Frequently Asked Questions About Zika


Q: What is the Zika virus?

A: Zika virus is a mosquito-borne virus that is a member of the flavivirus group. This group includes several other viruses that cause serious, sometimes life-threatening diseases such as yellow fever, dengue fever, West Nile and Japanese encephalitis.

Zika virus has been known for decades to circulate in Africa, and Asia and more recently in the Pacific Islands, but very few cases of human disease were documented before 2007. In May of 2015, the first infections were confirmed in Brazil. Since then, the Brazilian government estimates that more than 1 million people have been infected with Zika virus. Zika is now confirmed to be circulating in 31 countries and territories in the Americas, including Mexico, and is likely present in even more.

Q: What are the symptoms of Zika virus?

A: In children and adults, Zika virus infection is generally mild – some develop flu-like symptoms, joint pain, eye inflammation and red rashes, while other people may not have any symptoms. In some cases, infection is associated with serious complications, including Guillain-Barre syndrome, a disorder where the immune system attacks the peripheral nerves and eventually causes paralysis. There is currently no vaccine to prevent Zika disease nor are there any treatments to resolve disease symptoms.

Q: How is Zika virus infection diagnosed?

A: During the first 3-5 days after the appearance of signs and symptoms (fever, fatigue, rash, conjunctivitis or red eyes, and joint pain) the infection can be diagnosed with a high degree of accuracy using a reverse-transcriptase polymerase chain reaction (RT-PCR) test to identify the genetic material of the virus in blood, saliva or urine. However, once the adaptive immune response appears and the virus is cleared from these samples, diagnosis relies on detecting this immune response itself, typically by identifying antibodies generated in response to the infection; the first of these to appear is IgM, which persists for only a few months, followed by IgG with lasts for years. Tests for these antibodies can be very useful in regions of the world where persons are not exposed to related viruses in the flavivirus group, of which Zika virus is a member. However, in locations like Latin America, Asia, Africa and the Caribbean, where many people are exposed to multiple flaviviruses like dengue or even vaccines for yellow fever or Japanese encephalitis, their pre-existing antibodies against these other flaviviruses can cross-react with Zika virus and produce false-positive results. Therefore, travelers returning to places like the United States, Canada and Europe with low levels of exposure to flaviviruses for most of their life can generally be effectively diagnosed at early or late stages of the acute Zika virus infection, but persons from dengue-endemic regions can only be reliably diagnosed soon after the appearance of signs and symptoms.

Q: Where in the Americas has Zika virus been identified?

A: According to the Centers for Disease Control and Prevention, active Zika virus transmission has been reported in over 30 countries and territories in the Americas. Currently, the affected countries include Aruba, Barbados, Bolivia, Bonaire, Brazil, Colombia, Costa Rica, Curacao, Dominican Republic, Ecuador, El Salvador, French Guiana, Guadeloupe, Guatemala, Guyana, Haiti, Honduras, Jamaica, Martinique, Mexico, Nicaragua, Panama, Paraguay, Puerto Rico, Saint Martin, Saint Vincent and the Grenadines, Sint Maarten, Suriname, Trinidad and Tobago, United States Virgin Islands, and Venezuela. According to the Pan American Health Organization, locally-transmitted Zika has not been reported in the United States but has been reported in the Commonwealth of Puerto Rico, the US Virgin Islands and American Samoa. The list of countries where Zika has been identified can change with new cases identified (CDC, PAHO).

Cases have been reported in people who have recently traveled to an affected region. Given the widespread recent outbreaks and spring vacation travel season, more Americans will likely contract Zika in this way.

It is likely that cases of Zika virus disease will occur locally in regions of the U.S. inhabited by the mosquito believed to be responsible for spreading the virus in most parts of Latin America and the Caribbean, Aedes aegypti. The southern U.S. is infested with this mosquito and therefore is at risk for local transmission of Zika in a manner similar to dengue and chikungunya viruses. Aedes albopictus has also been implicated in Zika virus transmission in Africa and occurs further north in the eastern U.S.

Q: What is the link between Zika and microcephaly? 

A: Microcephaly is a neurological condition where a baby is born with an abnormally small head because its brain did not develop correctly. These children almost always have lifelong mental retardation and many live many years, or die soon after or even before birth.

There have been reports in Brazil of microcephaly in babies of mothers who had been exposed to the Zika virus, and in a growing number of cases Zika virus has been detected in the amniotic fluid and tissues of several fetuses. However, more research is needed to confirm the presumed causal link. Nonetheless, the CDC suggests that pregnant women in any trimester should consider postponing travel to regions where the Zika virus is active. And women trying to become pregnant should consult with their doctor or health care provider before travel to those regions.

So far, the majority of babies born with microcephaly cases have not been confirmed with laboratory tests to be linked with Zika but the implementation of improved diagnostics in Brazil is resulting in more confirmations. However, in many cases experts cannot say with certainty that this condition was caused by the virus, and increased screening of newborns may have led to the identification of some borderline cases that may not reflect brain damage. More definitive case-control and prospective cohort epidemiological studies are underway to provide more definitive information.

