Diagnosis, epidemiology and human immune response to cryptosporidiosis

The protozoan parasite Cryptosporidium is now widely accepted as a cause of human gastroenteritis. The apparent lack of host specificity and the ability of the organism to undergo its entire life-cycle within the one host has important epidemiological implications. Studies here in Australia and in many other countries have shown Cryptosporidium to be an important pathogenic agent in gastroenteritis with an increased incidence in children, a strong rural connection and a possible seasonal trend in some places. The results of this study show that there are simple and sensitive methods for detecting Cryptosporidium which could be incorporated into the standard work up for gastrointestinal disease in the routine laboratory. The survey found that Cryptosporidium was the second most common faecal pathogen found after Campylobacter jejuni and therefore the most common intestinal parasite in Tasmania. The disease was found to have definite seasonal trends with peaks in late spring and autumn. Young children were more commonly affected and an association between contact with animals and consumption of unpastuerised milk was shown. Immunological studies of the different classes of antibodies produced after infection with Cryptosporidium show that there is a definite immediate IgA response in most patients followed later by IgM and then IgG. The one AIDS patient with cryptosporidiosis examined in this study showed an almost complete lack of humoral immune response to the infection and one patient possibly became reinfected.