness. For example:

• In one patient, uveitis developed 14 weeks after EVD was initially diagnosed, and the aqueous fluid contained infectious virus (Varkey et al., 2015).
• Another patient who had recovered from EVD developed meningitis 10 months after her initial diagnosis, and infectious virus was recovered in the cerebrospinal fluid (Mattia et al., 2016).

Although viral RNA and infectious virus may persist in certain bodily fluids after infection, the importance of persistent virus as it relates to the clinical manifestations during convalescence is unclear (CDC, nd c).

During the outbreak in West Africa, reports suggested that an atypical presentation of EVD may be observed in pregnant women and fetal death may occur even if the mother has recovered. For example:

• In Liberia, a pregnant woman presented in late pregnancy with mild lower abdominal and back pain, sparse contractions, and premature rupture of membranes, without fever or other signs or symptoms of EVD (Akerlund et al., 2015). Blood testing for Ebola virus was performed as part of routine care and returned positive with a high viral load. A vaginal swab tested on day 2 was also positive for Ebola virus. The mother died undelivered from complications related to EVD seven days after admission.

Consequently, pregnant women should be evaluated for Ebola if they have a possible exposure to Ebola virus and present with nonspecific signs and symptoms of EVD (e.g., abdominal pain) and/or pregnancy complications, such as preterm labor, vaginal bleeding, or premature rupture of membranes.

Symptomatic patients

• Even though there are no approved specific therapies for EVD, it is essential to make the diagnosis as early as possible so that infection control procedures can be implemented to reduce the transmission of the virus, and so supportive measures can be initiated before the development of irreversible shock.
• Patients who present with signs and symptoms consistent with EVD (fever and/or severe headache, weakness, muscle pain, vomiting, diarrhea, abdominal pain, or unexplained hemorrhage) should be assessed to determine the likelihood of recent exposure to Ebola virus (Table 2). In particular, they should be asked if they traveled to an area with a recognized Ebola epidemic or had contact with a patient with possible EVD disease within the 21 days prior to the onset of symptoms (CDC, nd g).

A confirmed case of EVD requires laboratory-confirmed diagnostic evidence of Ebola virus infection.

Infection control precautions should be used for all symptomatic patients who may have been exposed to Ebola virus (i.e., those who have had a high, moderate, or low-risk exposure). Infection control precautions should also be used for patients whose risk of exposure is unclear at the time of their initial presentation until a medical evaluation can be performed.

Persons under investigation for EVD should undergo testing for Ebola virus by reverse-transcription polymerase chain reaction (RT-PCR) facilitated by local and state health officials.

Persons under investigation for EVD should also be evaluated for other possible febrile diseases, including those that are common in areas where the patient traveled or resided (e.g., malaria, typhoid, influenza).

The specific triage system used during the initial assessment of a patient with possible EVD may vary depending on the setting (e.g., emergency department, ambulatory clinic) and the known history of transmission in the community (CDC, nd j).

For example, medical facilities, especially those in areas with widespread Ebola transmission, should designate areas for screening patients (CDC, nd k).

In addition, the types of PPE that are recommended for health care personnel caring for a patient depend upon the patient's clinical symptoms. The PPE used when caring for patients whose condition is associated with a high risk of direct contact with body fluids (e.g., presence of vomiting, diarrhea, bleeding) are different from those used when evaluating a patient who does not present a hazard due to body fluid exposure (CDC, nd l,m,n). In all settings, only essential personnel who are trained in proper donning and removal of PPE should interact with the patient.

Asymptomatic individuals

• Asymptomatic individuals who have had a possible exposure to Ebola generally do not require strict isolation precautions. Such patients should be monitored so that they can be isolated if fever or other signs or symptoms occur. However, additional restrictions may be required depending upon the type of exposure.

The risk of exposure to the Ebola virus helps to guide the evaluation and management of both symptomatic and asymptomatic individuals.

Patients are at risk for EVD if they have had an exposure that occurred within 21 days before the onset of symptoms. However, the level of exposure risk ranges from high, to moderate, to low, or no known identifiable risk. For health care workers, the level of exposure risk increases with the number of patients with known EVD they are caring for. Individuals may also be at risk if they have handled bats or nonhuman primates from endemic areas of Africa.

These following guidelines were put forth by the CDC to identify at-risk individuals during the 2014 - 2016 outbreak in West Africa (CDC, nd i).

• High risk: A high-risk exposure includes any of the following:
  • Percutaneous (e.g., needle stick) or mucous membrane exposure to blood or body fluids (e.g., feces, saliva, sweat, urine, vomit, and semen) of a person with symptomatic EVD.
  • Exposure to the blood or body fluids of a person with symptomatic EVD without appropriate PPE.
  • Processing blood or other body fluids of a person with symptomatic EVD without appropriate PPE or standard biosafety precautions.
  • Direct contact with a dead body without appropriate PPE in an area where a recognized Ebola epidemic is occurring.
  • Having lived in the immediate household and provided direct care to a person with symptomatic EVD.
• Moderate risk: Some risk of exposure includes any of the following:
  • In areas where a recognized epidemic is occurring:
    • Direct contact while using appropriate PPE with a person with symptomatic EVD (or his/her body fluids).
    • Any direct patient care in other health care settings.
  • Close contact in households, health care facilities, or community settings with a person with symptomatic EVD. Close contact is defined as being within approximately three feet (one meter) of the infected person for a prolonged period of time while not wearing appropriate PPE.
• Low (but Not Zero) Risk: A low-risk exposure includes any of the following:
  • Having been in a country where a recognized epidemic is occurring within the past 21 days and having no known exposures to Ebola virus.
  • Having brief direct contact (e.g., shaking hands), while not wearing appropriate PPE, with a person with Ebola while the person was in the early stage of disease.
  • Brief proximity, such as being in the same room (but not an Ebola patient care area) for a brief period of time, with a person with symptomatic EVD.
  • Direct contact while using appropriate PPE with a person with symptomatic EVD (or their body fluids) in countries without widespread transmission or cases in urban settings with uncertain control measures.
  • Travel on an aircraft with a person with EVD while the person was symptomatic.
• No Identifiable Risk: Some exposures or situations have no identifiable risk of infection. These include:
  • Contact with an asymptomatic person who had contact with a person with EVD.
  • Contact with a person with EVD before the person developed symptoms.
  • Having been more than 21 days previously in a country where a recognized epidemic is occurring.
  • Having been in a country with Ebola virus cases, but without widespread transmission or cases in urban settings with uncertain control measures, and not having any other exposure as defined above (e.g., direct contact with a patient with EVD).
  • Having remained on or in the immediate vicinity of an aircraft or ship during the entire time that the conveyance was present in a country where a recognized epidemic is occurring, and having had no direct contact with anyone from the community.

