A rare fungal infection spreads to unexpected areas of the US.

A rare fungal infection believed to occur primarily in the northern Midwest and parts of the Southeast is actually more common in other parts of the United States than expected, new research published Wednesday revealed.

The disease, called blastomycosis, can be difficult to diagnose, in part because it can look like other respiratory infections. And the longer it goes undiagnosed, the more it needs to be treated.

The infection is caused by a fungus called Blastomyces dermatitidis, which proliferates in moist soil and in decaying trunks and leaves. Blastomycosis is considered an “endemic mycosis”, that is, a type of fungal disease that only occurs in a specific geographical area.

The fungus Blastomyces dermatitidis, which causes the blastomycosis infection, thrives in moist soil and on decaying logs and leaves.Smith Collection/Gado/Getty Images file

Although it is well known in areas surrounding the Great Lakes, the Ohio River Valley and the Mississippi River Valley, it is a bit surprising that the infection appears in Vermont, as the new study, published in the journal Emerging Infectious Diseases, found. the Centers for Disease Control and Prevention.

“Usually, when you talk about blastomycosis, you don’t think about Vermont,” explained Dr. Arturo Casadevall, professor of Molecular Microbiology and Immunology at the Johns Hopkins Bloomberg School of Public Health. But “recently several works that have been published suggest that fungal infections They are spreading throughout the countryand this is one of them.”

Dr. Brian Borah, medical director of Vaccine Preventable Disease Surveillance at the Chicago Department of Public Health, who led the study, said, “It’s a big question whether we’ve been able to detect cases that we didn’t know about before or whether we’re seeing an increase in the cases”.

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However, the epidemiology of other fungal diseases across the country has been changing, Borah said, adding, “I don’t think blastomycosis is immune to those patterns.”

Blastomycosis is rare, and can cause respiratory symptoms, fever, and body aches in about half of people who become infected by inhaling Blastomyces spores. Most cases are mild, but if untreated, blastomycosis can cause serious illness or death.

“One of the big problems with fungal diseases is that they are not reportable,” meaning that public health departments do not require doctors to report cases of disease they see to the state, explained Casadevall, who was not involved in the study. new study.

Only five states – Arkansas, Louisiana, Michigan, Minnesota and Wisconsin – have public health surveillance for blastomycosis. This means that the prevalence of the disease outside these regions is unknown.

Borah, who previously was a Centers for Disease Control (CDC) epidemic intelligence officer assigned to the Vermont Department of Health, said there had been some reports of blastomycosis cases in the northeast, starting in a couple of studies, as well as anecdotes from doctors and veterinarians in Vermont.

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Without public oversight, Borah and his team turned to health insurance claims to determine how many patients were treated for blastomycosis in Vermont from 2011 to 2020.

The data included all claims from Medicare and Medicaid beneficiaries in the state and about 75% of Vermont residents who had other health insurance. The team was able to identify 114 cases over the 10-year period. 30% of them required hospitalization. With an average rate of 1.8 cases per 100,000 residents annually, Vermont had higher rates of blastomycosis than all but one state that monitors the disease, according to the study. Wisconsin, the state with the highest rate of blastomycosis, has an average of 2.1 cases per 100,000 residents.

Gaining ground

A study published in 2022 suggested that around 10% of diseases caused by fungal infections are diagnosed outside regions where fungi are known to be endemic.

According to Dr. Bruce Klein, professor of Pediatrics, Medicine, Medical Microbiology and Immunology at the University of Wisconsin-Madison, the fact may be due to several causes. These pathogens can get on shoes when people travel. New construction can stir up soil – and the fungi it harbors – and release spores into the air in places where they were not thought to exist.

“Blastomyces dermatitidis grows as a mold, which produces spores. When those spores are altered in their physical state, they become aerosols that are breathed into the lungs“Klein explained, adding that wind and rain, and not just human intervention, can cause spores to spread through the air.

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Recent studies have shown that climate change is also expanding the range of fungi that can make people sick. Human-caused climate change is modifying rainfall patterns, increasing drought in some regions – an environment that favors fungi such as Coccidioides, which causes Valley Fever – and causing more flooding and humidity in others.

Rising temperatures and extreme weather events, such as storms, floods, droughts and hurricanes, affect soils and can redistribute fungi, explained Asiya Gusa, associate professor of Molecular Genetics and Microbiology at Duke University, who studies how Fungi adapt to thermal stress.

“That’s going to increase human exposure to fungi and also expose those fungi to higher temperatures,” he said. “There is a fear that with increased humidity and warmer weather, we could see more spore accumulation.”

Early studies have suggested that heat could influence fungi that until now have not been able to withstand body heat and evolve to survive in the human body.

“Climate change is the 800-pound gorilla in the room,” Casadevall said. “That could greatly change the epidemiology of these diseases.”

difficult to diagnose

Once Blastomyces dermatitidis spores penetrate the lungs, a person’s body heat triggers a transformation in the shape of the fungus. The spores transform into yeast cells protected by thick armor, one of the reasons fungal infections can be so difficult to treat, Klein explained.

Another reason is that fungal cells look much more like human cells than plant or bacterial cells, making it difficult to develop drugs that can attack and kill fungi without also damaging human cells.

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Fungal infections are more worrying in people with immune problems. Most serious fungal infections occur in this population group. However, blastomycosis usually affects healthy people, according to Klein.

“This is a notable difference compared to many other fungi that are weaker and occur in people whose immune system is weakened,” he said, adding that two other fungal diseases – Valley fever and histoplasmosis, which also occur in specific regions of the United States – also behave this way.

There is likely a dose-response relationship, meaning the more spores a person breathes in, the more likely they are to get sick. The fungus is usually found in small pockets, often in humid forests, which means people are not exposed to it all the time, Klein explained.

Most cases of blastomycosis are mild. About 95% are completely treatable with antifungals, but it can take up to a year to clear an infection that has spread beyond the lungs, Klein said.

The difficult thing is that fungal infections often look like other diseases and can go unnoticed for weeks or months. This is especially true in places where fungal infections such as blastomycosis and Valley Fever are not thought to occur.

“These infections most commonly resemble common pneumonia or another respiratory illness,” Klein explained. “These are more common than blastomycosis, so people are usually treated for these other problems first and may see a doctor, once, twice, three times, and receive several courses of antibiotics as the fungal infection progresses.”