The Centers for Disease Control and Prevention has warned pregnant women against travel to several countries in the Caribbean and Latin America where the Zika virus is spreading. Infection with the virus appears to be linked to the development of unusually small heads and brain damage in newborns. Here are some answers and advice about the outbreak.
What is the Zika virus?
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 last 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.
How is the virus spread?
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.
How do I know if I've been infected?
Until recently, Zika was not considered a major threat because its symptoms are relatively mild. Only one of five people infected with the virus develops 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. 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 molecular testing.
How does Zika cause brain damage in infants?
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 is not known exactly how common microcephaly has become in that 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 more than 3,500 reported cases. (Reporting of suspected cases commonly rises during health crises.)
Does it matter when in her pregnancy a woman is infected with Zika virus?
The most dangerous time is thought to be during the first trimester. Experts do not know how the virus enters the placenta and damages the growing brain of the fetus. Closely related viruses, including yellow fever, dengue and West Nile, do not normally do so. Viruses from other families, including rubella and cytomegalovirus, sometimes do.
Is there a vaccine? How should people protect themselves?
There is no vaccine against the Zika virus. Efforts to make one have just begun, but creating and testing a vaccine normally takes years and costs hundreds of millions of dollars. Because it is impossible to completely prevent mosquito bites, the Centers for Disease Control and Prevention has advised pregnant women to avoid going to regions where Zika is being transmitted and has advised women thinking of becoming pregnant to consult doctors before going.
Travelers to these countries are advised to avoid or minimize mosquito bites by staying in screened or air-conditioned rooms or sleeping under mosquito nets, wearing insect repellent at all times and wearing long pants, long sleeves, shoes and hats.