PYTHIOSIS – A New Canine Disease

    Pythium Insidiosum is a fungal like organism that infects several species including dogs and causes death in the vast majority of cases.   Pythium infections are essentially non responsive to antibiotic or antifungal treatments and surgical resection of lesions saves only 20-25% of infected animals.  The incidence of Pythium infections in dogs is not known, but the number of confirmed cases has risen dramatically in the last 5 years. Cases in the U.S. have gone from less than 10 a year just 5 years ago to more than 100 cases per year. Experts in the field estimate that 200-300 cases of canine pythiosis will be confirmed in 2008, and many more cases will be undiagnosed or misdiagnosed.

     Additionally, the number of animals exposed to Pythium is not known.  Since Pythium is more commonly found in warm wet environs, it may be assumed that dogs that frequent these environs are more likely to be exposed making Field Trial retrievers prime candidates for exposure.  It is believed that dogs that have had significant exposure to Pythium Insidiosum will have developed Pythium specific antibodies.  These antibodies are easily detected via a simple blood test.  In an effort to estimate the number of animals which have come in contact with Pythium Insidiosum, Pan American Vet labs is conducting a serologic survey of dogs which compete in Field Trial competitions.  PAVL is providing a free blood test for Pythium antibodies when samples are submitted with the attached survey data sheets which have been completed. Test results will be immediately provided to the submitting party (owner/vet) and complete survey data will be provided when the survey is complete. 

    In order to do the blood test 3-5 ml of blood in a red top tube or 1-2 mls of serum should be submitted to the PAVL diagnostic laboratory at the following address. Please complete the attached form. Click this link for form!

Pan American Veterinary Labs

166 Brushy Creek Trail
Hutto , TX 78634
Phone: 800.856.9655
Fax: 512-846-2140







Complete Pythium Details

The genus Pythium comprises about eighty-five species. Pythium species are common pathogens causing disease in plants and fishes. The species of this genus are among the most destructive plant pathogens, inflicting serious economic losses of crops by destroying seed, storage organs, roots, and other plant tissues. Pythium Insidiosum is the only species reported to cause infections in mammals. The disease caused by this unique microorganism has been termed pythiosis and causes life threatening infections in cats, dogs, cattle, equines, captive polar bears, and humans. This disease is also known as Phycomycosis, “Florida Horse Leeches”, Swamp Cancer and other colloquial names.  The disease is worldwide in distribution and is especially prevalent in tropical regions.

Pythium propagates by producing motile Oospores which travel through standing water and infect new hosts.  Oospores which come in contact with susceptible animals may invade via breaks in the skin or the intestinal mucosa and set up infection.    

Canine pythiosis presents as cutaneous or subcutaneous lesions or as tumor like lesions in the intestinal tract. The fact that dogs frequently drink stagnant water and eat grass that may contain elements of P. Insidiosum explains the high number of intestinal pythiosis cases in canines. 

The cutaneous and subcutaneous lesions are denuded of hair and perforated by fistulous sinus tracts that discharge a serosanguineous exudate. Lesions are often located on the dog’s tail, legs, thorax, and abdomen. The hard stony masses (kunkers) observed in equine pythiosis are not present in dogs with this disease. Microscopic examination shows multifocal areas of necrosis with eosinophils and a moderate number of neutrophils and macrophages. The hyphae of P. insidiosum are found in the center of eosinophilic micro abscesses.

Canine gastrointestinal pythiosis is characterized by vomiting, weight loss, and sporadic diarrhea. Formation of hard gastrointestinal tumor-like masses and areas of thickness and mucosal ulceration are common. The infection may spread to adjacent tissue such as pancreas, uterus, and mesenteric lymph nodes. Histopathology examination of the mucosa shows ulceration, atrophy, and hyperplasia. Eosinophils, plasma cells, macrophages, epithelial cells and giant cells are detected in infected tissues.

In the past diagnosis of Pythiosis was difficult as the symptoms mimic several unrelated disorders and the hyphae of P. Insidiosum are difficult to detect in histopathology exam unless Silver stain or other special stains are employed. Now, however, diagnosis of Pythiosis is quickly and easily accomplished via a simple blood test which detects Pythium specific antibodies in the blood of the patient.  This test has demonstrated greater than 90% sensitivity and specificity for detecting infected animals.

Traditional treatment options for Pythium infected dogs include surgical resection of infected tissues and antifungal medications.  Overall success when using one or more of these treatment options is only +/- 25%.  Recently the USDA has approved an Immunotherapy treatment product.  This product consists of purified proteins derived from Pythium Insidiosum.  These proteins are injected into the infected patient in an effort to elicit an immune response which will kill the invading Pythium.  In horses this treatment is successful in >90% of cases, however, in canine cases the success rate is nearer 50%.  Work continues on a new version of this product which will demonstrate a higher success rate in dogs.

Please help us in this quest to study and understand this disease and create a more effective treatment.


Bob Glass


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