Here's what you need to know about Zika virus

Aedes aegypti, one type of mosquito that can transmit Zika virus.
Aedes aegypti, one type of mosquito that can transmit Zika virus.
dgarkauskas via Flickr Creative Commons

Zika virus has grabbed the world's attention and sparked anxiety since late 2015, after thousands of infected Brazilian women had newborns with birth defects and the virus spread rapidly through numerous countries. Here are answers to the most common questions about Zika.

What is Zika virus?

Zika virus is a flavivirus related to yellow fever, dengue, West Nile and Japanese encephalitis viruses. In almost every instance, people are infected via a mosquito bite, specifically from an Aedes species mosquito (A. aegypti or A. albopictus). These mosquitoes have been found in several parts of California, including Los Angeles, Orange, Riverside and San Bernardino counties. 

What are its symptoms?

First, it's important to point out that only about one in five people infected with Zika virus gets sick. 

The illness is usually mild and lasts for several days to a week. The most common symptoms are fever, rash, joint pain or conjunctivitis, also known as "pink eye." Other common symptoms include muscle pain and headache. 

People usually don’t get sick enough to go to the hospital, and they very rarely die of Zika.

So why did the World Health Organization declare a global health emergency?

Even before experts concluded that Zika causes microcephaly (the term describing the abnormally small head of a newborn), the strong evidence suggesting that it did (thousands of microcephalic babies born to Brazilian mothers who were infected with the virus while pregnant) led the WHO to act. In Feb. 2016, WHO Director-General Dr. Margaret Chan called the possible link "an extraordinary event and a public health threat to other parts of the world."

On April 13, 2016, the U.S. Centers for Disease Control and Prevention concluded that Zika causes microcephaly and other severe fetal brain defects. 

The CDC notes that while women who are infected with Zika during pregnancy have "an increased risk" of having a baby with microcephaly or other severe brain defects, "it does not mean ... that all women who have Zika virus infection during pregnancy will have babies with problems ... some infected women have delivered babies that appear to be healthy."

CDC Director Tom Frieden said on April 13 that the agency is "launching further studies to determine whether children who have microcephaly born to mothers infected by the Zika virus is the tip of the iceberg of what we could see in damaging effects on the brain and other developmental problems."

The CDC recommends that pregnant women and women trying to become pregnant postpone travel to areas with high rates of Zika. Those who insist on going should talk to their doctor or other health care provider first, and all travelers should strictly follow steps to avoid mosquito bites during the trip.

Here is the latest list of CDC travel advisories for Zika-affected countries and territories. And here is the agency's guide to preventing mosquito bites

The  Zika virus usually remains in the blood of an infected person for about a week, but it can be found longer in some people. 

How is Zika treated?

There is no vaccine to prevent, or medicine to treat, Zika infections. You can only treat the symptoms. The CDC recommends the following: Get plenty of rest, drink lots of fluids and take medicine such as acetaminophen for fever and pain. Do not take aspirin or other non-steroidal anti-inflammatory drugs. If you are taking medicine for another condition, talk to your health care provider before taking additional medication.

I heard that Zika can also be transmitted through sex. Is that true?

The CDC says an infected man can pass the virus to his partner through sex.

There have been a handful of such cases in the U.S., including one in California, in San Diego County. A woman contracted Zika through sex with her infected partner after he returned from traveling to Colombia. Both developed a fever and rash and subsequently recovered. The women did not become pregnant. 

Health officials in Dallas reported in February that a patient had been infected through having sex with someone who had recently returned from Venezuela, one of the countries with a Zika outbreak. Both individuals tested positive for the virus, and there have been no documented cases of mosquito-transmitted Zika in Dallas.

The CDC says an infected pregnant woman can pass the virus to her fetus during pregnancy, or while delivering her child. There are still a number of unknowns in this area. You can read more about what the CDC knows - and doesn't know - about Zika and pregnancy and birth outcomes here.

The CDC recommends that pregnant women and men with a pregnant partner who have traveled to an area with Zika activity should "consistently and correctly use condoms during sex ... or abstain from sexual activity for the duration of the pregnancy." 

For non-pregnant women and men with a non-pregnant partner who had possible exposure to Zika from travel or sexual contact, the CDC recommends condoms or abstention for at least eight weeks after their return. The agency recommends these couples wait at least eight weeks after their possible exposure before trying to get pregnant.

For women and men who have been diagnosed with Zika and experienced symptoms, the CDC recommends:

The recommended waiting periods are three times longer than the longest known risk period for people in these situations, according to the CDC.

While it issues guidelines on how to avoid sexual transmission, the CDC says "mosquito bites remain the primary way that Zika virus is transmitted." 

So how much am I at risk of contracting Zika?

From Jan. 1, 2015 through Aug. 26, 2016, there were 189 confirmed cases in California; 188 of them contracted the virus while traveling abroad, and as noted above, a San Diego County woman contracted it through sex with her infected partner after he returned from Colombia. Two women infected with Zika have given birth to infants with Zika-related microcephaly. There have been 25 infections in pregnant women.

There have been no cases of Zika being passed in California through a mosquito bite. 

This story has been updated.