Histoplasmosis in Dogs

Histoplasmosis refers to a fungal infection caused by the Histoplasma capsulatum fungus. Dogs usually ingest the fungus when they eat or inhale contaminated soil or bird droppings. The fungus then enters the dog's intestinal tract, where it causes a diseased condition to develop.

Symptoms

The most common symptoms for dogs are lack of appetite, weight loss, depression, and diarrhea with straining. Other potential signs may include:

• Coughing
• Difficulty breathing (dyspnea), associated with harsh lung sounds
• Unable (or unwilling) to exercise
• Enlarged lymph nodes (lymphadenitis)
• Lameness
• Eye and skin changes
• Fever, up to 40 degrees Celsius (104.0 degrees Fahrenheit)
• Pale gums and moist bodily tissues (mucous membranes)
• Yellowish discoloration of the gums and other bodily tissues (known as jaundice or icterus)
• Enlargement of the liver and spleen (hepatosplenomegaly)

Causes

The primary cause of this infection is the ingestion of the Histoplasma capsulatum fungus. The fungus may be inhaled when contaminated soil is disturbed, such as what happens when dogs scratch or dig in the dirt, or through contact with contaminated bird droppings, including that from poultry, and bat droppings.

Other causes for histoplasmosis include:

• Diarrhea and anemia — may be a severe hookworm infection
• Enlarged liver, spleen or lymph nodes — consistent with lymphoma
• Respiratory problems — may be distemper, bacterial pneumonia, or heart disease

Diagnosis

A chemical blood profile, complete blood count, and urinalysis will be conducted. While blood tests may confirm the presence of histoplasmosa antibodies, this only means that your dog has been exposed to the fungus, and not necessarily that the dog is in a diseased state as the result of exposure. Further differential testing will confirm or rule out the actual state of histoplasmosis.

In order to settle on the correct course of treatment, your veterinarian will want to differentiate the symptoms of histoplasmosis from the syptoms of other diseased conditons. Severe chronic diarrhea and weight loss can indicate a variety of conditions for dogs, including lymphocytic plasmacytic enteritis, eosinophilic enteritis, lymphoma, chronic parasitism, and exocrine pancreatic insufficiency.