Understanding Zika

What is Zika virus disease?

Zika is a mosquito-borne virus that has been linked to microencephaly (small head circumference, with brain damage), abnormal brain development, Guillain-Barré syndrome (GBS), miscarriage, stillbirth, and other serious health outcomes. Zika virus can also be spread from a mother to her child during pregnancy or birth. Other means of transmission include sexual intercourse with an infected person, blood transfusion with infected blood, or direct exposure to the virus in research facilities. The number of cases in the U.S. began to decline in 2017, and there were no cases transmitted in the U.S. in 2018 or 2019.

Before 2015, cases of Zika virus were only sporadically reported in African or Asian countries. Brazil, in May 2015, reported the first locally transmitted case (an individual was infected by a mosquito bite) in the Americas; since then, outbreaks have occurred in many countries and territories, causing experts such as the World Health Organization’s Marcos Espinal to estimate that 3 to 4 million people worldwide will be affected over a 12-month period. In 2016, locally transmitted (mosquito-to-human) cases have been reported in 32 countries including the U.S.

Most of the cases of Zika virus in the U.S. have, so far, resulted from travel outside the country. Hundreds of travel-associated Zika infections (in people who recently traveled to areas with active Zika virus outbreaks or had sexual contact with someone who had) have been reported to the U.S. Centers for Disease Control and Prevention (CDC), including, as of June 2016, hundreds of pregnant women in U.S. states and territories. In August 2016, the CDC announced that locally-transmitted cases of Zika virus had been identified in parts of Florida.

Recognizing the serious risks for pregnant women and their unborn babies—fetal death (miscarriage or stillbirth) and abnormal brain development (microcephaly)—the World Health Organization (WHO) on February 1, 2016 declared the Zika outbreak an international public health emergency. The declaration came after an international panel of experts met and agreed that while “a causal relationship between Zika infection during pregnancy and microcephaly is … not yet scientifically proven,” it is “strongly suspected” and calls for the “urgent need” for coordinated international efforts to investigate the relationship better. The panel also cited patterns of recent spread, the broad geographic range of the Zika-carrying mosquito species, lack of a vaccine, diagnostic challenges, and the absence of population immunity in newly affected countries as “causes for concern.” The WHO strengthened its language about the virus’s effects, on June 9, 2016 acknowledging that “[b]ased on research to date, there is scientific consensus that Zika virus is a cause of microencephaly and GBS.”

In addition, the CDC has issued a travel advisory that pregnant women avoid traveling to areas where Zika virus is known to be active, including international destinations and those within the continental U.S. affected by the disease. 

In 2016, to stem the transmission of Zika virus and related health effects, the CDC added recommendations about pregnancy planning after Zika exposure. For women who have been diagnosed with the virus or have symptoms of it, the CDC recommends waiting at least 8 weeks from when symptoms first develop before trying to become pregnant. Men with possible Zika virus exposure who are considering attempting conception with their partner, regardless of whether or not they have symptoms, are recommended to wait at least 6 months before having unprotected sex. For women and men who were possibly exposed to the virus but have had no symptoms, the CDC recommends waiting 8 weeks before trying for pregnancy. Those who live in areas where Zika transmission is ongoing should consult with their health care provider about risks and risk reduction before trying for pregnancy.

What are the symptoms of Zika virus disease?

An estimated 80 percent of people infected with the virus have no symptoms. If symptoms do occur, they likely start a few days after exposure to the virus and are generally mild—fever, rash, muscle and joint pain, headache, and conjunctivitis (pink eye)—and last for two days to a week. Some people report experiencing a recurrence of symptoms weeks later. Hospitalization is seldom required, and death is rare. However, CDC experts suggest that the full scope of the disease’s neurological effects are not known yet. According to the CDC, there is an association with Guillain-Barre syndrome, in which paralysis results from the body attacking its own cells, and acute disseminated encephalomyelitis, with swelling of the brain and spinal cord.

The most recent outbreaks of Zika virus disease in Brazil has implicated Zika virus in multiple cases of fetal death and microcephaly. Public health officials in that country have confirmed more than 400 cases of microcephaly to date, and are investigating more than 4,000 suspected cases. By comparison, Brazil typically has about 160 babies born with microcephaly each year. 

How is Zika virus treated?

Treatment for the virus itself generally includes rest and fluids. Patients may use acetaminophen if needed. However, aspirin and non-steroidal anti-inflammatory drugs such as ibuprofen should be avoided because the symptoms and transmission of Zika virus overlap with those of dengue, another mosquito-borne virus that has a higher risk of hemorrhage in the presence of non-steroidal anti-inflammatory drugs.

