Climate change hastening the spread of fungal pathogens, says U-M researcher
While ticks and the maladies associated with these minute vampirish insects get a lot of media attention, lurking in the not-too-distant shadows we find several other and potentially more ominous vectors of disease—the fungal pathogens.
Jennifer Head works to put a spotlight on these villains that use the air we breathe as their pathway to infecting a host. But due to their relative obscurity, fungal pathogens are often overlooked—or have their presence misdiagnosed—when patients present acute respiratory complications and other symptoms associated with these illnesses.
“The World Health Organization’s release of a fungal priority pathogen list has brought greater recognition to these diseases, but there is still a very small community working on fungal pathogens,” said Head, an assistant professor of Epidemiology at the University of Michigan School of Public Health.
“The state of the science is not close to being equivalent to the state of research being done on major tick-borne diseases.”
ALSO READ: Connecting climate change to fungal diseases
Head’s research on blastomycosis, Valley fever, histoplasmosis and other fungal pathogens is centered on gaining a clearer picture of these diseases, and identifying the segments of the population at greatest risk and the geographic areas and environmental conditions where these fungal pathogens are likely to thrive.
“We need to better understand where the pathogen lives, and the risk it presents to humans,” she said.
Blastomycosis is a fungal infection that can present as a pulmonary illness after the inhalation of spores. It can be asymptomatic for some individuals, or present severe life-threatening complications in others.
Valley fever’s spores can produce a cough, fever, and extreme fatigue. Histoplasmosis is often associated with more subtle symptoms, but it does have the potential to cause fever, cough and shortness of breath that can persist for long periods of time, or the infection can migrate to the eye, causing tiny scars and, sometimes, loss of vision later in life.
“When a human encounters spores from these pathogens, they are susceptible to infection,” Head said. “Although a lot of human-pathogenic fungi are opportunistic and only infect people who are immunocompromised, these three can infect otherwise healthy individuals.”
Head said these fungal pathogens usually appear in the soil or decaying wood and their spores can be released into the air by anything that breaks up the soil, such as the equipment used in agriculture and construction, or even the wind.
“And every fungal species has its niche where it prefers to live,” she added.
Blastomycosis is most often found in plant material and soil in the midwestern, south-central, and southeastern US. Head said Michigan, Minnesota and Wisconsin are among the few states that document and report cases of blastomycosis, totaling in the hundreds annually, but this number is increasing.
“It is certainly a rare disease, but substantial under-reporting likely takes place,” she said. “Some states that are not reporting at all probably have more cases than Michigan.”
Valley fever is more common in arid soils of the southwest, particularly Arizona and California—deriving its name from California’s San Joaquin Valley—although it also appears in Nevada, Utah, New Mexico, Texas and Washington. In 2023, California health officials reported almost 10,000 cases of Valley fever, the highest total on record.
Histoplasmosis is found in the Mississippi and Ohio River valleys, and is more common in areas in areas where bats and birds nest.
Some fungal pathogens are naturally occurring in the environment, while others are invasive in origin. Head’s extensive research illustrates that fungal pathogens are on the rise, and their accomplice in this sinister development—climate change.
READ MORE about Jennifer Head’s work in the Washington Post
“In the case of Valley fever in California, we've seen increases of over ninefold in incidents over the past two decades, but even more concerning when we look at some areas which have historically been wetter and cooler, we see dramatic increases of over 15-fold,” she said.
“We really need to understand why that's happening, and there's a lot of evidence to suggest that climate change is responsible for the spread of Valley fever throughout California as well as other parts of the Southwestern United States. We need a better understanding of how the risk to humans will change due to climate change.”
Head added that protecting the population from exposure to fungal pathogens is not an easy task.
“For ticks, the recommendations are easier—wear long pants in tick-prone areas and do tick checks when you return home. It’s much harder with fungal pathogens, and I would never tell anyone to wear an N-95 mask while hiking in the woods.”
She thinks the best approach is education and awareness.
“I hope we can develop and share a better understanding of where pathogenic fungi are more likely to live and make people aware that if you experience unexplained respiratory symptoms, ask your physician about these illnesses,” she said. “There are anti-fungal medications available, but many physicians don’t think of these diseases when they see the symptoms.”
Head said that some patients with blastomycosis have been initially diagnosed with cancer before the source of their ailment was pinpointed, while other cases have been incorrectly labeled as pneumonia or another lung disease.
She is encouraged by the work being done on developing a vaccine for Valley fever, which would be the first for a fungal pathogen, but acknowledges that more support for vaccine development is needed.
“That work is still under-funded, but I hope we become more aware of these fungal pathogens and devote more attention and funding to studying them,” she said. “What makes them both fascinating and somewhat scary is how much we don’t know. There is so much to learn, and they are changing at the same time.”
Note: Head and her research collaborators at UC Berkeley, UC San Diego, and the California Department of Public Health recently developed a Valley fever incidence forecast for 2024-2025. Read the preprint in medRxiv.
Lead image description: Jennifer Head, left, and student researcher Sarah Dobson load an air filter on a drone in order to sample air for Coccidioides. (Photo credit: Yuan Zhu)
Written by Matt Markey
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Destiny Cook
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