Symptomatic Patients with Identifiable Risk

• Clinical findings that are consistent with EVD include fever and/or severe headache, weakness, muscle pain, vomiting, diarrhea, abdominal pain, or unexplained hemorrhage (CDC, nd g). Infection control precautions should be used for all symptomatic patients who have an identifiable risk for EVD. In addition, the hospital infection control program and other appropriate staff should be notified, as well as, local and state health departments.
• Such patients should be isolated in a single room with a private bathroom and with the door to the hallway closed. All health care workers should use standard, contact, and droplet precautions, as well as. PPE recommended for the care of patients with EVD.
• In patients who are suspected of having EVD, phlebotomy and laboratory testing should be limited to tests that are essential for diagnosing or ruling out Ebola virus, assessing for an alternative or concurrent infection (e.g., malaria), and/or emergency care (CDC, nd g). In consultation with local and state health officials, evaluation for other potential causes of their illness may also be indicated, particularly for those individuals whose recent history indicates a low risk of exposure to Ebola virus (CDC, nd o).
• In the United States, certain hospitals have been designated as "Ebola assessment hospitals" and are prepared to evaluate and care for patients with possible EVD until a diagnosis can be confirmed or ruled out (CDC, nd p,q).

Asymptomatic Individuals with Identifiable Risk

• Monitoring for symptoms and signs of EVD should be performed for asymptomatic persons who have had an exposure to Ebola virus at any risk level (i.e., high, moderate, or low risk).
• Such individuals should be monitored for 21 days after the last known exposure and should immediately report the development of fever or other clinical manifestations suggestive of EVD (CDC, nd g). The type of monitoring (e.g., self-monitoring and reporting versus direct observation by a designated health official), as well as, the need for travel restrictions, restricted movement within the community, and/or quarantine, depend in part upon the type of exposure. Specific guidelines for management of asymptomatic individuals with an exposure to Ebola virus are typically dictated by public health authorities.

Patients with No Identifiable Risk

• If after initial evaluation patients are determined to have no identifiable risk for Ebola virus infection, monitoring or diagnostic testing for EVD is not warranted. However, if patients have fever and other signs or symptoms of infection, they should be evaluated for other causes of febrile disease (e.g., malaria, Lassa fever, influenza). Appropriate infection control precautions will depend upon the patient's clinical findings, as well as, the specific pathogens that are being considered.

Indications

• Evaluation of all patients with suspected EVD should be done in conjunction with local and state health departments (CDC, nd g). In the United States, certain hospitals may be designated as "Ebola assessment hospitals," which are prepared to evaluate and care for patients with possible EVD until a diagnosis can be confirmed or ruled out (CDC, nd p,q).
• Testing for Ebola virus infection is performed in symptomatic patients with any possible risk of exposure to Ebola virus (high, moderate, or low risk).
• Testing is not warranted for patients who have an identifiable risk but no signs or symptoms of EVD. These patients should be monitored and tested if they become ill.
• Testing is not warranted for patients without any identifiable risk of exposure to Ebola virus.

Ebola virus is generally detectable in blood samples by RT-PCR within three days after the onset of symptoms. Repeat testing may be needed for patients with symptoms for fewer than three days (CDC, nd r). According to CDC guidelines for discharging a person who is under investigation for EVD, a negative RT-PCR test that is collected ≥72 hours after the onset of symptoms excludes EVD (CDC, nd s).

Patients who have confirmed EVD should be transferred to specialized Ebola treatment centers.

Diagnostic tests for Ebola virus infection are principally based upon the detection of specific RNA sequences by RT-PCR in blood or other body fluids. Viral antigens can also be detected using immunoassays. In the United States, any presumptive positive Ebola test should be confirmed at the CDC (CDC, nd t).

Nucleic acid testing

• RT-PCR tests that detect specific RNA sequences have become the standard method of diagnosing EVD. In spite of genetic diversity and the accumulation of sequence changes, RT-PCR testing remained effective through the conclusion of the West African epidemic. However, clinicians should be aware of possible viral RNA sequence differences when attempting to employ these assays in future Ebola outbreaks.
• Viral RNA is generally detectable in serum by RT-PCR within three days after the onset of symptoms (CDC, nd r). Results are available in approximately two to six hours, depending upon the assay that is used (Su et al., 2016).
• Repeat testing may be needed for patients with symptoms for fewer than three days (Su et al., 2016).
• A negative RT-PCR test that is collected >72 hours after the onset of symptoms rules out EVD (Su et al., 2016).
• Blood is the preferred specimen for testing. Testing of simultaneously collected blood and saliva specimens has shown that viral RNA levels are much lower in saliva. For example, in a group of 32 patients who were positive by blood testing, fewer than 10% were also detected by oral swab, indicating that saliva should not be used for diagnostic testing (Erickson et al., 2016). However, an oral swab from a cadaver may be useful for postmortem diagnosis because fatally infected patients have high viral titers in body fluids at the time of death.

