The World Health Organization meets next week to decide whether to declare Zika a global emergency.
The virus is spreading fast across the Americas, and WHO expects 3-4 million people to be infected over the next year. Scientists are urgently looking into whether the virus causes birth defects. "We know many people are concerned or scared," says Dr. Anne Schuchat of the U.S. Centers for Disease Control and Prevention.
Here are some answers to questions many are asking:
How worried should I be?
It depends on where you live. For most U.S. residents, Zika is unlikely to be a problem. That's because it take two factors for the virus to spread: actively infected people and the right kind of mosquitoes to spread it.
"For the average American who is not traveling, this is not a problem," Schuchat told reporters. It's winter now, and mosquitoes are scarce. Only Aedes aegypti mosquitoes are known for sure to spread Zika, and they're common only in the very southernmost states — south Florida, south Texas, Louisiana and Hawaii. Even there, they would have to bite someone already infected and then bite others very soon afterward, and with just the occasional traveler showing up with Zika, that is unlikely to happen much.
"You can say that there really is essentially no risk at all [now] because we don't have local Zika transmission in the United States," said Dr. Anthony Fauci, head of the National Institute of Allergy and Infectious Diseases. Dengue, a virus closely related to Zika that is spread by the same mosquitoes, has caused only a very few, very small outbreaks over the past few decades.
And 80 percent of people who get Zika don't even know it. The other 20 percent may get a rash, a fever or pinkeye, but Zika hardly ever causes serious illness.
But pregnant women planning to travel should worry. "For pregnant women who to plan travel: Please take this very seriously," Schuchat said. CDC has advised pregnant women to seriously consider postponing travel to any Zika-affected regions. That's because Zika is suspected of causing microcephaly, a serious birth defect in which the brain is underdeveloped.
Where is the Zika virus? When will it get to my state?
The occasional traveler will show up with Zika, but CDC says that's nothing to worry about. New York has five known cases, but it's cold and there are no mosquitoes, so there is no chance of spread. CDC reports 31 cases in travelers in 11 states and Washington, D.C, in the past year, as well as 19 cases in Puerto Rico and a single case in the U.S. Virgin Islands.
Fauci notes that many news outlets are publishing maps that show the known distribution of Aedes aegypti mosquitoes and their cousins, Aedes albopictus. "Don't make the assumption that you are going to see outbreaks in that distribution of mosquitoes," Fauci said. "That's just where the mosquitoes are." Again, those mosquitoes would need a pool of infected humans to bite before they could spread the virus. Right now, Zika is spreading fastest in tropical cities with dense populations and poor mosquito control. "We do think the living conditions in general in the United States — the lack of density, better air conditioning, wider use of screens — will keep us in better shape," Fauci said.
Florida has the dual risk of having the right mosquitoes and lots of travel to and from the affected areas. "We consider Florida a prime risk," said Jorge Rey, an entomologist at the University of Florida. "If you look at past histories, chikungunya and dengue have been transmitted in the Keys."
I just got bitten by a mosquito. Will I get Zika?
Not unless the mosquito has it. So if it was a mosquito in in a U.S. area where Zika hasn't been seen — which is all of the United States right now — the answer is almost certainly "no." If you are in a Zika-affected region, the answer is "maybe." Researchers do not know the "attack rate" — how many people get infected once Zika's in an area. They also do not know whether a single bite can transmit the virus or how long the mosquito has to have been infected to spread it. And if it's not an Aedes mosquito, also called a yellow fever mosquito, it does not transmit the virus.
We're headed to the Caribbean for our honeymoon. Should we worry?
You should definitely take precautions against getting bitten. That means long sleeves and long pants, use of a mosquito repellent such as DEET and staying inside when possible. There's a chemical called permethrin that you can spray on your clothing and gear to repel mosquitoes. And if you were planning on starting a family right away, you might want to rethink that. Women who might be pregnant are advised to avoid affected areas. Doctors know that the earlier in pregnancy a woman gets exposed to a virus or a toxin that can cause brain damage, the worse the effects are on the fetus. Until experts know more about the risks to a pregnancy, they advise taking care.
But a week or two after getting back, if you have not shown symptoms, it's probably safe to get pregnant. The virus doesn't stay in the body for long.
Authorities in El Salvador have taken the extreme step of advising women to not get pregnant at all for two years.
I'm pregnant and just got back from Brazil. What can I do?
Try not to worry. CDC says doctors should ask all pregnant women about their travel histories, and if they have symptoms of a possible Zika infection, they should get tested. That would be a rash and a fever. And women who have been to an affected area and whose fetus looks like it may have microcephaly on an ultrasound should also be tested. Then women should continue to get regular ultrasounds to watch for any signs of trouble.
CDC has guidelines here.
For women with no symptoms, it's not clear what they could or should do. No one knows whether a woman without symptoms could pass Zika virus to her baby. "We are working hard to find out. It's possible," Schuchat said. "There are other viral conditions that can do that. That's why we are taking this very seriously. It's difficult for women to hear and one of the reasons we encouraged women who are pregnant to postpone travel to affected areas."
And no one knows how many women who get Zika while pregnant will have a baby with microcephaly, or whether it's even Zika, or Zika alone, that is to blame.
My neighbors are from El Salvador. Are they going to spread Zika?
Any traveler who has just returned from a Zika-affected country with an active infection could potentially get bitten by a mosquito and spread Zika that way — if the right mosquitoes are around. The infection lasts for a few days to a week. It's unlikely anyone could transmit the virus after a week. So if you don't live somewhere with Aedes aegypti mosquitoes, or if your neighbor hasn't just returned with an infection, the answer is "no."
Can't they just kill all the mosquitoes?
People have been trying for hundreds of years to do that. Mosquito control can work — wetlands draining and aggressive control with pesticides. But wide use of the best bug killers, like DDT, stopped when their effects on the environment outweighed the benefits. Brazil actually did eradicate the Aedes aegypti mosquitoes that spread Zika, chikungunya, yellow fever and other diseases in the 1950s, but the mosquitoes gradually returned.
"Controlling this type of mosquito is difficult," Schuchat said. "It is easy to say, 'Get rid of the mosquito.' It is a lot harder to do it."
It's very hard to kill Aedes mosquitoes because they like to breed in unexpected places, such as bottle caps filled with water, trash cans and discarded tires. Brazil is experimenting with genetically engineered mosquitoes that lay dud eggs, but it's an early experiment. It's also trying fish that eat mosquito larvae, but that approach doesn't work for urban breeding sites.