Zika and Other Viruses Transmitted by Aedes Mosquitos

The Zika, chikungunya, and dengue viruses are transmitted by Aedes mosquitoes. All 3 viruses have overlapping clinical symptoms and may be found in the same geographic locations.

Outbreaks were reported throughout the world in 2015, but global cases have significantly declined since 2017.^1-3 Since May 2015, when Zika virus was first reported in Brazil, it has been detected in most regions of South America, the Caribbean, and Central America; parts of the South Pacific, Southeast Asia, India, and Pakistan; as well as many African countries.⁴ Zika virus transmission persists at low levels in several countries in the Americas and in other endemic regions.^3,4 There is currently no local transmission of Zika virus in the continental United States.²

The most recent information on global Zika virus risk can be found at https://wwwnc.cdc.gov/travel/page/world-map-areas-with-zika.⁴

Anyone living in or traveling to an endemic area is at risk if bitten by an Aedes mosquito. Persons in areas where Aedes mosquitoes are found may also be at risk as the virus expands its geographic range.⁵

For geographic distribution and additional modes of transmission, see Questions 2 and 5.

Approximately 80% of people infected with Zika virus are asymptomatic.³ When symptoms do occur, they are usually mild and may include fever, maculopapular rash, arthralgia, or non-purulent conjunctivitis. Symptoms typically last from several days to a week. Severe disease requiring hospitalization is uncommon, and fatalities are rare.³

The virus may be associated with Guillain-Barré syndrome, a rare paralytic condition that sometimes occurs after certain infections.³ Microcephaly and other congenital anomalies have been associated with Zika virus infection in pregnant women (see below).³ The association with microcephaly has not been seen in other viral illnesses transmitted by the Aedes mosquitoes.

In addition to mosquito-to-human transmission, Zika virus infection can be transmitted from mother to child during pregnancy, resulting in a congenital infection (see Question 6).^6,7 The virus can also be spread via sexual activity, blood transfusion, and laboratory exposure.⁸ The CDC recommends that pregnant women abstain from sex or use condoms for all sexual activity if their sexual partner has traveled to, or lives in, an area with active Zika virus transmission. This recommendation should be followed for the duration of the pregnancy.⁵

There is a theoretical concern that transmission could occur through organ or tissue transplantation. Although Zika virus RNA has been detected in human breast milk, no health problems due to Zika infection acquired through breastfeeding have been reported. Because the known benefits of breastfeeding are thought to outweigh the risks of Zika infection acquired through breastfeeding, the CDC recommends breastfeeding even in areas with risk of Zika virus acquisition.⁶

The Zika virus can be transmitted from a woman to her baby during pregnancy or around the time of birth, leading to microcephaly and other severe fetal brain defects.⁷ Congenital Zika virus syndrome is characterized by severe microcephaly, decreased brain tissue, damage to the back of the eye, joint problems such as club foot, and increased muscle rigidity. Not all babies born with congenital Zika virus infection have this typical presentation; some babies may experience slow head growth and develop postnatal microcephaly.

Approximately 1 in 10 pregnancies with laboratory-confirmed Zika virus infection results in a fetus or an infant with Zika virus–associated defects.⁸ The proportion of fetuses and infants with Zika virus–associated defects has been reported to be highest (15%) among those with first-trimester Zika virus infection.⁷ The full clinical spectrum of congenital Zika virus infection is available at Congenital Zika Syndrome and Other Birth Defects | Zika Virus | CDC.

It is estimated that Zika virus infection in a woman who is not pregnant would not pose a risk for birth defects in future pregnancies after the virus has cleared from the blood.⁸

Symptomatic persons

Testing can be performed in a symptomatic pregnant patient if they did either of the following:

• Lived in or traveled to an area with an active CDC Zika Travel Health Notice or an area with current or past Zika transmission
• Had sex with someone living in or who recently travel to an area with an active CDC Zika Travel Health Notice or an area with current or past Zika transmission; concurrent testing for dengue may be indicated.⁴

Concurrent Zika and dengue virus testing is recommended in non-pregnant symptomatic patients who live in or have recently traveled to an area with an active Zika Travel Health Notice or an area with current transmission outside the United States and its territories.⁴

Asymptomatic persons

Testing is not recommended for asymptomatic non-pregnant patients.⁴

In asymptomatic pregnant patients who have traveled to an area with an active CDC Zika Travel Health Notice during pregnancy, nucleic acid amplification test (NAAT) testing can be considered up to 12 weeks after travel.⁴

Paired serum and urine are the primary diagnostic specimens for Zika virus infection.⁷

The recommended tests include Zika virus RNA and/or IgM antibody tests. Concurrent testing for dengue virus may be indicated since symptoms overlap and the viruses are transmitted in the same regions by the same mosquito vector.⁴

Zika virus RNA testing should be performed during the acute phase of infection, generally up to 12 weeks after travel or symptom onset. Testing for dengue and Zika virus is recommended via nucleic acid amplification test (NAAT) and IgM testing on a serum specimen and Zika virus NAAT on a urine specimen.²

Zika virus IgM antibodies rise shortly after symptom onset and persist for up to 12 weeks or longer for months after infection, making it difficult to use Zika virus IgM tests to determine if women might have been infected before or after they became pregnant.⁷ The Zika virus IgM antibody test can exhibit cross-reactivity with antibodies from other flavivirus infections, such as dengue, West Nile, and yellow fever. Thus, confirmation of a Zika virus IgM non-negative test result should be conducted according to CDC algorithms. As the prevalence of Zika virus disease has declined, the lower prevalence increases the probability that positive test results are false positives.⁷

Refer to CDC.gov/zika/laboratories/lab-guidance.html for the CDC’s guidance for laboratory testing and indications.

For the latest information from the CDC, see “CDC Clinical Testing and Diagnosis for Zika Virus Disease” (https://www.cdc.gov/zika/hcp/diagnosis-testing/index.html, accessed March 21, 2025).

Additional information about the chikungunya virus and related available tests can be found at QuestDiagnostics.com/TestCenter/TestGuide.Action?dc=CF_Chikungunya.

For more information about testing for these 3 mosquito-borne viruses, refer to the CDC memorandum “Updated Diagnostic Testing for Zika, Chikungunya, and Dengue Viruses in the US Public Health Laboratories” at CDC.gov/zika/pdfs/denvchikvzikv-testing-algorithm.pdf (January 13, 2016).