According to a publication from the University of Wisconsin-Madison, analysis of a large outbreak of blastomycosis in Marathon County, Wisconsin in 2009 found that people of Asian descent were particularly prone to blastomycosis infection. Of the 55 confirmed cases in the outbreak, 20 were found to have Hmong ancestry.
Recently, researchers from the University of Wisconsin-Madison conducted a new study that identified a genetic signature in certain Hmong people that leaves them particularly vulnerable to the fungal infection.
About Blastomycosis
Blastomycosis is a fungal disease caused by the fungus blastomyces dermatitidis, which thrives in damp soil and decomposing wood — particularly throughout the Great Lakes and Mississippi River valley regions.
People can be infected when they inhale microscopic spores the fungus releases into the air for reproduction. Most people who inhale spores aren’t affected — but the fungus can cause flu-like symptoms, and even death in rare but particularly severe cases.
Wisconsin is one of the few states in both the Mississippi River and Great Lakes regions, and has some of the highest annual rates of blastomycosis infection in the country as a result. Occasional outbreaks affecting up to 100 people have been known to occur.
Genetic Vulnerability Identified in Hmong
The Hmong people are an ethnic group of southeast Asia. Most live in Southern China, Vietnam, or Laos, but the United States also hosts a sizable population. In the 2009 Marathon County outbreak, over one-third of the affected individuals were of Hmong descent.
Associate Professor of Medicine and Medical Microbiology Caitlin Pepperell and Dr. Bruce Klein with the University of Wisconsin-Madison led the new study into the genetic origins of blastomycosis vulnerability. What they found surprised them.
The research team sequenced and analyzed the genomes of Hmong participants. Of particular interest to the team were lengthy regions of homozygosity in the participants’ genomes.
Every gene humans inherit comes as a pair of alleles. Alleles that are identical are said to be homozygous. “Many disease-causing variants are homozygous,” Pepperell noted, because homozygous regions are more susceptible to expressing recessive traits — such as vulnerability to certain fungal infections.
By focusing on the comparatively small regions of the genome that were homozygous, researchers avoided the time-consuming practice of analyzing entire genetic sequences. The University of Wisconsin researchers found one of these homozygous stretches in an area of the genome associated with immune response to fungi.
The region they identified is responsible for the production of an important cytokine called interleukin-6 (IL-6). IL-6 is a vital precursor to interleukin-17 (IL-17), a protein that plays a central role in immune responses to fungal pathogens. Generally speaking, lower levels of IL-6 lead to lower levels of IL-17 — and therefore a weakened immune response to fungi.
Pepperell and Klein’s team found that the cells of certain Hmong participants with this genetic marker produced less IL-6, and therefore less IL-17. In a mouse model, low IL-6 levels were found to be associated with significantly fewer TH17 cells (the cells which secrete IL-17).
Dr. Klein called the research “extremely gratifying.” Identifying genetic weaknesses to blastomycosis and other fungal infections could prove useful for identifying those at-risk of severe adverse reaction.
What do you think of this interesting new research? Does it surprise you that certain population groups respond to some pathogens differently than others? Share your thoughts with Patient Worthy!
