Hantavirus Outbreak History: 1993–2026

📊 Americas Hantavirus Overview 2025

Beyond major named outbreaks, hantavirus causes an ongoing endemic disease burden across the Americas. The Pan American Health Organization (PAHO) reported 229 cases and 59 deaths across 8 countries in 2025 — a case fatality rate of 25.8%. Brazil, Argentina, and Chile account for the majority of cases. HPS remains an underappreciated cause of acute respiratory illness in rural Latin America.

See the complete Americas data table and global risk map →

🌧️ Why Hantavirus Outbreaks Cluster

Hantavirus outbreaks do not occur randomly — they follow predictable patterns linked to rodent population ecology:

• El Niño cycles: Wetter-than-normal winters in western North America produce abundant vegetation and seed crops, which cause explosive growth in deer mouse populations the following spring. The 1993 Four Corners outbreak directly followed a 1991–1992 El Niño event that caused an estimated 10× increase in regional deer mouse density. Epidemiologists now monitor rodent population indices as a leading indicator for HPS risk.
• Mast years (beech and oak): In Europe, bank vole population explosions follow mast years when trees produce an unusually large seed crop. These "vole years" reliably predict elevated Puumala virus NE cases in Finland and surrounding countries 12–18 months later.
• Human behavior: Opening closed structures (cabins, barns, storage units) that accumulated rodent contamination over winter is the most common trigger for individual HPS cases. The Yosemite 2012 outbreak resulted from canvas tent cabins that provided ideal rodent nesting sites.
• Travel: The 2026 MV Hondius outbreak demonstrated a new pathway — travelers contracting Andes virus in Patagonia and then seeding cases in non-endemic countries through person-to-person transmission aboard a closed vessel.