What is Histoplasmosis?

Histoplasmosis is a disease caused by a fungus named Histoplasma capsulatum. It can attack both dogs, cats and humans, and is also known as Darling's disease. Histoplasma capsulatum is found all over the world. In the United States, it is endemic to regions around the Mississippi River and the Ohio River Valley. It has for instance been found in bird litter and caves where bats live.

In low temperatures, Histoplasma capsulatum will grow as a brownish mycelium. When it is placed a body temperature, e.g. by infecting a dog, it will turn into yeast and cause disease.

Histoplasmosis symptoms in dogs

Dogs normally get Histoplasmosis by inhaling the fungi spores, and the lungs will then be the location for the primary infection. If Histoplasma capsulatum is eaten, the gastrointestinal tract of the dog can become the primary site of infection. From the primary site of infection, the organism can enter the bloodstream and spread throughout the body. It can for instance settle down in the eyes or in bone marrow.

Histoplasmosis symptoms in dogs varies depending on which organs that have become infected by the fungus. The dog can for instance develop lymphadenopathy, hepatomegaly, splenomegaly, or nasopharyngeal ulceration. The dog can also start coughing, lose weight, and suffer from persistent diarrhoea, anaemia and fever. GI ulceration have also been reported. Tracheobronchial lymphadenopathy can lead to breathing problems. If the skin is infected, nodular, ulcerated lesions that weeps can occur. Dogs with disseminated Histoplasmosis (when the Histoplasma capsulatum has spread from the original infection site) can also show retinal detachment, chorioretinitis and polyarthropathy.

In its acute stage, Histoplasmosis can be lethal for dogs within 2-5 weeks.

Histoplasmosis prevention for dogs

Since Histoplasma capsulatum is found all over the world and in many different environments, it is hard to prevent your dog from ever encountering it. Testing the environment or trying to kill off the fungi is rarely a feasible solution. You can however try to make your dog stay away from especially dangerous sites, such as spots where a lot of bird or bat droppings are found. Histoplasma capsulatum is known to occur in high levels in poultry houses, spots where litter from poultry houses are dumped, caves and other homes for bats, and in bird roots, especially if the birds in question are starlings. 

When a dog has successfully combated a Histoplasmosis infection, it will receive a partial protection against ill effects of re-infection. 

Histoplasmosis treatment for dogs

One of the most commonly used Histoplasmosis treatments for dogs are 10mg of Itraconazole per kilogram bodyweight each day. If the Histoplasmosis infection is mild or if treatment is started at an early stage, Ketoconazole is an alternative for the dog. The normal Ketoconazole dose is 10-15 mg per kilogram bodyweight and day, administered during 4-6 months. In severe Histoplasmosis cases, Amphotericin B or Amphotericin B lipid complex can be necessary to cure the dog, sometimes followed by a long Itraconazole treatment.

If the dog has been infected with Histoplasmosis but show no symptoms, the vet will normally abstain from treatment.

Fungal Infections in dogs: (click for more info)
Blastomycosis in dogs
Cryptococcosis in dogs
Histoplasmosis in dogs
Phycomycosis in dogs
Pythiosis in dogs
Ringworm in dogs
Sporotrichosis in dogs