Protothecosis. A pseudofungal infection

Summary Prototheca species are aerobic, unicellular, achlorophyllous algae that propagate asexually by endosporulation. They are ubiquitous in nature and have been isolated from the slime flux of trees, soil, water, animal waste and sewage. They can also be found in many food products. Since the genus Prototheca was identified in 1894 by Kruger, the phylogeny and taxonomic position of the organisms within this taxon have repeatedly been the subject of scientific controversy. Prototheca , which was first thought to be a fungus, is now generally considered to be the apochlorotic equivalent of Chlorella . Its close relationship with the photosynthetic alga Auxenochlorella protothecoides has been confirmed using chemotaxonomic strategies and on the basis of molecular data. Five species are currently recognized, of which two, Prototheca zopfii and Prototheca wickerhamii , have been proven to produce infections in mammals. Though extremely rare, Prototheca infections do occur in humans, with P. wickerhamii being the most frequent causative agent. Only slightly more than 100 human cases have been reported worldwide. Three major clinical forms of human protothecosis have been described: cutaneous, olecranon bursitis and disseminated as an opportunistic infection. The pathogenesis of Prototheca organisms remains unclear, but they are believed to be of low virulence and mostly infect patients with various forms of immunosuppression. Though no standardized pharmacologic protocol is available, treatment with antimycotic agents has proven to be effective. For localized lesions, surgical excision has been successful. Diagnosis of protothecosis depends on the results of either culture or histopathology. Although protothecal infections are sporadic and in most cases completely curable, they should not be ignored. On the contrary, they require close monitoring to provide a better understanding of the epidemiology and pathologic processes that accompany Prototheca infections. This article discusses the most essential issues concerning protothecosis and its etiologic agents.