Immunoassays

• A rapid chromatographic immunoassay (ReEBOV) that detects Ebola virus antigen can provide results within 15 minutes (Boisen et al., 2016). This assay can be useful to support a provisional diagnosis based on clinical exam and exposure history. However, the use of the ReEBOV assay alone could result in inappropriate admissions of uninfected persons to Ebola treatment units or fail to detect patients who are early in the disease course. Evaluation of ReEBOV in a field setting, using banked patient samples, found that the test gave a positive result in about 10% of cases in which EVD had been ruled out by RT-PCR. Additionally, it only detected about 90% of cases that were positive by RT-PCR (Boisen et al., 2016). In a laboratory setting, the lower limit of detection of this test in blood samples from infected macaques was 3 x 105 genomes/mL (Cross et al., 2016).
• In November of 2018, the US Food and Drug Administration cleared a second Ebola rapid antigen fingerstick test under an Emergency Use Authorization (FDA, nd). This test uses a portable battery-operated reader that allows testing to be performed at the point of care outside of the laboratory when more sensitive Ebola virus nucleic acid testing is unavailable. Similar to other antigen-based assays, false-negative results may occur. As such, results must be interpreted in the context of associated clinical and epidemiologic findings.

If testing is indicated, the local or state health department should be contacted immediately. Clinicians, nurses, and laboratory workers need to be aware that CDC select agent regulations apply to the handling of patient specimens confirmed to contain infectious Ebola viru (CDC, nd t). Additional details on collection and handling of specimens from patients with suspected EVD can be found in the CDC documents that provide guidance for laboratories and submission information (CDC, nd r). For clinicians outside the United States, the WHO has also issued guidance for the diagnosis, safe collection, and shipment of samples from patients with suspected EVD (WHO, nd c).

All health care workers involved in the care of patients with suspected or confirmed EVD should rigorously observe infection control precautions, including the proper use of PPE.

The mainstay of treatment for EVD involves supportive care to maintain adequate organ function (e.g., cardiovascular, respiratory, renal) while the immune system mobilizes an adaptive response to eliminate the infection (CDC, nd q). Whenever possible, such patients should receive care in designated treatment centers and by clinicians trained to care for such patients (CDC, nd q). Treating patients with EVD requires a multidisciplinary approach prior to, during, and following patient care (Garibaldi & Chertow, 2017). Although care provided to patients in low-resource settings has historically been limited efforts to provide more frequent monitoring and advanced care to patients in West Africa progressed during the 2014 - 2016 epidemic (Dickerson et al., 20108).

Several experimental antiviral therapies were used to treat patients during the 2014 - 2016 outbreak in West Africa, but their efficacy is unclear, and the availability of these drugs is limited. Consequently, decisions about whether to use antiviral therapy, as well as, the choice of therapy and the timing of administration, should be made in conjunction with public health agencies.

Fundamental aspects of supportive care involve preventing intravascular volume depletion, correcting profound electrolyte abnormalities, and avoiding the complications of shock.

During the outbreak in West Africa, 27 patients with EVD were treated in the United States or Europe, where they received aggressive supportive care (Uyeki et al., 2016). Among those patients, 82% survived. Specific lessons learned from the care of patients with EVD during the outbreak include (CDC, nd g).

Patients may lose large amounts of fluid through vomiting and diarrhea, requiring rapid volume replacement to prevent shock. Antiemetic and antidiarrheal agents may also be beneficial.201 Careful attention to the volume of fluid losses, as well as, intake will assist with fluid repletion targets.

When available, patients will benefit from hemodynamic monitoring and intravenous fluid repletion. However, patients in the early phase of illness who respond to oral antiemetic and antidiarrheal therapy may be able to take in sufficient fluids by mouth to prevent or correct dehydration (Kortepeter et al., 2016).

Patients may develop significant electrolyte disturbances (e.g., hyponatremia, hypokalemia, hypomagnesemia, and hypocalcemia) and may require frequent repletion of electrolytes to prevent cardiac arrhythmias.

Intensive nursing may be required in order to respond to the patient's changing clinical situation.

Patients who experience fluid losses from vomiting and diarrhea may require five or more liters per day of a balanced crystalloid solution. Fluid and electrolyte replacement can be administered orally (e.g., WHO-recommended oral rehydration salts) or intravenously (e.g., 0.9% sodium chloride solution). The approach depends in large part upon the stage of illness and the clinical presentation. For example, in resource-limited settings, oral therapy to prevent or correct dehydration may be suitable for patients in the early phase of illness who respond to oral antiemetic and antidiarrheal therapy (Kortepeter et al., 2016). However, patients in shock and those who are unable to tolerate or manage self-directed oral replacement therapy will require intravenous fluids.

The approach to fluid and electrolyte replacement will also depend upon the availability of resources (Perner et al., 2015).

In resource-limited areas with little or no monitoring and laboratory capacity, qualitative assessments of urine frequency, volume, and color, as well as, evaluation of skin turgor and mucous membranes, may assist in guiding volume replacement in the absence of more accurate measures.

In areas with greater resources, careful attention to the volume of fluid losses and intake, as well as, indirect assessments of intravascular volume status (e.g., vascular ultrasound, indwelling catheters for central venous pressure monitoring), will assist with fluid repletion targets. Electrolyte replacement should be guided by plasma values since patients can present with a range of abnormalities. For example, in a cohort study of patients admitted to a hospital in Sierra Leone, 32 of 97 presented with abnormal potassium levels, and the number who had hypokalemia and hyperkalemia were similar (19 versus 13, respectively).

