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Pythiosis (Phycomyosis or Swamp Fever) in Dogs

By: Dr. Bari Spielman

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Pythiosis, also known as Swamp Fever and Phycomycosis, is an infectious disease affecting primarily the gastrointestinal tract or skin of dogs and cats. The causative organism is Pythium insidiosum, a fungus that is in a class similar to yellow-green algae.

Pythiosis is seen more commonly in dogs than cats. Large-breed dogs, especially those used in hunting or field trial work near water are at higher risk. Labrador retrievers are most commonly affected with the gastrointestinal form, and German shepherds, the cutaneous (skin) form. Young to middle-aged male dogs are most commonly affected. Those exposed to warm freshwater lakes, swamps and ponds are most commonly affected. Most infections occur in the early spring, fall and winter months.

It is most common in warm humid parts of the country such as the Gulf Coast and Southern United States.

Transmission is by contact with infected spores that penetrate damaged skin or tissue. The organisms grow causing severe tissue damage that may include draining wounds that won't heal and ulcerations. Thickening of the gastrointestinal tissue may be severe and cause complete obstruction.

What to Watch For

Signs may include:

  • Chronic weight loss
  • Eventual emaciation
  • Intermittent vomiting
  • Diarrhea
  • Diarrhea with blood
  • Lethargy
  • Ulcerated (open/bloody) nodular (bumpy) skin lesions
  • Chronic nonhealing wounds (especially on legs, tail head, necks or perineum)
  • Skin masses


  • Baseline tests to include a complete blood count (CBC), biochemical profile and urinalysis are recommended in all patients.

  • Serologic testing, which are blood tests that measure antibodies or the individual's response to an organism or infection, may be helpful in the diagnosis of pythiosis. Very useful and accurate ELISA and immunoblot assay tests are available at Louisiana State University.

  • Definitive diagnosis is dependent on culture of the organism.

  • Radiographs (X-rays) of the abdomen are recommended.

  • Abdominal ultrasound may be helpful in certain cases.

  • Biopsy of the affected gastrointestinal tissue or skin, and isolation of the organism is diagnostic.


  • The treatment of choice is wide surgical excision of the affected area. Unfortunately, due to the advanced stage of disease that is often present, this is not possible.

  • Surgical removal of an intestinal blockage may not cure the disease; however, it may be the only option available to relieve life-threatening signs associated with a GI blockage.

  • Itraconazole (Sporanox®) (an antifungal agent) and terbinafine therapy may be recommended for several months following surgery.

  • Treatment using a Pythium vaccine is sometimes recommend but its success has not yet been thoroughly evaluated.


    Only 1 out of 5 patients respond to medical therapy alone. Prognosis is fair if lesions can be surgically removed. Prognosis is poor if medical therapy is used alone or lesions are not surgically removable.

    Home Care and Prevention

    Administer all medication and diet as directed by your veterinarian. If any change is noted in your pet's condition, notify your veterinarian.

    Unless the lesions are resectable or removable, the prognosis for long-term survival is poor. Minimize environmental exposure; keep your pet indoors if you live near warm, swampy bodies of water.

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