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Zika and Other Emerging Viruses Transmitted by Aedes Mosquitos

This is an outdated version of this FAQ. It was effective 05/04/2016 to 10/24/2016.

The current version is available here.

Question 1. Which emerging viruses are transmitted by Aedes mosquitoes?

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

Question 2. Where has the Zika virus been found?

Outbreaks have occurred in Southeast Asia and the Pacific Islands.1 In May 2015, Brazil reported the first outbreak of Zika virus infection in the Americas. As of April 2016, the Zika virus has been reported in 35 countries or territories in the Americas.2

Zika virus is not currently believed to be transmitted by mosquitoes in the continental United States, but has been reported in Puerto Rico. However, recent cases of Zika infection have been reported in U.S. travelers who returned from Central and South America and the Caribbean. The number of individuals diagnosed will likely increase as the outbreak grows.

Question 3. Who is at risk for Zika virus infection?

Anyone living in or traveling to an endemic area is at risk if bitten by a mosquito. In addition, persons in areas where the Aedes mosquitoes are found may also be at risk as the virus expands its geographic range. Aedes mosquitoes have been found in some areas of the southern United States, but local transmission at this point has not been seen. There are other reported modes of transmission (see Question 5).

Question 4. What are the signs and symptoms of Zika virus infection?

Most (80%) of the people infected with Zika virus are asymptomatic.1 When symptoms do occur, they are usually mild and may include fever, maculopapular rash, arthralgia, or nonpurulent conjunctivitis. Symptoms typically last from several days to a week. Severe disease requiring hospitalization is uncommon, and fatalities are rare.

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

Question 5. What other modes of transmission are there?

In addition to mosquito-to-human transmission, Zika virus infection can be transmitted from mother to child during pregnancy, resulting in congenital infection. The virus can also be spread via sexual activity, blood transfusion, and laboratory exposure. There is a theoretical concern that transmission could occur through organ or tissue transplantation. Although Zika virus RNA has been detected in breast milk, transmission through breastfeeding has not been documented. There are no current recommendations in the United States to avoid breastfeeding; however, the CDC recommends pregnant women abstain from sex or use condoms for all sexual activity if their male 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.3

Question 6. What is the potential risk of Zika infection during pregnancy?

Zika virus can be transmitted from a woman to her baby during pregnancy or around the time of birth, but it is currently not known how often this occurs. There has been a marked increase in the number of infants born with microcephaly in Brazil. Although it is unknown how many of these cases are related to Zika infection, at least some of the infants are known to be infected. There have also been some cases of confirmed Zika RNA in fetal loss specimens. Per the Centers for Disease Control and Prevention (CDC), the increased occurrence of microcephaly in Zika virus-affected areas is, at least in a significant proportion of cases, due to Zika. Additional studies are warranted to further investigate the association and to understand any other adverse pregnancy outcomes associated with Zika virus infection.

The CDC has issued a travel alert (Level 2, Practice Enhanced Precautions) for people traveling to certain regions and countries where Zika virus transmission is ongoing. The alert includes travel to multiple countries in the Caribbean, South America, Central America, Mexico, Samoa, and Cape Verde. As the outbreak is evolving quickly, please refer to the CDC for updated travel notices (http://wwwnc.cdc.gov/travel/notices).

Women who are pregnant, or are planning to become pregnant, are advised to postpone travel to affected areas if possible. Some countries are recommending that women try to postpone pregnancy until the outbreak is contained. Pregnant women in Zika virus-affected areas should protect themselves from mosquito bites by using air conditioning and screens to keep mosquitoes outdoors, using bed nets if unable to keep mosquitoes outdoors, wearing long sleeves and pants, and using permethrin-treated clothing and gear and insect repellents. Pregnant and lactating women can use all U.S. Environmental Protection Agency (EPA)-registered insect repellents according to the product label.

For additional information about pregnancy and the Zika virus, refer to these 2 websites:

Question 7. Who should be tested for a Zika infection?

Zika testing should be considered for symptomatic people who have been in an affected region within the 2 weeks before start of symptoms (incubation is 3 to 12 days after exposure). In addition, the CDC recommends testing pregnant women who have traveled to an affected region and who have 2 or more symptoms consistent with Zika infection or an ultrasound that shows fetal microcephaly or intracranial calcifications. The CDC also recommends testing asymptomatic pregnant women if they have traveled to areas with ongoing Zika virus transmission.

Criteria for evaluating and testing infants can be found in the CDC interim guidelines (see Question 9).

Question 8. Which tests should be considered for diagnosing Zika virus infection?

Zika infection shares epidemiologic and clinical features with chikungunya, dengue, and other infections. Molecular and/or serologic testing for Zika infection may be useful to determine the etiology of a given (usually travel-related) illness and guide further testing and management as needed.

The recommended tests include Zika virus RNA and/or antibody tests. It is further recommended that all persons suspected of having Zika infection be tested for chikungunya and dengue infections. The symptoms overlap, and the viruses are transmitted in the same regions by the same mosquito vector.

When infection is suspected, RNA testing should be performed during the first week after onset of symptoms. IgM antibodies usually develop before IgG and can be detected within a week after symptom onset. IgG antibodies generally appear 1-2 weeks after symptom onset. If the initial IgM test is negative, convalescent-phase specimens should be collected 2 to 4 weeks later and tested for both IgM and IgG antibodies.

There can be antibody cross-reactivity with flaviviruses such as dengue, Zika, West Nile, and yellow fever. Thus, confirmation of positive results may be appropriate under specific clinical conditions, such as pregnancy. The gold standard test for confirmation is a plaque-reduction neutralization test (PRNT). Contact your public health department for specimen submission requirements.

Question 9. Where can I get more information?

Additional information concerning the Zika virus can be found at QuestDiagnostics.com/Zika. For the latest information from the CDC, see the “CDC Guidelines for Health Care Providers” at http://www.cdc.gov/zika/hc-providers/index.html.

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

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



  1. Hennessey M, Fischer M, Staples JE. Zika virus spreads to new areas—region of the Americas, May 2015-January 2016. MMWR Morb Mortal Wkly Rep. 2016;65:55–58. DOI: http://dx.doi.org/10.15585/mmwr.mm6503e1.
  2. All countries and territories with active Zika virus transmission. Centers for Disease Control and Prevention Web site. http://www.cdc.gov/zika/geo/active-countries.html. Updated April 18, 2016. Accessed April 29, 2016.
  3. Oster AM, Brooks JT, Stryker JE, et al. Interim guidelines for prevention of sexual transmission of Zika virus-United States, 2016. MMWR Morb Mortal Wkly Rep. 2016;65 (Early Release):1-2. DOI: http://dx.doi.org/10.15585/mmwr.mm6505e1er.
This FAQ is provided for informational purposes only and is not intended as medical advice. A clinician’s test selection and interpretation, diagnosis, and patient management decisions should be based on his/her education, clinical expertise, and assessment of the patient.

Document FAQS.178 Version: 1
Version 1 effective 05/04/2016 to present
Version 0 effective 02/09/2016 to 05/03/2016