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Histoplasmosis
in dogs and cats |
In both dogs and cats, histoplasmosis occurs most commonly
in young animals (<4 years-of-age).
- The incubation period for histoplasmosis (12-16 days) is
much shorter than for blastomycosis.
- The primary route of infection is again through the respiratory
tract, but systemic spread occurs quickly in most cases.
Histoplasmosis in dogs:
DOGS COMMONLY DEMONSTRATE GASTROINTESTINAL SIGNS:
- Histoplamosis is manifest as a large bowel diarrhea due to
granulomatous
colitis with thickening of the bowel wall and mucosa, with
weight loss.
- The large bowel disease causes tenesmus and mucoid or frankly
bloody diarrhea, with inappetence and fever.
- The predilection for the gastrointestinal tract in dogs might
seem to suggest infection by ingestion, but this has not been
proven experimentally. In addition, more widespread systemic
evidence of disease is generally present pathologically.
- Ocular and bone lesions are less common than in canine blastomycosis.
Histoplasmosis in cats:
Cats are at least as sensitive to infection with H. capsulatum
as dogs. They most often present with respiratory and systemic
disease that develops over an insidious course. The organs most
commonly involved are:
- lung
- liver and spleen
- bone
- lymph nodes
Diagnosis of histoplasmosis in dogs and cats:
- cytology
of rectal scrapings or colonic biopsies in dogs (Culture from
feces is generally not useful.)
- The organism may appear as a narrow-necked budding structure
or simply as a non- budding organism. They are most commonly
present within macrophages or other phagocytic cells.
- Serologic assays can be used, but available serologic tests
for Histoplasma are often falsely negative in dogs.
- A urine Ag test is used very successfully in immunocompromised
human patients in whom serologic tests may be negative.
