Severe drought may have sparked Brazil's first urban yellow fever surge in decades

A study published in Science Advances links the unusually intense 2015 drought, amplified by El Niño, to Brazil's first major urban yellow fever epidemic since 1942. Simulations indicate that infected howler monkeys and other primates migrated toward cities in search of water, while dehydrated mosquitoes increased their biting frequency, facilitating virus transmission. The disease spread from late 2016, affecting more than 2,000 individuals and killing almost 750, with Haemagogus species driving most infections rather than the usual Aedes aegypti.

Researchers highlight that low human vaccination rates, deforestation, and the drought acted together as a “spark” for the outbreak. Boosted immunisation campaigns and vector control eventually curbed the spread. The work underscores the need to monitor drought conditions as climate change may make such scenarios more common.