Water Mold Infection (Pythiosis) in Dogs

Pythiosis is a disease caused by the pythium insidiosum water mold, or oomycete. It is generally contracted from swamps and other shallow standing water sources, particularly in climates where the water doesn’t freeze over. It can infect your pet either by ingestion or by contamination of a cut or wound in the skin. Pythium infestations are often fatal and timely diagnosis is vital in stopping further damage. Excision and possible amputation followed by aggressive therapy is usually the recommended course of action.

The water mold Pythium insidiosum can infect your pet, usually through contact with standing water. Pythiosis is a fungus-like organism called an oomycete and can be difficult to treat.

Symptoms from pythiosis will vary depending on the method of the infection. If the Pythium insidiosum water mold was ingested your pet is more likely to exhibit gastrointestinal disorders, whereas if the mold was introduced to the skin through a cut or wound the symptoms will be more centered around the skin.  

• Abdominal mass
• Blood in feces
• Bloody, pulpy skin lesions
• Chewing or scratching at lesions
• Chronic and progressive diarrhea
• Excessive drooling
• Lethargy
• Nodule, plaques, or ulceration on skin
• Vomiting 
• Weight loss

Types

Phycomycosis are a collection of diseases which can be caused by a number of different water molds and fungi. Pythiosis is the most common form of this disease in dogs. This disease is more common in dogs and horses, but other mammals can be infected. Some strains can infect humans as well but pythiosis is not transmissible between hosts. Other common phycomycosis varieties can include lagenidiosis and zygomycosis. 

Lagenidiosis

• Caused by a water mold of the Lagenidium species
• Lagenidiosis is similar in most respects to pythiosis, however, there is a higher incidence of multi-organ involvement with lagenidiosis

Zygomycosis

• This disease is caused by a bread mold rather than a water mold
• Usually infections from fungi in the class Zygomycetes invade the animal subcutaneously or in the nasal tissue
• It generally presents as localized chronic infections of the skin and nasal area, however, immunocompromised individuals with this infection may have a much more rapid and intense reaction

Pythiosis is caused by exposure to the water mold pythium insidiosum, either by ingesting it or by infection through a break in the skin. This mold resides mostly in environments with mild winters as it lives mainly in swamps and other forms of shallow standing water, and it cannot survive freezing. In the United States most cases of pythium infection are found in the warm gulf states such as Florida and Louisiana. Hunting dogs used to retrieve game birds are at increased risk of developing pythiosis as they are often hunting in areas with a great deal of standing water.

Your veterinarian will want to get the medical history of your pet and will most likely ask you questions regarding exposure to outdoor plants, water or animals. A physical examination will also take place and any recent weight loss will be noted. The veterinarian performing the examination may also feel a mass in the abdominal area of the affected animal. A sample of any masses may be taken for further examination and a complete blood count, biochemistry profile, and urinalysis are also likely to be done. Routine tests often fail to detect pythiosis as the organism is not actually a virus, bacteria or fungus, but rather an oomycete. Biopsies can also be difficult to culture, but will narrow the diagnosis down to one of several types of organism. Your veterinarian is likely to get a definitive diagnosis by testing of the serum for pythiosis antibodies or by polymerase chain reaction (PCR).

The treatment of choice for pythiosis is the aggressive surgical removal of any lesions. As there is a high rate of reoccurrence it is essential for your veterinarian to get all of the infected tissue. Wide margins will be given to any excised tissues. This applies to lesions on the skin or lesions encountered internally. Due to the severity of the disease if the lesions are found on only one extremity, the removal of the entire limb may be recommended to prevent the spread of the mold. Surgical excision and even amputation are no guarantee against this organism and surgery is generally followed by additional treatment methods. Immunotherapy may be attempted as this has had some success in treating pythiosis in humans and horses however the efficacy for dogs is much poorer. Chemotherapy may also be recommended to prevent the return of the oomycete. Canines tolerate chemotherapy better than humans in most circumstances. Only around 5% require hospitalization from the treatment itself. Hair loss is also less reported in dogs than in people, but some breeds (English Sheepdog, Lhasa Apso, Maltese, Schnauzer, Shih Tzu, and Poodle) are more prone to hair loss than others. Even with aggressive treatment pythiosis is often fatal.

After any surgical procedure it is important to keep the surgical site clean and free from dirt or debris. You will also need to keep your pet from interfering with the stitches or bandages, and examine the site for swelling, bleeding or pus, and to ensure that the stitches are intact. Complications from chemotherapy can occur and your veterinarian will want to do regular checks on your dog’s liver and kidney enzyme levels. Pets are often sent home the same day after chemotherapy, and though most of the drug is fully metabolized within the first few hours, some remnants of it can remain in the blood for several days. It is important to use gloves when dealing with bodily fluids and maintain good handwashing hygiene. Children, pregnant and nursing women and immunocompromised adults should avoid contact with the bodily fluids of an animal that has recently undergone chemotherapy. Your pet should be monitored closely for additional tumors and other symptoms during and after any chemotherapy treatments. Prognosis for pythiosis is poor even with aggressive treatment.