Genetic Analysis of MV Hondius Outbreak: Stable Andes Virus Strain Identified

Recent genetic sequencing of a patient involved in the cluster of cases linked to the cruise ship MV Hondius has provided critical insights into the nature of the outbreak. An international team of researchers, led by the University of Zurich and the Swiss National Reference Center for Emerging Viral Infections, has published the first complete genome sequence of the hantavirus responsible for the infections.

The findings, shared via the Virological.org platform, confirm that the pathogen is the Andes virus (ANDV), a type of hantavirus endemic to South America. For public health officials and clinicians, this genetic “blueprint” is essential for understanding how the virus spreads and ensuring that diagnostic tools remain effective.

Genetic Stability and the Patagonian Link

One of the most significant findings from the genomic analysis is the stability of the virus. Researchers found no evidence of “reassortment”—a process where different viral strains exchange genetic fragments to create new variants. This stability indicates that the current outbreak stems from a known viral lineage rather than a recent genetic mutation or mixing event.

By comparing this sequence against global databases, scientists discovered that the virus is closely related to the strains that caused outbreaks in Argentina during 2018 and 2019. The degree of genetic variation is minimal, falling within the expected margins for a virus evolving naturally within its animal reservoir.

This evidence supports the hypothesis of a “spillover” event, where the virus jumps from wild rodents to humans. Damien Tully, an associate professor at the London School of Hygiene & Tropical Medicine, noted that the sequence is “broadly consistent with what we would expect from a jump of the virus from its natural reservoir.”

The Challenge of Human-to-Human Transmission

While the virus appears stable, the Andes virus is particularly concerning because, unlike many other hantaviruses, it is known for its ability to spread between humans. The specific lineage detected in the Swiss patient is typical of those found in Chile and Argentina, which are frequently associated with human infections.

However, genetic data alone cannot fully explain the epidemiology of the cruise ship cluster. While phylogenetic analysis confirms a recent transmission event, it cannot yet determine the exact path of the infection. Piet Maes, president-elect of the International Hantavirus Society, explained that “genomic data alone cannot distinguish between direct acquisition from an animal and secondary transmission between people.”

Professor Tully added that with only one genome sequenced, it remains unclear whether the outbreak resulted from multiple independent introductions from animals or a single zoonotic event followed by person-to-person spread among passengers and crew.

Why Sequencing Matters for Diagnostics

Beyond tracking the origin of the outbreak, complete sequencing serves a vital practical purpose: validating diagnostic tests. Most laboratories rely on PCR (polymerase chain reaction) tests to detect the virus. These tests target specific nucleotide sequences in the viral genome.

If a virus mutates in those specific target regions, PCR tests can produce false negatives. The current analysis confirms that the Andes virus strain in this cluster has not mutated in these critical areas, meaning existing PCR tests remain effective for diagnosis.

Looking Forward

The rapid sharing of this genomic data is being hailed as a milestone for the public health response. However, the scientific community emphasizes that this is only the first step. To fully reconstruct the chain of transmission and determine if the virus is undergoing any functional changes as it spreads, researchers need more sequences from additional patients and potential animal reservoirs.

Continued surveillance remains critical to managing the cluster and preventing further spread of this rare but potent South American pathogen.