Fungus deadly to AIDS patients found to grow on trees

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This false-color electron microscope image
catches the fungus Cryptococcus gattii in the
act of producing its infectious spores. The club-
shaped blue structure is a reproductive organ
called the basidium, which projects off the
fungus body like an apple off a tree. The spores
are colored yellow, and are like seeds that can
give rise to a new organism. Credit: Center for
Microbial Pathogenesis, Duke University
Researchers have pinpointed the environmental
source of fungal infections that have been
sickening HIV/AIDS patients in Southern
California for decades. It literally grows on trees.
The discovery is based on the science project of
a 13-year-old girl, who spent the summer
gathering soil and tree samples from areas
around Los Angeles hardest hit by infections of
the fungus named Cryptococcus gattii (CRIP-
to-cock-us GAT-ee-eye).
Cryptococcus , which encompasses a number of
species including C. gattii , causes life-
threatening infections of the lungs and brain and
is responsible for one third of all AIDS-related
deaths.
The study, which appears Aug. 21 in PLOS
Pathogens, found strong genetic evidence that
three tree species—Canary Island pine,
Pohutukawa and American sweetgum—can serve
as environmental hosts and sources of these
human infections.
"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," said Deborah J. Springer, Ph.D.,
lead study author and postdoctoral fellow in the
Center for Microbial Pathogenesis at Duke
University School of Medicine.
A few years ago, Duke's chairman of Molecular
Genetics and Microbiology, Joseph Heitman
M.D., was contacted by longtime collaborator
and UCLA infectious disease specialist Scott
Filler, M.D., whose daughter Elan was looking for
a project to work on during her summer break.
They decided it would be fun to send her out in
search of fungi living in the greater Los Angeles
area.
The student sampled 109 swabs of more than 30
tree species and 58 soil samples, grew and
isolated the Cryptococcus fungus, and then
sent those specimens to Springer at Duke.
Springer DNA-sequenced the samples from
California and compared the sequences to those
obtained from HIV/AIDS patients with C. gattii
infections.
She was surprised to find that specimens from
three of the tree species were genetically almost
indistinguishable from the patient specimens.
The researchers also found that the C. gattii
isolated from the environment were fertile,
reproducing either by sexual or asexual
reproduction.
"That finding is important for long-term
prevalence in the environment, because this
fungal pathogen will be able to grow, reproduce,
disperse spores, and serve as a source of
ongoing infections," Springer said.
More information: "Cryptococcus gattii VGIII
isolates causing infections in HIV/AIDS patients
in Southern California: Identification of the local
environmental source as arboreal," Deborah J.
Springer, R. Blake Billmyre, Elan E. Filler, Kerstin
Voelz, Rhiannon Pursal, Piotr Mieczkowski,
Robert A. Larsen, Fred S. Dietrich, Robin C.
Mary, Scott G. Filler, and Joseph Heitman. PLOS
Pathogens, August. 21, 2014.