Scientists seeking a cause for the deadly hantavirus outbreak among visitors to California’s Yosemite National Park over the summer are investigating whether a spike in the deer mouse population, combined with the unusual design of some tent cabins that enabled mice to nest in the insulation, made it easier for people to contract the rare disease.
The San Jose Mercury News reported that experts consider another theory — that the virus recently mutated and became more transmissible to humans — a long shot.
The initial findings of federal health authorities who have sequenced the virus’ genome using samples from those who fell ill indicate that the virus has not changed, said Danielle Buttke, a veterinary epidemiologist with the National Park Service. But others continue to explore that theory until it can be definitively ruled out.
UC San Francisco researcher Dr. Charles Chiu agrees that the prevalence of deer mice and the tent cabin design are the most likely culprits.
But Chiu, who directs the UCSF-Abbott Viral Diagnostics and Discovery Center, plans to have his lab sequence genomes from all of the visitors who fell ill, as well as those in deer mice gathered in the Sierra, Bay Area and throughout California. He will then compare the current strains to historical ones.
“I think it’s more likely to be a change in the environment, but without doing the sequencing, I can’t exclude that and that’s why we’re doing the study,” said Chiu, an assistant professor of infectious diseases.
Unlike the flu virus, which changes so often the vaccine must be revised every year, the hantavirus has been relatively stable, Chiu said. Yet the possibility that a mutant or variant strain could develop still exists.
“The question really is: Do we have the whole story here?” Chiu said.
One thing nearly everyone agrees upon: The cluster of cases linked to Yosemite is highly unusual.
Nine people who spent at least one night at the park since June became infected with the virus, and eight went on to develop hantavirus pulmonary syndrome.
Three people died, and the rest are recovering. No vaccine, treatment or cure exists. Doctors try to keep people alive long enough for their immune systems to rid their bodies of the virus.
Seven of the infected people had stayed in the “signature” tent cabins in Curry Village. The cabins’ double-walled design enabled mice to nest undetected in the insulation between the two walls, Buttke said.