Oligoryzomys longicaudatus
Long-tailed pygmy rice rat; primary South American reservoir for Andes hantavirus in Argentina and Chile.
Last refreshed: 12 May 2026 · Appears in 1 active topic
Why is one small South American rat the source of the world's only human-to-human hantavirus?
Timeline for Oligoryzomys longicaudatus
Mentioned in: WHO upgrades Hondius Andes risk to MODERATE
Pandemics and Biosecurity- What animal carries Andes hantavirus?
- The long-tailed pygmy rice rat (Oligoryzomys longicaudatus) is the primary reservoir for Andes virus across Argentina and Chile. The rodent carries the virus chronically; humans become infected by inhaling aerosolised rodent excreta.Source: WHO / PAHO
- Where does the Andes hantavirus reservoir rodent live?
- Oligoryzomys longicaudatus is found across central and southern Argentina and Chile, including Patagonia, in grass-scrub ecotones, Forest margins, and agricultural areas frequented by both rural workers and tourists.
- Why does Andes hantavirus spread in El Niño years?
- El Niño produces mast-seeding years (unusually heavy plant seed production) that temporarily boost the food supply and population of O. longicaudatus. Larger rodent populations increase human exposure to infected animals and aerosolised excreta, typically followed by elevated hantavirus case counts.Source: PAHO
Background
Oligoryzomys longicaudatus, the long-tailed pygmy rice rat, is a small South American rodent species of the family Cricetidae found across central and southern Argentina and Chile, including Patagonia. It is the primary animal reservoir host for Andes virus (ANDV), the sole hantavirus with confirmed human-to-human transmission capacity, and for Andes-related hantaviruses circulating in the Southern Cone. As a reservoir, the rodent carries the virus chronically without becoming ill; transmission to humans occurs primarily through inhalation of aerosolised urine, faeces, or saliva from infected animals.
The species inhabits grass-scrub ecotones, Forest margins, and agricultural edges throughout its range, and is closely associated with human rural activity — farm buildings, grain stores, camping sites, and trekking trails in Patagonia. Andes virus was first characterised in Argentina and Chile in the 1990s following outbreaks of hantavirus pulmonary syndrome. The range of O. longicaudatus broadly defines the geographic distribution of Andes hantavirus risk.
Climate and land-use change are significant drivers of O. longicaudatus population cycles. El Niño / La Niña oscillations produce mast-seeding years (heavy seed production) that temporarily expand rodent populations, typically followed by elevated hantavirus case counts in affected areas. Research published in recent years documents northward range expansion of the species as Andean vegetation zones shift under climate warming, with implications for the geographic footprint of Andes hantavirus risk.
The zoonotic ecology of O. longicaudatus is directly relevant to the MV Hondius cluster: passengers and crew of the vessel undertook shore excursions in Patagonia (Argentina and Chile) before the cluster was identified, with rodent-exposure risk at trekking and camping sites. The WHO's PAHO had previously issued a December 2025 alert on elevated Andes activity in the Southern Cone, reflecting what was likely a mast-seeding cycle and associated rodent population surge.