Human protothecosis

Abstract

Human protothecosis is a rare infection caused by members of the genus Prototheca. Prototheca species are generally considered to be achlorophyllic algae and are ubiquitous in nature. The occurrence of protothecosis can be local or disseminated and acute or chronic, with the latter being more common. Diseases have been classified as (i) cutaneous lesions, (ii) olecranon bursitis, or (iii) disseminated or systemic manifestations. Infections can occur in both immunocompetent and immunosuppressed patients, although more severe and disseminated infections tend to occur in immunocompromised individuals. Prototheca wickerhamii and Prototheca zopfii have been associated with human disease. Usually, treatment involves medical and surgical approaches; treatment failure is not uncommon. Antifungals such as ketoconazole, itraconazole, fluconazole, and amphotericin B are the most commonly used drugs to date. Among them, amphotericin B displays the best activity against Prototheca spp. Diagnosis is largely made upon detection of characteristic structures observed on histopathologic examination of tissue.

FIG. 1.

Taxonomy of the genus Prototheca. (Reprinted from the website of the Prototheca Group, Institute for Animal Hygiene and Veterinary Public Health of the University Leipzig [http://www.prototheca.com], with permission.)

FIG. 2.

Protothecosis and Prototheca spp. (A) Histopathology by hematoxylin and eosin staining of cutaneous protothecosis shows morula-like structures (large arrow) and endospores (small arrow). Magnification, ×1,000. (B) Typical morphology is best observed with PAS. (C and D) Wet mount preparation with lactophenol cotton blue shows P. zopfii, with asymmetrical morula-like structures (C), and P. wickerhamii, with symmetrical morula-like structures (D). (E) Smooth, creamy, white, yeastlike colonies of P. zopfii on Columbia blood agar after incubation at 37°C for 24 h. (F) Staining of bronchoalveolar lavage fluid with calcofluor white also yields typical morula-like structures of P. zopfii.