Hantavirus remains a mystery

Yosemite National Park’s deadly summer outbreak of hantavirus has put the national spotlight on the mysterious respiratory infection, which is transmitted via the feces and urine of the deer mouse (pictured), demonstrating that physicians still have plenty to learn.

The virus was first identifid in the United States nearly 20 years ago. Officials are still puzzled by the nature of the virus—which infects some and leaves others unharmed—and what contributed to the increased number of cases this year, according to the Los Angeles Times.

Three of eight park visitors who got the virus this summer died, leading some officials to call the outbreak unprecedented, as having more than one hantavirus victim from the same location in the same year is rare. Health officials investigating the infections, believed to be contracted in a set of the park’s cabins, are concerned Yosemite’s international appeal will lead to infections abroad and have warned doctors worldwide to watch for symptoms.