Zika Virus Infection

The Zika virus is transmitted by daytime-active mosquitoes and has been isolated from a number of species in the genus Aedes. Zika virus is a mosquito-borne flavivirus primarily transmitted by Aedes aegypti mosquitoes. Aedes albopictus mosquitoes also might transmit the virus. A. aegypti and A. albopictus mosquitoes are found throughout much of the Region of the Americas, including parts of the United States, and also transmit dengue, chikungunya, yellow fever and West Nile viruses.

Studies show that the extrinsic incubation period for ZIKV in mosquitoes is about 10 days. Nonhuman (monkeys) and human primates are likely the main reservoirs of the virus, and anthroponotic (human-to-vector-to-human) transmission occurs during outbreaks.

The Zika virus is transmitted to humans primarily via the bite of an infected Aedes species mosquito. Aedes mosquitoes become infected when they bite an already infected individual, draw blood and contract the Zika virus. The Zika virus then spreads when the infected mosquito bites another individual.

Aedes mosquitoes typically breed and lay eggs in or near domestic water-holding containers (i.e., buckets, bowls, animal dishes, flower pots, vases, etc.). They are aggressive daytime biters, prefer to bite humans and live indoors and outdoors near humans.

The potential societal risk of the Zika virus can be delimited by the distribution of the mosquito species that transmit it (its vectors). The global distribution of the most cited carrier of Zika virus, A. aegypti, is expanding due to global trade and travel (Figure 4). A. aegypti distribution is now the most extensive ever recorded – across all continents, including North America and even the European periphery.

Global Aedes Aegypti Predicted Distribution (Figure 4)

The map depicts the probability of occurrence:
blue = none
red = highest occurrence
Aedes aegypti

Evidence of perinatal transmission of the Zika virus during pregnancy or childbirth is limited. Pregnant women can be infected with the Zika virus in any trimester. The incidence of Zika virus infection in pregnant women is currently unknown. Data on pregnant women infected with the Zika virus are limited. No evidence suggests pregnant women are susceptible to Zika virus infection or experience more severe disease during pregnancy (BBC, 2016).

It is possible that the Zika virus could be passed from a mother already infected with the Zika virus to the fetus during pregnancy. Perinatal transmission has been reported with other vector-borne viruses such as dengue and chikungunya. Studies are now being conducted on the possible perinatal transmission of the virus and its possible effects on the fetus.

So far, there are no documented reports of Zika virus transmission via breastfeeding. Zika virus RNA has been detected in breast milk, but Zika virus transmission through breastfeeding has not been documented. Because of the benefits of breastfeeding, mothers are encouraged to breastfeed even in areas where the Zika virus is found. Mothers in areas with Zika circulation should follow PAHO/WHO recommendations on breastfeeding (exclusive breastfeeding for the first 6 months, followed by continued breastfeeding with complementary foods up to 2 years and beyond) (BBC, 2016).

ZIKV can be transmitted through blood, but this is an infrequent mechanism. Zika virus RNA has been identified in asymptomatic blood donors during an ongoing outbreak. Standard precautions that are already in place for ensuring safe blood donations and transfusions should be followed.

ZIKV has been isolated in human semen.

Mosquito Factors

• Aedes mosquitoes, the main vector for ZIKV transmission, are widespread in all countries of the Americas Regions except Canada and continental Chile. Global warming is hypothesized to play a role in mosquitoes' survival, which thrive in warm and moist environments. Climate change associated with changes in precipitation patterns, humidity and temperature has helped expand the range of habitable places for mosquitoes.
• The number of mosquitoes biting humans infected with the Zika virus has multiplied.
• The number of mosquitoes surviving long enough to infect other humans has multiplied.

Human Factors

• Since this is a new virus in the Americas, the entire human population has not previously been exposed to Zika and therefore lacks immunity to the Zika virus.
• Constant international travel is transporting diseases to new locales.
• More and more people live in congested cities, making it easy for viruses to jump from individual to individual and for mosquitoes to find large concentrations of humans to bite.
• Human-caused microperturbations in ecologic balance can cause innumerable slumbering infectious agents to emerge unexpectedly.

