The Current Andes Hantavirus Situation in Argentina (May 2026)
Author: Ifrah Ahmad
Figure: The well-studied 2018–2019 Andes hantavirus outbreak in Epuyén, Argentina [7] resulted in 34 cases and 11 deaths associated with superspreader events in a town of only 1,749 people located in the rural Andes mountain foothills (red arrows). Recent spread of Andes virus cases into Buenos Aires (~14 million people) increases the risk of larger local outbreaks and global spread through transportation networks.
Argentina is experiencing a significant increase in Andes virus activity, including expansion into more populated regions and increasing mortality. Historically, outbreaks were concentrated in sparsely populated rural areas of the Andes mountain regions, limiting opportunities for large-scale spread. Expansion into more densely populated and globally connected cities increases the risk that local outbreaks can seed broader transmission networks. Unlike most hantaviruses, Andes virus is associated with established human-to-human transmission. The MV Hondius outbreak demonstrates how these factors can rapidly create risks of international spread, larger outbreaks, deaths, and broader societal disruption through modern transportation networks.
Recent reports indicate that Andes virus incidence and observed lethality in Argentina has risen substantially compared to previous years. Argentina records hantavirus cases by season, running from July of one year to the following June. There have been 101 cases thus far in the 2025-2026 season, compared to 57 in 2024-2025 and 75 in 2023-2024 [2] and an increase from 15.4% lethality over the past four years to 32% for cases that spanned most of 2025 [1]. Multiple sources report elevated activity in 2026. One Argentine Ministry of Health summary cited 41 confirmed cases so far in 2026 and stated incidence had exceeded the epidemic threshold [2]. Another report noted 42 cases in 2026, with “most” occurring in Buenos Aires Province [3].
Argentina has several endemic hantavirus regions:
- Patagonia (Chubut, Río Negro, Neuquén)
- Northwest (especially Salta)
- Central region including Buenos Aires Province
- Northeast (Misiones) [4]
A major concern raised by Argentine researchers is that cases are increasingly occurring outside the historically recognized rural Patagonia endemic zones. Buenos Aires, Argentina’s most populous province, currently has the largest total number of confirmed cases, while Salta has the highest incidence rate per population [4,5].
An important nuance is that Buenos Aires Province includes both dense metropolitan/peri-urban areas and extensive rural zones. Current reporting does not establish widespread urban person-to-person transmission in the urban area, but it does indicate expansion into much more densely populated regions than the earlier Patagonia outbreaks. Andes hantavirus cases appearing more frequently in more urban areas may affect the patterns and mechanisms of Andes virus transmission.
The increased rate of transmission and infection in the last 18 months is consistent with the recent rise in viral spread in more densely populated areas; if this continues, we could expect to see more frequent and larger outbreaks. As long as outbreaks were contained to rural endemic areas — isolated, small, low-density populations — natural limiting factors would keep the basic reproductive number (R0) low. However, as we see increasing spread in the urban/metropolitan or other more densely-populated situations, we can expect to see this pattern change. These risks locally and globally may also be further complicated by a 30% cut to the Argentine health budget, impacting epidemiological surveillance, and Argentina’s withdrawal from the WHO in March [5].
The Andes virus (ANDV) is the only hantavirus strain clearly associated with documented person-to-person transmission [6].
The key historical outbreak was the 2018–2019 Epuyén outbreak in Chubut Province:
- 34 confirmed cases
- 11 deaths
- estimated reproductive number before intervention: ~2.1
- documented superspreading events
- evidence compatible with aerosol transmission [7]
The NEJM study concluded that person-to-person transmission of Andes virus occurred and included multiple transmission generations [7].
Argentine researchers including Gustavo Palacios have emphasized that some transmission happened during ordinary social interaction and not solely during close and prolonged contact, and the outbreak required strong containment measures including quarantine, contact tracing, and isolation [8]. Similar information about ordinary social interactions leading to transmission are associated with the MV Hondius cruise ship outbreak [9]. Palacios also emphasized that the outbreak conditions studied in Patagonia were very different from conditions on a cruise ship. The Patagonia outbreak occurred in a sparsely populated rural region with substantial outdoor activity, whereas a ship inherently facilitates transmission [8].
