A seldom seen but often deadly mold that attacks people’s brains seems to be causing more trouble as of late.
Scientists at the University of Washington and the Centers for Disease Control and Prevention studied lab-confirmed reports of the fungus Cladophialophora bantiana. There has been a noticeable increase in detected cases over the past decade, the researchers found, particularly since 2023. Though these infections still appear to be rare, there is very little we clearly understand about the fungus, the researchers say, including how prevalent it truly is or even how it infects people in the first place.
“Reasons for the apparent increase are unknown,” the authors wrote in their paper, published late last week in the CDC’s Morbidity and Mortality Weekly Report.
A fungus on the rise
Human fungal infections are relatively uncommon compared to bacterial and viral ones, and brain infections are much rarer still. These life-threatening infections tend to be disseminated, meaning the fungi only invade the brain (and other parts of the body) after an initial infection elsewhere. Brain and other severe fungal infections also predominantly occur in people with already weakened immune systems.
C. bantiana is a strange, moldy exception to these rules. When inside the human body, it seems to prefer infecting the brain, typically causing abscesses (pockets of pus containing the fungus, the immune cells trying to fight it off, and other tissues). C. bantiana is also highly deadly when it causes illness, with a mortality rate ranging between 60% and 70% even with treatment. And it’s not picky about its victims either, according to study author Joshua Lieberman.
“It is capable of infecting apparently healthy people, not just immunocompromised patients in whom we normally worry about invasive fungal disease,” Lieberman, a microbiologist and associate professor of laboratory medicine and pathology at UW, told Gizmodo. Roughly half of infections are found in people with healthy immune systems, according to the authors.
The one saving grace is that cases are rarely documented in the U.S. That said, there is no routine national surveillance of C. bantiana, and doctors are not obligated to report suspected or confirmed cases to their health departments.
In this latest study, Lieberman and his team analyzed data from a specialized clinical reference laboratory at the University of Washington. Though only a single location, the UW lab has confirmed cases of C. bantiana across the country for many years. To get a better sense of any potential trends, they also compared the frequency of samples that tested positive for the fungi to the total number of samples sent in for all suspected fungal brain infections.
Between January 2009 and July 2026, there were 48 confirmed cases and one probable case of C. bantiana from 21 states and Washington, D.C., detected by the lab, the researchers found. Between 2009 and 2023, there were one to five cases detected annually. However, in 2024, there were eight cases, and in 2025, there were 14 cases.
The rise seems to have started in 2017 but became most apparent after 2021, according to Lieberman. Between 2017 and 2023, an average of 8.4 cases of C. bantiana were detected for every 1,000 brain and central nervous system specimens submitted for broad-range fungal testing at UW. From 2023 to 2025, however, this frequency had increased fourfold.
“We tried to control for increased testing as an explanation. Even though we tested more samples from the central nervous system over time, the number of C. bantiana cases increased faster. So we think the increase is real,” Lieberman said.
The mysterious mold
Though C. bantiana was first discovered in 1911, inside a brain abscess, we’re still largely in the dark about it. We don’t know where its natural environmental reservoir is, for instance. And we’re not fully sure how the fungus infects people, though there is evidence that people are sometimes initially infected through the skin or by inhaling it into their lungs before it travels to the brain via the bloodstream (in this study, 12% of specimens came from lung or other pulmonary tissue, bolstering the latter hypothesis).
“We need to understand where and how people are exposed. We think this is in the environment and people breath in spores, but we don’t know enough about where it occurs naturally,” Lieberman said.
We also don’t know why it likes our brains, nor why even healthy people can contract the infection. But the most concerning mystery about C. bantiana right now is its prevalence, and it’s a question that can only start to be resolved with more data, the researchers say.
“We need systematic data collection from clinical laboratories across the U.S. to understand how many cases there really are. Although we think cases are still rare, we don’t have a clear picture of the disease burden right now,” Lieberman said.
Unfortunately, C. bantiana isn’t the only fungal infection that’s seemingly becoming more of a danger in the U.S. and other parts of the world.
