The Andes virus is the infectious agent at the root of the MV Hondius episode. This page goes beyond the short glossary entry: it covers the virus's phylogeny, geographic distribution, transmission routes (including person-to-person), comparison with other American and Eurasian hantaviruses, and the sequencing results from the Institut Pasteur on the MV Hondius strain in May 2026.
Nomenclature and classification
The official species name in the ICTV 2024 taxonomy is Orthohantavirus andesense. It is one of 38 species in the genus Orthohantavirus (family Hantaviridae, order Bunyavirales). The common name "Andes virus" (ANDV) remains widely used in clinical literature and official communications.
The species groups several geographic strains that share ≥ 7% sequence divergence but remain within the same taxonomic unit: Andes-Cent, Andes-Lec, Andes-Or, Andes-Sout, Andes-Bermejo. The observed divergences between these strains are smaller than those separating Andes from the North American Sin Nombre virus.
Natural reservoir
Andes virus has an exclusive reservoir: the long-tailed pygmy rice rat (Oligoryzomys longicaudatus), a small sigmodontine rodent endemic to the Andes range, from northern Chile (Atacama) to the southern tip of Patagonia (Tierra del Fuego). The reservoir hosts the virus chronically and asymptomatically: it sheds it in urine, faeces and saliva throughout its life without suffering from infection.
This host specificity is typical of hantaviruses — virus and reservoir have co-evolved over millions of years. Each hantavirus species is associated with a distinct rodent reservoir, and this association determines the geographic distribution of human disease. Where the long-tailed pygmy rice rat lives, the Andes virus can be encountered. Outside that habitat (Argentine and Chilean Patagonia), no autochthonous circulation has ever been documented.
For the detailed rodent factsheet, see Which rodent carries hantavirus? The long-tailed pygmy rice rat, reservoir of Andes virus.
Geographic distribution in humans
Andes virus accounts for the bulk of hantavirus pulmonary syndrome (HPS) cases in South America, mainly in two regions:
- Southern Argentina: Buenos Aires, Río Negro, Neuquén, Chubut, Santa Cruz, Tierra del Fuego provinces. The Epuyén outbreak (Chubut, late 2018 — mid 2019) remains the major epidemiological episode, with 28 cases and 11 deaths officially attributed to the cluster (NEJM 2020).
- Southern Chile: Aysén, Magallanes and Los Lagos regions. Sporadic cases yearly.
Annual incidence in humans is low relative to the population (fewer than 100 confirmed cases per year for Argentina + Chile combined), but the high case fatality rate (~ 40%) makes it one of the most monitored emerging pathogens on the continent.
Transmission
Animal → human (primary mechanism)
As for all hantaviruses, the primary route is inhalation of aerosols contaminated with rodent excreta. Typical scenario: a human disturbs (dry sweeping, vacuuming, handling) an enclosed space frequented by long-tailed pygmy rice rats — forest cabin, attic, farm outbuilding — and inhales suspended viral particles.
Other routes are possible but marginal: rodent bite, direct contact with mucous membranes, ingestion of food contaminated with fresh excreta.
Person-to-person (specific to Andes virus)
Andes virus is the only hantavirus for which person-to-person transmission has been documented by a formal epidemiological study. The academic reference is the December 2020 New England Journal of Medicine paper on the Epuyén 2018-2019 outbreak (Martínez-Valdebenito et al.):
- The Epuyén cluster affected 28 people, 11 of whom died.
- Researchers reconstructed the transmission chain by sequencing: nearly all cases carried sequences identical to the index case.
- The reproduction number R, initially estimated at 2.12, dropped to 0.96 once quarantine measures were enforced — evidence that the chain relied on person-to-person transmission and that isolation broke it.
- A significant share of transmission appears to come from superspreader events: confined social events (weddings, family gatherings, parties) where a person in early symptomatic phase infected multiple close contacts simultaneously.
Characteristics of person-to-person transmission
- Requires close and prolonged contact with a symptomatic person: same household, direct care without PPE, shared confined spaces (plane, bus, car).
