Researchers have discovered a new strain of a potentially deadly fungus in Oregon, marking another step in the steady spread of Cryptococcus gattii from Vancouver Island to the Pacific Northwest and beyond.
"It's present in Oregon, and we haven't found it anywhere else yet," Joseph Heitman of North Carolina's Duke University Medical Center said yesterday of the new strain.
"That's not to say it doesn't exist somewhere in the environment, but we haven't found it ─ and we've looked hard," said Dr. Heitman, senior author of a paper published online Thursday in Public Library of Science Pathogens.
Duke researchers used DNA sequencing to identify the strain, a new variety of a fungus that has been tracked on Vancouver Island for the past decade.
In their paper, the scientists called for enhanced awareness of the fungus, which can cause cryptococcal disease and appears to be on an "inexorable expansion" in the region.
From 1999 through 2003, cases were largely restricted to Vancouver Island. Between 2003 and 2006, the outbreak expanded into mainland British Columbia and then into Washington and Oregon from 2005 to 2009, the paper says.
"Based on this historical trajectory of expansion, the outbreak may continue to expand into the neighbouring region of Northern California and possibly further," the researchers said.
C. gattii's North American sojourn began 2001, when British Columbia veterinarians began noticing a high number of animals ─ including cats, dogs and ferrets ─ coming down with cryptococcal disease. It also showed up in people.
Tests determined the illnesses were caused by C. gattii, which was widespread in Australia but had never been reported in Canada. (C. gattii is related to C. neoformans, which is found all over the world, while C. gattii had been associated with tropical areas.)
The British Columbia Centre for Disease Control determined the fungus had been showing up in humans as early as 1999. Vancouver Island now has one of the highest rates of infection in the world.
Researchers believe climate change could be a factor in the spread of the fungus from Australia to the Pacific Northwest.
Studies have determined the fungus can move by air, water and anthropogenically - that is, on people and even vehicles, Eleni Galanis, an epidemiologist with the British Columbia Centre for Disease Control, said yesterday.
Although Vancouver Island has emerged as a hotbed for cryptococcal disease, it remains rare. To date, there have been 270 human cases, or fewer than 30 cases a year, with a mortality rate of under 10 per cent, Dr. Galenis said.
The mortality rate of 21 C. gattii cases studied in the Pacific Northwest is running at about 25 per cent, but those cases have included only people who have been hospitalized, while the BCCDC tracks people who have tested positive but may not be hospitalized for the condition, Dr. Galenis said.
There is no vaccine for cryptococcal disease. In animals, symptoms can include runny noses and breathing problems. In people, the disease can result in pneumonia or meningitis. It can take several months to incubate after exposure.