This photomicrograph depicts the fungal organism Blastomyces dermatitidis, which causes blastomycosis. The organism is in its budding yeast form, which it assumes when inside an infected animal or human being, causing the disease.

Two large outbreaks of a sometimes deadly fungal infection in Wisconsin disproportionately struck Hmong residents, and now UW-Madison researchers think they know why: Hmong people are genetically more susceptible.

Hmong people are much more likely than whites to have two identical copies of genes that control certain immune response factors, greatly reducing their protection against the fungus that causes blastomycosis, the researchers reported recently in the journal mBio.

The finding suggests Hmong people should try to avoid exposure to the fungus, typically found in dirt near lakes or rivers.

The research could also help scientists explain why other ethnic minorities, including blacks and Hispanics, are at higher risk for similar fungal infections, said Dr. Bruce Klein, a UW-Madison infectious disease specialist who worked on the study.

Doctors should give special attention to such patients when they develop pneumonia or other symptoms of the infections, Klein said. “It’s important to get them in quickly and manage the infection so it doesn’t worsen and become fatal,” he said.

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Blastomycosis is found throughout the Midwest, and Wisconsin may have the highest rate in the country, according to the Centers for Disease Control and Prevention. People breath in spores that become yeast in the lungs and can cause pneumonia.

Symptoms can include fever, chills, cough, fatigue, chest or back pain, shortness of breath and crusty skin sores.

In 2009-2010, an outbreak struck 55 people in Marathon County, which includes Wausau; 20 of them were Hmong. Two people died, at least one of whom was Hmong, Klein said.

Another outbreak in 2015 sickened 90 people, most of whom had gone tubing on the Little Wolf River southeast of Wausau. Again, Hmong people were disproportionately affected, Klein said.

Both outbreaks were the largest ever reported in the U.S. at the time they occurred. In an investigation of the first outbreak, gardening and other outdoor exposures did not explain why such a high rate of Hmong people were sickened.

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Klein and other UW-Madison scientists, including Dr. Caitlin Pepperell, a microbiologist, and graduate students Donny Xiong and Mary O’Neill, studied blood samples from nine Hmong people involved in the first outbreak. They compared the samples with blood from people with European ancestry.

Hmong people were much more likely to have two identical copies — one from each parent — of genes that influence the production of immune responders called interleukin-6 and interleukin-17. Whites typically have two different copies of the genes. Having different copies is associated with higher levels of the immune factors.

With less IL-6 and IL-17, Hmong people are less able to fight off blastomycosis, Klein said.

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The genetic susceptibility may stem from less intermingling with other ethnic groups, Pepperell said. Hmong in Wisconsin have “experienced a long series of forced displacements and migrations,” which may contribute to genetic isolation, she said in a statement.

Many fungal infections — such as Candida auris, a significant global threat in recent years because of its resistance to many drugs — mostly harm people who are already ill.

Blastomycosis typically sickens healthy people, as do two similar fungi: histoplasmosis, which can come from droppings of bats and birds, and coccidioidomycosis, or Valley Fever, present in the San Joaquin Valley of California and other Southwestern states.

Blacks are at higher risk for all three infections than whites, Klein said. Hispanics appear to be at higher risk for blastomycosis and histoplasmosis, he said, and Valley Fever especially affects Filipinos.

It’s not clear if Hmong people are more susceptible than whites to histoplasmosis or Valley Fever, Klein said.

Hmong people should consider avoiding close exposure to soil near water or wear a mask when exposed, Klein said. Doctors, who typically suspect bacteria or viruses in patients with pneumonia, should be alert to the possibility of a fungal cause, especially among Hmong people and other minorities, he said.

Dogs can also get blastomycosis, especially in northern Wisconsin, Klein said. The infection is rarely spread from dogs to people or from person to person, he said.

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