Last week, the World Health Organization issued a global warning to travelers visiting Yosemite National Park, where three people have died recently after contracting the hantavirus and at least eight others have become sick.
First described roughly 20 years ago in the Four Corners region, the hantavirus is exceedingly rare (about 600 documented cases in the U.S.) but extremely deadly. Symptoms are fast-acting and virulent. There is no vaccine or cure. According to a Scientific American report, it kills more than one in three people who contract it.
Hantavirus is spread through contact with infected rodents, particularly wild deer mice, most often by inhaling dust contaminated with their droppings or urine. It is not transmitted human-to-human. In the United States, the result can be hantavirus pulmonary syndrome, a particularly deadly form of pneumonia. In Central and South America, the virus is also associated with hemorrhagic fever with renal syndrome. This form is very uncommon in the United States.
Though cases of hantavirus and infected rodents have popped up throughout the United States, the disease is most commonly associated with the high deserts of the U.S. Southwest. Its deadly appearance in Yosemite is alarming since very little is known about how hantavirus is spread.
One such effort to learn more is work done by University of Utah researchers in 2008 who released wild deer mice coated (above) with different colors of harmless fluorescent powder at 12 desert sites, then trapped dozens of mice the next day to determine how much exposure other mice had to colored mice. Their finding: Bigger, older mice were most likely to infect other deer mice with the hantavirus.
With no effective treatment or cure available, experts say the best remedy for hantavirus is to avoid contact with rodents as much as possible.