- Does not transmit during the asymptomatic incubation phase.
- No broad airborne transmission in the sense of measles, flu or COVID-19: range stays metres, not tens of metres.
- Accounts for 2 to 5% of all Andes virus cases observed, per CDC / NEJM estimates.
The 2026 MV Hondius cluster
The MV Hondius episode is the first documented cluster aboard a vessel at sea for Andes virus. Person-to-person transmission has been suspected since 7 May 2026 by WHO, based on:
- The implausibility of a collective initial exposure (no pygmy rice rats aboard a polar expedition vessel).
- The concurrency of cases, with incubation offsets consistent with a single transmission event around disembarkation from Ushuaia (1 April 2026).
- The epidemiological profile (149 people confined for 40 days).
Institut Pasteur sequencing, 15-16 May 2026
The Institut Pasteur has completed full-genome sequencing of the strain detected in the French MV Hondius passenger (admitted to Bichat, on ECMO). The results, announced by Minister Stéphanie Rist on 15 May 2026:
"No evidence suggests the emergence of a variant likely to be more transmissible or more dangerous."
— Stéphanie Rist, Minister of Health, 15 May 2026
The Institut Pasteur in a separate statement:
"No element suggests at this stage the emergence of a particular variant with new characteristics."
The sequence is very close to those of the other infected passengers and to Andes strains known to circulate in southern Latin America. This negatively settles the hypothesis of an emerging variant raised by infectious-disease physician Xavier Lescure (Bichat) on 12 May. The discussion around viral circulation in the cluster therefore stays framed by the classical Andes virus profile.
Comparison with other American hantaviruses
| Andes virus | Sin Nombre virus | Bayou virus | |
|---|---|---|---|
| ICTV species | O. andesense | O. sinnombreense | O. bayoui |
| Reservoir | Long-tailed pygmy rice rat (O. longicaudatus) | Deer mouse (P. maniculatus) | Marsh rice rat (O. palustris) |
| Human geography | Patagonia (AR, CL) | US Southwest, Canada | US Southeast |
| Main syndrome | HPS | HPS | HPS (rare) |
| Average CFR | ~ 40% | 30-35% | 30-40% |
| Person-to-person transmission | Yes, documented | No | No |
| Cluster at sea | Yes (MV Hondius 2026) | No | No |
For a full panorama including Eurasian strains (Hantaan, Seoul, Puumala, Dobrava-Belgrade), see Other hantavirus strains worldwide.
Incubation, clinical course, treatment
The incubation period for Andes virus is 7 to 42 days, median 18 to 24 days — the longest range observed for a human hantavirus. This characteristic explains why health authorities maintain medical surveillance of MV Hondius passengers and contacts for 42 days from their last possible exposure.
The HPS clinical picture follows a characteristic progression:
- Prodromal phase (3-5 days): fever, chills, myalgia, asthenia, headache. Indistinguishable from flu at this stage.
- Cardiopulmonary phase (24-48 hours): massive lesional pulmonary oedema (plasma extravasation into alveoli), cardiogenic shock. Acute respiratory distress requiring ICU admission.
- Recovery or death: the cardiopulmonary phase determines the prognosis. Mortality peaks between days 4 and 10 after symptom onset.
No specific antiviral is licensed against Andes virus. Management is exclusively symptomatic: intubation, mechanical ventilation, haemodynamic support, and in the most severe forms, extracorporeal membrane oxygenation (ECMO). Early diagnosis (PCR on blood or respiratory secretions) and rapid ICU admission are the main prognostic factors.
Learn more
- Glossary — Andes virus: short definition, sourced statistics, FAQ.
- Article — Which rodent carries hantavirus?: focus on the long-tailed pygmy rice rat.
- Article — Ushuaia landfill, index case hypothesis?: debate on the MV Hondius cluster's origin.
- Article — Other hantavirus strains worldwide: full Old World vs New World panorama.