Zika is a virus that is mainly spread by the bite of an infected mosquito, though other routes of infection are possible.

The virus was named in 1947 when scientists surveilling Uganda's Zika forest for yellow fever (a different viral illness) isolated the virus in samples taken from a rhesus monkey. The following year, the virus was recovered from a mosquito. In 1952, the first human cases were reported in Uganda and the United Republic of Tanzania.

Outbreaks of Zika have been documented in the Americas, Africa, Asia, and the Pacific Islands. The first outbreak in the Americas occurred in 2015, when the virus spread through Latin and Central America.

In July 2016, the first outbreak in the continental United States was traced to Miami-Dade County, Florida.

The Centers for Disease Control and Prevention (CDC) has an up-to-date world map showing areas with active Zika transmission.

According to the CDC, many people infected with the Zika virus will have mild symptoms or none at all. People usually don't get sick enough to require hospitalization, and symptoms last up to a week.

For pregnant women though, a Zika infection is extremely concerning, since it can cause birth defects. According to a CDC report, nearly one in seven babies born to women infected with Zika during pregnancy had health problems such as small head size, brain damage, and vision or hearing impairment. Research suggests that the virus may also be linked to Guillain-Barré syndrome (GBS), a rare but serious neurological condition characterized by generalized weakness.

Causes and Risk Factors of Zika Virus Infection

The Zika virus is spread primarily through the bites of infected Aedes mosquitoes (including the Aedes aegypti and Aedes albopictus species).

These types of mosquitoes frequently attack in the daytime hours, but they also bite at night. They usually lay eggs near standing water, and can survive indoors as well as outdoors. They're the same mosquitoes that transmit the viruses that cause dengue fever, chikungunya, and yellow fever.

The mosquitoes become infected when they feed on someone who already has the virus, and they spread it to other people through their bites.

There are other, less common ways that the Zika virus may be spread. Some of these reported modes of transmission have not been confirmed or require more research. It is not spread by respiratory droplets like SARS-CoV-2, the coronavirus that causes COVID-19 infection.

Mother to Child

Zika can be transmitted from a mother to her baby during pregnancy or around the time of birth.

The virus has been found in breast milk, and there have been reports of infection in breastfed babies. But there have been no reported cases of babies developing health problems related to breastfeeding from a woman with the Zika virus.

Blood Transfusion

There have been reports in Brazil of possible transmission of the Zika virus by blood transfusion, according to the CDC, but there have been no confirmed transfusion-related cases.

Through Sex

Health officials have confirmed that the Zika virus can be sexually transmitted through unprotected vaginal, anal, and oral sex. The virus remains active in semen longer than in other bodily fluids such as blood and urine.

An infected person can spread the virus before they develop symptoms or after their symptoms subside, known as asymptomatic transmission.

Laboratory and Healthcare Settings

There have been some reports of Zika virus infections acquired in laboratory settings.

There have not been confirmed cases of Zika virus transmission in a healthcare facility in the United States.

However, the CDC provides recommendations for healthcare providers to prevent possible exposure when there will be contact with an infected person’s blood or other bodily fluids.

Animals

According to the CDC, there have been no reports of pets or other animals becoming sick with the Zika virus or spreading it to humans.

But a recent study found that maternal Zika virus infection in nonhuman primates is associated with miscarriages and stillbirths.

How Is Zika Diagnosed?

Zika virus infection can be detected through a blood or urine test. There are tests available to detect the presence of the virus in the body or serological tests that look for antibodies your body makes to fight infection (although this test is not as accurate; the same test can detect viruses like chikungunya and dengue).

Testing for Zika is usually recommended if a person shows symptoms after having been in a high-risk area or having unprotected sex with a partner who has been in an area where Zika is common.

Pregnant women who may have been exposed to Zika should be tested. Your doctor will also want to test for infection if a fetal ultrasound shows possible Zika-associated abnormalities.

