Pythiosis (Water Mold Infection) in Dogs

dog in lake

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Pythiosis (otherwise known as water mold infection) is a rare fungal infection caused by the aquatic mold Pythium insidiosum that occurs in dogs. It is generally contracted when animals with open sores drink, stand, or swim in stagnant contaminated water.

What Is Pythiosis?

Pythiosis, sometimes called Water Mold Infection or Swamp Cancer, is a fungal infection caused by an organism called Pythium insidiosum. While not a true fungus, P. insidiosum is a type of water mold. It is characterized by gastrointestinal signs and/or dermatological signs and can be life threatening. It is contracted when a dog swims in contaminated water and/or drinks contaminated water and not only effects dogs. Cats, horses, cows, and even people can succumb to Pythiosis as well. 

Signs of Pythiosis in Dogs

  • Fever
  • Regurgitation
  • Long-term weight loss
  • Abdominal masses/pain
  • Enlarged lymph nodes

The most common sign seen in dogs that contract Pythiosis is extreme weight loss. This is usually is due to vomiting and diarrhea that is also caused by the disease process. Pythiosis can also effect the skin, though, causing ulcerative, draining lumps and fistulas that never seem to completely heal. These are typically located on the legs, abdomen, chest, face, and/or tail. Depending on the degree of inflammation associated with the nodules, the areas may either be a bit spongy feeling or quite firm to the touch.

Diagnosing Pythiosis

Many cases of Pythiosis don't ever develop clinical signs until the dog has been infected for a long time. This makes it difficult to diagnose based solely on a patient history of recently swimming in a pond. Instead, your vet may want to run various lab tests to check for signs of infection. If your dog has skin lesions, your vet will want to obtain samples to look at under the microscope. An ultrasound will allow your vet to visualize your dog's intestines and check for any abnormalities in the thickness and integrity of the intestinal walls. An intestinal biopsy will definitively show the presence of P. insidiosum. A full blood chemistry panel will check the organ function of your dog to ensure there is no systemic infection. There are also specialized blood tests that can check for the presence of the organism. The genera Pythium as whole is difficult to culture as it doesn't grow very well on the routine fungal culture media and bacterial contamination that can skew results is common.

Treating Pythiosis

It should be noted that a prognosis of pythiosis comes with a guarded to poor prognosis. Antifungals can be used, but less than 10 percent of cases fully recover from medications alone. The only truly curative measure that can be taken is complete surgical removal of any and all infected tissue. For skin lesions, this may involve a limb amputation. Any gastrointestinal involvement gets even trickier. Your vet may try removing pieces of intestine that are infected, but the prognosis is much graver if there is GI involvement. This is because the fungal infection can easily spread from the GI tract to other organs within the abdomen. The more it spreads the more difficult it becomes to completely excise all infected tissue. Again, surgery is not curative if it does not completely cut out all infected tissue.

If your dog only appears to have skin involvement, once all the infected tissue is removed your vet will want to put your dog on a highly digestible, high calorie diet. This will counteract any weight loss your dog suffered. Your vet will also put your dog on antifungal medications for anywhere from 3 to 6 months to help prevent any recurrence. 

What Dogs Are at Risk?

P. insidiosum can live in swamps, bayous, and ponds and is most often reported in the states surrounding the gulf coast. It isn't isolated to this region, though, and has been reported in Oklahoma, Arkansas, Missouri, Kentucky, Tennessee, North Carolina, South Carolina, New Jersey, Virginia, California, and Arizona. Additionally, cases have also been reported in Australia, Brazil, Burma, Columbia, Thailand, and Japan. Typically young, male retriever-type dogs are more at risk, but any water loving dog can be susceptible to infection. Dogs with open wounds may also be more at risk for infection. It does appear to be a seasonal infection, though, as most cases are reported between August and December.

Pythiosis can be a very serious concern for you and your dog. Preventing your dog from swimming in and drinking unclean, stagnant water is the best way to protect your dog from contracting this infectious water mold.