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.

Duration of Zika Virus Infection

About one in five people develop symptoms when infected with Zika, and the symptoms usually last for about two to seven days.

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.

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.
Related

Diseases Carried by Ticks, Mosquitoes, and Fleas Triple in the US

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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