MRI scans showing two brain lesions. The yellow arrow marks a lesion in the lower left temporal lobe surrounded by swelling, while the red arrow points to a 2.7-centimeter lesion in the occipital lobe. Credit: Cladophialophora bantiana brain abscess and concurrent pulmonary cryptococcus neoformans infection in a patient twenty years after renal transplantation, IDCases, 2022.

A fungus with a disturbing preference for the human brain appears to be turning up more often across the United States.

Cladophialophora bantiana is exceptionally rare but exceptionally dangerous. It most often causes brain abscesses — pockets of infected material that can damage surrounding tissue and dangerously raise pressure inside the skull. Even with aggressive treatment, 60 to 70 percent of patients have historically died. Stranger still, roughly half of those infected have no known condition weakening their immune system.

Now, researchers from the University of Washington and the Centers for Disease Control and Prevention report a sharp rise in detections. Their new report in the CDC’s Morbidity and Mortality Weekly Report identified 48 confirmed infections and one probable infection between January 2009 and July 2026. Cases came from 21 states and Washington, D.C. The median patient age was 68 years old.

From 2009 through 2023, the laboratory detected just one to five cases annually. That rose to eight in 2024 and 14 in 2025.

“Reasons for the apparent increase are unknown,” the authors wrote.

A Fungus That Somehow Set Up Shop in the Brain

Most serious fungal infections disproportionately strike people whose immune defenses have been weakened by cancer, transplantation or other illnesses. C. bantiana does not follow that rule particularly well.

“It is capable of infecting apparently healthy people, not just immunocompromised patients in whom we normally worry about invasive fungal disease,” Joshua Lieberman, a microbiologist and associate professor at the University of Washington and an author of the report, told Gizmodo.

Cladophialophora bantiana showing septate hyphae with branching at 40x magnification from brain biopsy. Credit: Case Reports in Infectious Diseases, 2019.

Scientists also do not know exactly where people encounter the fungus. It has rarely been recovered from environmental samples, and patients do not share a consistent exposure history. The leading hypothesis is that people inhale spores or acquire them through a skin wound. The fungus may then enter the bloodstream and somehow reach the brain.

The new data may offer some clues: 43 of the 49 infections, or 88 percent, were detected in tissue from inside the skull, while six were found in lung specimens. The lung cases lend support to inhalation as one route of infection.

CT scans of the chest showing two small hollowed lung masses. The yellow arrow marks a 15-by-18-millimeter mass in the right lower lobe, while the red arrow points to a 15-by-12-millimeter mass in the left upper lobe. Credit: Cladophialophora bantiana brain abscess and concurrent pulmonary cryptococcus neoformans infection in a patient twenty years after renal transplantation, IDCases, 2022.

C. bantiana‘s brain-seeking affinity has been documented for quite some time. A 2017 systematic review examined 120 reported cases in which C. bantiana had infected the brain. Nearly all of those patients — 97.5 percent — developed brain abscesses, and 65 percent died. More than half (58.3 percent) of the patients were considered otherwise healthy.

The new study, however, suggests something may have changed in how often the fungus is appearing, for the worse for humans.

Researchers first considered the most obvious and straightforward explanation. Perhaps doctors were simply submitting more samples for sophisticated fungal testing, and cases may have simply been underreported until recently. The University of Washington laboratory uses broad-range PCR, which searches samples for fungal genetic material and can identify organisms that ordinary cultures might miss. More samples being tested could naturally produce more C. bantiana diagnoses, even if the underlying infection rate had not changed.

To account for that, the researchers looked not just at the raw number of cases, but at how often C. bantiana appeared among all brain and central nervous system samples submitted for the same fungal test. From 2017 through 2023, the laboratory detected an average of 8.4 cases for every 1,000 samples tested. By 2025, that rate had risen to 26 per 1,000 — a 210 percent increase.

“We tried to control for increased testing as an explanation,” Lieberman told Gizmodo. “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.”

Why Now?

This particular study cannot explain why detections are rising. It is based on samples sent to a single reference laboratory, and the researchers had limited information about patients’ medical histories or possible exposures. Because C. bantiana is not routinely tracked nationwide, its true prevalence in the United States remains unknown.

One possibility is environmental change. “The other reasons that really jump to mind are a warming world and climate change,” Lieberman told MedPage Today.

The CDC notes more broadly that warming could favor fungi capable of tolerating higher temperatures, potentially making some better suited to surviving inside humans. But there is no evidence yet showing that climate change caused the rise in C. bantiana.

There is an intriguing parallel overseas. A 2024 nationwide French study found 23 infections from 2002 through 2022, including six in 2022 after years with no more than two annually. Researchers also found better outcomes among patients receiving aggressive surgery and prolonged combination antifungal treatment.

For doctors, the immediate message is to consider the fungus when an unexplained brain abscess does not yield an answer from routine testing. Surgical removal or drainage, when possible, alongside multiple antifungal drugs may offer the best chance of survival, although the odds are unfortunately not in the patient’s favor.

“We need systematic data collection from clinical laboratories across the U.S. to understand how many cases there really are,” Lieberman told Gizmodo. “Although we think cases are still rare, we don’t have a clear picture of the disease burden right now.”