The cruise ship cluster of hantavirus cases continues to grow. The World Health Organization reports that as of May 6 there were eight cases, three of whom are confirmed by laboratory testing as hantavirus. In recent days, we heard three passengers had died.

Now some passengers are being medically evacuated from the cruise ship MV Hondius. Other passengers have disembarked and are returning home. Swiss authorities have confirmed a passenger on the ship is now a confirmed case and is receiving care in a Zurich hospital.

I’m a public health physician with a special interest in respiratory diseases. I’ve also investigated a hantavirus outbreak.

Here’s what investigators want to know about the current cluster of cases. This includes gathering evidence to see if the virus is transmitting from person to person.

Back in 1993, there was an unknown pathogen

In 1993, I was a young epidemic intelligence service officer working at the United States Centers for Disease Control. I was deployed to the deserts of the south-western US to help investigate a frightening outbreak, mainly among Navajo people.

Adults in their 20s and 30s were becoming suddenly unwell. They would develop a fever and cough, then rapidly progress to severe respiratory failure as fluid leaked into their lungs. Some appeared well enough to be dancing in the evening and were dead within hours.

The investigation team was nervous. We did not yet know the pathogen, how it was spreading, or whether we were at risk.

One of the first recognised cases was a well-known runner, so we initially wondered whether infection might be linked to inhaling something stirred up in desert dust. A leak from a remote military biowarfare laboratory was also considered, as was plague that was endemic to the area.

After laboratory testing, the cause was identified as a new hantavirus, later known as Sin Nombre virus. The virus attacked the small blood vessels of the lungs and was linked to exposure to the urine, faeces and saliva of infected........

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