Where has the deadly hantavirus come from and how does it spread?

Three people with suspected hantavirus have been evacuated from the cruise ship MV Hondius, following an outbreak that has killed three passengers. The evacuees will be given medical care in the Netherlands.

The ship departed Ushuaia, Argentina, on 1 April and followed an itinerary across the South Atlantic, with stops at Antarctica, South Georgia, Nightingale Island, Tristan da Cunha, Saint Helena and Ascension Island.

Two people have died on the ship, and a third person died in South Africa two days after disembarking in Saint Helena. A British man who was also on the ship remains in intensive care in Johannesburg, South Africa.

A man in Switzerland who left the ship at the end of April has also reportedly tested positive for hantavirus after experiencing symptoms. Two British people who were on the ship but don’t have symptoms are self-isolating at home, the UK Health Security Agency has said.

What is hantavirus?

Hantaviruses are a group of viruses carried by rodents that can cause severe disease in humans. People usually get infected through contact with infected rodents or their urine, droppings or saliva.

In different parts of the world, there are different hantaviruses associated with different clinical syndromes. In the Americas, hantaviruses can cause a severe respiratory illness known as hantavirus cardiopulmonary syndrome (HCPS), which kills up to 50 per cent of people diagnosed. In Europe and Asia, hantaviruses cause haemorrhagic fever with renal syndrome (HFRS), which mainly affects the kidneys and blood vessels.

Worldwide, it is estimated that around 10,000 to over 100,000 infections occur annually, with the highest rates of infection in Asia and Europe.

According to South Africa’s National Institute for Communicable Diseases, two people who came off the ship have tested positive for the Andes virus, a form of hantavirus that causes HCPS. This virus is thought to be able to transmit from human to human among close and prolonged contacts.

What are the symptoms of hantavirus?

The initial symptoms often include fever, muscle aches, headache and gastrointestinal symptoms. Some patients then progress to respiratory illness. Diagnosis is usually made through specialist blood tests.

How is hantavirus spread?

The usual route of infection is exposure to infected rodents, particularly inhalation of virus from contaminated rodent urine, droppings or saliva.

“This is why investigations of suspected cases often focus on whether people may have had exposure to rodent-contaminated environments, food stores, cabins, storage areas or other enclosed spaces. Hantavirus is not generally considered easily transmissible between people,” said Roger Hewson at the London School of Hygiene & Tropical Medicine in a statement.

Infection may also occur, although less commonly, through rodent bites. Activities that involve contact with rodents such as cleaning enclosed or poorly ventilated spaces, farming, forestry work and sleeping in rodent-infested dwellings increase exposure risk.

According to the WHO, human-to-human transmission has been documented only for Andes virus in the Americas and remains uncommon. When it occurs, transmission between people has been associated with close and prolonged contact, particularly among household members or intimate partners, and appears most likely during the early phase of illness, when the virus is more transmissible.

How worrying is this outbreak?

Adam Taylor at Lancaster University in the UK says people should not be alarmed. “Hantavirus transmission typically requires contact with animal bodily products to transmit, rather than human to human,” he says. “Precautions are being taken on board to minimise risk, but these are just precautions.”

Hewson says it is important not to overinterpret the cruise ship setting. “The fact that cases have been identified in people associated with the same vessel does not by itself tell us whether exposure occurred on the ship, before boarding, during shore excursions, or through some other shared environmental exposure,” he said. “That is precisely why public health investigations, laboratory confirmation and where possible, virus sequencing are important.”