Conditions or ailments that are the cause of a problem that you see - your observation.

Your vet may diagnose

Pythiosis, Florida Horse Leeches

Synonyms: Bursatte, Cutaneous Phycomycosis, Ferida da Moda, Leeches, Gulf Coast Disease, Swamp Cancer


Pythiosis is a severe, invasive fungal infection of the skin in which a fungus (usually found on aquatic plants) invades and infects a pre-existing wound. This causes the wound to develop into an angry, rapidly growing red mass that often oozes a blood-tinged fluid.

Pythiosis is found worldwide in horses but is most common in swampy, tropical climates where the parasite lives in stagnant pools of water. There is some speculation that this infection is on the rise, and is spreading into cooler and drier regions. It mostly occurs summer and fall months.

Areas affected include the lower abdomen, lower limbs and chest, but infections can occur anywhere on the body. This infection can look like other deep fungal infections, non-healing wounds, or skin cancer. Left untreated, these lesions become large and ugly masses of angry, red tissue. Horses tend to bite or kick at the sores.

Diagnosis requires biopsy for confirmation. In areas where the condition is common, diagnosis is often presumed by appearance. A blood antibody test can be used to confirm the diagnosis.

Treatment involves surgical removal or debridement, along with the use of systemic antifungal medications. Pythiosis can be difficult and costly to treat.

my vet's role


Guarded to good with prompt treatment, which is aggressive surgical removal that may require anesthesia.

Fair to grave if the lesions are near or on critical structures such as tendons and joints, because surgical removal may be more difficult.

Poor for large lesions that have become well established. It can be a difficult condition to treat successfully and in some cases may cause disfiguring scars.

Related References:

Lavoie JP, Hinchcliff KW eds. Blackwell's 5 Minute Vet Consult: Equine. 2nd Ed. Ames: Wiley Blackwell 2008.

Author: Doug Thal DVM Dipl. ABVP