Cryptosporidium and other protozoa in diarrheal disease in less developed countries

Abstract

At least 18 species of intestinal protozoa in 14 different genera have been identified in the feces or intestinal juices of man (Table 1). Of these ten species are regarded as potential pathogens and can induce diarrheal disease. The degree of pathogenicity ranges from very high, as in Cryptosporidium sp. in which most infections are symptomatic, to very low, as in Dientamoeba fragilis and Blastocystis hominis in which symptomatic infections are very rare. Although by the turn of the century most species of intestinal protozoa had been identified and differentiated, considerable controversy still prevails regarding their significance as causes of human disease, with the exception of Entamoeba histolytica, Giardia lamblia, Cryptosporidium sp. and Balantidium coli. The difficulty encountered in making a rapid and accurate diagnosis, coupled with the ease with which untrained personnel can misdiagnose "protozoal forms" under the microscope, often leads to mistakes, particularly with regard to E. histolytica. On the other hand, the complexity of investigations of viral and bacterial agents have resulted in incomplete studies that emphasized or underestimated the intestinal protozoa. This paper reviews knowledge and experience in the diagnosis, clinical aspects, epidemiology and treatment of intestinal protozoal infections as seen in Central American populations. Emphasis will be placed on Crytosporidium, inasmuch as E. histolytica and G. lamblia are discussed by others in this conference.