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Blastomycosis

By Mike Aushwitz, D.V.M. - Kuenzi Family Pet Hospital, Waukesha, WI


Dr. MikeBlastomycosis refers to a fungal disease caused by Blastomyces Dermatitidis. The organism is acquired most commonly through the respiratory tract by inhalation of fungal spores, though inoculation of an open wound can also lead to infection, but much less commonly. The fungus seems to prefer rich, moist soil, though researchers have great difficulty isolating it from the environment. Wisconsin has many cases of Blastomycosis reported, many from Northern Wisconsin and along major river systems, though any rich, moist soil seemingly can harbor the organism. The Ohio and Mississippi River Valleys and South Eastern United States also have a significant prevalence of the disease.

After inhalation, the fungal spores have a morphological change to a yeast organism, which then can disseminate throughout the body. This explains the common systems of Blastomycosis which include Pneumonia, draining skin lesions, enlarged lymph nodes, chorioretinitis (blindness), osteomyelitis (lameness), and meningitis (neck pain, seizures). Most individuals are depressed, not eating, and run a fever.

Diagnosis of this disease can be a challenge. The gold standard test to date is positive identification of the organism via cytology of a sample from the animal. Occasionally, it may be found on a biopsy sample of a piece of tissue submitted to a pathologist. There are less reliable blood tests available that show previous exposure, but do not equate to current infection.

Prognosis depends on the extent of infection. This most certainly can be a fatal infection. Treatment involves antifungal medications that are effective if the disease is not too advanced. Several months of therapy are generally required. The medication is quite expensive. In case of eye infection, the eye may need to be removed if it is unsighted or if it is serving as a source of reinfection. If the brain is involved (meningitis) prognosis is worse as the drug does not penetrate the natural brain barrier very well.

Dogs by their nature are most susceptible to infection, though cats can also get the disease. People can also acquire this disease, though not from their infected pet. The fungal spores seem to be required to cause infection, therefore, the yeast form in an infected animal does not seem to be contagious to other animals or people. Nothing can really be done to prevent the infection, due to the ubiquitous nature of the organism. In the future, a vaccine may be developed which could block the progression of the disease after initial infection.

Reprinted by permission of Kuenzi Family Pet Hospitial from the November 2001 Newsletter.