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Detected cases of a rare fungus that invades brain tissue and causes severe infections have risen roughly fourfold in the United States over the past two years, according to new data. With a fatality rate of up to 70 percent reported in earlier research — and infections occurring even in people with healthy immune systems — US health authorities are working to determine the cause.
Researchers from the Washington University School of Medicine and the CDC jointly published findings on the prevalence of Cladophialophora bantiana infections in the latest issue of the Morbidity and Mortality Weekly Report, the US Centers for Disease Control and Prevention said.
The team analyzed specimens submitted to a Washington University clinical laboratory from January 2009 through July this year, identifying a total of 49 US cases — 48 confirmed and one probable infection.
The fungus is known to invade brain tissue and form abscesses. Earlier research has put the fatality rate among infected patients at 60 to 70 percent.
Cases of Cladophialophora bantiana have increased sharply of late, rising from three in 2023 to eight in 2024 and reaching 14 last year.
From 2009 through 2023, annual confirmed cases remained mostly in the single digits.
The detection rate — adjusted for the number of central nervous system specimens submitted for testing — also rose, climbing roughly fourfold between 2023 and 2025. The average detection rate from 2017 to 2023 was 8.4 cases per 1,000 specimens tested; by 2025 that figure had reached 26. Researchers said the increase in testing volume alone could not account for the change.
Cases were confirmed across 21 states and Washington, D.C. California recorded the most with six cases, followed by Florida and Texas with five each, and Pennsylvania with four.
The median age of confirmed patients was 68. Of the 49 specimens, 43 — or 88 percent — came from intracranial central nervous system tissue including the brain, while the remaining six, or 12 percent, were from lung tissue.
The researchers based their findings on data from a single laboratory. A formal nationwide surveillance system has yet to be established in the United States.
Cladophialophora bantiana is a fungus with a strong tendency to invade nervous system tissue.
Its cell wall contains melanin or a similar pigment, which classifies it as a black fungus — a group of fungi characterized by dark-colored pigmentation.
Infection can lead to cerebral abscesses, in which pus accumulates in brain tissue. Inflammation and swelling around the abscess can impair normal brain function.
Patients may experience headaches, dizziness, nausea and vomiting. Depending on the site of infection, symptoms can also include limb weakness, difficulty walking, speech impairment and altered consciousness.
Diagnosis is also difficult, as lesions seen on brain imaging can resemble those caused by tumors or other infectious diseases. Tissue biopsy, fungal culture and genetic testing are used to reach an accurate diagnosis.
Particularly notable is that the fungus can infect people with no apparent immune deficiency. According to the CDC, roughly half of previously documented cases showed no underlying condition or state that would have caused immunosuppression before infection. Brain abscesses have been reported not only in patients receiving immunosuppressive treatment but also in people who had been otherwise healthy.
A 2025 case report from India described a 64-year-old man with no clear immunodeficiency who developed severe headaches and dizziness; subsequent testing confirmed a brain abscess caused by the fungus.
The reasons for the increase in infections and the routes by which the fungus enters the human body remain unclear.
Researchers suggested the fungus may enter the respiratory tract through airborne spores, or penetrate through skin wounds and travel to the brain via the bloodstream.
The fact that 12 percent of all detected cases were found in lung tissue is cited as evidence supporting the possibility of respiratory transmission.
However, the fungus is rarely detected in natural environments, and patients' living conditions and exposure histories vary widely, making it difficult to identify a specific source of infection.
Whether the rise in cases is linked to changes in the fungus's habitat or its pathogenicity requires further research.
Treatment involves combining multiple antifungal agents. When a brain abscess has formed, surgical removal of infected tissue or drainage of pus may also be considered.
The CDC cited a 2024 French study of 23 patients, noting that those who underwent surgical removal or drainage of brain abscesses showed relatively favorable outcomes.
Clinicians were advised to consider the possibility of this fungal infection when treating patients with brain abscesses of unclear origin. The CDC said prompt antifungal treatment and a timely decision on surgery are necessary once infection is confirmed.
US health authorities have also moved to strengthen surveillance to systematically track cases. California's health department asked medical institutions and laboratories on Tuesday to cooperate in identifying and reporting related infections.
Researchers said the absence of a national surveillance system for this fungus in the United States makes it difficult to gauge the true scale of infections and identify transmission routes.
The investigation revealed that cases confirmed at one laboratory have increased rapidly in recent months. The CDC said expanding laboratory reporting and conducting additional epidemiological investigations are needed to identify risk factors and determine the cause of the rise.
rainbow@heraldcorp.com
