By Jill Pease
Highlights:
- In 2016, a Zika fever outbreak in the Americas sickened millions.
- In a small percentage of cases, Zika is known to cause serious birth defects when infection occurs during pregnancy.
- Today, there aren’t any active outbreaks of the mosquito-borne virus, but it is considered endemic in many parts of the world.
Ten years ago, a Zika fever outbreak in the Americas triggered a public health crisis. The virus that causes Zika fever infected millions, including an estimated 1.5 million people in Brazil alone. While most cases are mild, Zika has been linked to an autoimmune disorder known as Guillain-Barré syndrome and neurological birth defects that can cause lifelong disability.
In the years since, Zika has largely faded from public view, but does that mean we no longer need to worry?
A virus that hasn’t disappeared
Experts say the 2015-2016 Zika epidemic escalated because of a number of circumstances, including the introduction of a virus into populations with no prior immunity. And while today there are fewer cases and headlines, many of the underlying risk factors remain, such as dense urban populations, global travel — this summer’s FIFA World Cup is a prime example — and an expanding range of the mosquito species that carry the virus. Another outbreak could occur under the right conditions.
“Zika virus continues to circulate in the Americas as of 2026, though no large Zika outbreaks are currently ongoing,” said John Lednicky, Ph.D., a virology expert and research professor in the Department of Environmental and Global Health at the University of Florida College of Public Health and Health Professions.
The Pan American Health Organization reports that so far this year in the Americas there have been Zika cases in Argentina, Bolivia, Brazil, Colombia, Costa Rica, El Salvador, Guatemala, Honduras, Peru and Venezuela.
Scientists have answered many of the most urgent questions about Zika, including how it spreads and possible health effects. But a decade later, important gaps remain.
A surprising new report raises questions
A recent article co-authored by Lednicky and a group of investigators from the Universidad Centroccidental Lisandro Alvarado in Venezuela and the Icahn School of Medicine at Mount Sinai in New York City highlights how much there is still to learn.
The study reports on a case of a woman carrying fraternal twins who was infected with Zika nine weeks into her pregnancy. Previous studies suggest that about 5% of babies born to pregnant women infected with Zika experience birth defects, including microcephaly, a condition in which an infant’s head is much smaller than expected compared to other children the same age, reflecting abnormal brain development. In severe cases, microcephaly can lead to developmental delays, vision and hearing problems, seizures and feeding difficulties.
In the case described in the new study, one twin was born with microcephaly and the other was not. While there have been rare reports of Zika infection affecting one twin in the womb but not the other, this is the first documented case involving infection as early as nine weeks into pregnancy.
“Previously, most people assumed an infection with Zika virus early during pregnancy would result in both twins being infected and developing malformations,” said Lednicky, a member of UF’s Emerging Pathogens Institute. “The finding that only one of two twins developed congenital Zika syndrome raises many questions regarding how embryos and fetuses get infected in the womb by Zika virus.”
Global travel contributes to risk
Zika was first identified in Uganda in 1947 and later spread across Africa, Asia and islands in the Pacific before reaching the Americas.
Experts originally thought international athletes competing in Brazil for FIFA World Cup events may have brought the virus with them, but scientists studying the genome of the Zika virus in the Americas believe the source may have come from the large number of travelers visiting Brazil between 2012 and 2014 from countries with Zika cases.
Could international travel tied to events like the 2026 FIFA World Cup in North America increase opportunities for diseases like Zika to spread?
“There are always risks of acquiring respiratory virus infections and mosquito-borne infections when people are crowded together in open spaces,” Lednicky said. “Soccer is the world’s most popular sport, and there will be a large international presence at the World Cup games. World Cup attendees are at low risk of being infected by chikungunya and dengue viruses, and to a lesser degree, by Zika virus. A major reason for that is that the species of mosquito that carry these diseases are now present in many of the states that will host the World Cup games.”
How to protect yourself
Zika virus is transmitted by Aedes aegypti and Aedes albopictus mosquitoes, the same species that carry chikungunya, dengue and yellow fever viruses. These mosquitoes, which have white bands on their legs, have traditionally made their home in tropical regions, but their range has expanded to the southern and southwestern United States.
“The mosquitoes that transmit Zika virus are daytime biters, generally biting shortly after sunrise and several hours before sunset,” Lednicky said. “In particular, Aedes aegypti often takes multiple blood meals at a time, and that increases the risk of one mosquito infecting many people.”
To reduce mosquito exposure, the Centers for Disease Control and Prevention offers these recommendations:
- Use insect repellent registered by the Environmental Protection Agency
- Wear loose-fitting long shirts and pants when outdoors
- Keep screens on doors and windows to prevent mosquitoes from entering your home
- Remove any standing water from your yard so mosquitoes can’t lay eggs
Before traveling, check the CDC’s Zika travel health notices to determine the risk of Zika transmission at your destination. This is particularly important for women who are pregnant or women and their partners who are planning pregnancy within three months to limit the risk of Zika-associated birth defects.
“When Zika virus is found to be circulating in the community at large, women who plan to get pregnant and those who are pregnant need to be protected from exposure to the virus, and need to be monitored for Zika virus disease,” Lednicky said.