The Zika virus arrived in the United States in 2016, with local transmission reported in and around Miami, FL, and Brownsville, TX.
The virus causes birth defects in babies born to some infected pregnant women, including microcephaly, where babies are born with underdeveloped heads and brain damage. Zika has also been linked to Guillain-Barre syndrome, a condition in which the immune system attacks the nerves. It’s mainly spread through mosquitoes, although some cases of sexual transmission have been reported.
The CDC continues to issue travel warnings for pregnant women in countries where the disease is spreading.
What is Zika? How can you avoid it? WebMD answers your questions.
What Is the Zika Virus? How Do You Catch It?
The Zika virus, first identified in Uganda in 1947, is transmitted by Aedes mosquitoes, the same type of mosquito that carries dengue fever, yellow fever, and chikungunya virus. A mosquito bites an infected person and then passes those viruses to other people it bites. Outbreaks did not occur outside of Africa until 2007, when it spread to the South Pacific.
Zika can be spread through sex, usually after a person travels to an area where Zika has broken out and contracted the virus. Infected women and men can both pass the virus to sex partners -- even if they haven’t shown symptoms of infection, according to the CDC. In addition, infected pregnant women can pass the virus on to their fetus.
Some studies have also shown the virus can be found in blood, semen, urine, and saliva of infected people as well as in fluids in the eye.
What Are the Symptoms of Zika?
The disease can cause fever, rash, joint pain, and redness in the whites of the eye (conjunctivitis, or pinkeye). But most people won’t know they have it.
“Only about 1 in 5 people with the virus will exhibit symptoms,” says Adalja. “The vast majority have no symptoms at all.”
Symptoms can appear anywhere from 3 to 14 days after a bite from an infected mosquito, according to the CDC. They can last from several days to about a week.
Call your doctor if you develop symptoms and you live in or have visited an area where Zika is spreading, the CDC says -- especially if you are pregnant. Pregnant women who have Zika symptoms at any point during their pregnancy should be tested for Zika.
Once a person has been infected, scientists believe they are probably protected from future infections.
Is Zika Similar to Other Mosquito-Borne Illnesses, Such as Dengue Fever, Chikungunya, or West Nile Virus?
All can cause a variety of flu-like symptoms that range in severity and can last from a few days to more than a week. As with Zika, few people infected with dengue or West Nile will show any symptoms. While the same type of mosquitoes that spread Zika also spread dengue and chikungunya, many different types of mosquitoes spread the West Nile virus.
Zika is also the only one of those viruses known to be spread through sexual contact.
How Is Zika Treated?
There’s no treatment, but most people with symptoms do well with over-the-counter medications for aches and pains. The disease usually runs its course within a week or so.
The CDC recommends infected people get plenty of rest, drink fluids to prevent dehydration, and take acetaminophen for fever and pain. Aspirin or other nonsteroidal anti-inflammatory drugs (NSAIDs) should not be taken until dengue is ruled out, to reduce bleeding risk, the agency says.
There is no vaccine against Zika, but the National Institutes of Health is testing one in humans.
What Is the Connection Between Zika, Microcephaly, and Pregnancy?
Zika causes microcephaly in babies born to infected pregnant women, the CDC says. Microcephaly stunts a baby’s head growth, causing devastating, sometimes fatal brain damage, and it can result in miscarriage or stillbirth.
The virus has caused panic in Brazil since it first appeared there in May 2015. More than 2,100 babies in Brazil have been born with microcephaly or other birth defects linked to Zika. at the time, Brazil and several other nations advised women to postpone pregnancy.
Although there are many causes of microcephaly in babies, including infections during pregnancy, genetic problems, and exposure to toxic substances during pregnancy, the CDC says research has provided enough evidence to show that Zika is among those causes. Research has suggested that infection during the earliest stages of pregnancy, when a baby’s organs are still forming, seems to be linked to the worst outcomes.
However, some studies are showing that fetuses can be harmed by infection later in pregnancy, and evidence is emerging that microcephaly isn’t the only birth defect linked to Zika. In another report, the CDC describes five types of birth defects, including severe microcephaly, that are unique to Zika or rarely occur with other infections in pregnant women. They are:
- Decreased brain tissue with calcium deposits indicating brain damage
- Damage to the back of the eye
- Limited range of motion in joints, such as clubfoot
- Too much muscle tone, which restricts movement
Those effects in babies are called congenital Zika syndrome.
Since July 2018, the CDC had confirmed Zika infections in more than 2,474 pregnant women in the U.S. and more than 4,900 pregnant women in U.S. territories. Since 2019, there have been no confirmed Zika cases reported from U.S. territories.
The agency advises that women and men who have lived or traveled in areas with Zika infections and have a pregnant sex partner either use condoms or abstain from sex during the pregnancy.
All pregnant women in the U.S. should be evaluated for possible Zika exposure during each prenatal care visit, the CDC says, and all pregnant women with possible exposure should be offered Zika testing.
Which Countries Are in the CDC Travel Warning for Pregnant Women?
The CDC recommends that pregnant women and couples planning a pregnancy within the next 3 months consult with their health care provider before traveling to any country or territory where Zika transmission is ongoing.
A list of countries can be found on the CDC website. But it's important to keep in mind that the list changes frequently and needs to be reviewed frequently as countries become low risk or other countries are added.
Scott C. Weaver, PhD, director, Institute for Human Infections and Immunity, University of Texas Medical Branch at Galveston, is particularly concerned about pregnant women travelers.
