Andes virus has claimed international attention in 2026 as the pathogen behind the MV Hondius cruise ship outbreak. But what exactly is Andes virus, and what makes it scientifically distinct from the more than fifty other known hantavirus species? This article provides a complete overview of the Andes virus — its taxonomy, biology, geographic distribution, disease course, and the unique characteristic that makes it the most epidemiologically significant hantavirus in the world.
Andes Virus: Definition and Classification
Andes virus (ANDV) is a species within the family Hantaviridae, genus Orthohantavirus. It belongs to the same broad taxonomic group as Sin Nombre virus (responsible for the 1993 Four Corners outbreak in the US) and Hantaan virus (endemic to East Asia), but its biological and epidemiological properties are distinct from both.
Genus: Orthohantavirus
Species: Andes orthohantavirus
Primary reservoir: Long-tailed pygmy rice rat (Oligoryzomys longicaudatus)
Disease caused: Hantavirus Pulmonary Syndrome (HPS) / Hantavirus Cardiopulmonary Syndrome (HCPS)
Unique property: Only known hantavirus with documented human-to-human transmission
Like all hantaviruses, the Andes virus is a segmented, negative-sense, single-stranded RNA virus. It encodes three gene segments: the large (L) segment for the RNA-dependent RNA polymerase, the medium (M) segment for the envelope glycoproteins, and the small (S) segment for the nucleocapsid protein. The specific genetic sequence of the M segment is central to the virus's interaction with human cell receptors, and it is this segment that researchers analyze during gene sequencing to confirm viral identity — as was done on May 4–6, 2026 during the MV Hondius outbreak investigation.
Geographic Distribution of Andes Virus
The Andes virus is found in rodent populations across South America, with particularly high prevalence in the temperate and subalpine zones of the Andes mountain range. Countries where Andes virus and its closely related variants have been documented include:
Argentina and Chile account for the majority of documented Andes virus cases. The virus is named after the Andes mountain range and was first formally characterized in 1996 following outbreak investigations in Patagonia. The long-tailed pygmy rice rat, its primary rodent reservoir, inhabits grasslands, scrubland, and forest edges across these regions, which overlap significantly with rural farmland and popular trekking routes.
The 2026 index case — the Dutch passenger who first showed symptoms on April 6 — had traveled extensively through Argentina, Chile, and Uruguay in the months before boarding the MV Hondius, likely encountering Andes virus-infected rodents during that period.
What Makes Andes Virus Unique: Human-to-Human Transmission
The single most significant characteristic of Andes virus — the feature that elevates it above all other hantavirus species in terms of public health concern — is that it is the only known hantavirus with documented human-to-human transmission. Every other hantavirus species, including the highly lethal Sin Nombre virus and Hantaan virus, is transmitted exclusively through rodent-to-human contact. Andes virus breaks this rule.
Human-to-human Andes virus transmission was first documented during the 1995–1996 outbreak in Patagonia, Argentina, where epidemiological investigation revealed cases among individuals who had cared for infected patients without any rodent exposure. This pattern has been confirmed in subsequent outbreaks. The transmission mechanism is believed to involve close respiratory contact — similar in character to the spread of other respiratory pathogens — but requires sustained proximity rather than brief or casual interaction.
The WHO's position, based on accumulated evidence, is that Andes virus transmission between people is real but rare, occurring primarily among household contacts and healthcare workers providing unprotected close care to infected patients. The general public, without direct exposure to a confirmed case, faces minimal risk.
The 1996 Argentina Superspreader Event
One of the most striking examples of Andes virus transmission capacity occurred in El Bolsón, Argentina, where a single introduction of the virus into a community led to a chain of transmission resulting in 34 infections. This event — one of the earliest and most extensively documented examples of Andes virus person-to-person spread — demonstrated that under the right conditions, a single case could generate a significant cluster through sequential transmission.
The El Bolsón outbreak informed the foundational understanding of Andes virus epidemiology and remains a key reference in WHO and CDC guidance on hantavirus outbreak management. It established that Andes virus is capable of amplifying within close-contact social networks — a factor that public health authorities have kept in mind when assessing the MV Hondius outbreak, where passengers share confined spaces over weeks at sea.
Andes Virus and the 2026 MV Hondius Outbreak
Andes virus was officially confirmed as the causative pathogen of the 2026 MV Hondius outbreak on May 6, 2026, following gene sequencing of samples from infected passengers. Initial testing had identified a positive hantavirus result on May 4; the May 6 confirmation specified the Andes strain, consistent with the index case's travel history through South America.
The confirmation was significant for several reasons: it explained the cluster's unusual feature of apparent shipboard spread (Andes virus's human-to-human transmission capacity), it guided the clinical and infection control protocols applied to remaining passengers, and it triggered coordinated responses from the WHO, European Centre for Disease Prevention and Control (ECDC), and national health agencies in more than 20 countries.
Symptoms and Disease Progression of Andes Virus Infection
Andes virus infection in humans causes Hantavirus Pulmonary Syndrome (HPS), also described as Hantavirus Cardiopulmonary Syndrome (HCPS) in the South American literature. Disease progression follows a characteristic multi-phase pattern:
There is no approved antiviral treatment for Andes virus infection. Clinical management is entirely supportive, with aggressive ICU intervention — mechanical ventilation and ECMO when necessary — representing the best available therapy. Early recognition of the prodromal phase and rapid transfer to specialized care are the most critical factors in improving survival outcomes for Andes virus infection.