This disease is found in the central United States near the Great Lakes, the Appalachian Mountains, Texas, and the valleys of the Mississippi, Ohio, and Missouri rivers. These areas have nitrogen-rich soil that facilitates growth of the causative fungus (Histoplasma capsulatum).
In most cases, histoplasmosis is subclinical or inapparent, occasionally producing a mild respiratory infection. There is an acute intestinal form, however, that attacks the small bowel and colon. The principal signs are weight loss and intractable diarrhea.
A systemic form is characterized by fever, weight loss, vomiting, muscle wasting, coughing, enlargement of the tonsils and other lymph nodes, as well as involvement of the liver, spleen, bone marrow, eyes, skin, and rarely, the brain.
Spores are found in soil contaminated by the dung of bats, chickens, and other birds. Spores are breathed in by dogs, people, or other animals.
The diagnosis is made by chest X-ray, blood studies, and identification of the histoplasma organism in cytology, biopsy, or culture specimens.
Oral anti-fungal drugs of the imidazole group, including ketoconazole, itraconazole, and fluconazole, are particularly effective in treating histolpasmosis that is not life threatening. In dogs with severe infections, amphotericin B is often combined with one of the imidazoles. Amphotericin B is potentially damaging to the kidneys.
Anti-fungal therapy requires many months of drug use after the symptoms disappear. The disease will reappear if long-term suppression is not maintained. Anti-fungal drugs can be toxic and require close veterinary management.
Please contact your veterinarian if you suspect your pet may have this condition.
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