Phycomycosis is an uncommon condition of the gastrointestinal tract and skin most commonly found in dogs and horses. The condition is caused by a variety of molds and fungi, and individual forms include pythiosis, zygomycosis, and lagenidiosis. Pythiosis is the most common type and is caused by Pythium, a type of water mould. Zygomycosis can also be caused by two types of zygomycetes, Entomophthorales (such as Basidiobolus and Conidiobolus) and Mucorales (such as Mucor, Mortierella, Absidia, Rhizopus, Rhizomucor, and Saksenaea). The latter type of zygomycosis is also referred to as mucormycosis. Lagenidiosis is caused by a Lagenidium species, which like Pythium is a water mould. Since both pythiosis and lagenidiosis are caused by organisms from the class Oomycetes, they are sometimes collectively referred to as oomycosis. Pythiosis Pythiosis is caused by Pythium insidiosum and occurs most commonly in dogs and horses, but is also found in cats, cattle, and humans. In the United States it is most commonly found in the Gulf states, especially Louisiana, but has been found in midwest and eastern states. It is also found in southeast Asia, eastern Australia, New Zealand, and South America. Pythiosis occurs in areas with mild winters due to the organism surviving in standing water that does not reach freezing temperatures. Pythium occupies swamps in late summer and infects dogs who drink water containing it. The disease is typically found in young, large breed dogs. It is suspected that pythiosis is caused by invasion of the organism into wounds, either in the skin or in the gastrointestinal tract. The disease grows slowly in the stomach and small intestine, eventually forming large lumps of granulation tissue. It can also invade surrounding lymph nodes. Symptoms include vomiting, diarrhea, depression, weight loss, and a mass in the abdomen. Pythiosis of the skin in dogs is very rare, and appears as ulcerated lumps. Primary infection can also occur in the bones and lungs. In horses, subcutaneous pythiosis is the most common form and infection occurs through a wound while standing in water containing the pathogen. The disease is also known as leeches, swamp cancer, and bursatti. Lesions are most commonly found on the lower limbs, abdomen, chest, and genitals. They are granulomatous and itchy, and may be ulcerated or fistulated. The lesions often contain yellow, firm masses of dead tissue known as kunkers. It is possible with chronic infection for the disease to spread to underlying