Introduction
Many, if not most, cases of histoplasmosis in domestic dogs are subclinical, which means that no outward signs of illness are observable by their owners. In some cases, however, this fungal infection causes severe disease. The nature and extent of symptoms will depend upon the organ system(s) infected by the organism.
Symptoms of the Disorder
Histoplasmosis may be confined to the lungs or the gastrointestinal tract, or it may become systemic if the organism is disseminated throughout the dog’s body. Owners may notice one or more of the following signs, which unfortunately are fairly nonspecific:
- Loss of appetite (inappetance; anorexia)
- Weight loss
- Diarrhea
- Straining to defecate (tenesmus)
- Bloody stool (melena; hematochezia)
- Mucus or fat in the stool (steatorrhea)
- Exercise intolerance
- Lethargy
- Depression
- Difficult, labored breathing (dyspnea)
- Cough (usually chronic)
- Fever
- Vomiting
- Muscle wasting
- Enlarged tonsils
- Enlarged lymph nodes
As the infection progresses, dogs can become emaciated and can develop:
- Elevated heart rate (tachycardia)
- Elevated respiratory rate (tachypnea)
- Lameness
- Weeping, ulcerated sores on the skin or around the eyes
Ultimately, histoplasmosis can affect a number of canine bodily systems in addition to the gastrointestinal and respiratory tracts. The liver, spleen and lymph nodes are frequently affected and may become enlarged. Bones, bone marrow, adrenal glands, kidneys, mouth/tongue, eyes and testes also can be, but less frequently are, affected by the fungi.
Dogs at Increased Risk
Most dogs that become clinically infected with H. capsulatum participate in outdoor activities in endemic areas – especially dogs housed outdoors or used for tracking and hunting. Young adult, large-breed dogs seem to be at a slightly increased risk of developing symptoms of infection, although the reason for this is not known. There is no reliably recognized breed, age or gender predisposition to developing histoplasmosis. Dogs with other illnesses, and those who are poorly nourished or otherwise immunocompromised, have a greater chance of becoming infected and ill than do healthy animals.