Blastomycosis

Funguses (also called fungi) are parsitic spore-producing organisms. They obtain their nourishment by absorbing food from the hosts on which they grow. Many species of fungus exist in the environment, but only a very few cause infections. The primary source of most infections is soil. Some fungal infections can cause disease in otherwise healthy animals. The infection may be localized or may infect the entire body (systemic or generalized).

Systemic fungal diseases cause significant morbidity and mortality in dogs and cats. Blastomycosis, histoplasmosis, coccidioidomycosis, and cryptococcosis represent the four most common systemic fungal diseases. Young adult, large breeds generally are predisposed; cats usually do not have predictable predispositions. Intact cell-mediated immunity is essential to initial resistance to infection and response to treatment in animals.

Blastomycosis is one of the most common systemic fungal diseases in dogs in North America, but it is rarely diagnosed in cats. Blastomycosis, caused by Blastomyces dermatitidis fungus, exists in 2 different forms: a mycelial form (this form is present in the environment and is contagious)and yeast (this form is found in the tissues and is not contagieous). The mycelial form of blastomycosis can easily infect both humans and animals.

Young male dogs, especially hunting dogs, are at increased risk because of the increased contact with the contaminated soil. In dogs, blastomycosis most commonly affects the lungs. Dogs with cardiovascular involvement may have abnormalities in electrical conduction and valvular function, and may have a worse prognosis.

The typical route of infection is inhalation of Blastomyces. From the respiratory tract, the developing yeast form may spread throughout the body and affect multiple organ systems, most commonly the lymphatic, skeletal and central nervous systems, eyes and skin. Disseminated (systemic or generalized) disease often is associated with nonspecific signs of illness including lethargy, loss of appetite and fever, as well as signs referable to specific organ systems like chronic cough and difficulty breathing, eye problems and central nervous signs.

Diagnosis Diagnosis is typically made by detection of Blastomyces dermatitidis yeast in affected tissues. In experimental studies, a competitive binding inhibition enzyme linked immunosorbent assay (ELISA) is used to detect Blastomyces dermatitidis antigens in urine specimens from dogs with blastomycosis. Blastomycosis may be aggressive and require treatment. Dissemination from the lung is not unusual and can involve any organ. Diagnosis is often delayed because blastomycosis can mimic many other disease processes, including bacterial pneumonia and malignancy.

Treatment The treatment of choice is itraconazole. The administration of systemic corticosteroids may help to preserve the vision in a majority of dogs with ocular blastomycosis.

Dogs are the source of a wide range of zoonotic infections that pose a significant threat to human health. This is particularly the case for immuno-compromised people. Pathogenic bacteria and organisms (for example, Salmonella, Campylobacter and Cryptosporidium species, that may be dog derived) are a frequent risk to the health of immunocompromised persons. To prevent dangerous bacterial infections, it is highly recommended to maintain a clean personal environment and good hygiene practices.

Source: REf FILE #150:

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