Protothecosis

Protothecosis is a rare infection in humans. Infection is more common in cases of immunodepression (AIDS, leukaemia). The disease was reported originally from Sierra Leone, but cases were later identified in the New World (Panama, USA), South Africa, China, Vietnam and New Zealand. The disease is caused by Prototheca wickerhamii and P. zopfi (segbwema). These are aerobic unicellular round to oval algae which activity belong to the Chlorococcales [Chlorophyta or green algae] although they contain no chlorophyl and are colourless. They are typically 8-16 µm in diameter, but their size may vary from 3 to 30 µm. These algae reproduce by internal division of a mother cell, which produces two to fifty small endospores enclosed in a sheath (theca). This ruptures and the endospores are released, after which the cycle is repeated. The protozoa occur in still water, sewage sludge, mud and slime on trees. Various animals may be infected (cattle, dogs, rabbits, mice, rats, pigs, deer). Humans are infected via traumatic inoculation of the germ into the skin or via infection of an open wound. Infection is usually limited to the skin, where local granulomatous hyperkeratotic dermatitis results. Bursitis and tenosynovitis have been described. Sometimes there is systemic involvement, including chronic meningitis and retinitis. There have been cases of peritonitis after peritoneal dialysis. Diagnosis is made by biopsy. The protozoa are morphologically similar to mulberries. Confusion with yeasts is possible. For tissue sections a PAS [periodic acid-Schiff] or a Gomori methenamine silver stain are used. The algae can be cultured in vitro on glucose-containing media. Generally a blood agar and a Sabouraud medium are used. Growth is optimal at 30°C and is inhibited at 37°C. Treatment is surgical with or without amphotericin B. Ketoconazole has frequently been used with success, but requires long-term administration. The possible therapeutic roles of itraconazole and fluconazole need to be better determined.

Category: Medicine Notes