In its typical form, GBS is an acute polyradiculoneuropathy that produces a lower, bilateral, symmetrical sensorimotor development deficit associated with generalized areflexia. In many cases, there is a history of infection that causes the immune response in the nerves. Between 3.5 and 12% of patients die from complications during the acute phase. The annual incidence of GBS is estimated to be between 0.4 and 4.0 cases per 100,000 inhabitants yearly. In North America and Europe, GBS is more common in adults and increases steadily with age. Several studies indicate that men tend to be more affected than women.

GBS occurs when an individual's immune system attacks itself, particularly affecting the cells of the nervous system. This process can be initiated by infection with various viruses or bacteria. The main symptoms include muscular weakness and tingling (paresthesia) in the arms and legs. Severe complications can occur if the respiratory muscles are affected. The most seriously ill individuals need care in intensive care units.

Zika virus can cause other neurological syndromes (meningitis, meningoencephalitis and myelitis). The French Polynesian Health Authorities also reported an unusual increase in central nervous system abnormalities in fetuses and newborns registered during 2013 – 2014. This finding coincided with the Zika virus outbreak in the islands. None of the pregnant women described clinical signs of the Zika virus, but four women were found positive by IgM serology assays for flavivirus, suggesting a possible asymptomatic Zika virus infection.

• 17 malformations were registered:
  • 12 – fetal cerebral malformations or polymalformative syndromes, including brain lesions
  • 5 – brainstem dysfunction and absence of swallowing

The French Polynesian Health Authorities hypothesize that Zika virus infection may be associated with these abnormalities if mothers are infected during the first or second trimester of pregnancy.

World Health Organization (WHO) advises its Member States to implement or intensify surveillance of neurological and autoimmune complications in all age groups, particularly in situations of possible ZIKV circulation. This surveillance can be established as hospital-based, syndromic surveillance, or surveillance of cases. If case surveillance is implemented, a case definition should include GBS, Fisher syndrome, encephalitis, meningitis, and meningoencephalitis.

Fisher syndrome (or Miller Fisher syndrome) is characterized by impaired eye movements, abnormal coordination and loss of tendon reflexes. While the clinical triad (ataxia, ophthalmoplegia and areflexia) is easily recognizable, sometimes it overlaps with GBS, so some authors consider it a variant of GBS, associated with an autoimmune inflammation of nerves after an infection.

While in the Region of the Americas, such syndromes have not yet been reported, health services and practitioners should be alert to their possible occurrence to properly prepare health facilities for rapid detection and appropriate treatment of cases.

Microcephaly is a neurological disorder in which the occipitofrontal circumference is smaller than that of other children of the same age, race and sex. Maternal-fetal transmission of the Zika virus has been documented throughout pregnancy. Zika virus infection has been confirmed in several infants with congenital microcephaly and in fetal losses among women infected during pregnancy. The spectrum of outcomes associated with infection during pregnancy is not yet fully understood, nor are the factors that may increase fetal risk.

A large number of Brazilian newborns with microcephaly have been observed in parallel with the current Zika outbreak. It is unknown how many microcephaly cases are associated with Zika virus infection. Studies are being conducted to investigate the association between Zika virus infection and microcephaly, including the role of other contributory factors (e.g., prior or concurrent infection with other organisms, nutrition and environment). The full spectrum of outcomes associated with Zika virus infections during pregnancy is unknown and requires further investigation (ECDPC, 2015).

Brazilian Health Authorities have confirmed that newborns of mothers who had a Zika virus infection during the first trimester of pregnancy are at an increased risk of microcephaly or other congenital anomalies (ECDPC, 2015).

Zika virus infections have been confirmed in infants with microcephaly, although it is unknown how many microcephaly cases are associated with Zika virus infection. Furthermore, Zika virus RNA has been detected in the pathologic specimens of fetal losses, although it is unknown whether the Zika virus caused the fetal losses. Pregnant women can be infected with the Zika virus in any trimester.

The Brazil Ministry of Health continues to investigate the possible association between the Zika virus and a reported increase in the number of babies born with microcephaly. Due to concerns of microcephaly associated with maternal Zika virus infection, fetuses and infants of women infected with the Zika virus during pregnancy should be evaluated for possible congenital Zika virus infection and neurologic abnormalities.

