Climate change is reshaping the habitats of rodents and mosquitoes across South America, raising the risk that these animals will spread rare and emerging diseases to people, according to a report by The New York Times.
The shift is bringing wildlife into closer contact with humans and spreading uncommon infections. Scientists are now studying these territorial changes to try to spot health threats before they turn into major outbreaks.
The stakes are high because most emerging diseases originate in animals. The U.S. Centers for Disease Control and Prevention says three out of four new or emerging infections in humans come from other species. Scientists say it is impossible to predict which pathogen will cause the next pandemic, but identifying the environments that give rise to one is considered essential.
How climate change is altering rare diseases in South America
Changes in temperature and rainfall are altering the habitats of rodents that carry arenaviruses. A study published in April 2026 in the journal npj Viruses warned that viruses including Junin, Machupo and Guanarito are shifting their threat toward communities that were not previously exposed. Among the resulting illnesses is Argentine hemorrhagic fever, a serious disease transmitted through contact with waste from infected animals.
The effect is already visible in Argentina's pampas region, where Argentine hemorrhagic fever has gone from affecting mainly rural workers to causing urban infections in cities including Rosario and San Nicolas de los Arroyos. Urban growth into areas inhabited by the corn mouse, combined with a changing climate, is destroying old habitats and creating new pockets of health risk across the continent.
To limit the impact, scientists are analyzing epidemiological, meteorological and mapping data to sharpen surveillance and vaccination efforts. Marcela Uhart, a veterinarian at the University of California, Davis, told the Times that while it is not possible to foresee the next emerging illness, it is possible to predict or better understand the risk factors behind one. Transmission between people remains low, but prevention is still treated as a priority.
Why infectious diseases and zoonoses are rising in South America
Urban expansion into rural land is increasing contact between residents and wildlife. New neighborhoods, roads and ports are pushing into territory where pathogens unfamiliar to local populations circulate. The Pan American Health Organization has warned that urbanization, coastal development and other territorial changes are altering the distribution of infections and the vectors that carry them.
Deforestation and biodiversity loss are also reshaping animal habitats. Vulnerable species are disappearing, while adaptable carriers such as certain rodents are finding food and shelter in homes and crops. The World Health Organization says these environmental disruptions destabilize ecosystems and bring together species that once lived in isolation.
Gaps in surveillance, vaccination and diagnosis are making the spread worse. Argentina's Ministry of Health says the lethality of Argentine hemorrhagic fever, which ranges between 15% and 30% without treatment, falls to about 1% with early care using the Candid #1 vaccine dose or immune plasma administered within the first eight days of illness. Experts say the way forward is to integrate environmental monitoring with human and animal health efforts to prevent future outbreaks.
