Aerosolized Fungal Infection from Bats

By Jonathon Marioneaux

As promised, we will be continue our coverage of bats and their diseases this week.  Over the last several postings we have covered different diseases bats can carry and their place in folklore.  In many horror stories and movies the main antagonist resides in a cave which makes you wonder, what else is in that cave? One of the main diseases that can be contracted in caves is histoplasmosis, which as it turns out is a relatively common disease.  Researchers from Heliopolis Hospital in Brazil documented a case of oral manifestation in a patient in 2013 that provided clinical details to the history and progression of the disease.

Histoplasmosis is a fungal infection caused by Histoplasma capsulatum and has two variants—capsulatum and duboisii. The fungus is found in caves worldwide, however most clinical cases occur on the American continent.  H. capsulatum requires moderate temperatures and constant humidity to grow and does best in bird or bat guano.  The fungus is found in its hyphae form primarily in caves and reverts to its yeast form in human lungs due to the higher temperature.  The fungus is primarily transferred to humans in its aerosolized form during cave diving, giving it the nickname “Caver’s disease” and “Spelunker’s disease.” However, it can also be transferred any time soil aerosolizes, for example, during digging.

The disease has a relatively low mortality rate in immunocompetent people and may go undetected as mild flu symptoms. Yet in people with compromised immune systems, such as AIDS patients, it can reach mortality rates as high as 80% and can be a tool for AIDS diagnosis.  In some cases the disease can become chronic in the presence of underlying disease and become severe to life threatening.  Diagnosis of H. capsulatum can be difficult due to its mimicking of other diseases, such as tuberculosis, and limitations of diagnostic exams.  The gold standard for diagnosis is culturing of the fungi on dextrose slats which will show white or brown filamentous colonies.

The Brazil patient was initially admitted on complaints of oral lesions and shortness of breath to the Heliopolis hospital.  The initial diagnosis was tuberculosis, however radiography diffuse infiltrate of both lungs and negative acid-fast staining discounted this.  Subsequent tests showed CD4/CD8 lymphocyte count was normal, discounting HIV, and culture tests indicated fungi presence.  A biopsy of lung tissue showed Langhas-type multinucleated giant cells with variable amounts of lymphocytes consistent with histoplasmosis. The patient was treated with Itraconazol for six months and showed marked improvement.

The above example explains why the conversation between patient-doctor and doctor-doctor is very important.  Without knowledge of the patient’s history and the referral by the dentist it is possible that a positive diagnosis could never have been made. This is especially true with organisms which are hard to grow or mimic symptoms of other disease.  In addition, knowing the immunocompetent state of a patient can give clues to what type of pathogen might be present.

So, when going spelunking or anywhere near animal feces wear a mask or other protective covering to prevent infection from various diseases including H. cacsulatum. Bats are our friends and serve a much needed role in pollenating plants and keeping insects under control during the warm parts of the year.  Let’s not forget their contributions when discussing their role in disease transmission and the Hollywood spin put on them for Halloween. It is always advisable to take caution when handling bats of any species or geographic location to prevent the spread of numerous viral, bacterial, and fungal agents that they carry.

With Halloween upon us, this concludes our series on bats and their diseases. Next week, we will pick up coverage of birds (if you have a specific bird you would like me to cover send me an email) to get into the Thanksgiving spirit.

As always remember to wave at the next bat and thank them for their invaluable service to our ecosystem!

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