The diagnosis of Zika virus infection should be suspected in individuals:

• With characteristic clinical symptoms (fever, rash, headache, arthralgia, myalgia and conjunctivitis) and
• Relevant epidemiologic exposure (residence in or travel to an area where the Aedes mosquito is present and where travel-related or local cases have been reported within two weeks prior to the onset of illness).

The incubation period (the time from exposure to onset of symptoms) of Zika virus infection is not clear but is typically 2 to 12 days after the mosquito vector bite. One in four infected individuals (20 – 25%) develops disease symptoms (CDC, 2015). Among those who do, the symptoms/infection are usually mild and usually resolve within 2 to 7 days.

An estimated 80% of individuals infected with the Zika virus are asymptomatic.2 The Zika virus usually remains in the blood of an infected individual for a few days, but it can be found longer in some individuals.

Symptoms of infection with the Zika virus typically include:

• Acute onset of low-grade fever (37.8 to 38.5°C)
• Maculopapular rash (may or may not be present)

Maculopapular rash - wikipedia.org

• Arthralgia (notably the small joints of hands and feet)
• Conjunctivitis (nonpurulent)

Other commonly reported signs and symptoms include:

• Mild headaches
• Retro-orbital pain
• Asthenia (weakness or debility)
• Myalgia

More rarely observed signs and symptoms include:

• Dizziness
• Pruritus
• Mucous membrane ulcerations
• Anorexia
• Nausea/vomiting
• Diarrhea/constipation
• Abdominal pain (CDC, 2016b)

The differential diagnosis of Zika virus infection includes:

• Other viral causes of arthritis:
  • Dengue fever
    • Dengue and Zika virus infections present similar clinical manifestations and are transmitted by the same mosquito vector. They differ clinically in that dengue infection usually presents with a higher fever and more severe muscle pain, which may also be associated with hemorrhage. Coinfection with Zika, chikungunya and dengue viruses has been described. The diagnosis of dengue virus infection is established via serology (Maron, 2016).
  • Chikungunya
    • Chikungunya and Zika virus infections present similar signs and symptoms and are transmitted by the same mosquito vector. They differ clinically in that chikungunya usually presents with a higher fever and more intense joint pain, affecting the hands, feet, knees and back. The infection can be disabling, causing patients to bend over such that they cannot walk or rendering individuals unable to perform simple manual tasks such as opening a water bottle. Coinfection with Zika, chikungunya and dengue viruses has been described. The diagnosis of chikungunya virus infection is established via serology (CDC, 2015).
  • Parvovirus
    • Parvovirus infection can present with acute and symmetric arthritis or arthralgia, most frequently involving the small joints of the hands, wrists, knees and feet. The rash may or may not be present. The diagnosis is established via serology (Maron, 2016).
  • Rubella
    • Clinical manifestations of rubella include low-grade fever and coryza. A macular rash begins on the face and spreads to the trunk. Arthritis may be present. The diagnosis is established via serology.
    • A number of other viruses may also cause arthritis, including enterovirus, adenovirus and alphaviruses (Maron, 2016).
  • Measles
    • Clinical manifestations of measles include fever, cough, sore throat, coryza, conjunctivitis and lymphadenitis. Koplik spots may precede a generalized rash. The diagnosis is established via serology.
  • Leptospirosis
    • Leptospirosis is characterized by fever, rigors, myalgia, conjunctival suffusion and headache. Less common signs and symptoms include cough, nausea, vomiting, diarrhea, abdominal pain and arthralgia. It may be distinguished from a Zika virus infection by the presence of jaundice. The diagnosis is established via serology.
  • Malaria
    • Malaria is characterized by fever, malaise, nausea, vomiting, abdominal pain, diarrhea, myalgia and anemia. The diagnosis of malaria is established by the visualization of parasites on peripheral smear.
  • Rickettsial infection
    • Rickettsial infections with similar manifestations to the Zika virus include African tick bite fever and relapsing fever. African tick bite fever is observed among travelers to Africa and is characterized by headache, fever, myalgia, solitary or multiple eschars with regional lymphadenopathy and generalized rash. The diagnosis is established via serology. Relapsing fever is characterized by fever, headache, neck stiffness, arthralgia, myalgia and nausea. Diagnostic tools include direct smear and polymerase chain reaction.

