US officials warn 39 countries about risk of hantavirus among travellers to Yosemite

BMJ 2012; 345 doi: (Published 10 September 2012) Cite this as: BMJ 2012;345:e6054
  1. Bob Roehr
  1. 1Washington, DC

Six people have become infected and three have died in an outbreak of the rare but often lethal hantavirus infection in Yosemite National Park in California. The outbreak has been traced to a group of cabins and tents at the popular tourist destination. More than four million people a year visit the park.

“Early medical attention and diagnosis of hantavirus are critical,” park superintendent Don Neubacher said in a released statement. “We urge anyone who may have been exposed to the infection to see their doctor at the first sign of symptoms and to advise them of the potential of hantavirus.”

All cases so far have involved Americans, mostly from California. But as many as 10 000 summer visitors could potentially have been exposed to the pathogen at the infected campsite. Park officials have combed their records to identify and notify domestic visitors and have notified public health officials in 39 countries, who are now tracking down the travellers at risk.

Contamination with the virus seems to be limited to the Signature Tent Cabins in the Curry Village section of the park. Those facilities were closed and thoroughly cleaned in late August. Officials also have stepped up their monitoring of the deer mouse population for evidence of the infection and have reduced the population of the species around living areas in the park.

Hantavirus is not a single unique virus but rather a worldwide family of related pathogens with a variety of genetic and virulence factors. Rodents are its most common host, though it does not cause the animals to become ill.

Transfer to humans is believed to occur when a site contaminated with animal saliva, urine, and faeces containing the virus is disturbed, the virus becomes airborne, and a person inhales it.

Initial flu-like symptoms of infection appear in one to five weeks and can lead to severe respiratory distress and renal disease that require hospitalisation.1 Often the best way to identify a case is through a good case history of potential outdoor exposure. Although there is no treatment for the disease, it seems that early intubation to relieve respiratory distress can be helpful.2 Ribavirin has been used to treat kidney problems.3

A case study drawn from the current outbreak was used earlier this summer in an article in the New England Journal of Medicine to illustrate the problem of diagnosing the infection and treating patients.4

Numbers of reports of hantavirus disease in humans seem to be rising in Europe, but it is not clear whether that reflects an actual increase in incidence of disease or better diagnostic tools to distinguish it from other diseases with similar clinical symptoms.5 6

The UK’s Health Protection Agency is using information provided by the US National Park Services to contact about 100 travellers from the UK who may have been exposed to the virus during their stay at the park.

Vanya Gant, a London infectious disease specialist who has coauthored a paper on hantavirus disease in the New England Journal of Medicine, responded to a story on the outbreak in the Washington Post. She wrote on the journal’s website that she has a reservation this week at the cabins in question and intends to use it.

“The hit rate remains very low, and I would have thought that a good cleanout of any and all mouse droppings/fur etc under controlled conditions would be enough to reduce risk to undetectable levels,” she wrote. “The virus is also an RNA virus and I doubt it remains dangerous for very long.”


Cite this as: BMJ 2012;345:e6054