In resource-rich areas, clinicians may employ standard supportive measures for critically ill patients in shock, including invasive blood pressure and continuous pulse-oximetry monitoring. Hypotension may sometimes persist despite adequate volume resuscitation, requiring the use of vasopressor infusions such as norepinephrine. Aggressive volume resuscitation may contribute to the development of pulmonary edema and acute lung injury in the setting of shock may necessitate supplemental oxygen therapy (e.g., nasal cannula or face mask).

Invasive mechanical ventilation (intubation) may be the best option for patients with progressive respiratory failure (Wolf et al., 2015). When considering the management of such patients with EVD, clinicians should recognize that some types of respiratory support present a hazard of generating infectious aerosols. The use of noninvasive mechanical ventilation or high-flow oxygen therapy (e.g., Vapotherm) is generally not recommended given the potential for continuous aerosol production.

Additional supportive measures may be needed depending upon the patient's clinical presentation. These include:

• Analgesic agents to manage pain (e.g., abdominal, joint, muscle).
• Antiemetic medications to control nausea and vomiting.
• Anti-epileptic medications for those with seizures.
• Antimotility agents (e.g., loperamide) to control diarrhea and decrease fluid and electrolyte losses (Kortepeter et al., 2016).
• Antipyretic agents (e.g., acetaminophen, paracetamol) to decrease fever associated with EVD. Dose reduction of these agents may be needed for patients with progressive hepatic dysfunction. Nonsteroidal anti-inflammatory agents are generally avoided to help minimize the risk of renal failure, which can contribute to fatal disease.
• Blood products (e.g., packed red blood cells, platelets, fresh frozen plasma) for patients with coagulopathy and bleeding.
• Renal replacement therapy to manage severe multifactorial acute kidney injury (Connor et al., 2015). If dialysis is required, clinicians should refer to the CDC document on how to safely perform acute hemodialysis in patients with EVD (CDC, nd u).
• Total parenteral nutrition support for individuals with poor oral intake who are unable to tolerate a moderate- to high-calorie diet (Johnson et al., 2015).

As with other severely ill patients, persons with EVD may require evaluation and/or treatment of other concomitant or possible infections (e.g., malaria).

In addition, empiric antimicrobial treatment should be administered to patients with clinical evidence of bacterial sepsis, which may be a late complication:

• The choice of agent should provide adequate coverage for gram-negative pathogens (kreuels et al., 2014).
• Empiric gram-positive therapy should be added in certain patients, such as those with hospital-acquired pneumonia or indwelling central venous catheters.

In some case series from the Ebola epidemic in West Africa, empiric antimicrobial therapy was given to all patients at the time of initial presentation or to patients who had evidence of gastrointestinal dysfunction, even if clinical evidence of bacterial sepsis was absent. However, data to justify this approach are lacking.

EVD is associated with a high risk of fetal death and pregnancy-associated hemorrhage (CDC, nd g).

The CDC and the American College of Obstetrics and Gynecology have issued recommendations for the care of pregnant women with EVD (ACOG, 2014). However, there are no data to suggest whether cesarean or vaginal delivery is preferred or when the baby should be delivered. Thus, decisions regarding obstetrical care must be made on a case-by-case basis.

Experience from the West African epidemic supports the conclusion that early diagnosis and prompt initiation of care increase the likelihood that a patient with EVD will survive (CDC, nd g). In contrast, patients who have already developed evidence of severe intravascular volume depletion, metabolic abnormalities, and impaired oxygen delivery by the time treatment is initiated are at high risk of death.

Additional demographic, clinical, and laboratory findings from the 2014 - 2016 epidemic that were found to affect prognosis include:

• Age
  • Younger age was associated with a lower case fatality rate in the outbreak in Sierra Leone. In one study, the case fatality rate was 57% for patients <21 years old versus 94% for those >45 years of age (CDC, nd g).
• Gastrointestinal disease
  • In a review of 106 patients treated in Sierra Leone, 94% of patients with diarrhea died, compared with 65% without diarrhea (CDC, nd g).
• Gender
  • A study from West Africa comparing the outcome of EVD in men and women found a slightly higher case fatality rate in men. This may have resulted from delays in seeking treatment by some male patients.
• Viral load
  • Experience from Ebola outbreaks in West Africa, Uganda, and the Democratic Republic of the Congo has shown that patients with high Ebola virus RNA levels in the bloodstream have a higher mortality (CDC, nd g). For example, in a retrospective cohort study that followed 525 patients in Sierra Leone, a viral load ≥10 million copies/mL was a significant predictor of mortality.

Information on prognostic factors for EVD was also obtained during earlier outbreaks. Research based upon blood samples collected during the outbreak of Ebola Sudan virus disease in Gulu, Uganda in 2000, in which approximately 50% of patients survived infection, indicates that certain biomarkers are predictive of disease outcome (MCElroy et al., 2014). For example, proinflammatory cytokines have been associated with viremia, hemorrhage, and death, whereas soluble CD40 ligands have been associated with nonfatal outcomes (MCElroy et al., 2014). However, the clinical utility of these tests is yet to be determined, and they are not routinely available in clinical practice.

Other host factors may also be associated with clinical outcomes. For example, there was a significant association between HLA-B alleles and survival or death during the outbreak of Ebola Sudan in Gulu, Uganda. In addition, studies of Ebola virus infection in mice have found that different genetic backgrounds are linked with variations in disease severity (rasmussen et al., 2014).

Patients who survive EVD typically begin to show signs of clinical improvement during the second week of illness (CDC, nd g). In these patients, viremia also resolves during the second week, in association with the appearance of virus-specific IgM and IgG.

RT-PCR testing is used to help determine when a recovering patient can be discharged from a hospital. According to the WHO, individuals who no longer have signs and symptoms of EVD can be discharged if they have two negative RT-PCR tests on whole blood separated by at least 48 hours (WHO, nd d). A similar protocol was followed in a treatment center in Liberia (Kortepeter et al., 2016).