The preliminary diagnosis is based on the patient's clinical features, places and dates of travel and activities. Laboratory diagnosis is generally accomplished by testing serum or plasma to detect the Zika virus, viral nucleic acid or virus-specific immunoglobulin M and neutralizing antibodies.

The diagnosis is definitively established via reverse-transcription polymerase chain reaction (RT-PCR) or serology. These tests are performed at the United States CDC Arboviral Diagnostic Laboratory and some state health departments or the PAHO/WHO (CDC, 2015). 

• Reverse-Transcription Polymerase Chain Reaction (RT-PCR)
  • Within the first week (usually the first 3 – 5 days) after the onset of symptoms, the diagnosis of Zika virus infection may be established via RT-PCR tests on an acute-phase serum to detect Zika virus RNA.
  • Acute serum should be compared to convalescent serum obtained 2 – 3 weeks later.
  • RT-PCR testing for dengue virus and chikungunya virus should also be ordered.
• Serologic Testing (Immunoglobulin M (IgM) and Confirmatory Neutralizing Antibody Titers)
  • Virus-specific IgM and confirmatory neutralizing antibody titers detect specific antibodies against ZIKV in the serum, typically developing toward the end of the first week of illness.
  • Four days or more following the onset of symptoms, the diagnosis may be established by Zika virus serologic testing IgM and confirmatory neutralizing antibody titers.
  • Acute and convalescent sera should be obtained to detect an increased antibody titer in the paired samples with an interval of two to three weeks between both draws.
  • Serologic testing should also be ordered for dengue virus infection and chikungunya virus infection.
  • All serologic results should be interpreted with caution since there can be cross-reactivity with other flaviviruses, including dengue, West Nile, and yellow fever.
• Plaque-Reduction Neutralization Testing (PRNT)
  • Plaque-reduction neutralization testing can measure virus-specific neutralizing antibodies and discriminate between cross-reacting antibodies in primary flavivirus infections.

In 2016, Zika virus infection became a nationally notifiable condition. Healthcare providers are encouraged to report suspected cases to their state or local health departments to facilitate diagnosis and mitigate the risk of local transmission. State health departments are encouraged to report laboratory-confirmed cases to the CDC through ArboNET, the national surveillance system for arboviral disease.

Laboratory specimens may be sent directly to the CDC Arboviral Diagnostic Laboratory. Instructions are available online. Communication should be initiated with the laboratory via telephone (1-970-221-6400) prior to the shipment of specimens (CDC, 2015). 

Test results are generally available 4 to 14 days after the receipt of the specimen. Reporting times for test results may be longer during the summer months when arbovirus activity increases. Receipt a hard copy of the results takes at least 2 weeks after testing is completed. All results will be sent to the appropriate state health department. All healthcare providers should notify their state health department of direct submissions to the CDC.

Healthcare providers should question all pregnant women about recent travel. Pregnant women with a history of travel to an area with ongoing Zika virus transmission should be evaluated for Zika virus infection in accordance with CDC Interim Guidance protocols (AAP, 2012).

Because of the similar geographic distribution and clinical presentation of Zika, dengue and chikungunya virus infection, pregnant women with symptoms consistent with Zika virus infection should also be evaluated for dengue and chikungunya virus infections, in accordance with existing guidelines. Referral to a maternal-fetal medicine or infectious disease specialist with expertise in pregnancy management is recommended.

Laboratory testing of maternal serum for Zika virus infection, including RT-PCR, IgM and neutralizing antibody testing, is warranted for pregnant women(AAP, 2012):

• With a history of travel to an area with Zika virus transmission and
• Who reports the presence of two or more symptoms consistent with Zika virus infection (acute onset of fever, maculopapular rash, arthralgia or conjunctivitis) during or within two weeks of travel or
• Who have ultrasound findings of fetal microcephaly or intracranial calcifications

Laboratory testing for Zika virus infection is not indicated for pregnant women in the following categories (AAP, 2012).:

• Pregnant women with no travel history to an area with Zika virus transmission
• Pregnant women with a travel history to an area with Zika virus transmission but no clinical illness consistent with Zika virus infection and no ultrasound findings of fetal microcephaly or intracranial calcifications

It is possible that a pregnant woman with a relevant travel history and no clinical symptoms or positive ultrasound findings may have a fetus affected by the Zika virus infection in that asymptomatic Zika virus infection is common. The above interim guidance has been issued based on limited laboratory testing capacities, and these criteria may be revised.