While symptoms of Zika virus disease can be treated, microencephaly is a serious condition. For children who are severely affected, lifelong care is necessary. This can include physical therapy, respiratory therapy, and speech therapy.

How do children get Zika virus disease?

Children can acquire Zika virus disease from the bite of an infected mosquito. Zika virus can also be transmitted from pregnant women to their babies during pregnancy and birth. Although spread of Zika virus during labor and delivery has not been documented, the CDC emphasizes the use of “standard precautions” to protect health care personnel in obstetrical care settings. The CDC notes that the virus has been detected in blood, urine, saliva, and amniotic fluid. There is “potential for exposure to large volumes of body fluids” during labor, and even women who don’t have symptoms may carry the virus. “Standard precautions” include preventing contact between the patient’s body fluids and others’ mucous membranes, skin, and clothing; preventing providers from carrying possibly infectious materials between patients; and avoiding unnecessary exposure to sharp instruments.

The U.S. Centers for Disease Control and Prevention (CDC) maintains that mothers should not be worried that breastfeeding will lead to virus transmission, noting that “although Zika virus RNA has been detected in breast milk, transmission through breastfeeding has not been documented.” Because breastfeeding supports health during infancy and beyond, health experts encourage mothers to breastfeed even in areas where the virus is active.

Like many other viruses, Zika can survive for as long as 8 hours on nonporous surfaces, such as doorknobs and countertops. Fortunately, they have also found that common disinfectants that contain isopropyl alcohol and quaternary ammonium/alcohol are effective against the virus.

How can Zika virus be prevented?

No vaccine is available for Zika virus. Steps you can take to reduce your risk of contracting the virus include:

  • Limit travel to affected areas. Pregnant women are advised to avoid traveling to areas where Zika virus has been widely reported, whether international or U.S. destinations. Delay traveling to such areas until after your baby is born.
  • Avoid mosquito bites. Eliminate or avoid mosquito breeding grounds, such as areas of standing water; even small quantities of water can attract mosquitoes. Keep windows closed or use screens when indoors. When outdoors, wear long sleeves and pants, use permethrin-treated clothes and gear, and use effective insect repellent. 
  • Use insect repellent specifically targeted toward Aedes mosquitos that carry Zika virus. According to the U.S. Environmental Protection Agency (EPA), all insect repellents currently on the market, even those with DEET, can be used by pregnant or lactating women. (Pregnant women may choose to apply DEET repellent to their clothes rather than directly to their skin in an effort to minimize any exposure to toxins. They may also choose products with no more than 30 percent DEET concentration, which Consumer Reports suggests is adequate for effective protection and known to be safe.) For anyone over the age of 2 months old, use just enough repellent to cover your child's clothing and exposed skin (but never spray on your child's face; spray it on your hands, then wipe the child's face). Avoid reapplying unless needed; follow manufacturer's directions. For a list of the safest and most effective insect repellents for Zika virus, review the EWG’s guide here or Consumer Reports’ guide here.
  • Get a diagnosis. The CDC recommends that babies born to women who were infected with Zika virus during pregnancy be evaluated for congenital malformations. Since up to 80 percent of Zika virus cases have few or no symptoms and may therefore go unrecognized, mothers who have traveled to areas with ongoing cases of Zika virus who give birth to babies with symptoms should contact their baby’s health care provider for an evaluation. Treatment for Zika virus is not yet available, but birth defects caused by the virus can be mitigated by treatment.
  • Practice good hygiene. If someone in your household has signs of Zika virus, use a disinfectant with isopropyl alcohol or quaternary ammonium/alcohol to clean surfaces they come in contact with, such as doorknobs, light switches, and countertops. After cleaning, wash your hands well with soap and warm water for at least 20 seconds.

When should I call a doctor?

Obstetricians and pediatricians should talk with their patients to identify women who have spent time in affected countries during their pregnancy, have had close contact with travelers to such areas, and who have experienced symptoms common to Zika virus. Ultrasound monitoring or magnetic resonance imaging (MRI) may help to identify affected babies in utero.

Infants should be tested if they are born with signs of microcephaly or neurological impairment, or if their mothers have had positive or inconclusive tests for Zika virus.

For more information about Zika virus, visit the CDC and American Academy of Pediatrics (AAP) websites.

Last updated March 3, 2021

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