However, a commentary published during the West African epidemic recommended that, in resource-limited settings, the decision to discharge a convalescent patient should be based upon the absence of symptoms of EVD for 48 hours rather than RT-PCR testing (O’Dempsey et al., 2015). This approach is partly supported by a study that evaluated the presence of infectious virus over time in four patients with EVD (Spengler et al., 2015). Twenty-eight plasma samples were tested by RT-PCR, and isolation of the virus was subsequently attempted. Ebola virus was not isolated from plasma samples if the cycle-threshold value was >35.5 (higher cycle-threshold values indicate lower RNA levels) or if the sample was taken more than 12 days after the onset of symptoms.

Regardless of when an individual is discharged from the hospital, patients should receive information to help minimize the risk of transmission in the community (e.g., counseling on safe sexual practices) since the virus can persist in a variety of body fluids (e.g., urine, semen) for up to several months after the plasma tests negative for Ebola virus by RT-PCR.

Patients should be informed that clinical sequelae (e.g., joint pains, uveitis, meningitis) may develop weeks or months after the initial illness resolves.

The WHO suggests that patients be seen in follow-up two weeks after discharge, monthly for six months, and then every three months to complete one year (WHO, nd d).

• Males should have semen testing during these visits until they test negative for Ebola virus RNA.
• If fever develops, patients should be tested for Ebola RNA by RT-PCR and be evaluated for other causes of infection (e.g., malaria).
• Uveitis and meningitis may be suggestive of an Ebola relapse. If meningitis is suspected, a lumbar puncture should be performed (using appropriate PPE), even if the blood tests are negative for Ebola virus RNA.

Ebola virus survivors with ocular findings also require follow-up vision care. In a study of 137 EVD survivors, 50 had ocular findings. Visually significant cataracts were present in 46 patients at a median of 19 months from initial Ebola diagnosis. All patients tested negative for Ebola virus RNA by RT-PCR of ocular fluid, and 34 underwent cataract surgery, resulting in improved visual acuity (shantha et al., 2018).

There are no approved medications for the treatment of EVD or for post-exposure prophylaxis in persons who have been exposed to the virus but have not yet become ill. However, the 2014 - 2016 West African outbreak focused attention on the potential anti-Ebola activity of several drugs developed for other purposes. Additionally, it accelerated the evaluation of experimental therapies that had been developed to treat or prevent Ebola or Marburg virus infection and had demonstrated protective efficacy in laboratory animals (Fisher et al., 2018).

During the West African outbreak and subsequent outbreaks in the Democratic Republic of the Congo, several of these therapies were administered alone or in combination to individual patients on a compassionate use basis, and some were administered to cohorts of patients in nonrandomized trials. Only one novel therapy (ZMapp) was tested in a randomized trial, but it failed to recruit a sufficient number of subjects to yield a definitive outcome (Prevail, 2016). Because of these limitations, conclusive evidence of efficacy was not achieved for any novel therapy.

The following section summarizes reports of therapies that were given to patients in an outbreak setting and describes novel treatments that have shown efficacy in laboratory animals but have not been given to patients.

Experimental therapies given to patients during an outbreak setting include:

• Favipiravir
  • Favipiravir (T-705, Avigan) is a nucleoside analog that inhibits the replication of a wide range of RNA viruses and was effective in preventing the death of mice and nonhuman primates infected with Ebola virus (Bixler et al., 2018). The drug must be given orally, largely limiting its use to patients able to swallow tablets.
  • Two clinical trials of favipiravir were performed during the West African epidemic. The first, a nonrandomized trial performed in several Ebola treatment centers, was unable to detect a significant reduction in mortality or serum viral load when 99 adults and adolescents treated with favipiravir were compared with patients previously treated in the same centers (Sissoko et al., 2016). The second, also a retrospective nonrandomized study, compared patients given standard of care plus favipiravir over a 10-day period with those who had received standard of care alone during the preceding three weeks (Bai et al., 2016). A statistically significant increase in survival rate was seen in the favipiravir cohort (56 versus 35% in controls), but the study had numerous limitations, indicating that definitive proof of benefit would require a randomized controlled trial.
• Convalescent plasma and whole blood
  • Convalescent plasma and whole blood have been administered to patients with EVD both prior to and during the West African outbrea (WHO, nd e). However, there is no evidence that this treatment reduces mortality based upon findings from a nonrandomized trial from Guinea 234 and case series from outbreaks in central Africa (Kreuels, et al., 2014).
• ZMapp
  • ZMapp, a "cocktail" of three monoclonal antibodies (mAbs) targeting the Ebola virus surface glycoprotein, was shown in laboratory studies to protect rodents and nonhuman primates against Ebola virus infection. Treatment prevented the death of Ebola-infected macaques, even when it was initiated after the animals had developed fever, viremia, and other signs of illness (Qiu et al., 2014). This was the first time treatment had prevented the death of nonhuman primates that had developed signs of EVD.
  • ZMapp was evaluated in a randomized controlled trial involving 71 patients in Liberia, Sierra Leone, Guinea, and the United States (Prevail, 2016). Patients received either standard of care or standard of care plus three doses of ZMapp. Although there were fewer deaths in the ZMapp arm (22 versus 37%), the decline in the epidemic reduced patient enrollment so that the result did not meet the prespecified threshold for establishment of efficacy.
• mAb114
  • In addition to "cocktails" of several mAbs, such as ZMapp, individual mAbs have been evaluated in preclinical animal studies. A single mAb isolated from a survivor of EVD neutralized the virus in vitro and protected 100% of macaques from lethal infection when administered up to five days after virus challenge (Corti, et al., 2016). This agent has been administered to patients in the Ebola outbreak that was reported in the Democratic Republic of the Congo on August 1, 2018.
• GS-5734
  • The novel nucleotide analogue prodrug GS-5734 was found to be highly efficacious in macaques infected with Ebola virus, even when initiated three days after virus challenge (Warren et al., 2016). Studies of tissue distribution revealed drug penetration to the testes and central nervous system. The drug was given on a compassionate use basis to a nurse who survived EVD, but she relapsed nine months later with meningoencephalitis (CDC, nd e). Further testing will be needed to determine if the compound is capable of entering "sanctuary sites."
• Artesunate-amodiaquine
  • Artesunate-amodiaquine, an agent used to treat malaria, was found to have anti-Ebola activity in vitro. A possible in vivo effect of this agent was noted in an Ebola treatment center in Liberia, where patients were routinely treated for malaria. In this center, patients were typically given the anti-malaria drug combination artemether-lumefantrine, except for a 12-day period when supplies ran out, when all patients were instead given artesunate-amodiaquine. A retrospective analysis found that the case-fatality rate during that 12-day period was 50.7%, while before and after it averaged 64.4%.238 However, the authors acknowledged that an unrecognized toxicity of the first drug combination might also explain the observed difference.

