PROTOZOAL AGENTS - WHAT ARE THE DANGERS FOR THE PUBLIC WATER-SUPPLY

Safe and efficient treatment of drinking water has been one of the maj or public health advances of the twentieth century. People in develope d countries generally take for granted that their water is safe to dri nk, a luxury the majority of the world's population does not have. The leading cause of infant mortality in the developing world is infectio us diarrhea, and the prevalence of diarrheal pathogens is largely infl uenced by the quality and quantity of dean water available for drinkin g and washing. Until recently, modem water treatment had all but elimi nated these concerns in developed nations. Over the past two decades, however, the safety of our water supply has been threatened by the eme rgence of Cryptosporidium parvum, a protozoal pathogen. The hearty ooc ysts of this organism survive chlorination and filtration to cause a d iarrheal illness that, while unpleasant enough in healthy people, is d evastating in immunocompromised individuals. The 1993 Milwaukee outbre ak, in which 403,000 people developed diarrhea from drinking water tha t met all the updated federal safety standards, demonstrated the treme ndous public health importance of this organism. While earlier attenti on had focused on Giardia and amebic infections, the other ''emerging' ' protozoan besides Cryptosporidium is Cyclospora. This review discuss es the protozoal pathogens, including Cryptosporidium parvum, Giardia lamblia, Entamoeba histolytica, and Cyclospora cayetanensis, that caus e waterborne diarrheal outbreaks and the threats they pose to the publ ic.