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Zika and Other Emerging Viruses Transmitted by Aedes Mosquitos

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

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

Question 2. Where has the Zika virus been found?

Outbreaks have been reported throughout the world.1 In May 2015, Brazil reported the first outbreak of Zika virus infection in the Americas. As of September 2016, 48 countries or territories in the Americas, 8 countries in Oceania, and 1 country each in Africa and Asia are reporting active Zika infection.2

Local transmission of the Zika virus has occurred in the United States. As of September 14, 2016, there are a total of 3,176 Zika cases in the United States, as follows:

  • Locally acquired mosquito-borne cases reported: 43
  • Travel-associated cases reported: 3,132
  • Laboratory acquired cases reported: 1

All Countries and Territories with Active Zika Transmission (as of August 2016)

Zika virus map August 2016

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 an Aedes mosquito. In addition, persons in areas where the Aedes mosquitoes are found may also be at risk as the virus expands its geographic range.

There are other reported modes of transmission which may put people at risk (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 very 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. The Centers for Disease Control and Prevention (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.3

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.

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

The 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 have been infected. There have also been some cases of confirmed Zika RNA causing miscarriages. 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. As the outbreak is evolving quickly, please refer to the CDC’s 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, please refer to these Web pages:

  • Update: Interim guidance for health care providers caring for pregnant women with possible Zika virus exposure—United States, July 2016. CDC.gov/mmwr/volumes/65/wr/mm6529e1.htm?s_cid=mm6529e1_e
  • CDC guidance for travel and testing of pregnant women and women of reproductive age for Zika virus infection related to the investigation for local mosquito-borne Zika virus transmission in Miami-Dade and Broward Counties, Florida. Emergency.cdc.gov/han/han00393.asp

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

Testing for Zika virus infection should be limited to specimens collected from patients meeting the CDC’s clinical and/or epidemiological criteria for testing (see CDC.gov/zika/hc-providers/index.html). Criteria for evaluating and testing infants can be found in the CDC interim guidelines (see Question 9).

Question 8. Which tests should be used to diagnose Zika virus infection?

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.

Zika virus RNA testing should be performed during the acute phase of infection, generally up to 2 weeks after onset of symptoms.

IgM antibodies rise shortly after symptom onset and persist for up to 12 weeks; therefore, IgM antibody testing is most useful 2 to 12 weeks following the onset of symptoms.There can be antibody cross-reactivity with other flaviviruses, such as dengue, West Nile, and yellow fever. Thus, confirmation of Zika virus IgM positive or equivocal test results is necessary and should be conducted according to CDC algorithms. The gold standard test for IgM confirmation is a plaque-reduction neutralization test (PRNT).

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

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 “CDC Guidelines for Health Care Providers” at CDC.gov/zika/hc-providers/index.html.

Additional information about the 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 “Updated Diagnostic Testing for Zika, Chikungunya, and Dengue Viruses in the US Public Health Laboratories” (January 13, 2016) at 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. http://dx.doi.org/10.15585/mmwr.mm6503e1.
  2. All countries and territories with active Zika virus transmission. Centers for Disease Control and Prevention Website. http://www.cdc.gov/zika/geo/active-countries.html. Updated August 31, 2016. Accessed September 13, 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. http://dx.doi.org/10.15585/mmwr.mm6505e1er.
This FAQ is provided for informational purposes only and is not intended as medical advice. A physician’s test selection and interpretation, diagnosis, and patient management decisions should be based on his/her education, clinical expertise, and assessment of the patient.
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