Hantavirus in the US vs South America: Sin Nombre vs Andes Virus
The 2026 MV Hondius outbreak has placed two different hantavirus ecosystems in the same story. Passengers exposed in Patagonia are now being treated in European, North American, and Oceanian hospitals — yet the virus causing their illness, Andes virus, is fundamentally different from the hantavirus Americans most commonly read about: Sin Nombre virus. Here is how they compare.
Why Two Different Hantaviruses?
Hantaviruses co-evolved with specific rodent hosts over millions of years. Each continental landmass developed its own endemic cycles:
- North America: Sin Nombre virus → deer mouse (Peromyscus maniculatus)
- South America: Andes virus → long-tailed pygmy rice rat (Oligoryzomys longicaudatus)
- Europe/Asia: Puumala, Hantaan, Seoul, Dobrava → various Myodes and Apodemus species
When Pangaea separated and rodent lineages diverged, their hantaviruses went with them. The result is a global patchwork of hantavirus diversity with distinct geographic boundaries — until, as the Hondius case demonstrates, human travel erases those boundaries.
Hantavirus in the United States
The pathogen: Sin Nombre virus
Sin Nombre virus (SNV) was first identified in 1993 during a mysterious outbreak at the Four Corners region (Arizona, Colorado, New Mexico, Utah). In a matter of weeks, young, healthy Navajo individuals were dying of unexplained respiratory failure. The culprit, isolated by CDC researchers, was a previously unknown hantavirus they named Sin Nombre — Spanish for “without a name.”
The rodent reservoir
The deer mouse (Peromyscus maniculatus) is ubiquitous across the continental United States — found in all lower 48 states, in habitats from desert to boreal forest. This wide distribution means hantavirus risk exists across the entire country, not just the Southwest. However, the highest seroprevalence in deer mouse populations is in the Four Corners region and Great Basin.
Case numbers
The CDC has recorded approximately 850 confirmed HPS cases in the US since surveillance began in 1993. The annual case count typically ranges from 15–40, with peaks following La Niña years when rodent populations boom due to increased vegetation and seed availability.
In 2026, the US is tracking 19 confirmed cases (as of May 13), the highest since 2012. This is separate from the Hondius cluster — these are domestically-acquired exposures.
Case fatality rate
Approximately 35–40% historically for Sin Nombre HPS. The introduction of ECMO in the early 2010s has improved survival in severe cases, with some academic centres reporting survival rates above 70% in patients who receive early ECMO therapy.
Where the US cases occur
| State | Approx. historical cases | Primary exposure setting |
|---|---|---|
| New Mexico | 108 | Rural homes, agricultural buildings |
| Colorado | 96 | Cabins, rural homes |
| Arizona | 80 | Peridomestic, farming |
| California | 60+ | Yosemite-style cabin exposure |
| Montana/Wyoming | 40+ | Agricultural, outdoor recreation |
The Yosemite 2012 outbreak remains the most prominent US cluster: 10 cases linked to “Signature Tent Cabins” in Yosemite Valley; 3 deaths. Deer mouse infestations in cabin insulation were identified as the source.
Hantavirus in South America: Andes Virus
The pathogen: Andes virus
Andes virus (ANDV) was first characterised in 1997 following outbreaks in the southern Andean regions of Chile and Argentina. It causes HPS with a presentation clinically indistinguishable from Sin Nombre HPS — the same prodromal fever/myalgia, the same catastrophic pulmonary oedema. But it has one property that Sin Nombre does not: documented person-to-person transmission.
The rodent reservoir
The long-tailed pygmy rice rat (Oligoryzomys longicaudatus) inhabits the Andean valleys and Patagonian steppes of Chile and Argentina. Unlike the deer mouse, it is far more geographically constrained — and crucially, it was present in the cargo holds and below-deck areas of MV Hondius during its Antarctic voyage, where environmental sampling confirmed Andes virus RNA.
Case numbers
Argentina and Chile together report approximately 150–200 Andes virus HPS cases per year during peak seasons (autumn/winter, when humans and rodents share enclosed spaces). In 2026:
- Argentina: 112 confirmed cases, 37 deaths as of May 15 — above the 5-year average of ~105 cases for this period
- Chile: 12 confirmed cases, 3 deaths — Aysén region cluster growing
Case fatality rate
Approximately 30–35% for Andes virus HPS, comparable to Sin Nombre. Historical Chilean data show variability by region and year.
