Pythium insidiosum sp. nov., the etiologic agent of pythiosis (original) (raw)

1987, Journal of Clinical Microbiology

Pythium insidiosum sp. nov., the etiologic agent of pythiosis, a cosmopolitan disease of horses, cattle, and dogs, is described and illustrated. Pythiosis (5) is a cosmopolitan granulomatous disease of horses, cattle, and dogs (10, 16, 17, 18) that is caused by a long-unnamed "phycomycete." (The term pythiosis was proposed in 1980 by Chandler et al. [5] as a more appropriate name for the equine disease variously referred to as bursatii, Florida horse leeches, granular dermatitis, hyphomycosis destruens equi, phycomycosis, phycomycotic granuloma, and swamp cancer.) It is probable that the first reports referring to this disease were those of Smith (20) and Drouin (9), who observed the mycelial nature of the etiologic agent. Although the organism could be cultured, it could not be identified, as it did not sporulate. de Haan and Hoogkamer (7) gave an extensive description of several cases of diseased horses in Indonesia and named the disease hyphomycosis destruens. This name was extended by de Haan (6) to hyphomycosis destruens equi. In a publication by Bridges and Emmons (4), the etiologic agent was called Hyphomyces destruens. It was not clear from that publication whether the authors intended to introduce a new binomial or only a provisional name they were anticipating to validate in the future (see reference 21, article 34.1b). The binomial was proposed without a Latin description (21, article 36), and the nomenclatural type was not designated for H. destruens (21, article 37). The binomial H. destruens, therefore, was in direct violation of articles 34.1b, 36, and 37 of the International Code of Botanical Nomenclature (21). Bridges and Emmons considered H. destruens to be a phycomycete (zygomycete) on the basis of its morphology in equine tissue as well as its broad, branched, sparsely septate to coenocytic, nonsporulating mycelium in cultures. They could not induce sporulation when H. destruens was grown on a wide variety of media. They speculated that the fungus they had studied "may be a species of Mortierella." Austwick and Copland (1) reported that isolates recovered from horses afflicted with swamp cancer in Papua, New Guinea, formed biflagellate zoospores. Zoospore formation occurred when the isolates, grown on Sabouraud dextrose agar, were transferred to a sterilized aqueous medium of rotten maize silage. They concluded that H. destruens was a phycomycete belonging to the Pythiaceae in the Peronosporales and that it could be included in the genus Pythium Pringsheim. These investigators also stated that "Further work is in progress to establish whether it is a recognized or new species." However, additional work on the identity of this oomycete of the kingdom Protoctista was not published.