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Blastomycosis is a serious systemic fungal disease that primarily infects dogs and people. While there have been reported cases in a variety of animals including cats and horses, they are relatively rare. Dogs are 10 times more likely to develop the disease than people are. A big factor in determining which dogs get infected is directly related to their lifestyle and where they live.

Risk factors include living or spending time near water, disturbing the soil during excavation, construction, or gardening. Dogs that dig increase their risk, hunting dogs and hounds are infected much more frequently than house pets and younger dogs are more commonly infected, with the highest prevalence seen in 2-year-old dogs. But any dog can contract blastomycosis.

Blastomycosis is caused by a microscopic fungus that lives in sandy soil in close proximity to water and periodically releases invisible spores into the air, which dogs, other animals and people can inhale. Conditions must be perfect for the fungus to survive. The fungus occurs more frequently in the fall around wetlands and waterways, but it can occur in urban and suburban areas, too. The spores can travel in the wind for at least half a mile.

Blastomycosis cannot be transmitted from an infected animal to a healthy animal or from an animal to a person, it can only be acquired from inhaling the spores in the soil.

Blasto can be found in the Upper Midwest, Mid-Atlantic, Southeastern states, and in the Ohio, Missouri and Mississippi River valley and parts of Quebec, Manitoba, and Ontario. Blastomycosis is often found in small pockets instead of being widespread. It is believed that the range of blastomycosis continues to grow. I have seen several cases of Blastomycosis in Central IL where I live by the Vermillion River.

Symptoms Of Blastomycosis

Infection occurs from the dog inhaling the spores that are found in the soil. Blasto can infect multiple organs and produce various symptoms. At body temperature, the spores turn into yeasts and infects the lungs. Once Blastomycosis establishes itself in the lungs, it then enters into the bloodstream, blasto will spread to the skin, bones, joints, lymph nodes, kidneys, eyes or brain. Dogs show symptoms within a few weeks to a few months after inhaling spores. Symptoms include:

  • Loss of appetite
  • Weight loss
  • Persistant fever
  • Cough
  • Shortness of breath
  • Open sores or lumps that drain blood or pus
  • Blood in urine
  • Pain in a limb or joints, lameness
  • Cloudy, bulging, or red painful eyes
  • Enlarged lymph glands
  • Seizures or other signs of brain infection

Up to 85% of dogs with blastomycosis have lung lesions and an accompanying dry, harsh cough. Forty percent of dogs with blastomycosis have eye lesions including uveitis, retinal detachment, and hemorrhaging into the eye. Skin lesions that are ulcerated and draining are found in 20 to 40% of the infected dogs. Bone involvement and resulting lameness is present in about 30% of infected dogs.

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Treatment for Blastomycosis

Relatively few animals are exposed and infected with blastomycosis, but those that are require treatment. There are several treatment options. The most common treatment is the oral administration of the antifungal drug Itraconazole. This drug usually needs to be given daily for 60 to 90 days. It is a human drug and can be very expensive, particularly for a large dog, but it is currently the safest and most effective way to treat blastomycosis.

For dogs that can not tolerate or do not respond to Itraconazole, the injectable drug Amphotericin B can also be used. This drug is given intravenously several times a week. Because it is more toxic than Itraconazole, it is administered under close veterinary observation.

Ketoconazole (Nizoral) is occasionally used in milder cases where cost is a strong consideration. It is not as effective and is slightly more toxic than Itraconazole, and therefore, is not usually the first choice in treatments.

Most animals will have severe appetite loss and must be encouraged to eat or be force fed the first 7-14 days. Blastomycosis can be rapidly fatal if not diagnosed and treated promptly. Even with proper treatment, many dogs do not recover from the infection and relapses can occur.