Infectious Agent

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 also have been reported. Although Zika viral particles were found in the breast milk of 1 woman, and virus RNA has been detected in breast milk of 2 additional women, transmission of Zika virus through breastfeeding has not been documented.


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. In subsequent years, outbreaks of Zika virus disease were identified in countries in Southeast Asia and the Western Pacific. Zika virus was identified for the first time in the Western hemisphere in 2015, when large outbreaks were reported in Brazil. Since then, the virus spread throughout much of the Americas. (See www.cdc.gov/travel for current CDC travel notices for Zika virus.)

Clinical Presentation

Most Zika virus infections are asymptomatic. Symptomatic infections are generally mild. Commonly reported signs and symptoms include fever, maculopapular rash, arthralgia, and conjunctivitis. Other symptoms include myalgia and headache. During the outbreak in Brazil in 2015, the Ministry of Health of Brazil reported a marked increase in the number of infants born with microcephaly, although it is not known how many of these cases were associated with Zika virus infection. Zika virus RNA was subsequently identified in tissues from several infants with microcephaly and from fetal losses in women who were infected during pregnancy. (See Box 3-6 for more information about Zika and pregnancy.) Guillain-Barré syndrome also has been reported in some patients after Zika virus infection.

Box 3-6. Zika in pregnancy

Zika virus infection in a pregnant woman can cause microcephaly and other congenital brain abnormalities in the fetus. CDC recommends that pregnant women not travel to any area with ongoing local transmission of Zika virus. Pregnant women who travel to these areas should talk to their health care provider first and strictly follow steps to prevent mosquito bites. Women who are trying to become pregnant should consult with their health care provider before traveling to an area with ongoing local transmission and strictly follow steps to avoid mosquito bites during the trip.

People who have traveled to an area with Zika and have a pregnant partner should use condoms or not have sex (vaginal, anal, or oral) during the pregnancy.

Travelers who have returned from areas with Zika virus transmission should consider preconception counseling with their health care provider and wait to attempt conception until the risk for sexual transmission is believed to be minimal. For more information, visit www.cdc.gov/zika.

Health care providers can contact the CDC Zika Pregnancy Hotline (770-488-7100, ZikaMCH@cdc.gov or ZikaPregnancy@cdc.gov, or fax 404-718-2200) for clinical consultation on Zika virus infection in pregnancy.


Zika virus infection should be considered in patients with acute onset of fever, maculopapular rash, arthralgia, or conjunctivitis who live in or have traveled to an area with ongoing transmission in the 2 weeks preceding illness onset. Because dengue and chikungunya virus infections share a similar geographic distribution and symptoms with Zika, patients with suspected Zika virus infection should also be evaluated and managed for possible dengue or chikungunya virus infection. Other considerations in the differential diagnosis include malaria, rubella, measles, parvovirus, adenovirus, enterovirus, leptospirosis, rickettsiosis, and group A streptococcal infections.

For people with suspected Zika virus disease, Zika virus rRT-PCR should be performed on urine specimens collected <14 days after onset of symptoms or serum specimens collected <7 days after onset of symptoms. A positive rRT-PCR result confirms Zika virus infection, and no antibody testing is indicated. Serum IgM antibody testing should be performed if rRT-PCR is negative or for samples collected ≥7 days after illness onset. However, these serologic assays can be positive because of cross-reacting antibodies against related flaviviruses, such as dengue or yellow fever viruses. Virus-specific neutralization testing can be used to discriminate between cross-reacting antibodies in primary flavivirus infections, although neutralizing antibodies might still yield cross-reactive results in people who were previously infected or vaccinated against a related flavivirus (secondary flavivirus infection).

Health care providers are encouraged to report suspected Zika virus disease cases 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 States and Territorial Epidemiologists case definitions. Pregnant women with laboratory evidence of Zika virus infection should be reported to the US Zika Pregnancy Registry or the Puerto Rico Zika Active Pregnancy Surveillance System for clinical follow-up.


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. Aspirin and other nonsteroidal antiinflammatory drugs (NSAIDs) should be avoided until dengue can be ruled out to reduce the risk of hemorrhage. People infected with Zika, dengue, or chikungunya virus should be protected from further mosquito exposure during the first week of illness to reduce the risk of local transmission. Pregnant women with laboratory evidence of Zika virus infection should be evaluated and managed for possible adverse pregnancy outcomes.


Avoiding mosquito bites can protect against Zika virus infection (see Chapter 2, Protection against Mosquitoes, Ticks, & Other Arthropods). Using condoms during sexual contact with people with possible Zika virus infection also may reduce transmission risk. For more information on sexual transmission of Zika, see Zika and Sexual Transmission on the CDC website (www.cdc.gov/zika/transmission/sexual- transmission.html). Zika virus likely can be spread through blood transfusions. Blood donors returning from areas with active transmission of Zika virus should defer donation for 4 weeks after return (or 4 weeks after resolution of symptoms, if they become ill with symptoms consistent with Zika virus). Mothers are encouraged to breastfeed infants even in areas where Zika virus is circulating, as available evidence indicates the benefits of breastfeeding outweigh any theoretical risks associated with Zika virus infection transmission through breast milk.

CDC website: http://www.cdc.gov/zika


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Tai-Ho Chen, J. Erin Staples, Marc Fischer