How worried should you be about hantavirus?

As of May 6th three cases among those on board had been confirmed and five more were suspected. Of those eight people, three have died. Although information about the outbreak is still patchy, the World Health Organisation (WHO) and other health bodies say the risk of hantavirus infections globally remains low.

Human infections with hantavirus are rare. Such cases are usually caused by the inhalation of airborne particles from the droppings or urine of rodents such as mice and rats, in which the virus is endemic. Further spread from infected humans to others is rarer still, though not unheard of. Very close contact—such as physical intimacy and interactions between health-care workers and patients—has historically been a prerequisite. Although no human-to-human transmission on MV Hondius has yet been confirmed, the cramped cabins and common areas of a cruise ship are an ideal environment for it to occur. The fact that the wife of the first passenger who died was infected, along with the ship’s doctor, is worrying.

At least three of the infected individuals from MV Hondius have been diagnosed with the Andes strain of hantavirus, which is found in rodents in Argentina, and is known to spread between people. It starts with flu-like symptoms but can progress to severe breathing problems that require intensive hospital care. The mortality rate for those infected can be as high as 50%.

For now, the WHO is working with officials in Argentina and on board the ship to reconstruct the movements and contacts of infected passengers in the eight weeks before they developed symptoms, the longest known incubation period for the virus. Samples retrieved from patients are also being sequenced to help determine where the infection began and how it spread.

Such insights will help authorities better understand the risk to the remaining passengers. With the exception of those who have fallen ill, who were taken off the ship at Cabo Verde and airlifted to European hospitals, nobody has been allowed to disembark since May 3rd. (One infected passenger disembarked before falling ill and took himself to a hospital in Zurich.)

In the meantime, the WHO has brokered a plan for those on board to leave the ship at the Canary Islands, a territory of Spain, when the ship arrives there around May 10th. The country’s health minister said that Spanish passengers would be quarantined at a military hospital, whereas other nationals will be repatriated if they are asymptomatic. The details of these plans were still being hashed out as The Economist went to press. But if they are carried out responsibly, the chances of a global health disaster are, thankfully, low.