Zika Virus

Overview

Zika virus belongs to the flavivirus family, which also includes Dengue and West Nile virus. The virus spreads most often through the bite of infected Aedes aegypti and Aedes albopictus mosquitoes and, less commonly, through sexual contact.

Most people who acquire Zika virus do not become sick. However, the virus poses serious risks to people who are pregnant, as it can cause severe birth defects in the developing fetus.

Zika virus was discovered in the Zika forest in Uganda in 1947. The virus had circulated in areas of Africa and Southeast Asia but was not known to cause large outbreaks. In 2007, it caused an outbreak in Yap Island in Micronesia. In 2013, the virus caused an even larger outbreak in French Polynesia.

In May 2015, the Pan American Health Organization issued an alert regarding the first confirmed Zika virus infection in Brazil. Cases then spread across South and Central America, as well as the Caribbean, including Puerto Rico and the U.S. Virgin Islands. The first cases of locally transmitted Zika virus in the continental United States were confirmed in Florida in July 2016, followed by Texas in November 2016. No cases of mosquito-transmitted Zika virus have been detected in the United States since 2018.

Signs and Symptoms

About 1 in 5 people who acquire Zika virus may develop symptoms. When symptoms do occur, they are usually mild and last for several days to a week after infection.

Symptoms may include:

• Fever
• Rash
• Conjunctivitis (also known as ‘pink eye’)

Related Health Effects

Zika virus can cause serious health effects, especially during pregnancy and, in rare cases, in adults.

Effects on the developing fetus

Pregnant women who acquire Zika virus can pass the infection to their babies during pregnancy or around the time of birth. During fetal development, Zika virus can cause microcephaly, a serious birth defect of the brain in which a baby’s head is abnormally small and can be associated with incomplete brain development. Research shows that acquiring Zika during pregnancy can also cause congenital anomalies in the developing fetus.

Zika virus has also been associated with other fetal development problems, including:

• Eye defects
• Hearing loss
• Impaired growth

Effects in adults

In rare cases, Zika infection may lead to Guillain-Barré syndrome (GBS). GBS is an autoimmune disorder in which damaged nerve cells cause muscle weakness and, sometimes, partial or complete paralysis. Most people recover from GBS, but some have permanent damage. In rare cases, GBS leads to death.

Causes and Risk Factors

Zika virus is most typically transmitted to humans through the bite of infected Aedes mosquitoes, like other members of the flavivirus family including dengue and yellow fever. Zika virus is also classified as a sexually transmitted infection (STI) because it can be transmitted sexually. Returning travelers who acquired Zika have passed the virus on to their sexual partners.

Risk factors include:

• Living in or traveling to areas where Zika is circulating
• Being pregnant while in an area with active Zika transmission
• Having sexual contact with a person who has acquired Zika

Prevention Guidance

There is currently no licensed vaccine to prevent Zika virus infection, though multiple vaccine candidates are in development. The following prevention measures are recommended:

• Pregnant women should not travel to areas with Zika.
• People who must travel to areas with Zika should talk to their healthcare provider first and strictly follow steps to prevent mosquito bites during the trip.
• Women who are pregnant or thinking about getting pregnant are advised not to travel to areas where Zika infection has been reported.
• Preventing mosquito bites can reduce the risk of infection and transmission.
• For information on how to protect yourself and your partner from Zika during sex, visit CDC Zika prevention.

Diagnosis

Accurate diagnostic tests for Zika virus infection are needed to distinguish it from other flavivirus infections. Tests are also needed to identify women who have been infected with Zika virus during pregnancy and may be at risk for developing fetal complications. Blood, organ, and tissue donor screening tests are also needed to ensure the safety of transfusion and transplantation in areas of active mosquito-borne virus transmission. 

Currently, Zika virus can often be detected during the acute phase of infection (when symptoms are at their worst) and up to 14 days after the onset of symptoms using diagnostic tests for viral genes. Prior Zika infection can be detected by antibody-based tests that use proteins that bind to viruses; however, these tests may also detect or cross-react with antibodies against other flaviviruses, particularly dengue virus. A positive antibody test does not definitively confirm prior Zika virus infection in areas where there may have been possible co-infection or prior infection with dengue and other related viruses.

Treatment and Management

There is currently no medicines or treatments for Zika infection.

Find Clinical Trials

Clinical trials uncover better ways to prevent, diagnose, treat, and understand diseases and conditions. To ensure results apply to everyone, volunteers of all ages, sexes, and backgrounds, including both healthy individuals and those with specific medical conditions, are needed. Find clinical trials on Zika.

Community Support

• Centers for Disease Control and Prevention - Zika
• Centers for Disease Control and Prevention - Zika Travel Information
• Centers for Disease Control and Prevention - Information for Families Living with Birth Defects
• Centers for Disease Control and Prevention – Travelers Health Contacts

Note: This resource list is for informational purposes only. It is not comprehensive, and an organization’s inclusion does not constitute an endorsement by NIH. 

Research Information

The National Institutes of Health (NIH) is the largest public funder of biomedical research in the world. NIH invests most of its budget in medical research seeking to enhance life and to reduce illness and disability. NIH-funded research has led to breakthroughs and new treatments helping people live longer, healthier lives, and building the research foundation that drives discovery.

NIH is working with its partners in government, academia, and the pharmaceutical and biotechnology industries to better understand Zika virus, the disease it causes, and ways to combat it. Because Zika virus is related to dengue and West Nile virus, NIH scientists and grantees have long studied these related viruses, providing a springboard to accelerate Zika investigations and may yield good approaches to developing therapeutics and vaccines.

NIH is supporting the development of treatments for Zika virus infection. NIH is screening a library of approved drugs for potential activity against Zika. One goal is to develop a broad-spectrum antiviral drug that could treat a variety of flaviviruses, including Zika. NIH is also supporting efforts to develop monoclonal antibodies capable of neutralizing Zika virus.

NIH also supports a comprehensive vector biology research program to advance science and identify approaches to control or prevent mosquito-borne diseases, including Zika.

Find NIH-funded research projects using NIH RePORTER, a searchable database of current and past research projects supported by NIH and other federal agencies.