The MV Hondius outbreak has drawn global attention. Andes virus has been confirmed in passengers, and three people have died [10]. The ship departed from Ushuaia, Argentina on April 1, 2026. Approximately 30 passengers dispersed internationally before the outbreak was recognized on April 14, while the majority were dispersed on May 10. While 8 cases were confirmed before the disembarkation on May 10, an additional 3 passengers tested positive during their flights to France, Spain and the United States.
A central scientific and public health question is what happens after potentially exposed individuals disperse internationally during the long incubation period that may extend to 45 days or longer [8]. Given the potential for increased transmission and a significantly high mortality rate, strong monitoring and containment of the virus is central to limiting its spread and risk to the general population. Effective quarantine of exposed individuals is essential. Hesitation by WHO and national public health agencies to take the kinds of actions that stopped the outbreak in Epuyén raise the risk of a much larger spread, increased deaths and societal disruption globally.
References
1. Epidemiological Alert Hantavirus Pulmonary Syndrome in the Americas Region, PAHO, Dec 2025. https://www.paho.org/sites/default/files/2025-12/2025-12-19-epidemiological-alert-hantavirus-engfinal_0.pdf
2. Unione Sarda. “Hantavirus: Argentina clarifies, 41 cases of infection have already been recorded in 2026.” May 2026. https://www.unionesarda.it/en/world/hantavirus-argentina-clarifies-41-cases-of-infection-have-already-been-recorded-in-2026-b26e90wh
3. CNN World. “ The country where lethal hantavirus cases are on the rise. Experts blame climate change.” May 9, 2026. https://www.cnn.com/2026/05/09/americas/hantavirus-cases-double-argentina-climate-change-latam-intl
4. FluTrackers / Argentine Ministry summaries discussed in: Avian Flu Diary. “Argentina MOH Statement and Special Bulletin.” May 2026. https://afludiary.blogspot.com/2026/05/argentina-moh-statement-and-special.html “So far this year, 42 new cases have been reported, and since the beginning of the season (epidemiological week 27 of 2025), the total number of confirmed cases has reached 101.”
5. El País. “El brote de hantavirus pone en la mira al gobierno de Milei…” May 2026. https://elpais.com/argentina/2026-05-06/el-brote-de-hantavirus-pone-en-la-mira-al-gobierno-de-milei-por-la-salida-de-la-oms-y-los-recortes.html “The biggest concern is that cases have begun to be detected outside the four endemic areas. This happens in the province of Buenos Aires, the largest and most populated in Argentina, where the virus has moved away from the river basins to spread to other areas.”
6. El País. “Así es el virus de los Andes, la única cepa de hantavirus que se transmite de persona a persona.” May 2026. https://elpais.com/salud-y-bienestar/2026-05-06/asi-es-el-virus-de-los-andes-la-unica-cepa-de-hantavirus-que-se-transmite-de-persona-a-persona.html
7. Martínez VP et al. “Person-to-Person Transmission of Andes Virus.” New England Journal of Medicine. 2020;383:2230–2241. https://www.nejm.org/doi/full/10.1056/NEJMoa2009040
8. El País interview with Gustavo Palacios. “Este patógeno es más virulento y puede haber contagios en cadenas.” May 7, 2026. https://elpais.com/ciencia/2026-05-08/gustavo-palacios-experto-en-hantavirus-este-patogeno-es-mas-virulento-y-puede-haber-contagios-en-cadenas.html
9. The Atlantic. “A Foundational Myth About Hantavirus.” May 12, 2026. https://www.theatlantic.com/ideas/2026/05/hantavirus-outbreak-cruise-ship/687140/
10. WHO Disease Outbreak News. “Andes hantavirus disease associated with cruise ship travel.” 2026. https://www.who.int/emergencies/disease-outbreak-news/item/2026-DON599