by JW
My generation has grown up being told that smoking is bad for you and it causes countless ailments. One thing that no one thought to warn us about is microbes that can cause things such as acute respiratory distress syndrome, and the dimorphic fungus Blastomyces dermatitidis is one of those microbes. It was first found in Canada in 1910 but as also been found in Midwestern and southern United States as well as parts of Canada that are along bodies of water like the Great Lakes (1). Diagnosis and identification of this fungus is primarily done from a histological exam on sputum or bronchial washings where they are looking for a broad-based budding yeast with refractile cell walls (2). When asexually reproducing by budding, often the daughter cells are as large as the mother cell before detachment. Patients that come into a hospital with an infection of B. dermatitidis often aren’t diagnosed until it is too late. In a study from a rural area of northwestern Ontario, Canada, A 27-year old woman went to an emergency department with signs of labored breathing and decreased air entry into the left upper lung (2). The first few days of being in the hospital the patient was stable, but after five days the hospital staff requested that the patient be airlifted to an intensive care unit in another facility. After only being in the intensive care unit for a day the patient went into cardiac arrest, and the cause of death was determined to be from acute respiratory distress syndrome.
My generation has grown up being told that smoking is bad for you and it causes countless ailments. One thing that no one thought to warn us about is microbes that can cause things such as acute respiratory distress syndrome, and the dimorphic fungus Blastomyces dermatitidis is one of those microbes. It was first found in Canada in 1910 but as also been found in Midwestern and southern United States as well as parts of Canada that are along bodies of water like the Great Lakes (1). Diagnosis and identification of this fungus is primarily done from a histological exam on sputum or bronchial washings where they are looking for a broad-based budding yeast with refractile cell walls (2). When asexually reproducing by budding, often the daughter cells are as large as the mother cell before detachment. Patients that come into a hospital with an infection of B. dermatitidis often aren’t diagnosed until it is too late. In a study from a rural area of northwestern Ontario, Canada, A 27-year old woman went to an emergency department with signs of labored breathing and decreased air entry into the left upper lung (2). The first few days of being in the hospital the patient was stable, but after five days the hospital staff requested that the patient be airlifted to an intensive care unit in another facility. After only being in the intensive care unit for a day the patient went into cardiac arrest, and the cause of death was determined to be from acute respiratory distress syndrome.
While
some infections of B. dermatitidis result
in hospitalization, most infected patients remain asymptomatic (3). A more
common illness caused by B. dermatitidis
is Blastomycosis and is caused by inhaling the fungus from the environment in
its mold phase and it converts to a yeast phase in the lungs. Often patients
that have symptoms of Blastomycosis aren’t correctly diagnosed because the
illness can mimic those of bacterial pneumonia, acute respiratory distress
syndrome, or tuberculosis. Symptoms of blastomycosis typically appear after two
to six weeks of incubation of the yeast phase in the lungs. Most often it involves
the lungs and approximately 50% of pulmonary infections do not require
treatment, however blastomycosis can affect nearly every organ including the
skin, bones, eyes, and others. Symptoms of the illness are only considered a
confirmed illness when the symptoms persist even after multiple courses of
antibacterial therapy. Patients with an acute case are often given
antibacterial medications and experience improvement within two to three weeks.
This improvement is actually from the self-limited nature of the infection and
not from the treatment with antibacterial medications.
A survey in
Wisconsin showed that the average annual incidence for blastomycosis was 40.4
per 100,000 persons in one county (3). However, mandatory public health
reporting for this illness is not required everywhere. It is only required in
six states in the United States and only two Canadian provinces, making the
true rate of occurrence of this infection in humans unknown. However, while we
don’t know the true infection rate in humans, we do know that B. dermatitidis also infects animals,
and especially dogs. In the same areas of Wisconsin where they reported blastomycosis,
they also reported canine cases to be high at the same rate. One report even
showed that as many as a third of patients who had blastomycosis and owned a
dog reported that their dog was diagnosed with blastomycosis, some times even
before the patient themselves (3).
While the fungus
B. dermatitidis is in its mold phase
in nature it produces conidia, which are spores that are produced from asexual
reproduction and are placed at the end of branching filaments called hyphae.
This structure is shown in the picture below. The conidia are aerosolized during
activities where the soil or decaying wood are disturbed. There are
occupational risk factors for the blastomycosis disease. People that live in
densely wooded areas with moist soil, open bodies of fresh water, and those
that spend a large amount of time in these outdoor environments are at a higher
risk of inhaling the aerosolized conidia. There is a higher amount of cases
reported in men than in women and that most likely has something to do with men
having more of an exposure to the environment with jobs that require moving
wood and farming.
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The virulence of B.
dermatitidis is difficult to evaluate given that the clinical course of
blastomycosis is seen to be correlated with the amount of aerosolized conidia
initially inhaled. Without consistency for the amount of inoculum inhaled in
the cases reported, it is difficult to tell if the difference in the disease
process is from the virulence of from the amount that was inhaled. This means
that it is difficult to tell if acute respiratory distress syndrome is caused
from a prolonged infection with B.
dermatitidis conidia or if it the amount of conidia that the patient first
encountered. Most cases of blastomycosis-induced acute respiratory distress
syndrome follow weeks to months of symptoms for pneumonia before development as
seen in the case study of the 27 year old woman from rural Ontario, Canada.
This map above shows the areas that
B. dermatitidis is located at in
blue. As shown from the multiple reports out of Wisconsin and the map above,
the area of this state is surrounded by the Great Lakes along with having lakes
in the state itself. The other factor of decaying wood being a source for
conidia is also very common for Wisconsin as the state is 46% covered in trees.
With the ecosystem like this in Wisconsin it’s no wonder that there is such a high
reporting of blastomycosis (4). There are occupational risks for those working
outside in the south and Midwestern regions of the United states and Canada
because we still aren’t able to understand how the virulence of the fungus
comes into play for how the infection of B.
dermatitidis. It can either be a mild form of blastomycosis that is
asymptomatic or a life threatening illness such as acute respiratory distress
syndrome which leads to complications. While the dangers of smoking are still
ever present, there are a few other things to watch out for that can cause lung
problems, especially if you work outside in Wisconsin.
(1) Kroll, R. R., & Grossman, R. F. (2013). Pulmonary
blastomycosis in a professional
diver: An occupational risk. Canadian
Respiratory Journal : Journal of the Canadian Thoracic Society, 20(5),
340–342.
(2) Dalcin D, Rothstein A, Spinato J, Escott
N, Kus JV. Blastomyces gilchristii as cause
of fatal acute respiratory distress
syndrome. Emerg Infect Dis. 2016 Feb [11/5/16]. http://dx.doi.org/10.3201/eid2202.151183
(3) Castillo, C. G., Kauffman, C.
A., & Miceli, M. H. (2016). Blastomycosis. Infectious
Disease Clinics of North America,
30(1), 247–64. doi:10.1016/j.idc.2015.10.002
(4) Natasha Kassulke, K. E.
(2005). Fast forestry facts -- Wisconsin Natural Resources magazine -- December
2005. Retrieved from http://dnr.wi.gov/wnrmag/html/supps/2005/dec05/forest.htm
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