This study was carried out to investigate different aspects of the epidemiology of the common intestinal protozoan infections in children in KwaZulu-Natal. The main aspects studied were to: i . monitor changes in the prevalence and intensity of the common intestinal protozoons in children after receiving antihelmintic drugs, ii. determine whether environmental and/or socio-economic factors are important in the prevalence of the common intestinal protozoons, iii. determine the occurrence of Cryptosporidium parvum in stool samples of paediatric patients with gastroenteritis and in healthy school children. Intestinal protowan species often co-occur with intestinal nematodes in infected children and it is important to determine the effect that anti-nematode treatment has on concomitant protozoan infections. The study included the analysis of stool samples by the Formol-Ether Concentration Technique, exam ination of the obtained sediments for intestinal helminths and protozoan species, and treatment of nematode-infected individuals. Four surveys were carried out to determine the prevalence and intensity of intestinal protozoons in school children before and after anthelmintic chemotherapy, and the X(2) test was used to determine significant changes. Prevalences and intensities of helminths were determined for significant changes after treatment using the Student's t-test. Additional pre- and post-treatment prevalence data were obtained from four schools in Health Region A of KwaZulu-Natal. The prevalence of Ascaris lumbricoides decreased significantly from 75.2% to 9.7% after the first treatment, that of Trichuris trichiura decreased from 77.7% to 62. 1%, and hookworm infections (presumably Necator americanus) dropped fromI2.7% to 1.0% and remained very low for the rest of the study. Very few individuals were infected with protozoan species and for statistical analysis, these were combined. The prevalence of protozoan infections increased from 33.0% to 50.3% after the first treatment and from 35% to 42% after the second treatment. The prevalence of A. lumbricoides decreased significantly again after the second treatment while there was no significant decrease in the prevalence of T. trichiura. The intensities (number of eggs/gram of feaces) of the three nematodes also decreased significantly after the two treatments. It is recommended that children who have been treated for nematode infections should also be examined for protozoan infections, and these should also be treated accordingly. A retrospective analysis of protozoon prevalence data from different surveys in KwaZulu-Natal was done in order to detennine the importance of environmental and/or socio-economic factors in the distribution of intestinal protozoons. These data were plotted on the map of KwaZulu-Natal using Geographic Information System (GIS). Univariate analysis was carried out to determine significant correlations between the prevalences of protozoan species and selected variables. The significant correlations obtained were moderate and no strong correlations were obtained. Univariate stepwise regression analysis was performed to determine the factors that combine best in facilitating the transmission of protozoan species and significant associations were obtained between the prevalence of protozoon species and a combination of environmental and socio-economic factors. In most cases, the association between prevalence and mid-summer temperature and rainfall were the most significant. This is an indication of increased summer transmission. Altitude was significantly correlated only with the prevalence of Endolimax nana. The fact that moderate correlations were obtained between prevalence of intestinal protozoons and climatic and socio-economic factors indicates that these factors are important in the distribution of the common intestinal protozoons. However, lack of strong correlations suggests that in addition to climatic and socio-economic factors, there are other factors that have an effect on the distribution of intestinal protozoan species. In the multivariate analysis where the variables were simultaneously considered, the presence of electricity was the only factor that was significantly associated with the variation seen in the prevalence of intestinal protozoons in the different study locations. Cryplosporidium parvum is a parasitic protozoon that is associated with severe fatal diarrhoea in children and immunocompromised individuals. Oocysts of this parasite were found in 18.2% of stool samples collected from children (aged 6 to 48 months) who were admitted in the paediatric wards at King Edward VIII Hospital, Durban. The stool samples were firstly concentrated using the Formal-ether method and the obtained sediment was mixed with the Sheather's Sucrose solution and examined microscopically. No oocysts were found in stool samples collected from older primary school children. Although the diarrhoea in these children might have also been due to other causes, the results obtained further show the importance of C. parvum as a cause of diarrhoea in children below the age of five years. Knowledge of the epidemiology of C. parvum is crucial in the control of this parasite as there is currently no effective treatment. More intensive surveys are needed in detennining the epidemiology of this pathogen in the South African population. / Thesis (M.Sc.)-University of Natal, Durban, 2001.