By Barry C. Fox, M.D., University of Wisconsin
The most common fungal infections that cause body-wide or systematic diseases in humans are histoplasmosis, blastomycosis, and coccidioidomycosis. All three grow as mold in the laboratory and as yeast in the human body. What sets these diseases apart is the fact that they they inhabit a unique geographic area of the United States.
‘Walking Pneumonia’ and a Boy Scouts Camp
A father and son go on a Boy Scout trip to North Wisconsin that includes several nights at a camp near the Eagle River. The camp has 40 acres of pine and hemlock forest. The camp sees more than 6,000 visitors annually, who participate in all kinds of outdoor activities, including lectures and ecology projects.
After about six or eight weeks of their stay, the son gets fever, a dry cough, and chest pain. It is found that several of the boy’s friends, who are also scouts, are all ill with similar symptoms. On the other hand, a health officer at the Wisconsin Public Health Department is getting an unusual number of case reports of elementary school students visiting their primary care physicians with fever, severe cough, chest pain, and this diagnosis of “walking pneumonia”. Chest x-rays reveal multiple nodular-appearing spots in the lungs.
Eventually, several children were diagnosed with blastomycosis that is commonly found in the drainage area of the Mississippi River valley.
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Blastomycosis
A large epidemiologic investigation was undertaken to locate the source of the mold that caused blastomycosis. Epidemiologists found clues that linked the children to summer scouting activities. This evidence raised the suspicion that the fungal infection may have been acquired near the place where the children were staying.
Several scout groups were interviewed to locate the source of the blastomycosis, and it was deduced that the most likely exposure was the beaver pond where the ecology was taught.
The closer the children were to the beaver pond, the more likely they were to catch the illness. The relationship of beavers to an outbreak of blastomycosis had not previously been described. Environmental features, such as the chemistry of the soil, air humidity conditions, and the presence of beaver excrement, likely combined in the right formula to allow blastomycosis to flourish.
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Most Cases of Endemic Mycoses are Asymptomatic
Histoplasmosis and blastomycosis are commonly found in the drainage area of the Mississippi River Valley. However, isolated cases of both diseases may occur in other parts of the country.
Coccidioidomycosis, on the other hand, is unique to southwestern United States, including areas of Arizona, New Mexico, and Southern California. All three endemic mycoses have one of three clinical presentations.
It is seen that most cases are asymptomatic or, at worst, a mild respiratory infection that generally does not get reported, or even come to medical attention. When a more significant load of fungal spores is inhaled, this will lead to pneumonia. Usually, with a normal immune system, the body will recover without specific antifungal therapy.
On rare occasions, these fungal diseases can spread outside the lung throughout the body, including the brain, liver, and spleen. The disease is labeled as “disseminated”.
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The Pervasive Nature of Fungal Infections
Several decades ago, a massive outbreak of a fungal disease occurred in Indianapolis. Almost 40 percent of young adults and 9 percent of persons older than 55 who lived in certain parts of Indianapolis were presumed to be infected based on serological or blood test data.
The data represented nearly 100,000 individuals. The outbreak was unusually severe, and there were 15 deaths and 46 cases of progressive disseminated histoplasmosis.
Over the course of four months, patients started to present with symptoms of dry cough, coughing up blood, chest pain, fever, and body aches. Since different patients consulted different physicians, it took several months before the scope of the outbreak was known. It was quite surprising that despite a large epidemiologic investigation, no exact common source outbreak location was identified.
Are Bird or Bat Droppings the Culprit?
Histoplasmosis was, however, cultured from all over Indianapolis. Cases appeared to have clustered near the center of the city along the White River and Fall Creek that ran through Indianapolis. An old amusement park close to the center of the outbreak and demolition activities for a new tennis stadium was strongly suspected as the exact source of the fungus. The mold especially likes to live in the soil where bird or bat droppings provide extra nutrients to support its growth.
One of the bigger lessons learned from the Indianapolis outbreak was the capacity to inflict a large incidence of disease in a major metropolitan area, a harbinger of concerns of bioterrorism.
Common Questions about Fungal Diseases Unique to the United States
The most common fungal infections that cause body-wide or systematic diseases in humans are histoplasmosis, blastomycosis, and coccidioidomycosis.
Histoplasmosis and blastomycosis are commonly found in the drainage area of the Mississippi River Valley.
Coccidioidomycosis is unique to the southwestern areas of the United States, including Arizona, New Mexico, and Southern California.
