Sometimes called swamp cancers, species of the Pythium genus are parasitic water molds. Of the around 200 species of Pythium pathogens, Pythium insidiosum is the only one that causes disease in animals. The rest of these pathogens affect only plants or fish. Pythiosis is relatively rare but is becoming increasingly more common in dogs and horses. This disease is most often seen in those two animals but also affects cats, cattle, captive polar bears and humans.
Two types of Pythiosis affect dogs. The most serious type, canine gastrointestinal pythiosis, infects the bowel, causing it to thicken and swell. Large abdominal masses are the result of this condition, which often ends in loss of bowel tissue. The other type effects the skin of the dog and is called cutaneous pythiosis. This form causes lesions to form on the perineal area, the legs, abdomen and face. These lesions eventually turn black and rot.
Pythium insidiosum thrives in wet environments and grows fastest during rainy seasons. Dogs who drink warm standing water get the disease, but they can also catch it simply by walking through wet grass or eating wet grass. The spores enter the body through the digestive tract and through open wounds. Certain kinds of dogs are more susceptible to the disease. German shepherds, Cavalier King Charles spaniels and Labrador retrievers seem to be the most common victims, especially when young.
The symptoms of canine gastrointestinal pythiosis are quite serious and include vomiting with or without visible blood, diarrhea, blood in the stool, lethargy, appetite loss, weight loss, fever, enlarged lymph nodes and large abdominal masses. The symptoms of cutaneous pythiosis are outwardly visible and painful for the dog; they include wounds that swell, become infected with pus and don't heal. These sores are the result of abscesses in the skin that cause tissue to rot.
A variety of treatments are available, the most effective being immunotherapy and antifungal medications. Surgical removal of lesions and infected tissues is effective if the entire infection is removed; otherwise, it returns. Typically, the antifungal and immunotherapy treatments immediately follow surgery to prevent the disease symptoms from recurring. The best treatment involves boosting the animal's own immune system to help him fight off the infections with immunotherapy vaccines.
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