Mysterious Brain Fungus Is Spreading in the U.S.
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A mold that settles in the brain and kills up to two-thirds of those infected is turning up more and more often in the United States: That is the finding of a report just published by the U.S. Centers for Disease Control and Prevention and the University of Washington in the Morbidity and Mortality Weekly Report. The pathogen is called Cladophialophora bantiana, a black mold that was previously considered extremely rare. Why cases are rising, the researchers cannot explain.
From a Handful of Cases to 14 a Year
For the report, the researchers analyzed samples from a large reference laboratory. Between 2009 and July 2026, they found 48 confirmed infections and one probable infection in 21 states and Washington, D.C. For a long time, there were one to five cases a year; in 2024 there were eight, and in 2025 there were already 14.
The authors say more testing alone does not explain the increase. Measured against the number of central nervous system samples tested, the rate rose from an average of 8.4 cases per 1,000 samples in 2017 to 2023 to 26 per 1,000 in 2025, an increase of about 210 percent. “So we think the increase is real,” said Joshua Lieberman, one of the study’s authors.
Healthy People Are Affected Too
The fungus is dangerous mainly because it attacks the brain and forms abscesses there. Despite aggressive treatment, 60 to 70 percent of patients in earlier case series died. The best chance of survival comes from a combination of surgical removal of the abscesses and several antifungal drugs over a long period.
Who gets infected is also unusual. Most serious fungal infections affect people with weakened immune systems, but with this pathogen, about half of those who fell ill had no known immune deficiency. The median age of patients in the current report was 68. Exactly how infection occurs is unclear. The leading hypothesis: Spores are inhaled or enter the body through a skin wound and then travel through the bloodstream to the brain.
Climate Change as a Possible Cause
So far, there are only hypotheses for the rise. Dr. Lieberman considers rising temperatures and climate change possible factors, but there is no evidence for that yet. The search is made harder by the fact that the fungus is rarely found in environmental samples and patients have no common source of infection. The study itself also has limits, because it relies on data from a single laboratory and knows little about the patients’ medical histories. Dr. Lieberman is therefore calling for systematic data collection by laboratories across the United States.
There is still no reason to panic: With 14 cases a year in a country of more than 330 million people, the infection remains extremely rare. As with other fungi that have spread recently, such as the multidrug-resistant yeast Candida auris, experts see it as a warning sign, however: Fungal infections are becoming more common, and there are only a few effective drugs against them.
