Zika virus is a single-stranded RNA virus of the Flaviviridae family, genus Flavivirus .
Transmission occurs through the bite of an infected Aedes species mosquito. Intrauterine, perinatal, sexual, laboratory, and possible transfusion-associated transmission have been reported. Zika virus has been detected in human milk, but the risk of transmission through breastfeeding is unknown.
Zika virus was first identified in Uganda in 1947. Before 2007, only sporadic human cases were reported from countries in Africa and Asia. In 2007, the first documented Zika virus disease outbreak was reported in the Federated States of Micronesia. Subsequent outbreaks of Zika virus disease occurred in countries in Southeast Asia and the Western Pacific.
Zika virus was identified for the first time in the Western hemisphere in 2015, with large outbreaks in Brazil. The virus then spread throughout much of the Americas, with 48 countries and territories reporting local transmission. In 2016, large outbreaks occurred in the Caribbean (Puerto Rico and the US Virgin Islands), and limited local transmission was identified in the mainland United States (parts of Florida and Texas). Since then, the number of reported Zika virus disease cases in the Americas has declined in all regions, though there have been occasional increases in reporting from some countries. Current information on Zika virus transmission and travel guidance can be found at wwwnc.cdc.gov/travel/page/zika-travel-information.
Most Zika virus infections are asymptomatic. Symptomatic infections are generally mild. Commonly reported signs and symptoms include fever, maculopapular rash, arthralgia, and nonpurulent conjunctivitis. Other symptoms include myalgia, headache, edema, vomiting, retroorbital pain, and lymphadenopathy. Severe disease requiring hospitalization and deaths are uncommon. However, Guillain-Barré syndrome and rare reports of encephalopathy, meningoencephalitis, myelitis, uveitis, and severe thrombocytopenia have been associated with Zika virus infection.
Vertical transmission of the virus leads to congenital Zika virus infection; sequelae include microcephaly with brain anomalies (and other serious neurologic consequences) and fetal loss. The full range of functional disabilities caused by congenital Zika virus infection is not yet known. Short-term follow-up studies of young children with postnatal Zika virus infections have not identified neurodevelopmental problems; longer-term studies are needed, especially among infants infected during the neonatal period.
Zika virus infection should be considered in patients with a clinically compatible illness who recently traveled to an area with ongoing transmission or who had sex with someone who lives in or traveled to those areas. Patients with suspected Zika virus infection should be evaluated and managed for possible dengue or chikungunya virus infection. Many other infectious diseases can appear similar to Zika virus infection, including malaria, dengue, rubella, measles, parvovirus, adenovirus, enterovirus, leptospirosis, rickettsiosis, and group A streptococcal infections.
Zika virus diagnostic testing can be accomplished using both molecular and serologic methods. Although false positives can occur, nucleic acid testing (NAT) provides confirmed evidence of recent infection and is the preferred test for people with suspected acute Zika virus disease. For returning nonpregnant travelers with suspected Zika virus disease, NAT should be performed on specimens collected <14 days after symptom onset.
Zika virus IgM antibodies typically develop within 3 days of symptom onset. However, IgM might be detectable for months after the initial infection, making it difficult to determine the timing of infection. In addition, false-positive IgM test results can occur because of nonspecific reactivity or cross-reactivity with other flaviviruses (such as dengue, West Nile, or yellow fever viruses). As incidence and risk of Zika virus infection decreases, a higher proportion of positive IgM tests will be falsely positive. Neutralizing antibody testing should be performed to confirm positive IgM test results and discriminate between cross-reacting antibodies. However, neutralizing antibodies might not distinguish Zika virus and cross-reacting antibodies in people previously infected with or vaccinated against a related flavivirus (secondary flavivirus infection).
Perform Zika virus IgM testing on NAT-negative specimens or serum collected ≥14 days after onset of symptoms. Pregnant women with recent possible Zika virus exposure and a clinically compatible illness should have concurrent NAT and IgM testing on specimens collected ≤12 weeks after symptom onset. For asymptomatic pregnant women, Zika virus testing is not routinely recommended unless there is ongoing Zika virus exposure. Additional information on diagnostic testing for Zika virus can be found at www.cdc.gov/zika/hc-providers/testing-for-zika-virus.html.
Most state health departments and many commercial laboratories perform Zika virus NAT and IgM testing. Confirmatory neutralizing antibody testing is available through several state health departments and CDC’s Division of Vector-borne Diseases: 970-221-6400. Health care providers are encouraged to report suspected cases of Zika virus infection to their state or local health departments to facilitate diagnosis and mitigate the risk of local transmission in areas where Aedes species mosquitoes are active. Zika virus disease is a nationally notifiable condition. State health departments should report laboratory-confirmed cases to CDC according to the Council of State and Territorial Epidemiologists case definitions.
No specific antiviral treatment is available for Zika virus disease. Treatment is generally supportive and can include rest, fluids, and use of analgesics and antipyretics. Because aspirin and other nonsteroidal anti-inflammatory drugs (NSAIDs) can increase the risk of hemorrhage in patients with dengue, avoid use of these medications until dengue can be ruled out. People infected with Zika, dengue, or chikungunya virus should be protected from further mosquito exposure during the first week of illness to decrease the possibility of local transmission. Carefully evaluate pregnant women with laboratory evidence of Zika virus infection; closely manage these cases for possible adverse pregnancy outcomes. Guidance for the diagnosis, evaluation, and management of infants with possible congenital Zika virus infections is available at www.cdc.gov/pregnancy/zika/testing-follow-up/evaluation-testing.html.
No vaccine or preventive drug is available. However, several candidate vaccines are in various stages of development. All travelers to areas with Zika virus transmission should take steps to avoid mosquito bites to prevent the risk of Zika virus and other vectorborne infections (see Chapter 3, Mosquitoes, Ticks & Other Arthropods). Persons with possible Zika virus exposure who want to reduce their risk for sexual transmission of Zika virus to an uninfected partner should use condoms or abstain from sex. Blood donations in the United States are now routinely screened for Zika virus RNA to reduce the risk of transfusion-associated transmission.
Pregnant women should avoid travel to any area with risk of Zika virus transmission. Pregnant women who travel to one of these areas should talk to their health care provider before traveling and strictly follow steps to avoid mosquito bites or sexual transmission during travel. There is no restriction on the use of insect repellents by pregnant women if used in accordance with the instructions on the product label. Male partners of pregnant women who travel to areas with risk of Zika virus transmission should abstain from sex or use condoms for the duration of the pregnancy to avoid sexual transmission to their pregnant partners. Women and their partners who are trying to become—or who are interested in becoming—pregnant should take steps to protect themselves from Zika virus infection. Mothers are encouraged to breastfeed infants even after possible Zika virus exposure, as available evidence indicates the benefits of breastfeeding outweigh the theoretical risks associated with Zika virus infection transmission through breast milk.
CDC website: www.cdc.gov/zika
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J. Erin Staples, Stacey W. Martin, Marc Fischer