Zika Virus

What Zika virus is

Zika virus was first identified in Uganda in 1947. For decades it caused only small outbreaks. In 2015 to 2016, a large epidemic spread through Brazil and the Americas, and doctors linked it to a sharp rise in babies born with microcephaly (a small head and underdeveloped brain). Since then, transmission has fallen, but the virus continues to circulate at lower levels in parts of the Americas, Africa, Southeast Asia and the Pacific. Local mosquito spread has occurred in the continental US only rarely, in Florida and Texas in 2016 and 2017.

How Zika spreads

• Mosquito bites: mainly Aedes aegypti and Aedes albopictus, which bite during the day and also spread dengue and chikungunya.
• Sex: vaginal, anal or oral sex, and sharing sex toys. The virus can persist in semen for longer than in blood, and can be passed on by people without symptoms.
• Pregnancy: from the pregnant person to the fetus at any stage, and around the time of birth.
• Blood transfusion and organ transplant: rare.

Zika does not spread through casual contact. Breastfeeding is still recommended, because no harm from Zika in breast milk has been shown and the benefits of breastfeeding are clear.

Zika symptoms

Most people infected with Zika, roughly 4 out of 5, have no symptoms. When symptoms occur, they begin 3 to 14 days after infection and last 2 to 7 days:

• an itchy, raised, red skin rash of small spots, often starting on the face and spreading to the body
• low fever, usually under 38.5 °C (101.3 °F)
• joint pain, particularly in the hands and feet, sometimes with swelling
• red eyes without discharge (non-purulent conjunctivitis)
• headache and muscle aches
• tiredness

Zika, dengue and chikungunya compared

Because the three viruses share mosquitoes and regions and look alike early on, travelers with fever are often tested for all three.

Zika and pregnancy

Zika infection during pregnancy can cause congenital Zika syndrome, which includes:

• severe microcephaly with a partly collapsed skull
• brain damage with calcium deposits and reduced brain tissue
• eye damage, including scarring of the retina
• joints fixed in bent positions (contractures)
• stiff muscles that limit movement
• later problems with seizures, swallowing, hearing, vision and development

In US registry data, about 1 in 20 pregnancies with confirmed Zika infection resulted in a birth defect, with higher rates when infection occurred in the first trimester. Infection later in pregnancy can still cause harm. Babies can look normal at birth and develop problems later, so follow-up is recommended.

Advice for pregnancy and planning

• Pregnant people should not travel to areas with a current Zika outbreak. Check the CDC travel page for your destination, as risk levels change.
• If your partner has traveled to an area with Zika risk, use condoms or avoid sex for the rest of the pregnancy.
• If you are planning pregnancy after possible exposure, CDC advises waiting before trying to conceive: at least 2 months if only the female partner traveled, and at least 3 months if the male partner traveled, using condoms during that time.
• Tell your prenatal care provider about any travel, even if you felt well. Testing and extra ultrasound scans may be offered.

Guillain-Barré syndrome

Zika can trigger Guillain-Barré syndrome, an immune attack on the nerves that causes weakness and tingling, usually starting in the legs and spreading upward, days to weeks after infection. It is rare but can affect breathing and needs hospital care. Most people recover, though recovery can take months.

How Zika is diagnosed

Testing is advised for people with symptoms after possible exposure, and for pregnant people with possible exposure according to current CDC guidance:

• RNA tests (RT-PCR) on blood and urine detect the virus itself, usually in the first one to two weeks after symptoms start.
• Antibody tests (IgM) can detect infection later but often cross-react with dengue and other related viruses, so confirmatory testing may be needed.
• Prenatal ultrasound to look for brain changes in the baby.
• Newborn evaluation: head size, eye exam, hearing test and brain imaging for babies with possible exposure.

Treatment

There is no specific antiviral medicine for Zika.

• Rest and drink plenty of fluids.
• Take acetaminophen (paracetamol) for fever and pain at the label dose.
• Avoid aspirin and NSAIDs such as ibuprofen until dengue has been ruled out, because they increase bleeding risk in dengue.
• Antihistamines and calamine lotion may ease itchy rash.
• Prevent mosquito bites during the first week of illness to stop local spread.

Pregnant people with Zika are cared for by specialists in maternal-fetal medicine, with serial ultrasounds. Babies with congenital Zika syndrome need long-term care from pediatric neurology, eye, hearing and developmental teams.

Prevention

There is currently no licensed Zika vaccine.

• Use EPA-registered insect repellent containing DEET, picaridin, IR3535 or oil of lemon eucalyptus; apply sunscreen first, then repellent.
• Wear long sleeves and pants, and treat clothing with permethrin.
• Stay in places with window screens or air conditioning, and use a bed net if needed.
• Remove standing water around the home, where Aedes mosquitoes breed.
• Use condoms or avoid sex during and after travel as recommended above.
• Continue to prevent mosquito bites for 3 weeks after returning from a Zika area, even if you feel well, so you do not infect local mosquitoes.

Frequently asked questions

What are the symptoms of Zika virus?

Most people have no symptoms. When they occur, they include an itchy red rash, low fever, joint pain, red eyes, headache and muscle aches, starting 3 to 14 days after infection and lasting about 2 to 7 days. The illness is usually mild and rarely needs hospital care.

How long should I wait to get pregnant after Zika exposure?

CDC advises waiting at least 2 months after travel or symptoms if only the woman was exposed, and at least 3 months if the man was exposed, using condoms throughout. If both partners traveled, wait at least 3 months. Check the latest CDC guidance before trying to conceive.

Can Zika be transmitted sexually?

Yes. Zika can spread through vaginal, anal and oral sex, even from a partner without symptoms. The virus can persist in semen longer than in blood. Condoms or avoiding sex reduce the risk, and are especially important if you or your partner is pregnant.

Is there a vaccine for Zika?

No licensed vaccine for Zika is available. Several candidate vaccines have been tested in clinical trials, but none is approved yet. Protection depends on avoiding mosquito bites, following travel advice, especially in pregnancy, and safer sex after possible exposure.

Is Zika still a risk for travelers?

Zika transmission has dropped greatly since the 2015 to 2016 epidemic, but the virus still circulates at lower levels in parts of the Americas, Africa, Asia and the Pacific. The risk for most travelers is low, but pregnant people and couples planning pregnancy should check current CDC travel advice.