Merck Manual

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Quick Facts

Zika Virus Infection

By

The Manual's Editorial Staff

Last full review/revision Mar 2020
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What is Zika virus infection?

Zika virus infection almost never makes children or adults very sick. But Zika virus is very dangerous to an unborn baby (fetus).

  • Zika can be spread by mosquitoes, sex, or blood transfusion

  • A pregnant woman with Zika infection can pass it to her baby

  • Most people have no symptoms or get only mild symptoms, such as fever, rash, joint pain, and red eyes

  • Babies born to mothers infected with Zika virus may have birth defects of their brain, including an abnormally small head (microcephaly)

  • There's no treatment for Zika virus infection, but rest and acetaminophen to relieve fever and pain can help

How do people get Zika virus infection?

The Zika virus is spread mainly by:

  • Mosquitoes

Zika virus also can be spread by:

  • Sex

  • Blood transfusion

  • A pregnant woman to her baby before birth

If you're infected with Zika virus, you can spread it to your partner during sex:

  • Even if you don't have symptoms

  • Before symptoms start

  • While having symptoms

  • Weeks or even months after your symptoms have gone away—Zika virus can stay in a man's semen for up to 6 months

The mosquitoes that spread Zika virus live in warmer climates. So most Zika infections occur in South America and the Caribbean. However, people who visit those areas from other parts of the world can return home with a Zika infection.

What are the symptoms of Zika virus infection?

You may have no symptoms or mild symptoms. Symptoms usually last 4 to 7 days and include:

  • Fever

  • Bumpy red rash

  • Pain in your joints and muscles

  • Red, irritated eyes

  • Headache

How does Zika affect babies?

Zika virus infection during pregnancy can cause birth defects of the baby's brain, including an abnormally small head (microcephaly). Babies with microcephaly can have problems such as:

  • Seizures

  • Delays in development (for example, they may sit, stand, and walk later than usual)

  • Decreased mental ability

  • Problems with movement and balance

  • Problems eating or swallowing

  • Problems hearing or seeing

How do doctors tell if I have Zika virus infection?

Doctors diagnose Zika based on:

  • Blood tests

  • Urine tests

How do doctors treat Zika virus infection?

Right now, there's no medicine to cure Zika virus infection.

Doctors will have you:

  • Rest

  • Drink fluids to make sure there's enough water in your body

  • Take acetaminophen to ease pain and fever

Don't take aspirin or ibuprofen unless you've seen a doctor and know for sure that you have Zika virus infection. If you have dengue fever, which can have similar symptoms to Zika, taking aspirin or ibuprofen can be dangerous and cause bleeding.

If you're pregnant, doctors may:

  • Do ultrasonography every 3 or 4 weeks to check the development of your baby

How can I prevent Zika virus infection?

The best ways to prevent Zika virus infection are to:

  • Avoid being bitten by mosquitoes

  • Avoid unprotected sex with a partner who has or may have the infection

To avoid mosquito bites:

  • Wear long-sleeved shirts and long pants

  • Stay in places that have air conditioning or window and door screens to keep mosquitoes out, or use a mosquito bed net

  • Use insect repellents containing DEET (diethyltoluamide) on uncovered skin—but don't use insect repellents on babies under 2 months old

  • Treat clothing and gear with permethrin insecticide (don't put it directly on your skin)

Pregnant women should avoid traveling to areas where Zika virus is common (see current Zika Travel Information).

If you're pregnant and your sex partner lives in or travels to a place where Zika virus infection is common, you should do one of the following during the pregnancy:

  • Don't have sex (vaginal, anal, or oral)

  • Always use barrier birth control (such as a condom or dental dams) during sex

If your female sex partner has been diagnosed with Zika or has symptoms of Zika, you should do one of the following:

  • Not have sex for at least 8 weeks

  • Use condoms or dental dams during sex

If your male sex partner has been diagnosed with Zika or has symptoms of Zika, you should do one of the following:

  • Not have sex for at least 6 months

  • Use condoms during sex

Zika virus stays in a man's semen longer than in other body fluids.

NOTE: This is the Consumer Version. DOCTORS: Click here for the Professional Version
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