What you need to know about Zika virus, which is "spreading explosively" in the Americas: http://nyti.ms/23yjgFz
  1. What is the Zika virus?
    A tropical infection new to the Western Hemisphere. 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. Few of us have immune defenses against the virus, so it is spreading rapidly. Millions of people in tropical regions of the Americas may now have been infected.
  2. How do I know if I’ve been infected?
    It’s often a silent infection, and hard to diagnose. Only one of five 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. And there is no widely available test for Zika infection. To detect it, a blood or tissue sample from the first week in the infection must be sent to an advanced laboratory.
  3. How is the virus spread?
    Mosquitoes — but not every species. There has been one report of possible spread through blood transfusion and one of possible spread through sex. The virus was found on one occasion in semen.
  4. Which mosquitoes?
    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 U.S. only in Florida, along the Gulf Coast, and in Hawaii – although it has been found as far north as Washington, D.C. The Asian tiger mosquito is also known to transmit the virus, but it is not clear how efficiently.
  5. How might Zika cause brain damage in infants?
    Experts aren’t certain how it happens, or even whether the virus is to blame. The possibility that Zika causes microcephaly – unusually small heads and damaged brains – emerged only 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 even find that Zika virus is not the main cause, although circumstantial evidence suggests it is.
  6. What is microcephaly?
    Babies with microcephaly have unusually small heads. The consequences can vary from child to child, but in most cases, the infant’s brain may not have developed properly during pregnancy or may have stopped growing in the first years of life. These children may experience a range of problems, like developmental delays, intellectual deficits or hearing loss. There is no treatment for an unusually small head — just therapies to deal with any consequences.
  7. What countries should pregnant women avoid?
    About two dozen destinations mostly in the Caribbean, Central America and South America. The CDC's website has the latest, most updated list: http://wwwnc.cdc.gov/travel/page/zika-travel-information
  8. I’m pregnant and I recently visited a country with Zika virus. What do I do?
    The CDC's guidelines are complex and may change, but in short: Some women should get blood tests, and just about all should get ultrasound scans to see if their fetuses are developing microcephaly. Pregnant women who have visited any area with Zika transmission should consult a doctor. The CDC says that those who have had symptoms of infection during their trip or within 2 weeks of returning should have a blood test for the virus.
  9. I’m of childbearing age, but not pregnant and not planning to get pregnant. Should I go to an affected country?
    We talked to a specialist who works with high-risk pregnancies and infectious disease at Massachusetts General Hospital, who advises strict use of birth control to ensure you don’t get pregnant, if you want to visit a country where Zika transmission has been reported.
  10. I’m pregnant now, but wasn’t when I visited one of the affected countries. What’s the risk?
    Very low, experts say. With rare exceptions, the virus does not appear to linger in the body, and people who recover from the infection are immune.
  11. 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 – when some women do not realize they are pregnant. Experts do not know how the virus enters the placenta and damages the growing brain of the fetus.
  12. Should infants be tested?
    Federal health officials say that newborns should be tested if their mothers have visited or lived in any country experiencing a Zika outbreak and if the mothers’ own tests are positive or inconclusive. The reason, officials said is that infection with the virus could be linked to defects in vision and hearing, among other abnormalities.
  13. Is there a treatment?
    No. The symptoms are mild – when they appear at all – and usually require only rest, nourishment and other supportive care.
  14. How should people protect themselves?
    There is no vaccine against the Zika virus. Efforts to make one have just begun, and creating and testing a vaccine normally takes years. Travelers to regions where Zika is being transmitted 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.
  15. If Zika virus has been in Africa and Asia for decades, why wasn’t a link to microcephaly detected earlier?
    It may be that the virus never had struck such a large population without immunity. Until recently, health officials paid little attention to Zika virus. The first alarms about microcephaly were raised only in October, when doctors in the northeastern state of Pernambuco reported a surge in babies born with it.