Many people infected with the virus don't have any signs or develop only mild symptoms, so the infection may go undetected.

Prognosis of Zika Virus Infection

It's estimated that about 80 percent of people who get Zika virus never have symptoms. When symptoms do occur, they're usually mild. It's very unusual for Zika to require hospitalization or lead to death.

Microcephaly is a birth defect in which babies are born with abnormally small heads because the brain has not developed properly or has stopped growing. The prognosis for infants born with microcephaly as a result of being infected by Zika in utero is not clear. A report published in the Pediatric Infectious Disease Journal in 2017 estimated the fatality rate for confirmed cases of microcephaly at 8.3 percent.

A study of 1,450 infants that used data from the U.S. Zika Pregnancy and Infant Registry reported that 14 percent of 1-year-old children who were exposed to Zika virus in utero had health issues potentially related to exposure, which included birth defects or neurodevelopmental abnormalities.

Treatment and Medication Options for Zika Virus Infection

There is no vaccine for Zika, and treatment of the viral infection usually involves managing the symptoms because there are no proven antiviral therapies available.

To relieve symptoms of the virus, the CDC recommends that you:

Drink plenty of liquids to prevent dehydration
Get plenty of rest
Take acetaminophen to reduce pain and fever
Don't take aspirin, ibuprofen, or any nonsteroidal anti-inflammatory drugs (NSAIDs) without talking to your doctor
Tell your physician about all the medications you're taking if you become infected with the Zika virus

Alternative and Complementary Therapies

You may see a variety of herbs or natural products touted as a way to prevent or treat the Zika virus. According to the CDC, there's no credible evidence that any of these products can be used to prevent or treat Zika.

Prevention of Zika Virus Infection

Experts say the best form of prevention is to protect yourself and others from getting bitten by mosquitoes in the first place.

If you've been diagnosed with Zika, avoid contact with mosquitoes during the first week of illness to prevent the further spread of the virus.

There are several ways to protect yourself:

Use an Environmental Protection Agency (EPA)–registered insect repellent with active ingredients such as DEET and picaridin.
The EPA offers an online search tool to help you choose the right repellent. But don't use insect repellent on babies younger than two months of age.
Wear long pants and long-sleeved shirts
Find lodging with air-conditioning or screens to keep mosquitoes outside
Treat clothes with the insecticide permethrin
Sleep under a mosquito bed net if you’re sleeping outdoors
Cover a baby's crib, stroller, or carrier with mosquito netting
Remove stagnant water that may collect in places like planters, buckets, birdbaths, or trash containers.

Since Zika can be transmitted through sex, the use of condoms can reduce the risk of infection. Zika can be sexuallytransmitted from someone who has no symptoms,

so consider whether a sexual partner has lived in or traveled to a place with a high risk of Zika.

Women who are pregnant or trying to become pregnant should consider avoiding any travel to areas with risk of Zika.

Complications of Zika Virus Infection

Although most people recover from Zika within a week, there can be serious complications related to the virus.

Pregnancy and Zika

Pregnant women should take special precautions to protect themselves, because Zika virus infection has been linked to miscarriage and birth defects.

The CDC recommends that women who are pregnant or trying to become pregnant should consider postponing travel to areas where Zika is a concern. If expectant mothers must travel, they should talk to their doctor ahead of time and come up with a strategy to prevent exposure to mosquitoes and practice safe sex.

Pregnant women returning from an area with a risk of Zika should contact their doctor immediately if they show any symptoms.

The CDC advises men who plan to conceive not to have unprotected sex for at least three months after any possible Zika exposure or symptoms since the virus can survive in semen for a prolonged period.

Microcephaly

Zika infection during pregnancy has been linked to microcephaly. The condition may be apparent at birth or develop in a child's first few years of life.

Microcephaly often leads to developmental delays and intellectual disabilities. It has also been linked to seizures, movement and balance problems, hearing loss, vision problems, and difficulty swallowing. Severe cases can be life-threatening.

