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A rare but emerging infectious disease is sparking concern for dog owners. Pythiosis, a disease caused by an algae-like fungal organism called Pythium insidosum, can make dogs extremely sick. There are two types of pythiosis that can occur in dogs, one more common than the other. Being aware of where, why, and how pythiosis can be contracted can help you keep your pet safe and healthy.

Pythium insidiosum thrives in ponds, swamps, wetlands, and bayous. It’s most prominent in the fall and early winter. Dogs typically contract pythiosis through swimming, wading in, or swallowing infected water. The pythium zoospores in the water may also enter the dog’s system through small cuts on their paws or skin.

The fungus has been identified in parts of California, Arizona, and Wisconsin, but is most commonly found in swampy areas of the southeastern United States.

Here’s what to know about pythiosis in dogs, including signs, symptoms, treatment, and prevention.

Irish Water Spaniel wearing a harness standing in a field off leash.
Julie Morrish/Shutterstock

What Are the Symptoms of Pythiosis in Dogs?

There are two forms of pythiosis: gastrointestinal and cutaneous. According to AKC Chief Veterinarian Dr. Jerry Klein, dogs more commonly contract gastrointestinal pythiosis. Any dog breed can develop pythiosis, but most dogs that are affected are young, and are often hunting or sporting dogs. It’s important to note that affected dogs often don’t show symptoms until they’ve been infected for a long time. Dogs with pythiosis may display the following symptoms:

Gastrointestinal Pythiosis

According to Dr. Klein, this form of pythiosis affects dogs’ digestive tract and causes the tissues of the stomach and intestines to thicken, causing obstruction. Symptoms to look for include:

  • Wasting (Involuntary weight and muscle loss)
  • Fever
  • Vomiting
  • Diarrhea (often containing blood)
  • Trouble defecating
  • Abdominal pain
  • Enlarged lymph nodes

AleksandarNakic/Getty Images Plus

Cutaneous Pythiosis

Cutaneous pythiosis develops as lesions on dogs’ bodies, generally on the legs, tail, head, neck, rectal area, or thigh. Lesions are often itchy, and dogs can hurt themselves by scratching them.

“These swollen ulcerated pus-filled lesions appear on the dog’s skin as invasive masses of non-healing nodules,” Dr. Klein notes. “The tissue can then become necrotic with the affected skin eventually turning black and sloughing.”

Diagnosing Pythiosis in Dogs

There are two tests that your veterinarian may order for diagnosing pythiosis. One is a blood test, the other is a biopsy.

The blood test, known as a Pythium insidiosum ELISA test, will test for antibodies in the dog’s blood, indicating exposure to the fungal organism. The second test requires a biopsy sample obtained from skin lesions or abdominal masses, depending on the type of pythiosis.

Bulldog puppy getting a check-up at the vet.
©mutluproject -

Treating Pythiosis in Dogs

There are limited treatments for gastrointestinal pythiosis. Prognosis is usually poor, especially if there’s no early intervention.

Hospitalization may be necessary for dogs actively infected with pythiosis. Dr. Klein explains that dogs with pythiosis will typically have the affected tissue surgically removed. In some cases, amputation may be necessary. Following removal of the tissue, dogs may be prescribed a lengthy protocol of antifungal medication. These treatments can last from 3 to 6 months, to reduce risk of recurrence.

Antifungal treatments are lengthy, and can cause severe side effects. The medications could cause severe liver and kidney damage. Regular blood tests throughout treatment are a necessity. Abdominal ultrasounds are also beneficial in monitoring intestine health during pythiosis treatment.

Excessive weight loss typically occurs in pythiosis. It’s important for dogs to receive high calorie, easily digestible food to counteract this. This will also help aid in the recovery process.

Dr. Klein notes that immunotherapy work is being conducted for pythiosis in horses. Currently, there aren’t conclusive positive results for dogs.

Preventing Pythiosis in Dogs

Entlebucher Mountain Dog jumping into a lake.
©Evdoha -

Knowing the signs and symptoms of pythiosis in dogs is also crucial as this disease continues to emerge across the United States.

Dr. Klein would recommend that dog owners take measures to keep their pets away from areas infected with spores of the fungal organism. Swamps, bayous, ponds, and wetlands are considered high-risk areas. They’re ideal breeding grounds for pythiosis.

In hopes of helping vets consider a diagnosis of pythiosis, Dr. Klein also suggests using a journal to track when and where your dog could have been exposed to these environments.

If your dog exhibits any signs of pythiosis, tell your veterinarian right away. These include chronic wasting along with vomiting or diarrhea, or if they have lingering, non-healing wounds. Time is of the essence in diagnosing and treating pythiosis, so it’s important to act quickly.

This article is intended solely as general guidance, and does not constitute health or other professional advice. Individual situations and applicable laws vary by jurisdiction, and you are encouraged to obtain appropriate advice from qualified professionals in the applicable jurisdictions. We make no representations or warranties concerning any course of action taken by any person following or otherwise using the information offered or provided in this article, including any such information associated with and provided in connection with third-party products, and we will not be liable for any direct, indirect, consequential, special, exemplary or other damages that may result, including but not limited to economic loss, injury, illness or death.
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