Side-by-side comparison
| Andes virus | Sin Nombre virus | |
|---|---|---|
| Geography | Argentine & Chilean Patagonia | Western United States & Canada |
| Reservoir | Long-tailed pygmy rice-rat (Oligoryzomys longicaudatus) | Deer mouse (Peromyscus maniculatus) |
| Discovered | 1995 — El Bolsón outbreak | 1993 — Four Corners outbreak |
| Person-to-person | Yes — ~12% of cases | No documented |
| Case-fatality | 25–35% | ~36% |
| Annual cases | ~150 (Argentina + Chile) | 20–40 (USA + Canada) |
The transmission divide
Andes virus's documented person-to-person transmission is one of the most consequential differences between hantaviruses. It changes everything about outbreak response: contact tracing, hospital isolation, public-health communication. Sin Nombre virus, despite being closely related and clinically similar, has never been observed to transmit between humans even in well-studied family clusters or healthcare exposures.