Explainer: What Hantavirus is and how it spreads

A suspected outbreak of hantavirus aboard the MV Hondius has drawn international attention—not because the virus is new, but because of where it may have surfaced. 

Two Dutch people and a German national have died after a suspected hantavirus outbreak on the MV Hondius, a cruise ship run by Oceanwide Expeditions, according to the World Health Organization (WHO). The global health agency said it was investigating three others, including two crew members, who became sick on the ship, which is now docked off of Cape Verde in Africa, Time writes.

While investigations led by the World Health Organization are ongoing, the episode offers a window into a little-known but potentially deadly disease and how it spreads.

What is hantavirus?

Hantavirus is not a single pathogen but a group of viruses carried primarily by rodents. Each strain is typically linked to a specific host species, in which the virus can persist without causing illness. Humans, however, can become infected through exposure to contaminated urine, droppings, or saliva—most often by inhaling viral particles released into the air when these materials are disturbed. The Centers for Disease Control and Prevention notes that transmission can also occur through contaminated food or, more rarely, bites.

The geography of hantavirus varies. In the United States, cases have historically been concentrated in the Southwest, particularly the Four Corners region, where surveillance began after a 1993 outbreak. Since then, fewer than 1,000 confirmed cases have been recorded, but the mortality rate—around 35 per cent—makes it one of the more severe infectious diseases relative to its rarity. In South America, including parts of Argentina, different strains circulate, some of which behave differently in terms of transmission.

Where did it come from?

One of the key questions raised by the cruise ship incident is how a rodent-borne virus might appear in a maritime setting. According to Amesh Adalja of the Johns Hopkins Center for Health Security, there are two plausible explanations: rodents could have been present onboard, or exposure may have occurred during shore excursions in endemic areas before symptoms developed. The incubation period for hantavirus can range from several days to a few weeks, making it possible for infections to emerge well after initial exposure.

Another layer of uncertainty involves transmission dynamics. In most cases, hantaviruses are not contagious between humans. However, Kartik Chandran of the Albert Einstein College of Medicine points out that the Andes virus—found in parts of South America—is a notable exception, capable of spreading through close contact. Determining whether this or another strain is involved requires laboratory sequencing, which health authorities are currently undertaking.

Clinically, hantavirus infections can escalate quickly. Early symptoms often resemble flu-like illness: fever, fatigue, headaches, and nausea. In more severe cases, the disease progresses to affect the lungs, leading to fluid buildup and acute respiratory distress. Some forms also impact the kidneys, potentially causing internal bleeding and organ failure.

There is no specific antiviral cure. Treatment is largely supportive, focusing on oxygen therapy, fluid management, and intensive care when needed. While experimental vaccines and antibody therapies have shown promise in animal studies, experts say limited funding has slowed their development for human use.

By Sabina Mammadli