Andes Virus: South American Hantavirus With Human-to-Human Transmission

Andes orthohantavirus (ANDV) is the most consequential hantavirus species for global public-health planning. It is the only hantavirus with confirmed person-to-person transmission, first documented in a 1996 cluster in El Bolsón, Argentina, and repeatedly verified in the southern Andes ever since. Its case-fatality rate sits near 35%, comparable to Sin Nombre virus, but ANDV's transmissibility is what places it on every WHO emerging-pathogen watchlist.

Geography and reservoir

The natural host is the long-tailed pygmy rice rat, Oligoryzomys longicaudatus, which inhabits the Patagonian steppe and Valdivian temperate forest. Endemic transmission is documented from approximately 35°S to 50°S, spanning western Argentina, southern Chile, and increasingly southern Brazil and Uruguay. The rodent's range expanded northward during the 2018–2024 series of warm, wet austral winters, and serosurveys now place ANDV-positive rodents as far north as Mendoza and Bariloche.

Cluster countries

• Argentina — Río Negro, Chubut, Neuquén, Salta provinces.
• Chile — Aysén and Los Lagos regions historically dominate; Magallanes increasing.
• Uruguay — sporadic; first laboratory-confirmed autochthonous cases 2019.
• Brazil — closely related Araraquara virus, with overlapping clinical phenotype.

Human-to-human transmission

ANDV is unique among hantaviruses in producing secondary cases without rodent exposure. Documented routes include:

• Household contact — sharing bedding or close prolonged contact during the prodromal phase.
• Sexual contact — virus has been isolated from semen of convalescent patients.
• Healthcare workers — pre-symptomatic and symptomatic patients have infected staff during procedures generating respiratory aerosols.

Secondary attack rates in confirmed ANDV households range from 5–15%, meaningfully above background. The 1996 El Bolsón outbreak chain contained 18 cases; clusters in 2019 (Epuyén, Argentina) and 2022 (Cochrane, Chile) reproduced this pattern.

Clinical course of ANDV-HPS

Andes virus disease is functionally a more aggressive form of HPS:

1. Prodrome (days 1–5) — fever ≥38.5°C, intense thigh and lumbar myalgia, dry cough often absent. Thrombocytopenia and a left shift on CBC are diagnostic clues.
2. Cardiopulmonary phase (day 4–7) — abrupt onset of dyspnea progressing to non-cardiogenic pulmonary edema; cardiac index drops; lactate climbs.
3. Diuretic / convalescent phase — survivors typically show rapid resolution within 48 hours of stabilization.

ECMO availability has lowered observed mortality at tertiary centers in Buenos Aires and Santiago to under 25%, but rural CFR remains close to 50%.

The 2026 cluster signal

The 2026 outbreak was triggered by a cluster in Río Negro province, Argentina, with eight initial cases linked to a tourism lodge. Subsequent investigation identified probable household-to-household transmission chains, suggesting the inter-person R₀ may be higher than the 2019 baseline of approximately 0.6. The most consequential export event remains the MV Hondius cruise ship, where infected passengers seeded onward chains across multiple ports.

Trade the open question: Will a second EU country confirm Andes virus by June 15?

Prevention

• Avoid travel to known active clusters during outbreak alerts.
• Standard rodent-exclusion: seal entry points ≤6 mm, wet-clean droppings with 1:10 bleach, ventilate closed cabins ≥30 minutes.
• For close contacts of confirmed cases: 21-day fever monitoring, isolation if symptomatic.
• Healthcare workers: full airborne PPE (N95 + face shield) for any aerosol-generating procedure on suspected ANDV cases.

Comparison with other New World hantaviruses

See Sin Nombre virus, the North American counterpart, which shares the rodent-aerosol route but lacks confirmed person-to-person transmission. For the broader virus family, see the complete hantavirus guide.