This story is part of a partnership between MedPage Today and VICE News.
The World Health Organization has announced that it will convene an emergency meeting to discuss Zika virus, which is spreading "explosively" through the Americas.
Although Zika was once a virus thought to only cause flu-like symptoms, it's now been linked to a rare birth defect in which babies are born with abnormally small heads and underdeveloped brains, a condition known as microcephaly.
"The possible links, only recently suspected, have rapidly changed the risk profile of Zika, from a mild threat to one of alarming proportions," WHO Director General Margaret Chan said in a statement this week. "The increased incidence of microcephaly is particularly alarming, as it places a heart-breaking burden on families and communities."
Here's what you need to know:
What is Zika?
Zika is a virus that It causes a fever, rash and conjunctivitis (pinkeye), but can also cause headaches and muscle aches in some patients.
Only about one in five people who are infected with the virus will get sick, and symptoms usually last no more than a week, according to the Centers for Disease Control and Prevention.
Patients with Zika virus usually don't need to be hospitalized, and they rarely die.
How is it treated?
It's usually treated with rest and fluids plus over-the-counter pain medications (acetaminophen but not aspirin or ibuprofen) to manage symptoms.
Is it new?
Not exactly, but it's new to the Americas.
Zika was first discovered in 1947 when a monkey in Uganda became infected with the virus, but it wasn't reported in humans for another 20 years. The virus remained in Africa and Asia as part of small outbreaks until 2007.
Why are we talking about it now?
The virus arrived in Brazil in May 2015. In November, the Brazilian Ministry of Health announced that there was a possible link between the newly arrived virus and a tenfold increase in babies born with microcephaly.
It's now spread to 24 countries nearby, according to WHO.
On Jan. 15, Hawaii state health officials confirmed that a baby had been born there with microcephaly, and that its mother likely had Zika infection when she was living in Brazil in May.
The WHO and the CDC have both warned pregnant women to avoid traveling to regions where the virus has been reported. And five countries — Colombia, Ecuador, El Salvador, Honduras, and Jamaica — have urged women to delay getting pregnant.
What is microcephaly?
Microcephaly is a condition in which babies have heads that are abnormally small for their age group because they didn't completely develop in the womb.
But microcephaly isn't a disease, it's a symptom. And it can have a variety of causes, including genetics. It can also occur when the pregnant mother gets sick with a virus, such as chicken pox, and that virus gets passed on to her unborn baby. Exposure to drugs and other toxic chemicals in the womb can also result in microcephaly.
It's not necessarily fatal, but it can be. Those who survive may have developmental issues, but others may go on to live normal lives.
So how do we know Zika is causing it?
We don't know for sure, but Chan said a causal relationship is "strongly suspected." Right now, there's only proof of an association between the two.
How is Zika spread?
Zika virus spreads when people receive bites from infected Aedes aegypti mosquitoes. This species of mosquito is also responsible for spreading dengue fever and chikungunya.
Aedes aegypti is usually found about as far north as Georgia in the United States, Dr. William Schaffner, chairman of preventive medicine at Vanderbilt University Medical Center, told VICE News earlier this month. He said we'll see whether its cousin, Aedes albopictus, which is more common in North America, can carry and spread Zika, too.
The virus likely arrived via infected travelers, who were bitten by local mosquitoes. Once it's in the local mosquito population, it can spread to humans in that region. Some say it's possible it arrived in Brazil with the FIFA World Cup.
Are there cases in the United States?
There has been no transmission of Zika virus in the continental United States, but Dr. Anne Schuchat, the principal deputy director of the Centers for Disease Control , said yesterday during a telebriefing that 31 people in 11 states and Washington, DC have been diagnosed with Zika after contracting it abroad.
There are also 19 lab-confirmed cases in Puerto Rico and one in the Virgin Islands.
Is there a vaccine?
There is currently no vaccine to prevent Zika virus, and U.S. health officials have said we are years away from one.
However a Canadian scientist told Reuters that human trials on one potential vaccine could begin as soon as August, meaning an emergency vaccine could be available before the end of 2016.
What can we do to avoid Zika?
For now, NIH director Dr. Francis Collins said travelers should take precautions, especially if they are pregnant or plan to become pregnant.
"If an individual has to live or work in such a region, CDC recommends strict precautions to avoid mosquito bites, including wearing protective clothing, using insect repellents, and sleeping in rooms with window screens or air conditioning," Collins wrote on his blog.
But the CDC has issued travel warnings, urging pregnant women to avoid travel to a growing list of places. One of the reasons for this is because it's not yet known whether a pregnant woman infected with Zika but without symptoms can have a baby with one of the birth defects associated with the virus.
"We're taking it very seriously, and we know it's a difficult thing for women to hear," Schuchat said. "It's one of the reasons that we've urged women who are pregnant to consider postponing travel to the affected areas. It is a possibility, but we don't have the strong evidence of how often it happens or what the risk is."
What about getting rid of the mosquitoes?
There will also be efforts to control the mosquito population, but Schuchat said it's "somewhat difficult" to control Aedes aegypti because they are aggressive daytime biters. Efforts will likely include eliminating breeding sites and outdoor spraying.
What are health officials doing?
The WHO announced that it will convene a International Health Regulations Emergency Committee to discuss Zika on Feb. 1 in Geneva, Switzerland. There, they will determine whether the Zika outbreak is an international public health emergency.
Dr. Anthony Fauci, director of the US National Institutes for Allergy and Infectious Diseases, said many national and international groups will be meeting over the next few months.
These will be "meetings from international collaborators getting together to get and compare the research agendas and trying to synergize on research," he said. "You'll hear more of it."