Zika virus testing of maternal serum includes (AAP, 2012):

• RT-PCR testing for symptomatic pregnant women with onset of symptoms within the previous week.
• IgM and neutralizing antibody testing should be performed on specimens collected 4 days or later after the onset of symptoms. Cross-reaction with related flaviviruses (e.g., dengue or yellow fever) is common with antibody testing. It might be difficult to distinguish Zika virus infection from other flavivirus infections. Consultation with state or local health departments might be necessary to assist with the interpretation of results.

Laboratory evidence of maternal Zika virus infection includes (AAP, 2012):

• RT-PCR detected Zika virus RNA in any clinical specimen.
• Positive Zika virus IgM with confirmatory neutralizing antibody titers 4-fold or higher than dengue virus neutralizing antibody titers in serum. Testing is considered inconclusive if the Zika virus neutralizing antibody titers are less than 4-fold higher than dengue virus neutralizing antibody titers.

Zika virus infections have been documented through intrauterine transmissions resulting in congenital Zika virus infection and intrapartum transmission from a viremic mother to her newborn (Vogel, 2015).

Zika virus RNA by RT-PCR testing of amniotic fluid can be performed to detect intrauterine Zika virus infection. However, the sensitivity and specificity of this approach for diagnosing congenital infection are unknown. It is reasonable to offer amniocentesis to women at 15 weeks or greater gestational age with a history of travel to an area with Zika virus transmission and either positive/inconclusive laboratory testing for Zika virus infection or relevant ultrasound findings (fetal microcephaly or intracranial calcifications).

Amniocentesis is associated with an overall 0.1% risk of pregnancy loss when performed at less than 24 weeks of gestation (Vogel, 2015). Amniocentesis performed at 15 weeks or later gestational age is associated with lower rates of complications than those performed at earlier gestational ages. Amniocentesis performed at 14 weeks or less of gestational age is not recommended. Healthcare providers should discuss the risks and benefits of amniocentesis with their patients. It is unknown whether a positive amniotic fluid RT-PCR result is predictive of a subsequent fetal abnormality and, if so, what proportion of infants born after infection will have abnormalities. A positive RT-PCR result on amniotic fluid should be considered suggestive of intrauterine Zika virus infection and potentially useful to pregnant women and their healthcare providers.

Serial ultrasound examinations (every three to four weeks) are appropriate to monitor fetal growth and anatomy in pregnant women with laboratory evidence of Zika virus infection in serum or amniotic fluid (Vogel, 2015). Data on fetal ultrasound findings in infected pregnant women is limited. One small study reported variable fetal ultrasound findings that may include lower-than-expected head circumference for the time of gestation (e.g., more than two standard deviations below the mean), focal brain abnormalities in areas such as the cerebellum and intraocular and brain calcifications.

For live births, Zika virus laboratory testing is recommended for:

• Infants with microcephaly or intracranial calcifications were born to women who traveled to or resided in an area with Zika virus transmission while pregnant.
• Infants born to mothers with positive or inconclusive test results for Zika virus infection.

Because the diagnosis of Zika virus infection is made through molecular and serologic testing, including RT-PCR for viral RNA and IgM and plaque reduction neutralization test (PRNT) for Zika virus antibodies, it is currently unknown which type of testing most reliably establishes the diagnosis of congenital Zika virus infection. The CDC recommends molecular and serologic testing of infants being evaluated for evidence of a congenital Zika virus infection.

The following Zika virus testing on infants per CDC interim guidelines includes (Vogel, 2015):

• Test infant serum for Zika virus RNA per RT-PCR, Zika virus IgM and neutralizing antibodies, and dengue virus IgM and neutralizing antibodies. If possible, the initial sample should be collected either from the umbilical cord or directly from the infant within 2 days of birth.
• If cerebrospinal fluid (CSF) is obtained for other studies, test for Zika virus RNA by RT-PCR, Zika virus IgM and neutralizing antibodies, dengue virus IgM and neutralizing antibodies.
• The mother's serum should be tested for Zika virus IgM and neutralizing antibodies, as well as dengue virus IgM and neutralizing antibodies, if not already performed during pregnancy.
• Testing frozen and fixed placental and cord tissue for Zika virus RNA by RT-PCR.
• Testing of cord serum for Zika and dengue virus IgM and neutralizing antibodies.

