A rare tropical fungus has found its way into Washington state infecting at least four residents, two of whom have died, a health official said.

Cryptococcus gattii, invisible to the naked eye and found mostly in trees and soil, has infected at least four residents this year, two of them fatally, county health officer Greg Stern said.

The fungus first appeared in British Columbia six years ago and is believed to have crossed the border into Washington's Whatcom County.

"I'm concerned about the emergence of a new disease, but it still is relatively rare and that part is reassuring," Stern said. "Even on Vancouver Island and the B.C. mainland, where the assumption would be fairly significant exposure to the spores, very few people get sick."

Scientists haven't found a way to reduce the risk of getting the disease, he noted.

Cryptococcus gattii is sometimes resistant to medication that is used to treat a more common, related fungus, Cryptococcus neoformans, which typically infects people whose immune systems are impaired.

Courtney Blomeen, 16, of Blaine, the county's fourth known case this year, first thought she had a severely strained shoulder muscle and a chest cold last month, but a computer imaging scan revealed otherwise.

"I couldn't breathe, it scared me so much," her father, Greg Blomeen, told The Bellingham Herald. "Her left lung had completely blocked off. There were marble-sized nodules that were showing bright white. It was so bad that the one lung was at collapse."

The next day the teenager and her parents had to stay in a special room at Children's Hospital in Seattle until doctors confirmed that the lung problem was not contagious.

Back at her mother's house in Blaine, she still finds breathing difficult at times and expects to be on anti-fungal medication for about a year but is glad to be getting better.

"There's not much air space in there," she said. "Other than that, it's not that bad. I can walk now."

When Cryptococcus gattii infections usually begin in the lungs but can also spread to the brain and develop into deadly meningitis.

The fungus was believed to be largely confined to the tropics until 2001, when it was first diagnosed on Vancouver Island. Since then it has been found in dogs, cats, horses and porpoises, as well as humans, and has been blamed for the death of eight people in British Columbia.

Spores of the fungus have been found on trees and in soil, air and water throughout eastern Vancouver Island, mainland areas around Vancouver and more recently on a fence post just south of the border, health officials said.

No parks or other areas in British Columbia have been closed to the public because of the fungus.

"I certainly don't recommend people stop going outdoors or avoid being near trees," Stern said. "That's not likely to make a difference."

Out of about a million people who are exposed to the fungus annually in the province, 20 to 30 become seriously ill and a total of about eight have died, British Columbia health officials say.

Most British Columbia residents who contracted the illness had healthy immune systems, but 45 percent — like the Blaine teenager — were smokers, and 73 percent had smoked at one time.

Other ailments also may be a factor, Stern said, noting that one of those who died of the fungus in Whatcom County had a compromised immune system from other factors.

— Associated Press