Pythium spp

From Dog
Cutaneous pythiosis in a dog[1]
Intestinal pythiosis in a dog. The mass is adhered to the intestines, pancreas and lymph nodes[2]

Pythium spp are an aquatic oomycete which sometimes causes pythiosis, a dermal or gastrointestinal infection in dogs in tropical and subtropical areas[3].

Infection is acquired through small wounds via contact with water that contains motile zoospores or other propagules (zoospores or hyphae). They subsequently disseminate into the surrounding tissues[4]. Depending on the site of entry, infection can lead to different forms of pythiosis i.e. a cutaneous, vascular, ocular, gastrointestinal and a systemic form, which is rarely seen. The infection is not contagious; no animal-animal or animal-human transmission has been reported so far.

Co-infections with other fungi are common, such as Blastomyces dermatitidis[5].

Species which are pathogenic to dogs include:

  • Pythium insidiosum

Clinically affected dogs often present with fever, ulcerative subcutaneous nodules[6], enteritis and lymphadenitis. In gastric infections, severe segmental thickening of the gastrointestinal tract can occur, leading to weight loss, vomiting, diarrhea, and death[7][8].

In dogs with gastric granuloma formation, blood tests may reveal marked hyperglobulinemia and hypercalcemia due to interference with calcium absorption[9].

Diagnosis is based on cytologic evaluation, histologic examination with special stains, and immunohistochemical analysis of tissues collected antemortem or at necropsy[10]. Histological examination usually reveals areas of necrosis surrounded by a pyogranulomatous infiltrate[11]. Definitive diagnosis requires PCR analysis of submitted samples at a referral laboratory[12].

Treatment can be difficult due to the systemic spread and slow-growing nature of this mycosis.

Debulking of masses is recommended, followed by antifungal chemotherapy.

Drugs such as amphotericin B, itraconazole, ketoconazole or turbinafine[13] for 4 - 6 months are empirically recommended.

Prognosis is guarded in most cases.


  1. PAV Labs
  2. Pereira DI et al (2010) Cutaneous and gastrointestinal pythiosis in a dog in Brazil. Vet Res Commun 34(3):301-306
  3. Chindamporn A et al (2009) Antibodies in the sera of host species with pythiosis recognize a variety of unique immunogens in geographically divergent Pythium insidiosum strains. Clin Vaccine Immunol 16(3):330-336
  4. Gaastra W et al (2010) Pythium insidiosum: an overview. Vet Microbiol 146(1-2):1-16
  5. Connolly SL et al (2012) Dual infection with Pythium insidiosum and Blastomyces dermatitidis in a dog. Vet Clin Pathol 41(3):419-423
  6. Thieman KM et al (2011) Diagnosis and treatment of truncal cutaneous pythiosis in a dog. J Am Vet Med Assoc 239(9):1232-1235
  7. Berryessa NA et al (2008) Gastrointestinal pythiosis in 10 dogs from California. J Vet Intern Med 22(4):1065-1069
  8. Schmiedt CW et al (2012) Treatment of intestinal pythiosis in a dog with a combination of marginal excision, chemotherapy, and immunotherapy. J Am Vet Med Assoc 241(3):358-363
  9. LeBlanc CJ et al (2008) Hypercalcemia associated with gastric pythiosis in a dog. Vet Clin Pathol 37(1):115-120
  10. Supabandhu, JM et al (2008) Isolation and identification of the human pathogen Pythium insidiosum from environmental samples collected in Thai agricultural areas. Med Mycol 46:41-52
  11. Pereira DI et al (2010) Cutaneous and gastrointestinal pythiosis in a dog in Brazil. Vet Res Commun 34(3):301-306
  12. Neto RT et al (2010) Cutaneous pythiosis in a dog from Brazil. Vet Dermatol 21(2):202-204
  13. Hummel J et al (2011) Successful management of gastrointestinal pythiosis in a dog using itraconazole, terbinafine, and mefenoxam. Med Mycol 49(5):539-542