Two tourists may have contracted the plague at Yosemite National Park

The US sees an average of seven cases per year

California Department of Public Health investigate the national park.

Two American tourists are believed to have contracted the plague after visiting California’s Yosemite National Park.

Authorities have closed the park’s Toulomne Meadows Campground and treated it with the insecticide deltamethrin to prevent the further spread of the disease, which is carried by squirrels, other small rodents and their fleas.

If left untreated, the historically devastating disease has a death rate of at least 50 per cent, but it can now be treated with antibiotics. A young girl from Los Angeles County fell ill from the plague last month following a visit to Yosemite, but has since recovered. The latest suspected case is an adult from Georgia, in the US South, who travelled to the area earlier this month.

Symptoms of the disease include fever, chills, nausea and swollen glands. The second Yosemite patient is the fourth case of the plague in the American West in 2015. Two people in Colorado died separately from the disease earlier in the year. There have been 40 reported cases of the plague in California since 1970, nine of whom died.

Overall, the US sees an average of seven cases per year, and California health officials said the risk to humans remained “low” at Yosemite, which welcomes some four million visitors annually.