The family Filoviridae contains three genera, Ebolavirus and Marburgvirus, which cause severe disease in humans, and Cuevavirus, which has only been detected as viral RNA in bats in Spain.
The Zaire species of Ebola virus, the causative agent of the 2014 -2016 West African epidemic, is among the most virulent human pathogens known. The case fatality rate in past outbreaks in Central Africa reached 80 to 90%, but the overall fatality rate in West Africa was approximately 40%.
In the past, Ebola virus was classified as a "hemorrhagic fever virus." However, that term is no longer used, because only a small percentage of patients actually develop significant bleeding, and it usually occurs in the terminal phase of illness.
Until the 2014 - 2016 epidemic in West Africa, all outbreaks of EVD had occurred in Central Africa or the Sudan.
The West African epidemic was the largest filovirus outbreak on record. It started in the nation of Guinea in late 2013 and was confirmed by the WHO in March 2014. The countries with widespread transmission included Guinea, Liberia, and Sierra Leone. EVD occurred in hundreds of healthcare personnel who were infected while caring for patients.
A number of patients with EVD (e.g., doctors and nurses infected in West Africa, returning travelers from the region) were treated in hospitals in the United States and Europe.
The reservoir host of Ebola virus is unknown. Evidence is accumulating that various bat species may serve as a source of infection for both humans and wild primates.
Person-to-person transmission is associated with direct contact with body fluids from patients with EVD or from cadavers of deceased patients. 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.
Infectious virus and/or viral RNA can persist for weeks to months in certain bodily fluids of convalescent patients. Examples include: semen, urine, and breast milk. However, the risk of transmission from persistent virus at these sites is not well established.
Human infection with Ebola virus can also occur through contact with wild animals (e.g., hunting, butchering, and preparing meat from infected animals).
Almost all data on the pathogenesis of EVD have been obtained from laboratory experiments employing mice, guinea pigs, and nonhuman primates. Case reports and large-scale observational studies of patients in the West African epidemic have provided additional data on pathogenesis that have been consistent with findings in animal studies.
The incubation period of EVD is typically 6 to 12 days, but can range from 2 to 21 days.
Patients with EVD usually have an abrupt onset of nonspecific signs and symptoms such as fever, malaise, headache, and myalgias. As the illness progresses, vomiting and diarrhea may develop, often leading to significant fluid loss. Patients with worsening disease display hypotension and electrolyte imbalances leading to shock and multiorgan failure, sometimes accompanied by hemorrhage.
Whether EVD is considered in the differential diagnosis of a patient with fever and flu-like symptoms will vary markedly depending upon the circumstances especially when a recognized Ebola epidemic is currently ongoing. For patients with clinical findings consistent with the disease (i.e., fever and/or severe headache, weakness, muscle pain, vomiting, diarrhea, abdominal pain, or unexplained hemorrhage), healthcare personnel should obtain a careful history to determine if the patient has had a possible exposure to Ebola virus within 21 days prior to the onset of symptoms.
All patients who have or are suspected of having EVD should be promptly isolated. Infection control precautions should be initiated and include hand hygiene, standard, contact, and droplet precautions, as well as, the correct use of appropriate PPE.
Hospital infection control staff, as well as, the local or state health department, should be contacted immediately.
Monitoring for signs and symptoms of EVD should be performed for asymptomatic individuals who have had an exposure to Ebola virus at any risk level (i.e., high, moderate, or low risk).
Medical evaluation of symptomatic patients with a history of exposure generally includes testing for Ebola virus and other likely pathogens. Whether laboratory testing for Ebola virus should be performed depends, in part, upon the relative likelihood that a patient was exposed to the virus and the presence of compatible clinical symptoms and/or laboratory findings.
Diagnostic tests for EVD are principally based upon the detection of specific RNA sequences by RT-PCR testing in blood or other body fluids. Ebola virus is generally detectable in blood samples within three days after the onset of symptoms. Repeat testing may be needed for patients with symptoms for fewer than three days duration.
The differential diagnosis will vary markedly with the clinical and epidemiologic circumstances. For example, travelers returning from West or Central Africa should be evaluated for illnesses commonly seen in those areas, such as malaria etc.
Because of its virulence and high infectivity, Ebola virus is classified as a Category A bioterror agent.
Effective treatment of EVD requires aggressive supportive care to correct volume losses from vomiting and diarrhea, correct electrolyte abnormalities, and prevent shock. Patients may also require evaluation and/or treatment of concomitant infections. Several investigational 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.
EVD is associated with a high risk for fetal death and pregnancy-associated hemorrhage. There are no data to suggest whether cesarean or vaginal delivery is preferred or when the baby should be delivered. As a consequence, decisions regarding obstetrical care must be made on a case-by-case basis.
Early diagnosis and prompt initiation of care increase the likelihood that a patient with EVD will survive. Patients who survive EVD typically show signs of clinical improvement during the second week of illness. After discharge from the hospital, patients should be monitored for at least one year.
To prevent transmission of Ebola virus, healthcare personnel should follow infection prevention and control recommendations from the CDC and the WHO:
- When caring for a patient with acute illness, precautions should include: isolation of hospitalized patients with known or suspected EVD, hand hygiene, the use of standard, contact, and droplet precautions, and the correct use of appropriate PPE.
- For most survivors, only standard precautions are needed when clinical evaluation and care are performed. However, additional precautions are needed for those who present with late stage manifestations of EVD, such as acute neurological or ocular symptoms.
- Additional strategies to prevent the spread of EVD include careful monitoring of individuals after a possible virus exposure, educating patients on how to reduce the risk of transmission through sexual contact or breastfeeding, and potentially vaccinating high-risk populations.