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Zika Virus: Answers to Your Questions

by Berkeley Wellness  

John E. Swartzberg, MD, is an infectious disease specialist at the UC Berkeley School of Public Health and Chair of the Editorial Board of He answers seven important questions about the Zika virus, how it spreads, and how you can protect yourself.

What is the Zika virus?

The Zika virus is in a family of viruses, called Flavivirus, that are spread by mosquitoes. Some other viruses in this family that cause disease in humans are West Nile, yellow fever, dengue, and St. Louis encephalitis virus. Zika virus was discovered in 1947 in the Zika forest in Uganda, and remained localized to Africa, Asia, and Micronesia for most of the past 70 years.

The virus exploded over a year ago in Brazil for reasons that aren’t totally clear. One idea is that international visitors to the 2014 World Cup soccer games in Brazil brought the virus to the Americas; another is that the virus was introduced by Pacific Island competitors in an international canoe event in Brazil that same year. Today the virus is found throughout South America, Central America, and Mexico.

Will the Zika virus spread to the United States?

It’s only a matter of time before we start seeing the Zika virus transmitted from mosquitoes to people in the United States. So far, we’ve seen fewer than 200 cases here, all in people who traveled to countries where Zika is endemic. And over 100 people have been infected in US territories: Puerto Rico, American Samoa, and the US Virgin Islands. But the World Health Organization estimates that three to four million people in the Americas will be exposed to the virus in the next 12 months, and the mosquitoes that spread the virus exist in the US. The virus is primarily spread by Aedes aegypti, the type of mosquito that also spreads yellow fever and dengue. This mosquito is common in the warm, humid climates of Florida, Hawaii, and the Gulf Coast states. Zika may also be spread by the Asian tiger mosquito (Aedes albopictus), which is also found in the US.

Although infrequent, the Zika virus can also be spread through sex and blood transfusions. For this reason, the Centers for Disease Control and Prevention (CDC) recommends that men who have traveled to areas where the Zika virus is active abstain from sex with their pregnant partners, or carefully use condoms during sex. Until more is known, it is prudent for people who have recently been to a Zika-endemic area to use barrier precautions (condoms for men) for a month after returning to the US.

My guess is that we will see many Zika cases in the United States, but we won’t see the Zika virus explode to the extent it did in South America. Our cooler climate makes it more difficult for the mosquitos to spread. We have more aggressive and effective mosquito control. And we have air conditioning in most buildings, which helps reduce contact with mosquitoes.

Also, humans are the primary hosts for the Zika virus—the major reservoir for it. With the West Nile virus, which is found in nearly every state, birds are the primary host, which makes that virus harder to control.

Who is most at risk from infection with the Zika virus?

Pregnant women, especially in their first trimester, are at greatest risk, and the risk is really to the fetus, not to the mother. After careful study, CDC scientists have concluded that Zika can cause microcephaly—brain damage—in developing fetuses. From October 2015 to January 2016 there were more than 4,000 babies born with microcephaly in Brazil, compared to an average of 150 cases a year. The virus has been found in amniotic fluid, spinal fluid, and brain fluid in some fetuses or infants with microcephaly.

We don’t know yet whether the Zika virus poses additional serious risk to children and adults. With the West Nile virus, we know that elderly people are at greater risk for West Nile encephalitis, but we haven’t seen that yet with Zika. In Brazil and other countries, they’ve also seen an increase of Guillain-Barré syndrome (a paralytic disease) following some Zika cases; it’s likely but not proven that the virus is to blame.

The CDC recommends that all pregnant women who have traveled to an affected country (or who become pregnant while in one of these countries) should consult with a doctor knowledgeable about this disease, and get a blood test to see if they’re infected with the virus. It also recommends that all women—pregnant or not—who live in those areas get tests.

This is all brand new, and it’s subject to change every day as we learn more.

What are the symptoms of Zika virus?

Infection with the Zika virus is usually a minor disease, which is why previously nobody paid much attention to it. About 80 percent of people with the infection don’t show any symptoms. And of those who do get sick, they usually have fever for a few days, and then it goes away.

If a person is infected, do they have the virus forever?

Our bodies are very good at controlling the Zika virus. The health risks appear to occur only during the few days when the virus is circulating in your body. And it appears that once you’ve recovered from Zika, you can’t get it again.

Is there a treatment for Zika virus?

There is no treatment for infection with the Zika virus. The CDC recommends rest and nourishment.

How can I protect myself from the Zika virus?

There is no vaccine to prevent Zika infection, although scientists at the National Institutes of Health and other institutions are working to develop one.

If you’re pregnant, avoid traveling to countries in South America and Central America, as well as Mexico and Samoa, which are affected by the Zika virus.

If you must travel to one of those countries, stay in hotels with air conditioning, put the insecticide permethrin on your outer clothes (or buy clothing treated with permethrin), and use insect repellent every few hours. For more tips, check the CDC’s Zika Prevention page.

Also see How to Prevent Mosquito Bites.

Originally published January 28, 2016. Updated April 13, 2016.