Fungus Behind AIDS Deaths Found Growing on Trees in Southern California

A 13-year-old girl’s science project has uncovered answers about a tree fungus that has been killing people with AIDS in Southern California for years.

The teen’s work was published last week in the journal PLOS Pathogens. She shares authorship with Deborah Springer, lead author and postdoctoral fellow in the Center for Microbial Pathogenesis at Duke University Medical Center.

A fungus called Cryptococcus is responsible for more than 600,000 deaths each year around the world, according to the Centers for Disease Control and Prevention (CDC). People with compromised immune systems are most susceptible, although healthy people have perished from it, too.

Dr. Otto Yang, an infectious disease specialist in Los Angeles, told Healthline that doctors in Southern California have been aware of this problem for some time. The assumption has been that the fungus grows on eucalyptus trees, a mainstay in southern parts of the Golden State. 

“It's only a threat to people with weak immune systems, although rarely a completely healthy person can get a severe infection with it,” Yang said.

But Springer and the work of middle school student Elan Filler shows that a particularly deadly species of Cryptococcus called gattii also grows on the Canary Island pine, New Zealand pohutukawa, and American sweetgum trees. All of these decorative trees are widely planted species on the West Coast of the United States. In San Francisco, pohutukawa trees have been deemed a nuisance because their roots have destroyed infrastructure.

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With the advent of modern antiretroviral therapy medications, few people with HIV progress to AIDS these days and become susceptible to the hazards the C. gattii fungus poses. But people with AIDS or otherwise compromised immune systems should take this new information as a travel advisory, Springer said.

Just as people who travel to South America are told to be careful about drinking the water, people with weakened immune systems 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.

“One shouldn’t be afraid of trees,” Springer told Healthline, “but if you are sick, you may not want to be sawing down a tree, which would cause the fungus to disperse and cause exposure.”

Fungi can be dispersed during earthquakes, tornadoes, dust storms, construction, and landscaping, the paper reported.

A few years ago, Elan’s father, Dr. Scott Filler, an infectious disease specialist at the University of California, Los Angeles, reached out to Dr. Joseph Heitman, chairman of Duke's department of molecular genetics and microbiology. Heitman and Filler have collaborated on projects in the past. When Filler told Heitman that Elan was looking for a summer project, he suggested that searching for fungi throughout Los Angeles could be a fun and useful adventure.

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Elan swabbed samples from more than 30 species of trees and obtained 58 soil specimens. She grew and isolated the fungus herself before sending them to Springer.

Springer then performed DNA sequences on the samples and compared them to those obtained from HIV and AIDS patients with C. gattii infections. These infections attack the lungs and the brain. The specimens from the trees were almost genetically identical to those from the patients.

They also found that the C. gattii remained fertile even after being removed from their environment and continued to reproduce, sometimes asexually. This demonstrates their hardiness, Springer said, and their ability to remain infectious.

A form of C. gattii different from the one that has been sickening California AIDS patients has been found in the Pacific Northwest. “It primarily infects people with healthy immune systems, or those with minor immune dysfunctions,” Springer explained.

Springer said young Elan performed her part of the research “with less oversight than most undergraduate students,” adding “she really took ownership and did a very good job.”

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