Epidemiology of Giardia lamblia and Cryptosporidium infections in childhood.

Giardia lamblia infections are now recognized as having a considerable health impact in industrialized regions, while the pathogenicity of G. lamblia in endemic areas has not been fully established. Cryptosporidium infections have emerged over the past two decades as a major health concern in developed and developing nations alike. In addition, the organism is implicated in persistent diarrhea and is associated with malnutrition and adverse growth effects in populations with high diarrhea morbidity rates. The immune response has been shown to be intimately involved with prevention of organism attachment to the intestinal epithelium, clearing of infection once it is established, and the development of protective immunity. Many unresolved issues remain regarding the immunologic response to parasitic infections. In addition, it is envisaged that future studies, using improved parasite detection methods, will shed light on the role of Giardia lamblia and Cryptosporidium in human disease. Some of the questions awaiting resolution relate to susceptibility of infection in certain population groups, the role of asymptomatic infection in parasite transmission, the association between G. lamblia infection and nutritional status in particular, and the pathogenic role of G. lamblia in endemic areas in general.