However, the overall evidence that Zika is responsible for the vast majority of these cases is strengthening:

  • Between 2010 and 2014 in Brazil, 139-175 babies were born with microcephaly each year. In 2015, there were more than 4,000 cases of this disease, coinciding with the arrival of Zika virus.
  • The Zika virus has been found in the amniotic fluid, and placenta of babies born with microcephaly, which has prompted Brazilian doctors to warn women not to become pregnant if possible, for the time being. Some of the hardest hit areas have declared a state of emergency.
  • The virus’s genetic material (RNA) has been detected in the tissues of some of the babies with microcephaly whose mothers were confirmed to have Zika during pregnancy.
  • Zika virus-specific IgM has been identified in the blood of newborn babies with microcephaly, indicating fetal infection.

Concerning the possibility of the Zika virus being transmitted in semen, several suspected cases have been identified in travelers returning to the U.S., 3 of these confirmed and 8 others under investigation, but it remains unclear how often this route of transmission occurs or how long the virus persists in infected men.

You can find CDC guidance for pregnant women at

Q: What is recommended for pregnant women at risk of Zika?

A: Women who are pregnant or are considering becoming pregnant should talk to their obstetrician and make sure they are familiar with the latest guidance from the CDC. This is particularly important if there has been recent travel to countries affected by Zika virus. Keep in mind that the virus is spreading rapidly so the list of countries affected may not reflect the current distribution due to the inherent lag in diagnostic testing and reporting. Click here for the CDC’s current information on travel to affected countries.

Q: What can people do to minimize their risk of becoming infected with Zika virus?

A: Currently no vaccine exists to prevent Zika virus disease. The best prevention is avoiding mosquito bites. If you or someone you know plans on traveling to countries where Zika virus (see map) or other viruses spread by mosquitoes are found, take the following steps:

  • Use insect repellents
    • When used as directed, insect repellents are safe and effective for everyone, including pregnant and nursing women.
    • Most insect repellents can be used on children in proper concentrations. Do not use products containing oil of lemon eucalyptus in children under the age of three years.
    • Repellents containing DEET, picaridin, IR3535, and some oil of lemon eucalyptus and para-menthane-diol products provide long lasting protection.
    • If you use both sunscreen and insect repellent, apply the sunscreen first and then the repellent.
    • Do not spray insect repellent on the skin under your clothing.
    • Treat clothing with permethrin or purchase permethrin-impregnated clothing.
    • Always follow the label instructions when using insect repellent or sunscreen and especially note recommendations for use on children.
  • When weather permits, wear long-sleeved shirts and long pants.
  • Use air conditioning or window/door screens to keep mosquitoes out of your home, hotel room or place of work. Remember that the mosquitoes believed to transmit Zika virus bite during the daytime as well as early morning and evening.
  • Help reduce the number of mosquitoes inside and outside your home or hotel room by emptying standing water from containers such as flowerpots or buckets.
  • If you live in areas inhabited by A. aegypti or A. albopictus, eliminate sources of standing water near your home to reduce populations of these mosquitoes and lower the risk of local Zika virus circulation if you or another traveler returns infected.

Q: What should I do if I was bitten by a mosquito?

A: the risk of being infected by a mosquito bite in the U.S. now during the winter is very low because local transmission has not been detected, and temperatures in most parts of the country are too cool for efficient mosquito transmission. If you were bitten by a mosquito in a region of Latin America or the Caribbean where Zika virus is circulating you should watch for signs and symptoms of infection. If you are pregnant or may have sex with a pregnant women you should consult your health care provider and follow the latest CDC guidance (add link here), which may include diagnostic testing and using protection or abstaining from sex.

Q: What should I do if I have symptoms consistent with Zika virus infection (fever, joint pains, rash, red eyes etc.)?

A: You should seek care and advice from your health care provider, and be sure to tell them if you have a travel history to a region where Zika virus is known to be circulating or a nearby location. But remember that many other infections can cause indistinguishable signs and symptoms, so do not panic, especially if you have not traveled to an endemic area and are not in a high-risk group (pregnant women or men who could have sex with a pregnant woman). For all other groups, Zika virus causes a mild disease that usually resolves within one week with no known long-term consequences.

Q: What should I do if my sexual partner just returned from an affected area or had Zika infection?

A: The CDC has issued guidance for these persons (link here). The rate of virus presence in the semen of infected men is unknown and how long the virus persists in the semen is also not known, so the risks for sexual transmission cannot be estimated. The safest approach would be to abstain from intercourse during pregnancy. If abstinence is not an option, then the use of condoms is recommended. Although we do not know for sure with Zika virus due to our lack of experience with this infection, condom use probably nearly eliminates the risk of sexual transmission.