The results of these assays can be falsely positive because of cross-reacting antibodies. Plaque-reduction neutralization testing (PRNT) can measure virus-specific neutralizing antibodies and discriminate between cross-reacting antibodies in primary flavivirus infections (e.g., dengue or yellow fever viruses).

Finally, histopathologic examination of the placenta and umbilical cord tissues with Zika virus immunohistochemical staining to detect Zika virus antigen on fixed tissue and Zika virus RT-PCR on fixed and frozen tissue can be considered (Vogel, 2015).

An infant is considered congenitally infected if Zika virus RNA or viral antigen is identified in any of the samples submitted, including testing of amniotic fluid and testing of the placenta or umbilical cord. In addition, Zika virus IgM antibodies with confirmatory neutralizing antibody titers that are 4-fold or higher than dengue virus neutralizing antibody titers in the infant serum or CSF constitute evidence of a congenital Zika virus infection. If Zika virus neutralizing antibody titers are less than 4-fold higher than dengue results, the results are inconclusive.

Fetal tissue testing is warranted for evaluation of fetal losses in women with a history of travel to an area of Zika virus transmission, together with either symptom consistent with Zika virus infection during or within two weeks of travel or findings of fetal microcephaly. In such cases, Zika virus RT-PCR and immunohistochemical staining should be performed on fetal tissues, including the umbilical cord and placenta.

As of 2016, no vaccine or antiviral medications are available to prevent or treat Zika virus infections. Effective vaccines exist for several flaviviruses. Vaccines for yellow fever virus, Japanese encephalitis and tick-borne encephalitis were introduced in the 1930s. The vaccine for dengue fever has just recently become available for use.

Work has begun towards developing a vaccine for the Zika virus, according to Anthony Fauci, Director of the National Institute of Allergy and Infectious Diseases. The researchers at the Vaccine Research Center have extensive experience working with vaccines for viruses such as West Nile virus, chikungunya virus and dengue fever (Fauci & Morens, 2016). Nikos Vasilakis of the Center for Biodefense and Emerging Infectious Diseases has predicted that 10 to 12 years may be needed before an effective Zika virus vaccine becomes available.

The goals of clinical management, whether pregnant or not, are supportive and include:

• Rest
• Drinking fluids to prevent dehydration
• Administration of acetaminophen and analgesics to relieve fever and pain, respectively

Aspirin and other nonsteroidal anti-inflammatory drugs (NSAIDs) like ibuprofen and naproxen should be avoided until dengue infection has been ruled out to reduce the risk of hemorrhage.

In pregnant women with laboratory evidence of Zika virus infection in serum or amniotic fluid, serial ultrasound examinations (every three to four weeks) are appropriate to monitor fetal growth and anatomy.

Because of similar geographic distribution and symptoms, individuals with suspected Zika virus infections also should be evaluated and managed for possible dengue or chikungunya virus infection.

Individuals infected with the Zika, chikungunya or dengue viruses should avoid mosquito bites during the first week to prevent other mosquitoes from becoming infected and reduce the risk of local transmission by passing the viruses on to other individuals.

To evaluate an infant for possible congenital Zika virus infection, microcephaly is defined as occipitofrontal circumference less than the third percentile, based on standard growth charts (e.g., Fenton, Olsen, CDC or WHO growth curves) for sex, age and gestational age at birth. For a diagnosis of microcephaly to be made, the occipitofrontal circumference should be disproportionately small in comparison with the length of the infant and not explained by other etiologies (e.g., other congenital disorders). If an infant's occipitofrontal circumference is equal to or greater than the third percentile but is notably disproportionate to the infant's length or if the infant has deficits related to the central nervous system, additional evaluation for Zika virus infection should be considered.

