Argentina is facing a sharp increase in Zika virus infections in 2025, with over 730 cases reported so far. This a significant rise from the 564 cases of the previous year.
Zika’s effects are often mild or even asymptomatic, but the virus remains a significant risk for pregnant women. The infection can cause microcephaly - where a baby’s head is much smaller in size than would be expected for its age - and other birth defects including eye abnormalities and developmental delays. In rare instances, the virus can cause Guillain-Barré syndrome in adults, a rare and pernicious autoimmune condition affecting the nervous system.
The virus is primarily transmitted by Aedes mosquitoes and first gained global attention during Brazil’s 2015-2016 epidemic. Previously, it had remained confined to equatorial Africa and Asia, relatively obscure until outbreaks in the Pacific and the Americas highlighted how quickly a virus can spread amongst a susceptible population.
Over a million recorded Zika virus cases swept the country where thousands of cases of microcephaly led the World Health Organization to declare it a global health emergency.
The threat now lies more in the surrounding countries than in Brazil itself. “The main progress that's been made is that Zika simply ran its course. And in most parts of Latin America, for example, it infected more than half the population” explains Dr. Scott Weaver, Director of the institute for human infections and immunity at the University of Texas Medical Branch, Galveston. “Those people are now immune and probably can never be reinfected.”
Compared with the rapid mutations of SARS-CoV-2 which stunned the world in the early 2020’s, Zika virus evolves much more slowly. This means that natural immunity to Zika is maintained for a much longer period.
The rising Zika cases in Argentina come at a bad time with the country still dealing with the after-effects of a major dengue outbreak in 2024. Spread by the same mosquito species, dengue infected over 330,000 people in the country and caused more than 200 deaths. This leads to complications in tracking the rise in Zika cases in Argentina.
“In many parts of the world where Zika is endemic, they don't have access to diagnostics, and they typically get misdiagnosed as dengue,” says Weaver. It is entirely plausible that the Zika case numbers in Argentina are far higher than recorded.
Current climate conditions also put the nation in a vulnerable place, as rising temperatures and increased rainfall due to global warming create favourable conditions for mosquito breeding farther from the equator. This has now exposed Argentina to new threats. “Many parts of Argentina have temperate climates, which means they're too cold most of the year to support transmission,” highlights Weaver. “That's because mosquitoes don't control their body temperatures, so they have to be in warm locations before they can transmit the virus from human to human.”
Moving forward, some work is underway to develop a Zika vaccine, for which there is currently no treatment or cure. But research is very limited. For now, governmental health services such as the CDC and NHS advise vigilance, and that pregnant individuals looking to travel to Argentina consult a healthcare professional before doing so. Weaver sums up the current situation, “I'm afraid we're not a lot better off than we were in 2015, aside from the herd immunity.”