The following therapies were administered to a few patients early in the West African Ebola epidemic, but their use was then discontinued:

• TKM-Ebola
  • A preparation of short interfering RNA (siRNA) targeting three different Ebola virus genes (TKM-Ebola) effectively blocked Ebola virus infection in laboratory rodents and nonhuman primates and was given to several patients in the United States (Wong et al., 2016). However, a Phase I trial was put on hold because of fever in some subjects, and the manufacturer subsequently discontinued production of all siRNA products for filovirus diseases.
• Brincidofovir
  • A prodrug of cidofovir, brincidofovir (CMX001) is under development for the treatment of cytomegalovirus, adenovirus, and other DNA virus infections. Early in the Ebola epidemic the compound was reported by the manufacturer to have in vitro activity against Ebola virus, and it was given to several patients (Florescu et al., 2015). Further testing, however, showed that the drug had no activity in Ebola-infected mice and its use was discontinued (McMullan et al., 2015).

The following therapies have shown promising activity against Ebola virus in laboratory animals, but have not been administered to humans:

• Antisense oligonucleotides (PMOs)
  • Chemically modified nucleic acid analogs, known as phosphorodiamidate morpholino oligomers (PMOs), are being developed for the treatment of a number of medical conditions, including filovirus infections. These molecules bind to specific sequences in messenger RNA, preventing translation. Combinations of PMOs were protective in mouse and guinea pig models of Ebola and Marburg virus disease and the use of such molecules targeting Ebola or Marburg virus were reported to be safe in a Phase I trial (Heald et al., 2014). The antisense molecule AVI-7537 is being developed for the treatment of Ebola virus infection (Warepta, 2018). but it was not administered to patients during the West African outbreak.
• BCX4430
  • The nucleoside analog BCX4430 inhibits viral RNA polymerase function, acting as a nonobligate RNA chain terminator (Taylor et al., 2016). BCX4430 protected mice against lethal Ebola virus challenge, and also protected mice, guinea pigs, and macaques infected with Marburg virus when treatment was administered as late as 48 hours after infection (Warren et al., 2014). Studies are underway to test the drug against Ebola virus challenge in macaques in preparation for eventual human trials (Taylor et al., 2016).

When caring for patients with confirmed or suspected acute EVD, health care personnel should follow infection prevention and control recommendations from the CDC and the WHO (CDC, nd v). These guidelines provide control measures needed to manage patients who are known or suspected to be infected with Ebola virus or other highly pathogenic agents.

Infection control recommendations for patients who present with acute infection include:

• Correct use of appropriate PPE
• If possible, aerosol-generating procedures should be avoided. However, if they must be performed, patients should be placed in an airborne infection isolation room (CDC, nd w)
• Isolation of hospitalized patients with known or suspected EVD
• Proper hand hygiene
• Use of standard, contact, and droplet precautions

The type of PPE used, and its careful placement (donning) and removal (doffing), are critical to preventing nosocomial transmission of Ebola virus. During the 2014 - 2016 epidemic, several patients were cared for in the United States. The staff at Emory University used full body suits and powered air-purifying respirators (PAPR) to help staff work for extended periods, decrease the physical discomfort of working in multi-component PPE, and avoid difficulties like fogged face shields (Ribner, 2014). The donning and doffing of PPE was always observed by another staff member.

The CDC and the WHO have issued detailed guidelines on the use of PPE for managing patients with suspected or confirmed EVD. The type of PPE depends in part upon the patient's clinical presentation (e.g., presence or absence of diarrhea, vomiting, bleeding). Clinicians should refer to these guidelines when caring for patients. The CDC has also released a video that demonstrates donning and doffing of PPE.

Highlights from these guidelines include the following:

• Rigorous and repeated training of health care workers in correct donning and doffing of PPE. In addition, health care workers should demonstrate competency in performing Ebola-related infection control practices and procedures.
• PPE should cover all clothing and skin, and completely protect mucous membranes. Such PPE includes double gloves, boot covers, fluid-resistant gowns or coveralls, single-use disposable hoods that cover the head and neck, single-use disposable full face shields, and PAPR or N95 respirators. Additional measures, such as waterproof aprons, may also be required depending upon the patient's symptoms. The combination of PPE used should be determined by the health care facility providing care.
• Health care workers should perform frequent disinfection of gloved hands using an alcohol-based hand rub, particularly after touching body fluids. In addition, they should immediately disinfect any visibly contaminated PPE using approved disinfectant wipes.
• A trained monitor should actively observe and supervise each worker donning and doffing PPE. Monitors should not serve as an assistant for taking off PPE.

