ZIKA VIRUS Q & A

Q: What is the Zika virus?
A: A tropical infection new to the Western Hemisphere.

The Zika virus is a mosquito-transmitted infection related to dengue, yellow fever and West Nile virus. Although it was discovered in the Zika forest in Uganda in 1947 and is common in Africa and Asia, it did not begin spreading widely in the Western Hemisphere until May, when an outbreak occurred in Brazil.

Until now, almost no one on this side of the world had been infected. Few of us have immune defenses against the virus, so it is spreading rapidly. Millions of people in tropical regions of the Americas may have had it.

Q: How is the virus spread?

A: Mosquitoes, but not every species.

Zika is spread by mosquitoes of the Aedes species, which can breed in a pool of water as small as a bottle cap and usually bite during the day. The aggressive yellow-fever mosquito, Aedes aegypti, has spread most Zika cases, but that mosquito is common in the United States only in Florida, along the Gulf Coast, and in Hawaii — although it has been found as far north as Washington, D.C., in hot weather.

The Asian tiger mosquito, Aedes albopictus, is also known to transmit the virus, but it is not clear how efficiently. That mosquito ranges as far north as New York and Chicago in summer.

Although the virus is normally spread by mosquitoes, there has been one report of possible spread through blood transfusion and one of possible spread through sex. The virus was found once in semen.

Q: How does Zika cause brain damage in infants?

A: Experts are only beginning to figure it out. Scientists do not fully understand the connection. The possibility that the Zika virus causes microcephaly — unusually small heads and damaged brains — emerged in October, when doctors in northern Brazil noticed a surge in babies with the condition.

It may be that other factors, such as simultaneous infection with other viruses, are contributing to the rise; investigators may find that Zika virus is not the main cause, although circumstantial evidence strongly suggests that it is. It is not known how common microcephaly has become in Brazil’s outbreak.

About 3 million babies are born in Brazil each year. Normally, about 150 cases of microcephaly are reported, and Brazil says it is investigating nearly 4,000 cases.

Q: What countries should pregnant women avoid?
A: About two dozen destinations mostly in the Caribbean, Central America and South America. The Pan American Health Organization believes the virus will spread in every country in the Americas except Canada and Chile. The latest updates to the CDC’s current list of countries and territories in which Zika virus is circulating can be found on the CDC website.

Q: How do I know if I’ve been infected? Is there a test?

A: It’s often a silent infection and hard to diagnose. Until recently, Zika was not considered a major threat because its symptoms are relatively mild. Only 1 of 5 people infected with the virus develop symptoms, which can include fever, rash, joint pain and red eyes. Those infected usually do not have to be hospitalized.

There is no widely available test for Zika infection. Because it is closely related to dengue and yellow fever, it may cross-react with antibody tests for those viruses. To detect Zika, a blood or tissue sample from the first week in the infection must be sent to an advanced laboratory so the virus can be detected through sophisticated molecular testing.

Q: I’m pregnant and I recently visited a country with Zika virus. What do I do?
A: Some women should get blood tests, and just about all should get ultrasound scans. On Jan. 19, the CDC issued interim guidelines for women in that situation and for their doctors. The guidelines may change.

Tips when traveling where Zika virus or other viruses spread by mosquitoes are found .