Andes Virus (ANDV): The Person-to-Person Strain
Andes virus is the most epidemiologically significant hantavirus in 2026 — the cause of the MV Hondius cruise ship outbreak, the first multi-country hantavirus cluster in history. It is the only hantavirus on Earth with confirmed person-to-person transmission, making it uniquely dangerous for outbreak amplification beyond the rodent-exposure index case.
As of May 9, 2026: 8 confirmed and probable Andes virus cases (6 lab-confirmed) across at least 4 countries, linked to the MV Hondius research vessel voyage from Patagonia. 3 deaths confirmed. No community spread detected. See the full outbreak report →
⚠️ What Makes Andes Virus Unique
All other hantaviruses require direct exposure to an infected rodent or its excretions to cause human infection. Andes virus breaks this rule: it can pass from one infected human to another. This has been documented in:
- Argentina household clusters (1995–2011): Multiple episodes of household contacts — especially intimate partners — developing HPS after exposure to an index case. In several clusters, 3–4 members of a single household were infected sequentially.
- El Bolsón, Argentina healthcare cluster (1996): Two healthcare workers who cared for an ANDV patient without full PPE subsequently developed HPS — the first documented healthcare-associated hantavirus transmission.
- MV Hondius, 2026: The first vessel-linked, multi-country ANDV cluster. The index source was likely one Dutch couple with prior Patagonia rodent exposure; subsequent cases among other passengers and potentially crew members followed sustained close contact during a 33-day voyage.
Critically, Andes virus does NOT spread through casual contact or shared building air. Secondary cases have consistently required sustained, intimate contact with a symptomatic index case. The virus is not airborne in the epidemiological sense. This limits outbreak size but makes hospital and household transmission real risks.
🐀 Reservoir & Geographic Range
The long-tailed pygmy rice rat (Oligoryzomys longicaudatus) is the primary reservoir for Andes virus. This small rodent inhabits the Andean foothills and Patagonian forests of Argentina and Chile, ranging from the Lake District southward through Patagonia to Tierra del Fuego.
The rodent's habitat corresponds precisely with the HPS endemic zone:
- Argentina: Neuquén, Río Negro, Chubut, Santa Cruz, and Tierra del Fuego provinces — the Andean corridor
- Chile: Bío-Bío, La Araucanía, Los Lagos, Aysén, and Magallanes regions
- Brazil: Andes virus-related strains in Rio Grande do Sul and São Paulo
International trekkers on classic Patagonian routes — the W Trek in Torres del Paine, the Fitz Roy circuit near El Chaltén, and the Los Glaciares backcountry — traverse prime Andes virus territory. Refugio huts along these routes are known to have rodent activity.
Andes Virus FAQ
How does Andes virus spread person-to-person?
Andes virus person-to-person transmission occurs through close personal contact with a symptomatic or recently symptomatic infected person — primarily household contacts and intimate partners. The exact mechanism is not fully characterized but is thought to involve respiratory secretions, saliva, or possibly aerosolized bodily fluids at very close range. It does NOT spread through casual contact, shared air in a room, or the respiratory droplet route the way COVID-19 or influenza do. The 2026 MV Hondius outbreak demonstrated transmission in a confined ship environment among people with sustained close contact.
Why is Andes virus the only hantavirus with person-to-person transmission?
This is an active area of research without a definitive answer. One hypothesis involves the specific receptor the virus uses to enter human cells. Another theory relates to differences in viral load in respiratory secretions between ANDV-infected and SNV-infected patients. A third possibility is that the long-tailed pygmy rice rat reservoir uniquely shapes the virus's evolution in ways that happen to permit closer human-to-human transmission. No other hantavirus — including close relatives of ANDV in South America — has been confirmed to spread person-to-person.
What is the risk of getting Andes virus in Patagonia?
Andes virus HPS cases are concentrated in specific eco-geographic zones of southern Argentina and Chile — particularly the Andean foothills, lake districts, and Patagonian forests where the long-tailed pygmy rice rat lives. For international trekkers, the primary risk scenarios are: staying in refugios (backcountry huts) with rodent activity, sleeping in rustic accommodations in rural Patagonian towns, and disturbing rodent habitat during trekking. Risk is real but manageable with precautions. Following the 2026 outbreak, Chile and Argentina have issued enhanced traveler advisories.
Is Andes virus more dangerous than Sin Nombre virus?
In terms of individual mortality, the two strains are comparable — both cause 15–40% case fatality rate in confirmed HPS cases. Andes virus may cause more prominent cardiovascular collapse (hence the HCPS designation). The greater danger of Andes virus is epidemiological: its person-to-person transmission capability means outbreaks can amplify beyond the index rodent-exposure case. The 2026 MV Hondius outbreak illustrates this — one couple's Patagonia rodent exposure propagated through a ship and across four continents.
Is there any treatment specific to Andes virus?
No specific treatment exists for Andes virus beyond supportive care (ICU, ventilation, ECMO for severe cases). This is the same situation as Sin Nombre HPS. Convalescent plasma from ANDV survivors has been explored as a therapeutic in Argentina — some observational data suggests benefit, but no RCT has confirmed this. The 2026 outbreak has accelerated discussions about deploying convalescent plasma from the outbreak's survivors. mRNA vaccines targeting ANDV glycoproteins are in Phase I trials.