5 interesting facts about Zika

A mosquito-borne virus is prompting worldwide concern because of an alarming connection to a neurological birth disorder and its rapid spread across the globe.

World Health Organization Director-General Margaret Chan called it an "extraordinary event" in declaring a public health emergency.

Here are five important things to know about Zika:

1. What is Zika and why is it so serious?

The Zika virus is a flavivirus, part of the same family as yellow fever, West Nile, chikungunya and dengue. But unlike some of those viruses, there is no vaccine to prevent Zika or medicine to treat the infection.

Zika is commanding attention because of an alarming connection between the virus andmicrocephaly, a neurological disorder that results in babies being born with abnormally small heads. It causes severe developmental issues and sometimes death.

Since November, Brazil has seen 404 confirmed cases of microcephaly in newborns. Seventeen of those cases have a confirmed link to the Zika virus. There were only 146 cases in 2014.

2. How is Zika spread?

The virus is most commonly transmitted when an Aedes mosquito bites a person with an active infection and then spreads the virus by biting others. Those people become carriers when they have symptoms.

On Tuesday, the CDC reported the first case of locally acquired Zika virus in the United States in the latest outbreak, but it was not from a mosquito bite. Instead it was passed via sex.

The case, which Dallas County, Texas, health officials announced, involved a patient who had sex with someone who had recently returned from Venezuela infected with the mosquito-borne virus. The patient had not traveled.

"There have been isolated cases of spread through blood transfusion or sexual contact and that's not very surprising," CDC Director Tom Frieden told CNN's Dr. Sanjay Gupta. "The virus is in the blood for about a week. How long it would remain in the semen is something that needs to be studied, and we're working on that now."

3. Where is the Zika virus now?

The Zika virus is now being locally transmitted in Barbados, Bolivia, Brazil, Cape Verde, Colombia, Costa Rica, Curacao, Dominican Republic, Ecuador, El Salvador, French Guiana, Guadeloupe, Guatemala, Guyana, Haiti, Honduras, Jamaica, Martinique, Mexico, Nicaragua, Panama, Paraguay, Puerto Rico, St. Martin, Suriname, Samoa, Tonga, the U.S. Virgin Islands and Venezuela, according to the CDC and WHO.

Zika has arrived in the United States from travelers returning from these infected areas and, in one case, through sexual transmission. The concern, of course, is whether imported cases could result in more locally transmitted cases within the United States.

The Aedes albopictus, or Asian tiger mosquito, which along with Aedes aegypti transmits Zika virus, is present in many parts of the United States.

4. What can you do to protect yourself against Zika?

With no treatment or vaccine available, the only protection against Zika is to avoid travel to areas with an active infestation. If you do travel to a country where Zika is present, the CDC advises strict adherence to mosquito protection measures: Use an EPA-approved repellent over sunscreen, wear long pants and long-sleeve shirts thick enough to block a mosquito bite, and sleep in air-conditioned, screened rooms, among others.

If you have Zika, you can keep from spreading it to others by avoiding mosquito bites during the first week of illness, the CDC said. The female Aedes aegypti, the primary carrier of Zika, is an aggressive biter, preferring daytime to dusk and indoors to outdoors. Keeping screens on windows and doors is critical to preventing entry to homes and hotel rooms.

5. What's being done to stop Zika?

Researchers are hard at work in laboratories around the world trying to create a Zika vaccine. A clinical trial for a Zika virus vaccine could begin this year, according to Fauci.

"While in development, it's important to understand we won't have a vaccine this year or even in the next few years, although we may be able to have a clinical trial start this calendar year," he said.

Health officials are implementing traditional mosquito control techniques such as spraying pesticides and emptying standing water receptacles where mosquitoes breed. The CDC encourages homeowners, hotel owners and visitors to countries with Zika outbreaks also to eliminate any standing water they see, such as in outdoor buckets and flowerpots.

Studies show local control is only marginally effective since it's hard to get to all possible breeding areas. And since Aedes aegypti has evolved to live near humans and "can replicate in flower vases and other tiny sources of water," said Foy, the Colorado microbiologist, the mosquitoes are difficult to find and eradicate.

Another prevention effort is OX513A, a genetically modified male Aedes aegypti, dubbed by critics as the "mutant mosquito" or "Robo-Frankenstein mosquito." The creation of British company Oxitec, OX513A is designed to stop the spread of Zika by passing along a gene that makes his offspring die. Since females only mate once, in theory this slows the growth of the population. Each OX513A carries a fluorescent marker, so scientists can track him.

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