The use of the recommended PPE for health care workers caring for patients with Ebola for extended periods of time can potentially result in heat-related illness, which was of particular concern in West Africa (CDC, nd x). Recommendations to help prevent such complications include: staying well hydrated, working short shifts until the health care worker can adjust to the heat, taking time to rest and cool down, and watching for signs of heat-related illness.

Health care workers who are pregnant should not provide care for patients with EVD. In addition to the increased maternal and fetal risks of EVD during pregnancy, PPE may not be well suited for pregnant health care workers.

Strict infection control precautions must be used when caring for pregnant patients with EVD. This should include PPE that is recommended for providers who are at high risk of exposure to bodily fluids. These precautions should be used even if the mother has recovered from infection, since data suggest that the fetus of a mother who survived EVD while pregnant may continue to harbor virus and be infectious (Akerlund et al., 2015).

If a patient with suspected or confirmed EVD is being cared for in a health care setting, specific precautions should be taken to reduce the potential risk of virus transmission through contact with contaminated surfaces. This includes frequent cleaning of the floor in the doffing area (i.e., where PPE is removed).

In a study that surveyed Ebola treatment centers in Sierra Leone, viral RNA was frequently detected on materials that had been in direct contact with patients (Poliquin et al., 2016). For example, Ebola virus RNA was detected on four of six gloves tested, despite lack of visible soiling. However, viral RNA was no longer detected after gloves were rinsed with chlorine solution.

The CDC has provided guidance for medical waste management, as well as, specific recommendations for environmental infection control in hospitals, health care settings in West Africa, and laboratories.

Patients who have recovered from EVD and have been discharged from the hospital may present for medical care during the convalescent period.

Interim guidance for the management of survivors of EVD have been issued by the CDC and the WHO (CDC, nd c) The types of infection control precautions that should be used depend upon the patient's signs and symptoms.

For most survivors who have recovered and been discharged after their acute illness, only standard precautions are needed when clinical evaluation and care are performed. According to the CDC, there is no evidence that survivors of EVD pose any special risk to health care personnel when this care involves contact with intact skin, sweat, tears, conjunctivae, saliva, and cerumen. Additionally, persons who have fully recovered from EVD and are not febrile do not pose a risk of Ebola virus exposure through phlebotomy since such patients are not viremic.

However, for patients who present during convalescence with late stage manifestations of Ebola disease, such as acute neurological or ocular symptoms, infection control practices recommended for evaluating persons under investigation for EVD should be used until testing for Ebola virus is negative.

Infection control precautions used for invasive procedures require special consideration if there is potential contact with body fluids from immunologically protected sites (e.g., semen, spinal or intraocular fluid). Such patients should be managed in consultation with local health departments and/or the CDC to determine appropriate PPE based upon a risk assessment of the potential exposure during the procedure.

When a woman becomes pregnant after clearing Ebola virus from her blood, only standard PPE is recommended during delivery since the fetus is presumed not to be infected. In addition, the CDC suggests that no special precautions are needed for patients who require spinal anesthesia, as long as the mother does not have neurologic symptoms suggestive of persistent disease (CDC, nd c)

Sexual transmission

• Several cases of EVD that occurred during the late phase of the 2014 - 2016 outbreak were attributed to sexual transmission, with supportive epidemiologic and molecular evidence. The CDC and WHO therefore suggest that patients with EVD refrain from sexual activity (oral, anal, vaginal) and that condoms should be used if abstinence is not possible. In addition, hand hygiene is recommended following contact with semen.
• It is not known when unprotected sexual activity can be safely resumed. For men, the WHO has suggested that the semen be tested for Ebola virus by RT-PCR three months after the onset of disease. Further recommendations are as follows:
  • For those men who test negative, the test should be repeated with an interval of one week between tests. Sexual activity can be resumed if their semen has tested negative for Ebola virus twice by RT-PCR.
  • For those men who test positive for Ebola virus at three months, testing should be repeated every month until their semen tests negative. The test should then be repeated with an interval of one week between tests. Sexual activity can be resumed if the semen has tested negative for Ebola virus twice by RT-PCR.
  • The WHO recommends that if semen testing is unavailable, men should practice safe sex for at least 12 months dating from the onset of illness.
• Studies evaluating the persistence of Ebola virus have detected viral RNA in vaginal fluids for up to 33 days and in semen for up to two years after the onset of EVD.
• The persistence of Ebola virus in semen was illustrated in a cross-sectional study in which semen was obtained from 93 men who had previous EVD (Deen et al., 2015). Among the nine patients who were evaluated two to three months after infection, all tested positive for Ebola virus in the semen using RT-PCR. In addition, 26 of the 40 men who were evaluated 4 to 6 months after infection, and 11 of the 43 men who were evaluated 7 to 9 months after infection had Ebola virus detected in the semen. In later studies, the virus was found to persist in the semen of survivors for a median of 115 days. An outbreak in Guinea was linked to a male survivor with onset of illness more than 500 days before (Diallo et al., 2016). In a study of 137 male survivors, 11 (8%) had RNA-positive semen two years after EVD onset (Fisher et al., 2018).

Breastfeeding and infant care

• Ebola virus has been isolated from breast milk and can be transmitted through close contact of an infected mother with her children. The CDC recommends that mothers who are under investigation for EVD, have confirmed infection, or have recently recovered should avoid breastfeeding (CDC, nd y).
• Where available, testing of breast milk can guide when it is safe for mothers who have survived EVD to resume breastfeeding. If Ebola virus RNA is detected, the breast milk should be retested every 48 hours until two consecutive negative results are obtained.
• In resource-limited settings, the risk of virus transmission during breastfeeding must be weighed against the risk of the infant becoming malnourished or developing diarrheal or respiratory disease or other infections if safe alternative options for feeding are not available.

