U.S. and international health authorities are raising the alarm about a tropical disease spreading rapidly in Latin America and the Caribbean that they suspect is linked to a devastating brain disorder in babies.
The U.S. Centers for Disease Control and Prevention and the World Health Organization conducted conference calls Thursday urging precautions and calling for the development of a vaccine to combat the mosquito-borne Zika virus.
Most of the time the virus doesn't sicken people, but about one in five has flu-like symptoms including fever, rash, joint pain and red eyes lasting up to a week. But officials suspect it may be linked to microcephaly, in which brain development is incomplete, in babies born to infected mothers.
While CDC and local public health experts downplayed the risk of a major epidemic spreading across the nation, there have been 31 reported U.S. cases of the Zika virus, all of them linked to international travel.
There have been thousands of Zika cases in affected countries, particularly Brazil, considered the epidemic's epicenter, and up to 4 million cases are predicted in the next year.
Zika is only spread by the Aedes genus of mosquitoes — sometimes known as tiger mosquitoes for their distinctive black and white markings — found in the United States but more common in tropical and subtropical zones.
"People are concerned largely in the southern United States, where it's warmer a majority of the year," said Dr. Anna Durbin, associate professor of international health at Johns Hopkins' Bloomberg School of Public Health. "Do I think, or most public health experts think, Zika will enter and spread rapidly through the United States? I'd say no, I don't think that."
Many experts believe the southern United States is most at risk because there are more of the carrier mosquitoes, though widespread use of screens, air conditioning and repellent likely will help contain any outbreaks. CDC officials noted that other outbreaks of diseases carried by the same type of mosquitoes such as dengue fever and chikungunya have been small.
CDC officials Thursday urged pregnant women to avoid traveling to countries with significant numbers of cases. The agency has issued travel warnings for about 20 countries. Public health officials in some of those places have advised women to delay pregnancy.
Some airlines have begun offering refunds for pregnant customers who have booked flights to affected countries.
The WHO said it will convene a committee to guide the international response. However, both the WHO and the CDC already have coordinated with Brazil and other affected countries to improve testing and reporting as well as mosquito control. Officials also said they will hold several meetings to coordinate research efforts.
CDC officials said those who can't avoid travel or who live in affected areas should take precautions, especially during the day when the mosquitoes are most active. Those precautions include wearing long sleeves and using repellent containing the active ingredient DEET, considered safe during pregnancy, said Dr. Anne Schuchat, the CDC's principal deputy director.
The first Zika case was reported in the United States in 2007, but many people don't know they have the virus because its sickens so few, and testing has been uncommon.
The CDC, however, has asked clinicians to be on the lookout and urged state health departments to begin testing or sending specimens to the agency. There have been 31 confirmed cases so far in 11 states and Washington, D.C., the CDC said, though it didn't specify which states Thursday.
Maryland health officials said they have not tested anyone directly for the virus but have sent samples to the CDC and are awaiting results.
Better testing and accounting could lead to a rapid uptick in the tally of U.S. cases, though those infected are still likely to be travelers, according to Schuchat and Dr. Anthony S. Fauci, director of the National Institute of Allergy and Infectious Diseases.
The virus is not believed to spread from human to human, though authorities are investigating a case of a couple who may have passed on an infection through sex. And while all of the U.S. cases so far have been among travelers, they acknowledged that local transmission is possible if the right mosquito bites an infected person and then bites another person.
"For the average American not traveling, this is not something they need to worry about, especially if they are not pregnant," Schuchat said. "Those traveling, please take this seriously."
She added that the situation can change rapidly.
"We don't understand as much about the virus as we want," Schuchat said.
Fauci said there is ongoing research into the basics of the virus. The National Institutes of Health had not spent any money studying Zika but now will use some of the $97 million set aside for other so-called flaviviruses, or those transmitted through mosquitoes or ticks. They include dengue fever, West Nile virus and yellow fever.
Studies also are underway to confirm suspicions that Zika is causing microcephaly, in which a baby is born with a smaller head than normal because brain development is incomplete, Fauci said. Brazilian health authorities have reported more than 3,500 microcephaly cases between October and January. Most babies die or have severe impairments.
Public health administrators also are studying the relationship between Zika and Guillain-Barre syndrome, an immune system disorder that can cause paralysis.
It wasn't until these serious illnesses began in tandem that international health officials took notice of Zika and began issuing preliminary alerts in May.
Fauci said government, academic and industry labs will focus not only on better understanding the virus but on developing better diagnostic tests and vaccines.
Testing for the virus now is complicated, said Dr. Matt Laurens, a pediatric infectious disease specialist and associate professor in the University of Maryland School of Medicine. If the test is not performed immediately, antibodies from a past yellow fever vaccine or exposure to dengue can confuse results.
Laurens also said any vaccine is still likely years away as scientists confirm safety and efficacy. The National Institutes of Health and at least two manufacturers who have worked on other similar vaccines say they plan to begin development efforts. The CDC said there could be a safety trial before the end of the year.
"We need a very safe product before we give it to pregnant women," Laurens said. "I would think women would be breaking down doors to get it."
What is the Zika virus?
It's a pathogen first identified in humans in 1952 and transmitted by the Aedes mosquito, common in tropical and subtropical areas.
Why is it a threat now?
Zika usually causes no symptoms or only mild flu-like symptoms, but authorities now suspect it is linked to the brain disorder microcephaly in babies and to the immune system disorder Guillain-Barre syndrome, which can cause paralysis.
How many people have become infected?
There have been 31 confirmed cases in the United States since 2015 and thousands of cases internationally, including in Brazil, which is the epicenter of the epidemic. Testing for the infection can be difficult and hasn't been widely performed.
Is there a vaccine?
There is no vaccine or specific treatment for the virus, though research is underway on a vaccine, and officials believe there could be a trial before the end of the year and a product potentially in the next several years.
What should people do?
The CDC has issued a travel warning for about 20 countries, and specifically urged pregnant women not to go to those countries. Officials say travelers should cover their bodies and use insect repellent, especially during the day when the mosquitoes are most active.
What do officials believe will happen in the United States?
CDC officials believe warmer southern states where there are more Aedes mosquitoes are most at risk for outbreaks. Based on their experience with other viruses carried by the same mosquitoes, pest-control efforts and use of screens and air conditioning will help limit outbreaks.
Sources: U.S. Centers for Disease Control and Prevention, World Health Organization