A rare strain of a potentially deadly airborne fungus is spreading into the northwestern United States from British Columbia, Canada, for the first time, according to a study in the Public Library of Science Pathogens journal.

Research revealed that since 1999, there have been 270 confirmed cases of the Cryptococcus-gatti strain in the U.S. and Canada, resulting in 40 fatalities. These include 50 cases in Washington state and Oregon since 2004, as well as numerous animal deaths.

The fungus is spread via airborne particles, but cannot yet be spread from person to person.

“These spores are really, really small, and they can be carried in the air,” Dr. Julie Harris, a fungal specialist for the Centers for Disease Control and Prevention told National Public Radio. “And so hypothetically anyone can inhale them.”

Native to tropical and subtropical regions, the fungal strain is worrisome to researchers because no one seems to understand how or why it surfaced in the temperate region of the Northwest.

“The disease was almost exclusively seen in tropical and subtropical areas of the world,” Dr. Harris said. “The hot spots were most Australia and Papua New Guinea, along with Egypt and parts of South America.”

Edmond Byrnes, a graduate student at Duke University and co-author of the fungal study told National Geographic he was concerned about the implications of the virus, and the potential impact it could have.

“The alarming thing is that it’s occurring in this region, it’s affecting healthy people, and geographically it’s been expanding,” he said.