WASHINGTON — A fungus that causes meningitis has sickened 19 people, four of whom died, in Oregon and Washington over the past four years, researchers report at a meeting of microbiologists and infectious disease experts.
The new findings indicate that the culprit, a yeast-like fungus called Cryptococcus gattii, is spreading gradually down the West Coast. Before 1999, the fungus was rarely encountered in North America. But that year a case cropped up on Vancouver Island in British Columbia, Canada. Since then, more than 200 people in British Columbia have been diagnosed with illness stemming from the fungus.
C. gattii naturally lives in foliage, particularly eucalyptus and rubber trees. Once airborne and inhaled, the fungus can infect people and animals. It doesn’t spread from person to person or between people and animals.
A related fungus called Cryptococcus neoformans causes lethal infections in immune-compromised people, such as those with HIV. While none of the 19 patients in Oregon and Washington had HIV, 11 were immune-compromised by other ailments or medications, says Sarah West, an infectious disease physician at the Oregon Health Science University in Portland. She reported the findings at a joint meeting of the Infectious Diseases Society of America and the American Society for Microbiology.
Like C. neoformans, C. gattii can be dangerous. Apart from the four deaths, 13 of the 19 patients required hospitalization longer than 11 days, West says. Ten of the patients had lung infections, five had meningitis and four had both, she says. Doctors treated the patients with antifungal drugs.
The Centers for Disease Control and Prevention in Atlanta is now monitoring these two states, as well as Montana, Alaska, Idaho and California, for C. gattii infections.
C. gattii normally shows up in subtropical parts of Australia, New Guinea, India and South America. Scientists speculate that the fungus made its way to North America from one of those regions, resulting in the Vancouver Island outbreak. West says some evidence suggests the fungus might have found a home in fir trees.
George Thompson, a physician at the University of Texas Health Sciences Center at San Antonio, says the key to controlling C. gattii will be to raise the level of suspicion surrounding the fungus. In North America, he says, “I think people just don’t look for it” as a possible explanation for troubling symptoms.
C. gattii can cause a prolonged cough, headache, fever, chest pain and other nondescript symptoms. Of the 19 Washington and Oregon patients, 12 went more than a week before being properly diagnosed.
C. gattii causes disease in people only sporadically. Most of those who come into contact with either form of cryptococcus don’t become ill, says Jeremy Farrar, an Oxford University physician based in Ho Chi Minh City, Vietnam. An HIV infection and other forms of immune suppression clearly place people at risk. But other people who get lung infections or meningitis from either form of cryptococcus might just be unlucky, he says.
“My guess is that in some very tiny way, these people have some defect in their immune system that makes them susceptible to crypto,” he says. That flaw is likely to be hardwired into a person’s innate immunity and not in the immune cells and proteins that make antibodies in response to specific pathogens, he says.
Since no such specific immune flaw has been identified, predicting who might be naturally susceptible remains a puzzle, he says.
How the fungus moves from place to place is equally mysterious, and existing antifungal drugs are sometimes inefficient in stopping an infection, says Thompson. He has developed a mouse model of the disease and is testing drugs against C. gattii in the animals.
“I think we may have seen only the tip of the iceberg with C. gattii-caused infections in the United States,” he says.