For all infants with possible congenital Zika virus infection, evaluation should include (DHHS, 2015):

• A comprehensive physical examination, including careful measurement of the occipitofrontal circumference, length, weight and assessment of gestational age.
• Evaluation for neurologic abnormalities, dysmorphic features, splenomegaly, hepatomegaly, rash, or other skin lesions. Full-body photographs and any rash, skin lesions or dysmorphic features should be documented. If an abnormality is noted, consultation with an appropriate specialist is recommended.
• Unless prenatal ultrasound results from the third trimester, a cranial ultrasound demonstrated no brain abnormalities.
• Evaluation of hearing by evoked otoacoustic emissions testing or auditory brainstem response testing, either before discharge from the hospital or within one month after birth. Infants with abnormal initial hearing screens should be referred to an audiologist for further evaluation.
• Ophthalmologic evaluation, including examination of the retina, either before discharge from the hospital or within one month after birth. Infants with an abnormal initial eye evaluation should be referred to a pediatric ophthalmologist for further evaluation.
• Other evaluations are specific to the infant's clinical presentation.

For infants with microcephaly or intracranial calcifications detected prenatally or at birth whose mothers were possibly infected with the Zika virus during pregnancy, evaluation should include:

• Testing the infant for Zika virus infection.
  • For infants with microcephaly or intracranial calcifications who have a positive or inconclusive test finding for Zika virus infection, healthcare providers should:
    • Assess the infant for possible long-term sequelae, including a repeat hearing screen at age 6 months, even if the initial screening hearing test was normal, because of the potential for delayed hearing loss as has been described with other infections such as cytomegalovirus.
    • Order an ophthalmologic evaluation, including retinal examination during the first month of life, given reports of abnormal eye findings.
    • Report the case to the state, territorial or local health departments.
  • For infants with microcephaly or intracranial calcifications with negative results on all Zika virus tests performed, healthcare providers should evaluate for other possible etiologies and treat as indicated. Evaluation should include:
    • Consultation with a clinical geneticist or dysmorphologist.
    • Consultation with a pediatric neurologist to determine appropriate brain imaging and additional evaluation (e.g., ultrasound, computerized tomography scan, magnetic resonance imaging and electroencephalogram).
    • Testing for other congenital infections such as syphilis, toxoplasmosis, rubella, cytomegalovirus infection, lymphocytic choriomeningitis, and herpes simplex virus infections. A pediatric infectious disease specialist should be consulted.
    • A complete blood count, platelet count, liver function, and enzyme tests, including alanine aminotransferase, aspartate aminotransferase, and bilirubin.
    • Consideration of genetic and other teratogenic causes based on additional congenital anomalies identified through clinical examination and imaging studies.
• Testing the mother for Zika virus infection if this testing had not already been performed during pregnancy.

Recommendations for long-term follow-up for infants with possible congenital Zika virus infection include (DHHS, 2015):

• Conducting additional hearing screen at age 6 months, plus any appropriate follow-up of hearing abnormalities detected through a newborn hearing screening.
• Carefully evaluate occipitofrontal circumference and developmental characteristics and milestones throughout the first year of life, with appropriate consultations with medical specialists (e.g., pediatric neurology, developmental and behavioral pediatrics, physical and speech therapy).
• Reporting the case to state, territorial or local health departments and monitoring for additional guidance as it is released.

For infants without microcephaly or intracranial calcifications detected prenatally or at birth whose mothers were possibly infected with the Zika virus during pregnancy, subsequent evaluation is dependent on results from maternal Zika virus testing (AAP, 2012).

• If the test results for the mother were negative for the Zika virus infection, the infant should receive routine care (e.g., newborn metabolic and hearing screens).
  • If the results of all of the infant's tests are negative for evidence of Zika virus infection, then no further Zika virus testing and evaluation are recommended.
• If the mother received positive or inconclusive results for Zika virus infection, the infant should be tested for a possible congenital Zika virus infection.
  • If any infant's samples test positive or inconclusive, the infant should undergo further clinical evaluation.
  • The infant should be followed to assess for possible long-term sequelae, which should include:
    • Cranial ultrasound to assess for subclinical findings, unless prenatal ultrasound results from the third trimester demonstrated no abnormalities of the brain
    • Ophthalmologic examination
    • Repeat hearing screen
    • Developmental monitoring and screening during the first year of life
  • The infant's case should be reported to the state, territorial or local health departments