“Especially in the first trimester or early second trimester, going to an area with Zika virus circulating is pretty risky,” he says. “... I certainly would not recommend that pregnant women travel to areas where epidemics are ongoing.”
Couples who are trying to have a baby should wait a few months to get pregnant if either partner has traveled to an area where Zika is spreading -- even if they did not have a confirmed infection, the CDC says. The agency advises women to wait 2 months and men to wait at least 6 months after possible exposure, even if the man did not have symptoms.
Men and women who have traveled to areas where Zika is spreading are advised to practice safe sex or abstinence for 6 months upon returning. The recommendation applies whether or not they are trying to get pregnant and whether or not they showed symptoms of Zika.
The only way to completely prevent Zika infection during pregnancy is to not travel to areas with risk of Zika and to use precautions or avoid sex with someone who has recently traveled to a risk area.
What if I'm Pregnant and I've Traveled to These Areas?
Talk to your doctor. They'll check on your baby's health, and you'll be screened for symptoms of the virus. If you have symptoms, other diseases such as dengue or chikungunya can be ruled out.
Pregnant women who have traveled to an area with Zika can be offered testing 2 to 12 weeks after returning, even if they have not shown symptoms, the CDC says.
Pregnant women with Zika should get ultrasounds every 3 to 4 weeks to monitor the baby's growth, the agency says.
What if I’m Not Planning to Get Pregnant?
To reduce the risk of sexual transmission, women who have possibly been exposed to Zika should use condoms in addition to their regular birth control method or abstain from sex for at least 8 weeks, the CDC says.
Men with possible exposure, even if they didn’t have Zika symptoms, should use a condom or abstain from sex for at least 6 months.
Where in the U.S. Are We at Risk?
Since 2018, no local mosquito-borne virus transmission has been reported in the continental United States.
The CDC says that detecting local spread of Zika is difficult, as a person may not show symptoms for up to 2 weeks after infection, if at all. In addition, diagnosis and investigation of cases can take weeks.
Aedes mosquitoes, which spread Zika, are found in every country in North, Central, and South America except for two: Canada and continental Chile, according to the WHO's Regional Office for the Americas.
How Are You Tested for Zika?
There are two ways to test for Zika. One test looks for pieces of the virus’s genetic code in people with active infections. But after the body clears the infection, which takes about 2 weeks after symptoms appear, that test won’t work.
The FDA has OK'd the emergency use of a more advanced version of this test that can distinguish whether a person has dengue, chikungunya, or Zika, rather than having to do three different tests. The new version is in qualified labs, the CDC says.
Since 80% of people with Zika don’t have symptoms, many people don’t know when they were infected and would not be eligible for this test.
Another test looks for proteins called antibodies made by the immune system to fight the virus. It can find antibodies in the blood up to 3 months after a person is infected.
But this test isn’t very specific. It may mistakenly show a person has had Zika if they’ve been infected with other viruses, including dengue and chikungunya. A positive or inconclusive test result means a follow-up test is done by the CDC or a CDC-authorized lab.
The FDA has approved this test, and the CDC is distributing it to qualified labs.
Testing of amniotic fluid in pregnant women can also be done, although it's not clear how well this test would work for Zika, according to the CDC.
Can Zika Lead to Other Health Conditions?
In rare cases, Zika has been linked to Guillain-Barre syndrome. That disorder can cause partial or complete paralysis, usually starting in the legs, most often temporary. An increase in that illness had been seen in areas such as French Polynesia and Brazil, where a Zika epidemic had taken place. Studies increasingly show a link between the syndrome and Zika.
Current CDC research shows that Guillain-Barre is strongly associated with Zika, however only a small portion of those infected actually get it.
There may be a link between Zika and an autoimmune disorder called acute disseminated encephalomyelitis (ADEM), according to research presented at the American Academy of Neurology conference. The immune system of a person with the disorder attacks the myelin coating around nerve fibers in the brain and spinal cord, similar to multiple sclerosis.
Doctors in March 2016 reported the first case of brain swelling linked to Zika, in an 81-year-old man who was on a South Pacific cruise. The man ran a fever and lapsed into a coma. They were diagnosed with meningoencephalitis, or swelling of the membranes that cover the brain and spinal cord. The Zika virus was found in their spinal fluid. The man recovered after 38 days in the hospital.
Later that year, the CDC announced the first Zika-linked death in Puerto Rico, of a 70-year-old man who died in February from severe thrombocytopenia, which causes a low blood platelet count that can lead to internal bleeding.
How Can I Prevent Zika?
If you plan to travel in affected areas, avoid mosquito bites by using repellent throughout the day. Also, wear long-sleeved shirts and long pants, indoors and out.
The mosquitoes that spread Zika are aggressive daytime biters often found indoors, which we’re not used to in the U.S., says Weaver, the Institute for Human Infections and Immunity director.
“You need to protect yourself all day long,” he says.
The CDC recommends using Environmental Protection Agency-registered insect repellents with DEET, picaridin, IR3535, oil of lemon eucalyptus (para-menthane-diol) or 2-undecanone. If you’re using sunscreen, apply that first and repellent second.
Around your home, use screens on windows and doors, and get rid of standing water -- in tires, buckets, planters, and flowerpots, for example -- as mosquitoes lay eggs near water.
Even those who don’t know they have Zika can spread the disease. Weaver says that people who have traveled to affected regions should be extremely vigilant against mosquito bites when they return home. The CDC also recommends using condoms or abstaining from sex for 8 weeks for women or 6 months for men to avoid sexual transmission.