Fungal Diseases
Fungus diseases may be divided into two groups. In the first group, the fungus affects just the skin or mucus membranes. Examples of this are ringworm and yeast stomatitis. In the second the disease can be widespread, in which case it is called systematic.
Systemic fungal diseases are not common in the dog. They tend to occur in chronically ill or poorly nourished animals. Prolonged treatment with steroids or antibiotics can change the animal's pattern of resistance and allow a fungus infection to get established. Occasionally, a dog in good health can come down with one of the systemic fungal diseases.
Norcardiosis, histoplasmosis, blastomycosis and coccidioidomycosis are diseases caused by fungi that live in soil and organic material. Spores, which resist heat and can live for long periods without water, gain entrance through the respiratory system or through the skin at the site of a puncture. Respiratory signs resemble those of tuberculosis. They are: chronic cough, recurrent bouts of pneumonia, difficulty in breathing, weight loss, muscle wasting and lethargy. Up and down fever may be present.
Fungal disease are difficult to recognize and treat. X-rays, biopsies, and fungal cultures are used to make the diagnosis in systemic cases. A fungus infection should be suspected when an unexplained illness fails to respond to a full course of antibiotics.
Systemic fungus infections do not respond to conventional antibiotics and require intensive veterinary management. Most fungi that cause disease in dogs can also cause illness in man. When the disease is systemic, many times euthanasia is recommended.
The following systemic fungal diseases can occur in the dog:
Norcardiosis, Actinomycosis, Cryptococcosis. These are respiratory or skin infections occurring in dogs often under a year of age. They also affect the lymph nodes, brain, kidney and other organs. Large tumorous masses which discharge material that looks like sulfa granules can appear on the legs or body.
Histoplasmosis. This is a disease caused by a fungus found in the central United States near the Great Lakes, the Appalachian Mountains, and the valleys of the Mississippi, Ohio, and St. Lawrence rivers. Spores are found in soil contaminated by the dung of chickens and other birds, or bats. In the majority of dogs the signs are those of a mild respiratory illness. There is a systemic form which attacks lymph nodes, small intestine and other organs. The principal signs are fever, weight loss, muscle wasting, enlargement of the tonsils and prolonged diarrhea which may become bloody. Do not allow dogs in chicken coops, caves or other places where birds or bats roost.
Blastomycosis. This disease is found in the same geographic distribution as histoplasmosis. The skin form is characterized by nodules and abscesses which ulcerate and drain. The systemic form is similar to histoplasmosis. The disease is difficult to treat and present a hazard to human health.
Coccidiodomycosis. In most dogs this is a mild respiratory infection, but the systemic form can spread to all organs of the body. It is found in dry dusty parts of the southwestern United States and in California. This is not the same disease as coccidiosis, which is spread by protozoan. The signs of systemic illness resemble those in histoplasmosis.