ABSTRACT
Pythiosis is a life-threatening infectious disease caused by the fungus-like organism, Pythium insidiosum, a Pythium species that was –rst introduced and validly published by De Cock et al. in 1987.1,2 In fact, the disease –rst occurred in horses in the middle of the nineteenth century, and the causative agent was –rst isolated as an unidenti–ed nonsporulated –lamentous fungus in 1901 by two Dutch researchers, de Haan and Hoogkamer.1,2 In 1974, Austwick and Copland reported that the pathogen isolated from horses should be placed in the genus Pythium because it produces bi¼agellate zoospores, which represent a distinctive morphological phase of members of this genus.3 P. insidiosum has been recognized by other names, including Hyphomyces destruens, Pythium gracile, and Pythium destruen; and the disease pythiosis has also been known under several different names, including hyphomycosis destruens, phycomycosis, swamp cancer, bursattee, kunker, cutaneous habronemiasis, granular dermatitis, espundia, and leeched.1-4 In addition to horses, pythiosis has been increasingly reported in other animals, including dog, cat, cattle, bear, and sheep.2 The –rst patient with human pythiosis was found in New Zealand in 1984, but the case was not reported in the literature until 1997.5 In 1985, two human pythiosis cases were diagnosed in Thailand.6 Since then,
human pythiosis has been documented from other countries: United States, Haiti, Brazil, Malaysia, and Australia.7-11
The hyphal phase of P. insidiosum is hard to distinguish from true –lamentous fungi, such as Aspergillus spp., Penicillium spp., and Zygomycetes, which cause infections with similar clinical features to pythiosis.12 This can lead to the misdiagnosis of patients with pythiosis. For this and other reasons, morphological characterization and culture identi–cation of P. insidiosum are dif–cult and time-consuming, and therefore, diagnosis of pythiosis is often delayed. Conventional antifungal agents are not effective for treatment of P. insidiosum infection because Pythium spp. lack the drug-targeted ergosterol biosynthesis pathway.13 Because β-glucan is a major cell wall component of fungi and Pythium species,14 Pereira recently tested the in vivo effect of caspofungin (a new antifungal drug that inhibits β-glucan synthase) on P. insdiosum infection in a rabbit model of pythiosis.15 While the drug slowed the growth of lesions, it was unable to eliminate the pathogen in the infected animals.15 Without a useful chemotherapeutic agent, the main treatment approach for pythiosis is radical surgery, which should be urgently performed to limit the progression of the disease. Many patients die as a result of advanced and aggressive infection. Early and correct diagnosis of pythiosis is crucial for proper treatment and a better prognosis.
