Zika Virus Overview 

Zika is a rare, mosquito-borne illness caused by the Flaviviridae virus. If a Zika-infected mosquito bites the human skin, the virus can travel into that person’s bloodstream. Zika can also pass to a fetus through the placenta during pregnancy. Less commonly, it can also be transmitted through sex and blood.

Most people with Zika don’t show any symptoms. When symptoms occur, they are usually mild and include:

Fever Headache Joint or muscle pain Pink eye (conjunctivitis) Rash Swollen lymph nodes (lymphadenopathy)

Zika can lead to complications, including:

Congenital disorders Guillain-Barré syndrome (an autoimmune disorder) Increased risk of stillbirth during pregnancy and spontaneous pregnancy loss

How Common Is Zika Virus? 

The first Zika virus outbreak in the U.S. was in 2016, and cases spiked that year. However, cases have been on the decline since 2018. 

In 2022, getting the Zika virus in the U.S. is very rare because there is no current outbreak. The following are Zika statistics from the United States and its territories over the past several years:

Of the 224 locally acquired cases in 2016, 218 were contracted in Florida, and six were contracted in Texas. There have never been reported cases in Alaska or Hawaii. The last reported locally acquired cases in the continental U. S. were in 2017. The last confirmed case in the U. S. territories occurred in 2019. There have been 32 documented travel-associated cases since 2019.

The following table provides facts from available statistics from 2015–2020 in the U.S. and U.S. territories.

Zika Virus by Age and Gender 

Previous reports show that the Zika infection rate is higher among people ages 20–49 and among people assigned female at birth. The following are statistics regarding the 5,168 confirmed Zika cases in the U.S. in 2016:

About 80% were 20–59 years old. The average age was 37. People assigned female at birth accounted for 3,307 (64%) of the cases. The majority of cases (95%) were related to travel. Forty-five cases were sexually transmitted; of those, 43 (96%) were people assigned female at birth.

These reports note that the sex differences in confirmed cases could be due to increased testing. The possibility of experiencing pregnancy complications and passing on congenital disorders influenced many non-menopausal adults to test.

Causes of Zika Virus and Risk Factors 

Flaviviridae, a virus that an Aedes aegypti mosquito can carry, causes Zika. The Aedes mosquito thrives in wet areas such as the Gulf Coast of the U.S., especially in the warmer months. The risk is highest when the Aedes mosquito is most active; two hours after sunrise and a few hours before sunset. 

Zika can spread through: 

Mosquito bites (most common)Pregnancy (from mother or parent to fetus)Barrier-free sex (penis-to-vagina transmission is more likely)Sharing blood (e. g. , through needles)

Risk factors for getting the Zika virus include:

Traveling or living in a warm, wet climateHaving unprotected (condomless) sex with an infected partnerBlood transfusions

What Are the Mortality Rates for Zika Virus?

The survival rate is the percentage of people who survive a disease for a specified time, but it may be presented in several different ways. 

The overall survival rate for non-congenital (adult) Zika is over 99%. Severe illness or death due to Zika is extremely rare. The following data is from the 5,168 U.S. Zika cases in 2016: 

There were 153 (3%) people hospitalized. There were 15 (0. 3%) people diagnosed with Guillain-Barré syndrome. There was one reported death.  

The Zika virus can cause pregnancy complications and congenital disorders related to the eye or brain. U.S. Zika 2016 outbreak statistics related to pregnancy or babies include:

About 5% of babies with birthing parents who had Zika during pregnancy were born with Zika-associated conditions present at birth. The highest number of congenital disorders occurred six months after the outbreak’s peak. Areas with widespread local transmission had four times the number of congenital disorders. Zika-associated congenital disorders occurred with two out of 25 (8%) infections in the first trimester, 6% in the second trimester, and 3. 8% in the third trimester.

Screening and Early Detection

Because the number of Zika cases is currently low, very few people require Zika testing. When needed, diagnosis occurs through the following blood tests:

Molecular: A molecular test detects a current Zika infection. Serological: The serological test looks for antibodies. It is not recommended for pregnant people because it can detect antibodies from past infections or similar viruses.

Testing is recommended if you:

Have symptoms of Zika, even if you feel betterTraveled to a country with a current Zika outbreakAre pregnant and have Zika-associated fetal anomalies on an ultrasoundHave delivered a baby with a congenital disorder that could be related to ZikaAre pregnant and were recently exposed

Anyone who travels to high-risk areas should take steps to prevent mosquito bites for three weeks upon returning home. They should also practice safer sex for several months because Zika can stay in semen for months after infection.

Avoid areas with an outbreak while pregnant. Have sex with barrier devices such as condoms or avoid sex, especially while pregnant. Remove standing water around your home. Stay indoors when possible. Use an Environmental Protection Agency-registered insect repellent when outdoors. Wear long-sleeve shirts or pants when outdoors.

As of July 2022, there are no current outbreaks of Zika worldwide. However, the most current significant outbreak was in India in November of 2021. 

Green or level 1: Low concern, take usual precautions Orange or level 2: Practice additional precautions, especially for at-risk populations Red or level 3: Avoid non-essential travel to that area

The following are regions that have had outbreaks in the past: 

AfricaFranceIndiaPacific IslandsSouth and Central AmericaSoutheast AsiaThe CaribbeanU. S. Gulf Coast

Summary

Zika is a rare virus most commonly spread to humans through bites from the Aedes mosquito. You can also spread it through sex and infected blood or to a fetus during pregnancy. Zika can cause pregnancy complications and congenital disorders. 

There are no medicines or vaccines to help prevent Zika, so other prevention techniques are important, especially for pregnant people. Those who travel can bring the virus back with them and should use prevention techniques after they return home.

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