The P2P question
This is the most important clinical distinction between Andes virus and every other hantavirus:
Documented P2P transmission events:
- Chilean household clusters in the late 1990s
- Argentine case series (several documented family clusters, 2000–2010)
- Healthcare worker transmission in a Chilean hospital (2002)
- Lyon, France, 2026: Hondius cluster — confirmed by genomic analysis (May 14, 2026)
The secondary attack rate in households is estimated at 10–15% (Nature Medicine, May 15, 2026). This is far below respiratory viruses but high enough to justify the WHO’s new 60-day household contact monitoring guidance.
Side-by-Side Comparison
| Feature | Sin Nombre (US) | Andes Virus (South America) |
|---|---|---|
| Reservoir | Deer mouse (P. maniculatus) | Long-tailed rice rat (O. longicaudatus) |
| Geographic range | All 50 US states (high risk: SW, Mountain West) | Chile, Argentina, parts of Brazil and Bolivia |
| Annual cases | 15–40 (US) | ~150–200 (Argentina + Chile) |
| Case fatality rate | ~35–40% | ~30–35% |
| Syndrome | HPS — pulmonary oedema, cardiorespiratory shock | HPS — clinically identical |
| P2P transmission | Not documented | Documented (household, ~10–15% SAR) |
| Treatment | Supportive; ECMO in severe cases | Supportive; convalescent plasma (investigational) |
| Incubation | 2–4 weeks | 2–4 weeks (up to 8 weeks) |
| 2026 notable event | 19 domestic cases — highest since 2012 | Hondius cluster: 14 cases across 11 countries |
How Did Andes Virus Reach 14 Countries?
The MV Hondius voyage illustrates a new vulnerability in the modern hantavirus landscape: globalised expedition tourism to endemic rodent habitats.
Antarctic cruise ships regularly visit Patagonian ports (Ushuaia, Punta Arenas) and sub-Antarctic islands where O. longicaudatus is endemic. The ship’s supply chain and shore excursions created opportunities for rodent contact. Once passengers returned to their home countries — each carrying a 2–4 week incubation period — the outbreak decentralised across three continents.
The US has 19 confirmed domestic cases this season, but also has Hondius-related passengers under monitoring — tracked by CDC separately in its Level 2 Travel Health Notice for Patagonia issued May 15.
Risk Assessment for 2026
| Scenario | Sin Nombre risk | Andes virus risk |
|---|---|---|
| Visiting US national parks, camping | Moderate (endemic, seasonal) | Very low (no reservoir) |
| Trekking in Patagonia | Very low (no US-like reservoir) | Moderate–high (endemic season) |
| MV Hondius returning passenger | Nil (wrong hemisphere) | Monitored; 60-day follow-up |
| Household member of Hondius case | Nil for SNV | Low (P2P documented; WHO guidance active) |
| Healthcare worker treating Hondius patient | Nil | Very low with standard PPE |
What Both Share: Prevention Basics
Despite their geographic and biological differences, preventing both Sin Nombre and Andes virus infection rests on the same foundations:
- Avoid disturbing rodent habitat — never sweep dry droppings
- Seal buildings — gaps >6 mm allow deer mice; even smaller gaps for O. longicaudatus
- Use N95 respirators and gloves during cleanup or work in high-risk environments
- Ventilate enclosed spaces before entering
- Seal food in metal or glass containers
- For Andes-specific risk: follow household contact protocols; mask use by symptomatic patients in home isolation
Key Takeaways
- Sin Nombre (US) and Andes virus (South America) are distinct viruses with different rodent reservoirs but similar HPS presentations
- Andes virus is the only hantavirus with P2P transmission — now confirmed in three continents (including the 2026 France event)
- The 2026 US HPS season is elevated at 19 cases — independent of the Hondius cluster
- Argentina’s 2026 season (112 cases, 37 deaths) is above average, driving the Hondius exposure risk
- R₀ ≈ 0.5 (Nature Medicine): Andes cannot sustain human-to-human chains — endemic spread remains rodent-driven
- Prevention is identical for both: avoid rodent aerosol, seal buildings, use PPE
Sources: CDC HPS surveillance data 1993–2026; PAHO weekly bulletin May 15, 2026; Nature Medicine rapid correspondence May 15, 2026; ECDC Rapid Risk Assessment May 15, 2026; CDC Level 2 Travel Health Notice Argentina/Chile May 15, 2026.
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