Common Fungal Diseases In Dogs : Part 2

FUNGAL DISEASES

Fungi are a large family that includes mushrooms. They live in soil and organic material. Many types of fungi spread via airborne spores. Fungus spores, which resist heat and can live for long periods without water, gain entrance to the body through the respiratory tract or a break in the skin.

Fungal diseases can be divided into two categories. There are fungi that affect only the skin or mucous membranes, such as ringworm and thrush. In the other category, the fungus is widespread and involves the liver, lungs, brain, and other organs, in which case the disease is systemic.

Systemic fungal diseases are not common in dogs. They tend to occur in chronically ill or poorly nourished animals. Prolonged treatment with steroids and/or antibiotics may also change the dog’s pattern of resistance and allow a fungal infection to develop. Suspect a fungus when an unexplained infection fails to respond to a course of antibiotics.

Good hygiene is important when handling and caring for a dog with any fungal infection. The risk to humans is low, but these are difficult diseases to treat.

CRYPTOCOCCOSIS

This disease, caused by the yeastlike fungus Cryptococcus neoformans, is acquired by inhaling spores found in soil contaminated by bird droppings, especially those of pigeons. In dogs, cryptococcosis involves the brain, eyes, lymph nodes, and skin. About 50 percent of the dogs with this fungus will also show respiratory signs. Signs of brain involvement are an unsteady gait, pressing the head against a hard surface or standing with the head up against a wall, circling, seizures, blindness, and dementia. Involvement of the inner structures of the eyes leads to blindness.

In the less common form that infects the skin, cryptococcosis produces firm nodules, primarily in the head area, that ulcerate and drain pus. The diagnosis is made by fungal culture and/or tissue biopsy. A cryptococcus latex agglutination test is available.

Treatment: 

Oral antifungal drugs of the imidazole group are partially effective when started early in the course of the disease. The response is uncertain and treatment is prolonged. Overall, the prognosis for dogs is guarded to poor.

BLASTOMYCOSIS

This systemic fungal disease occurs along the eastern seaboard, in the Great Lakes region, and the Mississippi, Ohio, and Missouri River valleys. The fungus is associated with moist, rotting organic debris protected from sunlight and enriched with bird droppings, particularly those of pigeons. The disease is acquired by inhaling infected spores. Dogs are considerably more susceptible to blastomycosis than are humans.

Most cases of acute canine blastomycosis involve the respiratory system and cause bronchopneumonia. About 40 percent of cases involve the eyes and skin, producing signs similar to those of cryptococcosis. Weight loss and lameness may also be noted. 

Microscopic identification of organisms in transtracheal washings or in fluid aspirated from infected tissues is the most efficient way to make the diagnosis. In difficult cases, biopsy and culture may be needed. Serologic tests also are available.

Treatment:

A combination of amphotericin B and one of the imidazoles appears to offer the best chance of successful treatment . Months of treatment are required, and some dogs may relapse months to years later.

SPOROTRICHOSIS 

This is a skin and subcutaneous infection acquired by contact with spores in the soil. The spores gain access through puncture wounds caused by thorns and splinters; therefore, the disease is seen most often in hunting dogs. Most cases are reported in the northern and central portions of the United States, especially along coastal areas and river valleys.

A nodular, draining, crusted sore forms at the site of the skin wound, usually on the trunk or head. There may be several small firm nodules in the lymph glands that form a chain beneath the skin. On rare occasion the disease becomes systemic and spreads to the liver and lungs. The outlook for these dogs is guarded.

The diagnosis is made by removing a piece of tissue and examining it under the microscope; or more conclusively, by growing the fungus in culture. A fluorescent antibody test can be performed on infected tissue or serum.

Treatment:

Response is excellent when the infection is limited to the skin and surrounding tissues. Potassium iodide (a saturated solution) has been used, but care must be taken due to possible toxicity. Antifungals of the imidazole group are therefore the agents of choice. Treatment needs to be continued for a month after clinical signs are resolved.