The epidemiology of intestinal infectious disease has changed substantially since the 1980s in Africa and in the rest of the world. With the spread of HIV, parasites previously thought to be of minor importance have assumed a major profile and some previously unrecognized parasites have been found in human hosts. Cryptosporidiosis (infection with Cryptosporidium parvum) and isosporiasis (infection with Isospora belli, now renamed Cystoisospora belli) were thought of as unimportant occasional infections with protozoa of minor significance, while human infection with microsporidia was completely unknown before it was recognized in HIV-infected patients. These infections are now understood to pose important public health problems throughout the continent. Giardia intestinalis (also called G. lamblia or G. duodenalis), the first human protozoal parasite to be identified over 200 years ago with the first microscopes, remains an important parasite, especially of children. Although microsporidia have now been re-classified with the fungi, we consider them here as they cause a similar profile of problems to the protozoa. Amoebiasis is considered in Chapter 53.