By Matt McMillen 

Reviewed by Hansa D. Bhargava, MD

Birth defects linked to the mosquito-borne Zika virus represent an international public health emergency, the World Health Organization declared.

“There is an urgent need to do a lot more work,” said Margaret Chan, MD, director-general of the WHO. “We need a coordinated international response to make sure we get to the bottom of this.”



The declaration will speed up research into the suspected connection between the virus and cases of microcephaly in babies of infected pregnant women. Microcephaly causes devastating, sometimes-fatal brain damage, and it can result in miscarriage or stillbirth. A cause-and-effect link with the Zika virus hasn’t been definitely established, though.

Meanwhile, officials in Dallas County, TX, reported Feb. 2 that one person caught Zika through sexual activity.

“The patient was infected with the virus after having sexual contact with an ill individual who returned from a country where Zika virus is present,” the Dallas County Health Human Services department said in a statement.

The WHO on Jan. 28 said the virus was “spreading explosively” in the Americas. “The level of concern is high, as is the level of uncertainty,” Chan told the organization's executive board.

The agency predicts 3 million to 4 million people could be infected with the virus this year in the Americas.

Experts previously warned the virus is likely to spread in the United States.

Doctors have seen cases of it in travelers coming back from the Caribbean and Central and South America.

Zika has prompted a CDC travel warning for areas of those parts of the world, with the agency cautioning pregnant women to "consider postponing travel" to more than 25 countries and territories.

The virus has caused panic in Brazil since it first appeared there in May. More than 4,000 babies in Brazil have reportedly been born with microcephaly, and the Brazilian government has taken the unprecedented step of advising women to avoid pregnancy until the crisis has been solved. Since the virus has spread to other countries, several other nations have advised women to put off getting pregnant.

 “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.”

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.

The virus has been found in human semen, and one case of it possibly spreading person-to-person has been described, according to the WHO's Regional Office for the Americas. 

Although the Dallas County case is not the first ever report of Zika spreading through sexual activity, officials had said more evidence was needed to confirm whether it can be sexually transmitted.

But “this increases our awareness campaign in educating the public about protecting themselves and others,” Dallas County Health and Human Services Director Zachary Thompson said. “Next to abstinence, condoms are the best prevention method against any sexually transmitted infections.”

There has also been one report of possible spread of the virus through a blood transfusion, according to the CDC.

What are the symptoms of Zika virus?

The disease can cause fever, rash, joint pain, and conjunctivitis, also called pinkeye. But most people won’t know they have it.

“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, a disorder that can cause partial or complete paralysis, most often temporary. An increase in that illness has been seen in areas such as French Polynesia and Brazil, where a Zika epidemic has taken place, but research hasn't established a direct relationship between the two, according to the WHO’s Regional Office for the Americas.

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-countermedications 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.

The CDC said in a Jan. 15 statement that it tested samples provided by Brazilian health authorities from two pregnancies that ended in miscarriage and two infants with microcephaly who died shortly after birth. In the two full-term infants, the Zika virus was present in the brain. In all four cases, genetic testing showed the virus was the same as the Zika strain circulating in Brazil. All four mothers reported having a fever and a rash consistent with Zika virus during their pregnancies, the CDC says.

"Health authorities in Brazil, with assistance from the Pan American Health Organization, CDC, and other agencies, have been investigating the possible association between Zika virus infection and microcephaly in infants," according to the CDC. Additional studies are needed, the agency says, and more are planned.

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.

What countries are in the CDC travel warning for pregnant women?

The CDC travel warning covers countries where Zika transmission is ongoing: Brazil, Colombia, El Salvador, French Guiana, Guatemala, Haiti, Honduras, Martinique, Mexico, Panama, Paraguay, Suriname, Venezuela, and the U.S. territory of Puerto Rico.

On Jan. 22, the CDC added Barbados, Bolivia, Ecuador, Guadeloupe, Saint Martin, Guyana, Cape Verde, and Samoa to the warning. On Jan. 26, it added the U.S. Virgin Islands and the Dominican Republic. On Feb. 1, it added American Samoa, Costa Rica, Curacao, and Nicaragua. On Feb. 3, it added Jamaica and Tonga.

Pregnant women in any trimester are advised to avoid travel to those areas, the CDC says. Those who must travel, as well as women who are thinking about becoming pregnant, should talk to their doctor first and "strictly follow steps to avoid mosquito bites" during their trip. 

What if I'm pregnant and I've traveled to these areas?

Talk to your doctor. She'll check on your baby's health, and you'll be screened for symptoms of the virus. If you have symptoms, other diseases such as dengue or chikungunya can be ruled out. 

While there's no commercially available test for Zika, a blood test can be done by the CDC and some state health departments if your symptoms have appeared in the past week, the agency says. Testing of amniotic fluid can also be done, although it's not clear how sensitive or specific this test would be for Zika, according to the CDC.

Pregnant women with Zika should get ultrasounds every 3 to 4 weeks to monitor the baby's growth, the agency says. 

Are we at risk of an outbreak in the U.S.?
Weaver earlier said Zika's arrival in the U.S. was likely, as it can be carried by travelers from the Caribbean or Latin America. He also noted the tourist season has just begun. And Rio de Janeiro, Brazil’s second largest city, will host the 2016 Summer Olympics in August, which will draw people from around the globe.

But he saysit’s unlikely we will experience the same mass outbreaks, because we are not exposed to mosquitoes on the same level as people in Latin America and the Caribbean are.

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.”
Aedes mosquitoes, which spread Zika, are found in every country in North, Central, and South America except for two -- Canada and continental Chile, according to the WHO's Regional Office for the Americas. The agency "anticipates that Zika virus will continue to spread and will likely reach all countries and territories of the region where Aedes mosquitoes are found."

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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