Zika Virus - Epidemiology

Zika Virus
What is Zika?
Zika is a virus that is transmitted to people primarily through bites of infected mosquitoes. Most people exposed to Zika virus will have no symptoms or only mild symptoms. The primary concern about this virus is that it can pass from an infected mother to her baby during pregnancy and cause serious birth defects. People exposed to Zika virus who have no symptoms are said to have a Zika virus infection; those who have symptoms are said to have Zika virus disease. Both conditions will be referred to as “Zika” below.
Where does Zika occur?
Zika is a risk in many countries and territories, and has been found in the Americas, Pacific Islands, and parts of Africa and Asia. For a map showing where Zika is a risk, see the Centers for Disease Control and Prevention (CDC) webpage on areas at risk for Zika. Because the mosquitoes that spread the virus are found around the world, it is possible that outbreaks will occur in new countries and territories. Some limited spread of Zika virus by mosquitoes in the continental United States has occurred, but this has not occurred in Virginia. For a map of where the mosquitoes that could spread Zika virus are located in the United States, see CDC’s Zika webpage on the geographic range of mosquitoes.
How does Zika spread?
Zika virus is usually transmitted to people through the bite of an infected mosquito. The primary mosquito that spreads Zika virus is the yellow fever mosquito (Aedes aegypti); the Asian tiger mosquito (Aedes albopictus) can also spread the virus. An infected person will have the virus circulating in their blood, especially in the first week of illness. If a mosquito bites an infected person while the virus is still in the person’s blood, the mosquito can become infected. If the infected mosquito lives long enough for the virus to multiply and spread to its salivary glands, the mosquito can then bite another person to pass on the virus. People who are infected but who are not sick can still pass the virus on to mosquitoes that bite them. Zika virus can also be transmitted from an infected mother to her baby during pregnancy. A person with Zika virus can infect his or her sex partner through unprotected sex, even if the infected person is not sick. The virus can also be spread through blood transfusion.
Who gets Zika?
Anyone who lives in or travels to an area with risk of Zika, and has not already been infected, can get Zika. Anyone who has unprotected sex with someone who lives in or travels to these places can also become infected. For a map of areas with risk of Zika, see the CDC webpage on areas at risk for Zika.
What are the symptoms of Zika?
About 80% of people who are infected with Zika virus do not become sick. For the 20% who do become sick, the most common symptoms include fever, an itchy rash, joint pain, conjunctivitis (red eyes), headache, and muscle pain. The illness is usually mild and the symptoms typically last several days to a week.
How soon do symptoms occur?
Symptoms, if present, can appear within 3 to 14 days after exposure to Zika virus.
How dangerous is Zika?
Zika virus infection during pregnancy can cause the fetus to develop microcephaly and/or other severe birth defects. Microcephaly is a birth defect in which a baby’s head is much smaller than expected. CDC estimates 6% of babies born to moms with Zika during pregnancy will have Zika-associated birth defects, such as damage to the brain, eye damage, and/or microcephaly at birth. An estimated 9% of babies born to moms with Zika during pregnancy can have neurodevelopment abnormalities such as hearing loss, limb defects, seizures, microcephaly after birth, and slowed growth or development. In a small number of infected people, there have also been reports of neurologic syndromes, such as Guillain‐Barré Syndrome (GBS). Ongoing studies are investigating the connection between GBS and Zika.
What special precautions should pregnant women take to prevent Zika?
Pregnant women should not travel to areas with Zika outbreaks. Pregnant women should talk to their healthcare providers to carefully consider the risks and possible consequences of travel to other areas with risk of Zika. For a map of areas with Zika outbreaks and areas with Zika risk, see CDC’s Zika webpage on areas at risk for Zika. If a pregnant woman does travel, she should talk to her healthcare provider before travel and take the following steps to prevent Zika infection:
Prevent mosquito bites
Choose an EPA‐registered insect repellent with one of the following active ingredients: DEET, picaridin, IR3535, oil of lemon eucalyptus or para-menthane-diol, or 2-undecanone, and use the repellent according to the product label. When used as directed, EPA-registered insect repellents are proven safe and effective even for pregnant and breast-feeding women.
Use the repellent day and night because the mosquitoes that transmit Zika virus bite during the day, but will also enter buildings and bite at night.
Use permethrin‐treated clothing.
Cover exposed skin by wearing long sleeves, socks, pants, and hats.
Sleep indoors in rooms with screened windows or air‐conditioning, or use a bed net if you sleep in a room that is exposed to the outdoors.
Practice safe sex
For the rest of the pregnancy, use a condom every time during sex, or abstain from sex to prevent potential Zika transmission.
After returning, she should talk to her healthcare provider about her travel to an area with risk of Zika. If you think you have Zika, see your healthcare provider. Your healthcare provider may test your blood or urine for Zika virus and other similar conditions.
What special precautions should couples trying to become pregnant take to prevent Zika?
Couples planning to become pregnant within three months should work with their healthcare providers to carefully consider the risks and possible consequences of travel to areas with a Zika outbreak or other areas with risk of Zika. For a map of where Zika is occurring, see CDC’s webpage on areas at risk for Zika. If a member of the couple travels to an area with a Zika outbreak or other areas with risk of Zika, the couple should take these steps to prevent Zika infection:
Follow the same recommended steps for pregnant women to prevent mosquito bites (above).
Consider waiting for a period of time before trying to become pregnant. If only the female partner traveled, the couple should abstain from sex for at least two months from when symptoms began (if sick) or after returning from travel (if not sick). If only the male partner traveled, the couple should wait at least three months from when symptoms began (if sick) or after returning from travel (if not sick). If both partners traveled, the couple should wait three months from when symptoms began (if sick) or after returning from travel (if not sick). While waiting to conceive, couples should either avoid sex or use condoms every time during sex or sexual activities.
What is the treatment for Zika?
There is no specific treatment for Zika. Healthcare providers can only provide supportive care to relieve symptoms. This may include rest, fluids, and over‐the‐counter medicine, such as acetaminophen.
How can Zika be prevented?
There is no vaccine to prevent Zika. Infections can be prevented by avoiding mosquito bites and sexual exposure to the virus. Avoid mosquito bites includes wearing long‐sleeved shirts, long pants and socks, using insect repellent or permethrin‐treated clothing (especially during the daytime when mosquitos are active), use air conditioning or window/door screens to keep mosquitoes outside. Eliminate standing water from containers in yards (including bird baths, flower pots, buckets) to stop mosquito breeding. People who have returned from travel to an area with risk of Zika should also follow steps to avoid mosquito bites for three weeks after returning to prevent them from passing Zika virus to local mosquitoes that could spread the virus to others.