Zika

Introduction

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 it 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. Occasional increases in cases have been noted from some countries, and cases are infrequently identified in U.S. international travelers returning from Zika virus–endemic countries. In 2023, only 7 Zika virus disease cases were reported in U.S. 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, non-purulent conjunctivitis, and maculopapular rash. Other symptoms can include edema, headache, lymphadenopathy, myalgia, retro-orbital pain, and vomiting. Death and severe disease requiring hospitalization are both uncommon. Guillain-Barré syndrome and rare reports of encephalopathy, meningoencephalitis, myelitis, uveitis, and severe thrombocytopenia have been associated with Zika virus infection. Zika virus infection during pregnancy can result in congenital Zika virus infection; sequelae include microcephaly with brain and ocular anomalies, 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, within 2 weeks of illness onset, lived in or recently traveled to areas with current or past Zika virus transmission or had recent 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 dengue virus infection. Other considerations in the differential diagnosis include adenovirus, chikungunya, enterovirus, leptospirosis, malaria, measles, Oropouche, parvovirus, rickettsiosis, rubella, and group A streptococcal infections.

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 two 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 is typically performed on cerebrospinal fluid and serum. Zika viral RNA has been detected in other specimens including amniotic fluid, whole blood, semen, tissue, and urine. Due to the temporal nature of Zika viral 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) and non-specific reactivity. Plaque reduction neutralization testing can be used to confirm Zika virus infection and can help discriminate between cross-reacting antibodies with other primary flavivirus infections. However, neutralizing antibodies might still yield cross-reactive results in people 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 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 virus from mosquito bites during the first few days of illness to decrease the possibility of further Zika virus transmission.

Carefully evaluate pregnant women with laboratory evidence of Zika virus infection; closely manage these patients during pregnancy and carefully evaluate live-born infants for clinical features associated with intrauterine infection. See guidance for the diagnosis, evaluation, and management of infants with possible congenital Zika virus infections.

Prevention

No vaccine or preventive medication is available for Zika virus. All travelers to areas with possible Zika virus transmission should take steps to avoid mosquito bites during the day and night to prevent Zika virus and other vector-borne infections (see Mosquitoes, Ticks, and Other Arthropods chapter). If used in accordance with the instructions on the product label, there are no restrictions on the use of insect repellents by women who are pregnant.

Advise people with possible Zika virus exposure who want to reduce the risk for sexual transmission of Zika virus to an uninfected partner to use condoms or not have sex following exposure. The time frames that males and females can transmit Zika virus through sex are different because the virus persists longer in semen than other bodily fluids. The time frames shown in Table 4.22.1 start as soon as a person departs a location with a risk of Zika transmission, even if asymptomatic, or from the start of their symptoms or the date of Zika diagnosis.

All travelers returning to the United States from an area with current or past transmission should be advised to take steps to prevent mosquito bites for 3 weeks to decrease the possibility of local transmission. Although blood donations in the United States were previously screened for Zika virus RNA, the U.S. Food and Drug Administration ceased this requirement in 2021 because the virus no longer has sufficient incidence to affect the potential donor population.

Pregnancy

Healthcare professionals should review CDC's Zika travel guidance with pregnant women, their partners, and women planning pregnancy before travel. CDC does not have accurate information on the current risk of Zika virus exposure in many geographic areas. Recommendations are based on whether travel is planned to a geographic area with an active CDC Zika Travel Health Notice or with current or past Zika virus transmission.

Because Zika infection during pregnancy can cause severe birth defects associated with congenital Zika syndrome, advise women who are pregnant to avoid travel to areas with an active Zika Travel Health Notice. If a woman who is pregnant chooses to travel, she should be advised to strictly follow recommendations to prevent mosquito bites and sexual transmission during and after travel as specified in Table 4.22.1 (see Mosquitoes, Ticks, and Other Arthropods).

Travelers with a pregnant partner should consider the reasons for travel, ability to prevent mosquito bites, and potential risk of transmitting Zika to their pregnant partner. If they choose to travel to an area with an active Zika Travel Health Notice, advise them to prevent mosquito bites and sexual transmission during and after travel.

Pregnant women and their partners considering travel to areas with current or past transmission of Zika virus should be informed of the possible risks to the fetus. In deciding to travel, they should consider the destination, reason for traveling, and their ability to consistently prevent mosquito bites. If a pregnant woman or her partner chooses to travel, she should be counseled to strictly prevent mosquito bites and sexual transmission during and after travel using the time frames specified in the Prevention section (see Mosquitoes, Ticks, and Other Arthropods and Sex and Travel chapters).

Planning pregnancy

Women planning to become pregnant and their partners who travel to areas with an active Zika Travel Health Notice should prevent mosquito bites and sexual transmission during and after travel and be advised to delay pregnancy following travel using the specified time frames in Table 4.22.1.

Women planning to become pregnant and their partners who travel to areas with current or past Zika virus transmission should prevent mosquito bites and sexual transmission during and after travel. If they are concerned about the risk of Zika, they can consider delaying their pregnancy according to the time frames to prevent sexual transmission. CDC supports shared patient-provider decision-making to determine time frames to wait before trying to conceive after possible Zika virus exposure. Some couples might choose to wait shorter or longer periods depending on individual circumstances (e.g., age, fertility, or details of possible exposure), healthcare professional judgment, and an assessment of risks and possible outcomes.

Breastfeeding

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 (see Travel and Breastfeeding).

Table 4.22.1: Time frames for preventing sexual transmission of Zika virus¹

Notes

¹Methods to reduce sexual transmission of Zika virus include condoms or abstinence.

²Time frames are measured from the date a person departs a location with a risk of Zika transmission (even if asymptomatic) or from the start of symptoms or date of diagnosis.