Emerging Enteric Protozoa: Cryptosporidium, Cyciospora, and Microsporidia
The sometimes desperate search for an etiology of severe, life-threatening, and persistent diarrhea in patients with AIDS has led attention to three "new" or emerging protozoan enteric pathogens: Cryptosporidium, Cyclospora, and microsporidia. All three of these emerging enteric protozoa disrupt the intestinal epithelium and tend to cause persistent diarrhea. A recent longitudinal review in a community hospital suggests that elderly patients may also be predisposed to cryptosporidiosis, as 36% of infected patients in the study were 63 years of age or older. The prognosis is clearly better in individuals whose CD4 counts return toward normal, and preliminary results from two studies evaluating the efficacy of highly active antiretroviral therapy document improvement in either diarrhea or parasite shedding in patients with cryptosporidiosis or microsporidiosis. Since glutamine-coupled sodium absorption remains largely intact (and may be superior to glucose), oral rehydration and nutrition therapy (ORNT) holds promise both in rehydration and in speeding repair of disrupted bowel function in patients with cryptosporidial and other persistent diarrheas. Cyclosporiasis appears to have a striking summer rainy-season seasonality like cryptosporidiosis and has been associated with drinking contaminated water despite apparently adequate chlorination. Cryptosporidium, Cyclospora, and microsporidia clearly pose increasingly recognized threats to both immunocompetent and immunocompromised individuals through food and water supplies. Improved detection and animal models are needed in order to better understand the pathogenesis and epidemiology of Cyclospora infections, and little is known about the reservoir and potential vehicles and means of transmission of microsporidia.
