California trees host fungus deadly to patients with HIV/AIDS

The pathogenic fungus Cryptococcus gattii, which has been causing sickness in patients with HIV/AIDS for decades in Southern California, was isolated from tree species not previously reported as hosts, according to new study results published in PLOS Pathogens.

Cryptococcus species are responsible for more than 1 million brain and respiratory infections each year and cause one-third of all AIDS-related deaths, according to researchers.

“Just as people who travel to South America are told to be careful about drinking the water, people who visit other areas like California, the Pacific Northwest and Oregon need to be aware that they are at risk for developing a fungal infection, especially if their immune system is compromised,” study researcher Deborah J. Springer, PhD, a postdoctoral fellow in the Center for Microbial Pathogenesis at Duke University School of Medicine, said in a press release.

Outbreaks of C. gattii are ongoing in the western United States and Canada. However, only two environmental isolates of the fungus have been reported from California, suggesting an unknown reservoir is frequently causing infections in patients with HIV.

According to Duke University, the 13-year-old daughter of study researcher and UCLA infectious disease specialist Scott G. Filler, MD, was looking for a science project to work on during her summer break. Filler and colleagues recommended that she collect samples of C. gattii from the environment around Los Angeles. She obtained 109 samples from more than 30 tree species and 58 soil samples. After growing and isolating the fungus, Filler’s daughter sent the specimens to Springer at Duke University for genetic analysis.


The researchers found that specimens from three tree species — Canary Island pine, pohutukawa and American sweetgum — were almost genetically identical to samples taken from patients in the area, suggesting that the environmental isolates have been the source of human infections.

C. gattii isolated from these hosts was also found to be fertile and to produce abundant spores, allowing the pathogen to expand its reach and increasing the risk for infection.

“That finding is important for long-term prevalence in the environment because this fungal pathogen will be able to grow, reproduce and disperse spores, and serve as a source of ongoing infections,” Springer said.

Disclosure: The researchers report no relevant financial disclosures.

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