Disseminated histoplasmosis in a horse.

The research studies a case of disseminated histoplasmosis in a 12-year-old horse mare. This was due to Histoplasma capsulatium, a fungus generally found in the soil and can infect animals and humans, causing mild pneumonia or a more serious threat for those who are immunocompromised.

About Histoplasma Capsulatum and Histoplasmosis

• The study focuses on Histoplasma capsulatum, a naturally-occurring fungus that generally lives in the soil. This fungus has two forms: a septate mycelium, and a unicellular, budding yeast form in tissues.
• Small microconidia produced by the mycelium can cause infection, usually entering the body through the respiratory system via aerosols or ingested fomites.
• In immunocompetent humans and animals, exposure to this fungus usually results in a mild, self-limiting pneumonia. However, in immunocompromised individuals, it can pose a severe threat, leading to histoplasmosis, a condition that the Centers for Disease Control (CDC) uses as a criterion for defining AIDS in patients.
• In the United States, the fungus is highly prevalent in the Ohio and Mississippi river valleys and is also found in Texas, Virginia, Delaware, and Maryland. In these areas, 20-50% of AIDS patients have been found to have disseminated histoplasmosis, a severe form of the disease in which the fungus spreads from the lungs to other parts of the body.

The Case Study

• The researchers examine the case of a 12-year-old mare from Purdue University Large Animal Hospital, who showed severe weight loss and anorexia for 7 weeks. She had previously been treated for a respiratory infection with penicillin, dexamethasone, and vitamin B12. On presentation, she was found to be depressed and dehydrated, showed signs of respiratory distress, and had begun to exhibit signs of diarrhea.
• Initial diagnostic tests included a complete blood count, chemistry panel, thoracic radiographs, a tracheal wash, and bronchoalveolar lavage. An examination of the thoracic radiographs suggested pneumonia and presence of a mass in the lungs, while the blood count pointed towards inflammation and other abnormalities.
• Liver enzymes were also mildly to moderately elevated, indicating potential liver damage and cholestasis, a condition where bile flow is reduced or blocked.
• The mare, unfortunately, passed away before further diagnostic procedures, such as an ultrasound, could be performed.

Given these findings, the research presents an in-depth look into a case of histoplasmosis in a horse, highlighting the various symptoms, complications, and health threats that the Histoplasma capsulatum fungus can pose to animals.