A 2015 Zika virus epidemic in northeast Brazil was followed by a spike in reported cases of microcephaly. Studies have suggested a strong association between microcephaly and Zika virus infection.

Research and Statistics: How Many People Have Zika?

The CDC’s national database keeps track of any reported cases of the Zika virus in the United States.

In 2020, there were three Zika virus disease cases reported in the United States; each of those cases were travelers returning from infected areas.

There were 48 Zika virus disease cases reported in the U.S. Territories (Puerto Rico was the only territory with reported cases) and those cases were all presumed to be acquired from local mosquito-borne transmission.

By comparison, in 2016, there were 5,168 Zika virus cases reported in the U.S, 224 of them through local mosquitoes. There were 36,512, cases in the U.S. Territories, and almost all of them through local mosquito-borne transmission. That number included 35,395 cases in Puerto Rico, 986 cases in the Virgin Islands, and 131 cases in American Samoa.

Zika Today and New Research

In February 2016, the World Health Organization (WHO) declared Zika a public health emergency and launched a worldwide effort to coordinate development of vaccines and treatments.

In June 2018, researchers constructed the most detailed structure of the Zika virus so far, which may help in the development of future vaccines or drugs.

Researchers are also exploring ways the Zika virus might actually be used to treat certain cancers such as neuroblastoma, a common form of childhood cancer, by attacking cancer cells.

Related Conditions of Zika

Guillain-Barré Syndrome

Several countries have reported increases in cases of Guillain-Barré syndrome (GBS) following Zika outbreaks.

Guillain-Barré syndrome is a serious disorder in which the immune system damages the lining of nerve cells, causing muscle weakness and sometimes paralysis. It is rare, but usually occurs after a respiratory or gastrointestinal viral illness, with one to two cases diagnosed each year for every 100,000 people in the United States.

Research suggests that Guillain-Barré syndrome is strongly associated with Zika, but only a small percentage of people with Zika virus infection get GBS. The CDC is continuing to investigate the possible link.

Other Insect-Borne Diseases

According to recent CDC figures, the number of so-called vector-borne diseases transmitted by mosquitoes and other insects like ticks more than tripled between 2004 and 2016. Reported cases surged from 27,388 in 2004 to over 96,000 in 2016 for a total of 642,602 cases over the 13-year span — and those numbers may be vastly underreported.

Just as alarming as the increase in known diseases is the fact that nine new germs spread by mosquitoes and ticks have been discovered in the United States and its territories since 2004. These include the Bourbon virus, a rare and deadly tick-borne disease that was first spotted in Bourbon County, Kansas, in 2014, and the Heartland virus, which is most likely transmitted by lone star ticks and is endemic to midwestern and southern states.

Resources We Love

Centers for Disease Control and Prevention (CDC)

The CDC offers science-based, data-driven info on Zika in the United States and abroad, including the basics about the virus, tips on prevention and mosquito control, and up-to-date maps and statistics.

World Health Organization (WHO)

The WHO directs and coordinates international health within the United Nations. Check out their website for comprehensive coverage of Zika, including fact sheets on the virus and associated conditions, updates on outbreaks, and answers to common questions.

National Institute of Allergy and Infectious and Diseases (NIAID)

Part of the National Institutes of Health, the NIAID undertakes and supports research into infectious, immunologic, and allergic diseases. On their website, you can find the latest news about treatment and vaccine research.

Additional reporting by Lynn Marks.

Editorial Sources and Fact-Checking

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Zika: Symptoms & Causes. Mayo Clinic. February 6, 2021.
Zika Transmission Methods. CDC. July 24, 2019.
Zika: Sexual Transmission & Prevention. CDC. May 21, 2019.
Healthcare Exposure to Zika and Infection Control. CDC. December 12, 2017.
Zika and Animals. CDC. November 15, 2018.
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