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Warnings about a recent outbreak of hantavirus at Yosemite National Park have spread beyond the United States after a British health organization announced it was contacting citizens believed to be at risk.

The Health Protection Agency said in a statement Monday that officials were “providing health advice and information … about the ongoing situation in the U.S.” to about 100 people believed to have traveled to the national park between June 10 and Aug. 24.

The organization said it was also working with the U.S. and European centers for disease control and prevention in responding to the outbreak.

Six cases of the rare, rodent-borne disease have been linked to the park, two of which were fatal. Park officials have traced five of the cases to the “signature tent cabins” in Curry Village, one of the Yosemite’s most popular campgrounds, and said a design flaw allowed mice to get inside the walls of the insulated cabins.

Yosemite officials have sent emails and letters to some 3,100 people who reserved any of the 91 signature tent cabins between June 10 and Aug. 24, urging them or anyone in their party to seek immediate medical attention if they start to show the initial flu-like symptoms of the disease.The U.S. Centers for Disease Control and Prevention said last week than an estimated 10,000 peoplestayed in the signature tent cabins during that time.

Spread through urine, droppings or saliva of infected rodents, hantavirus takes between one and six weeks before causing symptoms in humans, officials said. The disease is generally transmitted when people come in contact with an enclosed area that has been infested by mice.

The disease is rare — 587 cases were diagnosed nationwide from 1993 and 2011, of which about one-third were fatal, according to the CDC.

But the cases at Yosemite are perhaps even more rare. Both park officials and public health authorities said they had not heard of more than one case of the disease in the same location within a year.

News of the outbreak has rattled recent visitors. Rangers have fielded thousands of calls from concerned travelers, and a spokeswoman with the concessionaire that handles park lodging said there was a 20% cancellation rate on a usually sold-out Labor Day weekend.