Histoplasmosis in Dogs

German Shorthaired Pointer pointing on the shoreline

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Histoplasmosis is an infection caused by a specific type of fungus. While this is not an extremely common type of infection, dogs in certain parts of the country are at a higher risk for contracting it. Knowing how to prevent a dog from becoming infected, how the infection may affect your dog, and what can be done about histoplasmosis are important for owners with at risk dogs to understand.

What Is Histoplasmosis in Dogs?

Histoplasmosis is an infection of the fungus Histoplasma capsulatum. When a dog inhales spores of H. capsulatum, the spores travel through the trachea and into the lungs. There they multiply and a histoplasmosis infection results. Infections can also occur in the intestines if the dog breathes the spores in through its mouth instead of its nose. If this occurs then the spores can also spread into the bloodstream or lymphatic system. Once in these systems, the infection can continue to spread to major organs such as the liver, skin, spleen and more. This type of whole body infection is called a systemic infection.

Signs of Histoplasmosis in Dogs

  • Fever
  • Weight loss
  • Lethargy
  • Anorexia/lack of appetite
  • Coughing
  • Difficulty/labored breathing
  • Diarrhea
  • Tarry stools
  • Bloody stools
  • Difficulty defecating

The symptoms of histoplasmosis in dogs are varied depending on the severity of the infection and what parts of the body it has infected. Overall, a dog that isn't feeling well will typically have a decrease or lack of appetite and lose weight as the amount of food consumed can't keep up with the calories that are burned from day to day. A decrease in activity will also occur if a dog with histoplasmosis isn't feeling well, especially if it also has a fever.

If histoplasmosis is in the airway, coughing and labored breathing may occur. This is due to the infiltration of the fungal spores in the breathing passages which makes it difficult for air to circulate normally.

If histoplasmosis is in the intestinal tract, symptos related to the digestive tract may be seen. Diarrhea in addition to dark, tarry stools or red, bloody stools are common if H. capsulatum has made its home in the intestines but difficulty passing stool could also occur.

Causes of Histoplasmosis in Dogs

Dogs with high exposure to H. capsulatum spores from warm, moist soil where it thrives can develop histoplasmosis if they inhale the spores. It is often found around rivers and lakes and bird and bat feces are also commonly found in soil infected with Histoplasma capsulatum.

Diagnosing Histoplasmosis in Dogs

Aside from a physical examination and discussion of symptoms that you are seeing in your dog, tests need to be run in order to definitively diagnose histoplasmosis. Blood and urine screening along with X-rays will be performed and if other diseases are ruled out a cytology or histopathology from certain tissues or fluids that may be affected will be done. Occasionally surgery will need to be performed in order to obtain a tissue sample. If the H. capsulatum fungus is seen on these tests then the dog has histoplasmosis.

Treatment of Histoplasmosis in Dogs

Unfortunately histoplasmosis can be fatal in some dogs but with several months of antifungal medications the chances of survival are better than they used to be. Advanced antifungal drugs are now used that are less toxic than the old drugs that were our only options at the time. Dogs that have infections that are limited to their airways typically do better than dogs that have systemic infections. Side effects of the medications can still cause some issues, though, so regular monitoring of blood work and X-rays will be needed as treatment occurs.

How to Prevent Histoplasmosis in At Risk Dogs

Dog owners that live in areas where the soil is kept moist and warm near rivers and lakes should be careful about letting their dogs spend time in and around the shoreline. Areas with at risk dogs include the Mississippi, Ohio, and Missouri river valleys along with the Great Lakes and St. Lawrence seaway regions. Dogs that frequent these areas are more likely to come in contact with H. capsulatum spores.

If your dog is at risk for contracting histoplasmosis, it is best to avoid the soil surrounding these bodies of water. You can also talk to your veterinarian about what you can do to boost your dog's immune system to help its natural defenses.