Transmission of Schistosoma -The Managil Area, Sudan

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Hilali, Abdel Moneim Hassan Mohamed
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Schistosomiasis, a parasitic disease in man and domestic animals caused by trematodes of the genus Schistosoma, is a major public health problem in Gezira-Managil Agricultural Scheme. While many studies on schistosomiasis transmission has been carried out in the Gezira area relatively little work has been done in the Managil area. In light of the relative lack of epidemiological information from the Managil area, the present study was undertaken to measure the prevalence and intensity of infection with S. mansoni in relation to factors like age, sex, occupation and others, to measure the incidence of S. mansoni infection, to observe human water contact patterns, to determine the seasonal changes in population densities and infection rates by schistosomes, and to provide a description of the dynamics of all aspects of transmission as a basis for the Blue Nile Health Project's schistosomiasis control programme in the area. The study was conducted over 22 months, i.e. from November 1988 to August 1990, in five villages in the Managil area. The study shows that S. mansoni is highly endemic in the area. The prevalence and intensity of infection varied greatly among villages and age groups. The overall prevalence in the five villages ranged from 33% to 55% and the overall geometric mean egg count per g faeces of intected people from 77 to 135. Prevalence and intensity of infection peaked in the age group of 10-14 years and declined with increasing age. However, both prevalence and intensity of infection increased again in males aged more than 40 years, indicating that water contacts of an occupational nature may be important in this area. Transmission is very intense as judged from incidence rates although these rates vary greatly among villages. Human water contact activities were concentrated to a few sites close to each village. Water collection accounted for more than 40% of the total acts of water contacts observed at each village demonstrating the problems of maintaining functioning water supply systems in the villages. For both males and females, the age group of 10-14 years was involved in relatively more water contacts than the other age groups. Although, females had a greater frequency of water contacts than males, males were invalid In more high-risk water contact activities such as swimming and playing in water. The frequency of human water contacts fluctuated during the season and paralleled the fluctuations in the density of schistosome infected Biomphalaria pfeifferi. The schistsome intermediate hosts in the area, Biomphalaria Pfeifferi and Bulinus truncatus are widely distributed and occur in a patchy manner with a few sites accounting for most of the total number of snails collected. Schistsoma mansoni-infected B. pfeifferi were found primarily from a few sites close to the villages. The intermediate host snails undergo great seasonal fluctuations in density with peak density during the hot and dry season, i.e. April-June. Similarly, transmission of S. mansoni is most intense during this season. These findings together with the observed human water contact patterns clearly points to the locality and seasonality of the transmission. It is concluded that the S. mansoni transmission pattern is similar to that of the Gezira although it appears that overall densities of the intermediate hosts are lower in the Managil than in the Gezira area. The relevance of these findings for schistosomiasis control in the area is discussed.
Transmission of Schistosoma -The Managil Area, Sudan.