Monitoring and travel restrictions

• Persons who have had a possible exposure to Ebola virus should be monitored for signs and symptoms of disease. Monitoring should continue for 21 days after the last known exposure. The development of fever and/or other clinical manifestations suggestive of EVD should be reported immediately.
• During the West African epidemic, the CDC and WHO provided information about restrictions on travel and transport of asymptomatic persons who had been exposed to Ebola virus.

Vaccination

• No approved vaccines are available to prevent the spread of Ebola virus.36 However, as a result of the epidemic in West Africa, accelerated paths were developed for vaccine testing and introduction into field use (Levine et al., 2015). During two Ebola outbreaks that were reported in the Democratic Republic of the Congo in 2018, health care workers and close contacts of patients were vaccinated using a vesicular stomatitis virus-Zaire Ebola (VSV-Ebola) virus vaccine.
• Prior to the epidemic in West Africa, a number of experimental vaccines had successfully protected nonhuman primates against an otherwise lethal Ebola virus challenge. These included a DNA vaccine followed by a recombinant human adenovirus type 5 (Ad5) vector encoding the Ebola Zaire and Sudan surface glycoproteins (GP), the recombinant Ad5 vaccine alone, a virus-like particle vaccine, a recombinant vesicular stomatitis virus (VSV) vector encoding Ebola surface GP, and a chimpanzee-adenovirus type 3 vaccine (ChAd3) encoding Ebola virus GP (Stanley et al., 2014). At the time the epidemic was recognized in 2014, the only vaccines that had been evaluated in humans were a multidose DNA vaccine and the recombinant Ad5 vaccine, which had both proven safe and immunogenic in Phase I trials (Sarwar et al., 2015). However, because recombinant Ad5 vaccines may be ineffective in persons with prior immunity to the adenovirus vector, the ChAd3 vaccine was believed to be more promising for human use.
• A WHO expert panel that convened in September 2014 identified both the ChAd3 and VSV vaccines as the most advanced candidates for use in the West African outbreak, principally because both promised to be protective after a single inoculation (WHO, nd e). Both vaccines were evaluated in healthy volunteers during the epidemic, as were an Ad26.ZEBOV vaccine and a recombinant vaccinia Ankara (MVA) vaccine encoding the Ebola glycoprotein (MVA-BN-Filo), and they were all found to be immunogenic (Ledgerrwood et al., 2017). A six-month safety study found that the VSV vaccine was generally well tolerated, supporting its use for persons at risk of EVD (Halperin et al., 2017). Additional studies have confirmed these results. For example, a phase I randomized trial in Gabon found that an adult dose of 20 million plaque-forming units (PFU) was safe and immunogenic (Agnandii et al., 2017). A subsequent study in European and African adults found that all who received a single dose of 10 to 50 million PFU were still seropositive at two years (Huttner et al., 2018).
• The VSV vaccine was the only specific countermeasure proven to have protective efficacy against Ebola virus during the West African epidemic. In a large trial of ring vaccination in Guinea, the VSV vaccine was safe and effective in inducing rapid immunity against Ebola virus (Henao et al., 2015). When a new case of EVD was diagnosed, surveillance teams identified all close contacts of the patient and all contacts of those contacts. Each of these clusters was then randomized to receive the VSV vaccine either immediately or after 21 days: 3,528 subjects were randomized and 3,512 were vaccinated (2014 in the immediate arm and 1,498 in the delayed arm). To exclude individuals who were already infected with Ebola virus at entry into the study, only patients who developed disease ≥10 days after randomization were included in the analysis. Among immediately vaccinated individuals, no EVD was seen after day 10, while there were 16 new cases among those assigned to delayed vaccination, indicating a clear benefit of immediate vaccination. In addition, no recipient developed EVD more than six days after vaccination in either group. One febrile illness was the only serious side effect attributed to vaccination.
• The recombinant VSV vaccine may also have a role in preventing disease and death when administered promptly after an exposure. This was demonstrated in two laboratory studies in macaques, the first employing challenge with the Zaire Ebola virus, and the second employing the West African Makona strain (Marzi et al., 2016). Cross-protection by inoculation of a VSV-Marburg vaccine was observed in one of the studies, suggesting that innate immune responses to the vaccine may play an important role in protection. During the 2014 - 2016 West African outbreak, the VSV vaccine was administered as post-exposure prophylaxis on a compassionate use basis to close contacts of a patient with EVD, as well as, to two health care workers who sustained a percutaneous injury with a needle that had come in contact with a contaminated glove. All recipients remained well (Cnops et al., 2015).

Public health response

• The epidemic in West Africa demonstrated that an effective public health response requires effective communications between government authorities, medical professionals, and the local populace to explain the need for monitoring, sample collection and testing, and isolation and other infection control measures, and to explain the potential benefits of treatment. Preventive interventions also include educating and supporting affected communities to modify long-standing funeral practices and to avoid contact with bush meat and bats. Anthropologists and others with specialized knowledge of local cultures should therefore be included as members of response teams.
• Several measures were implemented to help contain the 2014 - 2016 outbreak. These included: (WHO, 2014)
  • The WHO declaring the Ebola outbreak a Public Health Emergency of Concern. This mandated countries to develop national preparedness capacities, including the duty to report significant events, conduct surveillance and contact tracing, as well as, exercise public health powers while balancing human rights and international trade.
  • The United Nations (UN) created a special mission to help contain the outbreak. This is the first time that the UN created a mission for a public health emergency.
  • In the United States, public health authorities monitored health care workers who cared for patients with EVD and travelers who arrived from areas with widespread transmission.
  • Community care centers were established in parts of West Africa to isolate patients who were awaiting Ebola diagnostic test results and to provide basic care (e.g., oral rehydration) to patients who had confirmed EVD pending transfer to Ebola treatment units.
  • The spread of Ebola virus was successfully limited in areas where there were adequate resources and an effective public health response.