abdominal straining. Extensive weight loss may be evident. Humans In humans, it can cause arteritis, keratitis, and periorbital cellulitis. This has previously been thought to be a rare disease with only 28 cases reported in the literature up to 1996. However, keratitis due to Pythium may be more common than previously thought, accounting for a proportion of cases that were due to unidentified pathogens. Although this disease was first reported in 1884 the species infecting humans - Pythium insidiosum - was only formally recognised in 1987. Diagnosis can be difficult in part because of a lack of awareness of the disease. It does not appear to be transmissible either animal to animal or animal to human. There appear to be three clades of this organism: one in the Americas, a second from Asia and Australia and a third with isolates from Thailand and the USA. The most probable origin of the organism seems to be in Asia. Most human cases have been reported in Thailand, although cases have been reported elsewhere. In humans, the four forms of the disease are: subcutaneous, disseminated, ocular, and vascular. The ocular form of the disease is the only one known to infect otherwise healthy humans, and has been associated with contact lens use while swimming in infected water. This is also the rarest form with most cases requiring enucleation of the eye. The other forms of the disease require a pre-existing medical condition, usually associated with thalassemic hemoglobinopathy. Prognosis is poor to guarded and treatments include aggressive surgical resection of infected tissue, with amputation suggested if the infection is limited to a distal limb followed by immunotherapy and chemotherapy. A recently published review lists nine cases of vascular pythiosis with five survivors receiving surgery with free margins and all except one requiring amputation. The same review lists nine cases of ocular pythiosis with five patients requiring enucnleation of the infected eye and four patients requiring a corneal transplant. Cats and other animals In cats, pythioisis is almost always confined to the skin as hairless and edematous lesions. It is usually found on the limbs, perineum, and at the base of the tail. Lesions may also develop in the nasopharynx. Rabbits are susceptible to pythiosis and are used for in vivo studies of the disease. Other animals reported to have contracted pythiosis are bears, jaguars, camels, and birds, although these have only been singular events.