Limited Zika Virus Outbreaks 'Likely' in US
The proboscis of an Asian tiger mosquito (Aedes albopictus), a virus vector common in North America, as it feeds on human blood.
Credit: CDC/James Gathany

It's likely that the United States will face small outbreaks of Zika virus, but widespread transmission of the virus here is not expected, health officials said today.

Zika virus is spreading rapidly in Central and South America, and there have been a few cases in the United States among travelers who caught the virus overseas. Although the virus isn't spreading locally in the United States yet, it is possible that it will, because the mosquitoes that transmit the virus are common in some parts of the country, said Dr. Anne Schuchat, principal deputy director at the Centers for Disease Control and Prevention. ("Spreading locally" means that mosquito bites an infected person, and then spreads the virus to another person in the vicinity.) 

"It's possible, even likely, that we will see limited Zika virus outbreaks" in the United States, Schuchat said today (Jan. 28) in a news conference.  

The United States has seen limited outbreaks of other mosquito-borne diseases that are more common in the world's tropical regions, including dengue fever and chikungunya virus. But the United States never had large outbreaks of these viruses, and the CDC said it does not expect large outbreaks of Zika virus here either.

That's because differences between the United States and Central and South America limit the spread of mosquito-borne viruses here. [Zika Virus - What You Need to Know (Video)]

For example, urban areas in the United States aren't as density populated as cities in Central and South America, Schuchat said. A densely populated area makes it easier for infected mosquitos to hop from person to person and spread the disease, she said.

Houses in the United States are also more likely to have window screens and air conditioning, and so people have less exposure to mosquitoes here, Schuchat said.

And the U.S. mosquito populations aren't as bad, though it can be hard to knock them out completely, Schuchat said.

Infection with the Zika virus usually causes no symptoms, but can lead to mild illness in some people, including fever, rash, joint pain or red eyes. Historically, outbreaks of the virus occurred in Africa, Southeast Asia and the Pacific islands, but last year, outbreaks began to occur in the Americas.

Health officials are concerned about a link between Zika virus in pregnant women and microcephaly, a birth defect in which the baby's head is abnormally small. In Brazil, there were more than 3,500 cases of microcephaly between October 2015 and January 2016, a significant increase from the average of about 150 cases per year. Researchers have also found Zika virus in the brain tissue of infants born with microcephaly, but the scientists are still investigating that link.

The CDC recently recommended that all U.S. pregnant women consider postponing travel to the areas where Zika virus is spreading, including 24 Latin American countries. These are Brazil, Colombia, El Salvador, French Guiana, Guatemala, Haiti, Honduras, Martinique, Mexico, Panama, Paraguay, Puerto Rico, Suriname, Venezuela, Barbados, Bolivia, Ecuador, Guadeloupe, Saint Martin, Guyana, Cape Verde, Samoa, the U.S. Virgin Islands and the Dominican Republic.

Researchers in the United States are working to better understand the disease and its effects on the body by developing animal models of the illness, said Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases. They're also working on new diagnostic tests and treatments for the disease, Fauci said.

There is no vaccine against Zika, and health officials don't expect to have a vaccine ready in the next few years. But an initial trial of an experimental Zika vaccine could begin later this year, Fauci said.

"We already have existing vaccine platforms to serve as a jumping-off point" for a Zika virus vaccine, Fauci said. Researchers can use a technique similar to the one used for developing a vaccine against West Nile virus, which is in the same family as Zika, Fauci said.

Experts emphasized that, right now, the Zika virus doesn't pose much of a risk to people living in the United States. "For the average American who's not traveling, this is not something they need to worry about," Schuchat said. But it is an important concern for people traveling, and health officials urge those who visit affected areas to take steps to prevent mosquito bites.

Follow Rachael Rettner @RachaelRettner. Follow Live Science @livescience, Facebook & Google+. Original article on Live Science.