Summary: | PYTHIOSIS is usually a granulomatous disease of skin and subcutis
in horses (Austwick and Copland 1974; Miller and Campbell 1982;
Mendoza and Alfaro 1986), and cattle (Miller, Bruce and Archer
1985), of skin and intestinal tract in dogs (ONeill-Foil, Short, Fadek
and Kunkle 1984; Miller 1985), and of skin and blood vessels in
man (Sathapatayavongs et a1 1989). The disease is caused by
Pythium insidiosum, a microorganism in the class Oomycetes,
kingdom Protista (de Cock et al 1987). P. insidiosum was previously
known under the names Hyphomyces destruens (Bridges and
Emmons 1961). Pythium sp (Austwick and Copland 1974) and P
gracile (Ichitani and Amemiya 1980). It is also known as swamp
cancer, leeches, bursatte, summer sores, espundia and others (de
Cock et a1 1987).
Pythiosis in horses is usually associated with the end of the rainy
season in tropical and subtropical countries. P. insidiosum develops
its life cycle in stagnant water producing biflagellated zoospores that
penetrate into the horse through open skin (Miller 1983). After two
days, successful zoospora skin penetration, one may observe a
swelling area of 5 mm in diameter that increasing rapidly until it
reaches 100 to 200 mm in diameter within about two weeks. Lesions
two to five months old are commonly reported in Costa Rica
(Mendoza and Alfaro 1986), usually due to fruitless treatments.
Surgical therapy is used widely to treat this disease (Miller
1981). However, it is not practical on limbs because critical
anatomical structures are located in these areas (McMullan et a1
1977). Furthermore, lesions can reappear if the necrotic masses
called 'leeches' or 'kunkers' which contain the hyphae of this
oomycete microorganism, are not removed completely.
Immunotherapy (vaccination with products derived from P.
insidiosum) have been successful in Australia and Costa Rica to
treat horses in early pythiosis, but not in chronic stages (Miller 1981;
Mendoza and Alfaro 1986). In addition, treatment with
Amphotericin B and iodine has also been reported (McMullan
1977), but Amphotericin B is expensive and time consuming; iodine
treatment requires many hours of attention daily, and both have toxic
side effects.
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