Author(s): Stacey Martin, J. Erin Staples

Infectious Agent

Zika virus is a single-stranded RNA virus of the Flaviviridae family, genus Flavivirus.

Transmission

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 breast milk, but the risk for transmission through breastfeeding is unknown.

Epidemiology

Zika virus occurs in tropical and subtropical regions. Since 2007, outbreaks of Zika virus disease have occurred throughout the Pacific Islands and in Southeast Asia. In 2015, Zika virus was identified in the Western Hemisphere, where large outbreaks occurred in Brazil. The virus then spread throughout much of the Americas, resulting in several hundred thousand cases. Since 2017, the number of reported Zika virus disease cases has declined worldwide, but occasional increases in cases have been noted from some countries. In 2020, only 4 Zika virus cases were reported in US international travelers. See current information on Zika virus transmission and travel guidance.

Clinical Presentation

Most Zika virus infections are either asymptomatic or result in mild clinical illness characterized by acute onset of fever, arthralgia, nonpurulent conjunctivitis, and maculopapular rash. Other symptoms can include edema, headache, lymphadenopathy, myalgia, retro-orbital pain, and vomiting. Severe disease requiring hospitalization and death are both uncommon. Guillain-Barré syndrome and rare reports of encephalopathy, meningoencephalitis, myelitis, uveitis, and severe thrombocytopenia have been associated with Zika virus infection, however. 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.

Diagnosis

Consider Zika virus infection in patients with acute onset of fever, arthralgia, conjunctivitis, or maculopapular rash who, ≤2 weeks of illness onset, lived in or recently traveled to areas with ongoing Zika virus transmission or had sex with someone who lives in or traveled to those areas. Because Zika and dengue virus infections have similar clinical presentations, patients with suspected Zika virus infection also should be evaluated for possible dengue. Other considerations in the differential diagnosis include adenovirus, chikungunya, enterovirus, leptospirosis, malaria, measles, parvovirus, rickettsiosis, rubella, and group A streptococcal infections (see disease-specific chapters in this section).

Zika virus disease is a nationally notifiable condition. Report suspected cases of Zika virus infection to state or local health departments to facilitate diagnosis and mitigate the risk for local transmission in areas where Aedes species mosquitoes are active. State health departments should report laboratory-confirmed cases to the Centers for Disease Control and Prevention (CDC) according to the Council of State and Territorial Epidemiologists case definitions.

Diagnostic Testing

Because Zika and dengue viruses share a similar global geographic distribution and cause infections that can be difficult to differentiate diagnostically, consider the global epidemiology of these 2 arboviruses when requesting testing and interpreting results. Zika virus testing guidance is updated as needed to address changes in the epidemiology. Current testing guidance is provided on the CDC website. Some state health departments and many commercial laboratories perform Zika virus nucleic acid amplification testing (NAAT) and IgM testing. Confirmatory neutralizing antibody testing is available at CDC’s Arboviral Diagnostic Reference Laboratory and selected health department laboratories.

Nucleic Acid Amplification Testing

NAAT is used to detect Zika viral RNA early in the course of infection and can be performed on amniotic fluid, whole blood, cerebrospinal fluid, semen, serum, tissues, and urine. Due to the temporal nature of Zika virus RNA in the body, a negative NAAT does not always exclude recent Zika virus infection. For this reason, Zika virus IgM antibody testing might be recommended in certain situations.

Serologic Testing

Serum IgM antibody testing can detect Zika virus–specific IgM antibodies that typically develop toward the end of the first week of illness and can remain detectable for months to years after infection, making the determination of the timing of infection difficult. Serum IgM antibody testing can result in a false-positive result due to cross-reacting antibodies against related flaviviruses (e.g., dengue virus, yellow fever virus). Plaque reduction neutralization testing (PRNT) can be used to discriminate between cross-reacting antibodies in primary flavivirus infections, but neutralizing antibodies might still yield cross-reactive results in people who were previously infected with or vaccinated against a related flavivirus (secondary flavivirus infection).

Treatment

No specific antiviral treatment is available for Zika virus disease. Treatment is generally supportive and can include use of analgesics and antipyretics, fluids, and rest. Because aspirin and other nonsteroidal anti-inflammatory drugs (NSAIDs) can increase the risk for hemorrhage in patients with dengue, avoid use of these medications until dengue can be ruled out.

Protect people infected with Zika, chikungunya, or dengue virus from further mosquito exposure during the first week of illness to decrease the possibility of local transmission. Carefully evaluate pregnant people with laboratory evidence of Zika virus infection; closely manage these cases for possible adverse pregnancy outcomes. See guidance for the diagnosis, evaluation, and management of infants with possible congenital Zika virus infections.

Prevention

No vaccine or preventive drug is available for Zika virus. All travelers to areas with Zika virus transmission should take steps to avoid mosquito bites to prevent Zika virus and other vectorborne infections (see Sec. 4, Ch. 6, Mosquitoes, Ticks & Other Arthropods). Advise people with possible Zika virus exposure who want to reduce the risk for sexual transmission of Zika virus to an uninfected partner to follow current CDC recommendations. Although blood donations in the United States were previously screened for Zika virus RNA, the US Food and Drug Administration ceased this requirement in May 2021 because the virus no longer has sufficient incidence to affect the potential donor population.

Pregnancy

Pregnant people should not travel to areas with ongoing Zika outbreaks. Before traveling to areas with current or past spread of Zika, pregnant people should discuss their travel plans with a health care provider. In deciding whether to travel, pregnant people should consider the destination, their reasons for traveling, and their ability to prevent mosquito bites. If used in accordance with the instructions on the product label, there are no restrictions on the use of insect repellents by people who are pregnant.

If a pregnant person or their partner travels to an area with current or past spread of Zika virus, advise the couple to use condoms or to abstain from sex for the entire pregnancy, even if the traveler does not have symptoms of Zika or feel sick. Couples trying to become pregnant who travel to areas with past or current Zika virus transmission should take steps to protect themselves from Zika and consider waiting to get pregnant according to the timeframes outlined in CDC guidance.

Mothers are encouraged to breastfeed infants even after possible Zika virus exposure, because available evidence indicates the benefits of breastfeeding outweigh the theoretical risks associated with Zika virus infection transmission through breast milk.

CDC website: Zika