# Rodent reservoirs

> Wild rodent species that chronically carry a hantavirus without apparent symptoms. The Andes virus reservoir is the rodent Oligoryzomys longicaudatus (colilargo) in Patagonia.

Canonical source: https://hantatracker.fr/en/glossary/rodent-reservoirs/

**Aliases**: rodent reservoir, animal reservoir, Oligoryzomys longicaudatus, colilargo

**Rodent reservoirs** are the wild rodent species that naturally host hantaviruses. In these animals, infection is **chronic and asymptomatic**: the virus replicates without causing disease but is continuously shed in urine, faeces and saliva. Human contact with these excretions is the main route of contamination. For Andes virus, the reservoir is the **colilargo** (*Oligoryzomys longicaudatus*) of Patagonia.

## The notion of animal reservoir

### Definition

In epidemiology, a **reservoir** is a host species in which an infectious agent persists durably and which serves as the source of transmission to other species, in particular humans. For hantaviruses, the reservoirs are almost exclusively wild rodents, with a **strict association rule**: each viral strain has its specific reservoir, the product of long co-evolution.

### Diversity

The WHO and the scientific community count more than **80 host species** of hantaviruses worldwide: 51 rodent species (the main ones), 7 bat species and 20 shrew-like species (shrews, moles). This diversity explains why new hantaviruses continue to be identified regularly as surveillance of wild animal populations expands.

## The colilargo, reservoir of Andes virus

### Description

*Oligoryzomys longicaudatus*, the **colilargo** ("long tail"), is a small sigmodontine rodent endemic to the southern Andes range. Its distribution extends from southern Peru down to Tierra del Fuego, across Chile and Argentina. It colonises diverse habitats: humid temperate forests, Patagonian steppes, edges of agricultural and peri-domestic areas.

### Population cycles

The colilargo's population density varies sharply, mainly with the cyclical proliferation of the **bamboo** *Chusquea* (species *valdiviensis*, *culeou*, etc.). This Andean bamboo flowers massively and synchronously every 60 to 70 years, producing huge quantities of seeds that constitute a major food resource for rodents. The mass proliferation that follows ("ratada" in Spanish) can multiply densities a hundredfold and historically coincides with peaks of human hantavirus pulmonary syndrome cases.

### Notable cases

In **1990**, more than one million hectares of *Chusquea valdiviensis* flowered simultaneously in Chile, triggering a population explosion of the colilargo and the appearance of human cases. It is in this context that Andes virus was identified for the first time a few years later. The **Epuyén** outbreak in 2018-2019 (Argentina) was preceded by a local increase in rodent densities.

## Reservoirs of the main other hantaviruses

| Strain | Reservoir | Location |
|--------|-----------|----------|
| Andes (ANDV) | *Oligoryzomys longicaudatus* (colilargo) | Argentine and Chilean Patagonia |
| Sin Nombre | *Peromyscus maniculatus* (deer mouse) | North America (western United States) |
| Hantaan | *Apodemus agrarius* (striped field mouse) | East Asia |
| Seoul | *Rattus norvegicus* (brown rat) | Global (urban areas) |
| Puumala | *Myodes glareolus* (bank vole) | Northern Europe |
| Dobrava | *Apodemus flavicollis* (yellow-necked mouse) | Balkans |

## Consequences for surveillance and prevention

### One Health

The **One Health** approach promoted by the WHO, FAO and WOAH integrates surveillance of rodent reservoir populations as a pillar of human hantavirus prevention. Monitored indicators include: density of sentinel populations, viral seroprevalence in trapped rodents, climatic and ecological conditions favourable to proliferation peaks, and predictive modelling of seasonal risk.

### For the general public

Limiting exposure to wild rodents is the main preventive measure: building tightness (sealing holes), airtight food storage, careful cleaning of spaces where rodents may have entered (cellar, attic, outbuilding), with prior spraying of diluted bleach and use of an FFP2/N95 mask. The common domestic rodents of European cities (mice, brown rats) do not carry Andes virus, but the brown rat can carry Seoul virus.

### For travellers

Travellers in endemic areas (notably Argentine and Chilean Patagonia) are advised to avoid rustic accommodation that has been closed for a long time and may be colonised by rodents, and to favour ventilated and recently cleaned accommodation. This is the likely route of contamination for the first MV Hondius patients, who were probably infected before boarding during stays in South America.