By Matt McMillen
WebMD Health News
Latest Infectious Disease News
Reviewed by Hansa D. Bhargava, MD
Jan. 7, 2016 -- The mosquito-borne Zika virus has caused panic in Brazil since it first appeared there in May. Nearly 3,000 babies in Brazil have been born with microcephaly, which causes devastating brain damage. Although a link between the two isn't definitely established, the Brazilian government has taken the unprecedented step of advising women to avoid pregnancy until the crisis has been solved.
"There's a lot of fear in Brazil. People are really scared of this virus," says Zika researcher Scott Weaver, PhD, director of the Institute for Human Infections and Immunity at the University of Texas Medical Branch at Galveston. "I have colleagues working there who see four to five births a day of infants with microcephaly."
Late last month, Zika was diagnosed for the first time in Puerto Rico, and officials believe it's likely to spread to the U.S.
To better understand the disease, its risks, and what it may mean for Americans, WebMD turned to infectious disease researchers such as Weaver as well as experts at the CDC and elsewhere.
What is the Zika virus? How do you catch it?
Zika virus, first identified in Uganda in 1947, is transmitted by the same type of mosquito that carries dengue fever, yellow fever, and chikungunya virus. A mosquito bites an infected person and then passes those viruses to other people it bites. Outbreaks did not occur outside of Africa until 2007, when it spread to the South Pacific.
What are the symptoms of Zika virus?
"Only about 1 in 5 people with the virus will exhibit symptoms," says Amesh Adalja, MD, a spokesman for the Infectious Diseases Society of America. "The vast majority have no symptoms at all."
Adalja also says the virus rarely causes major complications. "It's never been thought of as a severe infectious disease until now."
But in rare cases, Zika has been associated with Guillain-Barré syndrome, an autoimmune disorder that can cause partial or complete paralysis, most often temporary.
Is Zika similar to other mosquito-borne illnesses, such as dengue fever, chikungunya, or West Nile virus?
All can cause a variety of flu-like symptoms that range in severity and can last from a few days to more than a week. As with Zika, few people infected with dengue or West Nile will show any symptoms.
How is Zika virus treated?
There's no treatment, but Adalja says most people with symptoms do well with over-the-counter medications for aches and pains. The disease usually runs its course within a week or so.
What is the connection between Zika, microcephaly, and pregnancy?
Microcephaly stunts a baby's head growth, causing it to be much smaller than normal. The baby's brain often will not grow properly.
It's sometimes fatal, Weaver says. "Some fetuses are stillborn or [miscarried]. Of those that survive, many die early in age or have very severe lifelong cognitive problems."
J. Erin Staples, MD, PhD, a medical epidemiologist with the Arboviral Diseases Branch of the CDC, says it will take time to find the cause of microcephaly for the cases being reported in Brazil. There are many causes of microcephaly in babies, including infections during pregnancy, genetic problems, and exposure to toxic substances during pregnancy.
But Weaver says evidence is growing that many of the cases in Brazil are being caused or triggered by Zika.
It's possible that Zika has always triggered microcephaly, Weaver says. Before 2007, the disease struck in such small numbers that the link simply may have been missed.
"Or it may be that the virus has changed and has developed a different pattern of infection and replication in people that leads to infection of the fetus," Weaver says.
Will Zika enter the U.S.?
It's likely, as it can be carried by travelers from the Caribbean or Latin America, Weaver says, noting that the tourist season has just begun. Rio de Janeiro, Brazil's second largest city, will host the 2016 Summer Olympics in August, which will draw people from around the globe.
"As the virus continues to spread, the risk keeps growing for us," he says.
While that may sound dire, Weaver points out that it's unlikely we will experience the same mass outbreaks because we are not exposed to mosquitoes on the same level as are people in Latin America and the Caribbean.
Staples agrees. "We are not able to predict how much Zika virus will occur in the United States," she writes. "However, recent chikungunya and dengue outbreaks in the United States suggest that Zika virus outbreaks in the U.S. mainland may be relatively small and local."
What protective measures can be taken?
If you plan to travel in affected areas, avoid mosquito bites by using mosquito repellent throughout the day. Also, wear long-sleeved shirts and long pants, both indoors and out. The mosquitoes that spread Zika are aggressive daytime biters often found indoors, which we're not used to in the U.S., Weaver says. Mosquitoes here tend to feed at night outdoors.
"You need to protect yourself all day long," Weaver says.
Weaver is particularly concerned about pregnant women travelers.
"Especially in the first trimester or early second trimester, going to an area with Zika virus circulating is pretty risky," he says. "Even though the link between Zika and microcephaly is not completely solid, it's very likely that Zika is involved, and I certainly would not recommend that pregnant women travel to areas where epidemics are ongoing."
Even those who don't know they have Zika can spread the disease. Weaver advises people who have traveled to affected regions to be extremely vigilant against mosquito bites when they return home, especially during the first 10 days.
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