Transmission of Schistosoma haematobium in North Gezira, Sudan.

During this 14-month study, 128 765 Bulinus truncatus snails were collected from canals located near four villages in the northern part of the Gezira Irrigated Area, and were examined for patent trematode infections, by exposure to light. In all, 903 shedded cercariae, of which 424 were identified as S. haematobium, and one village, Bashagra, was the source of 80% of these S. haematobium infections. The highest density of snails occurred from March to May and the peak of snail infections occurred from June through August. The residents of the four villages and any adjacent small camps were examined for infection with S. mansoni and/or S. haematobium by collecting and examining stool and urine samples. The overall prevalences were 50% for S. mansoni and 20% for S. haematobium. The age prevalence curves were very different, with the prevalence of S. haematobium falling off more sharply in the over-20 age groups than was the case with S. mansoni. Observations at the human water contact sites suggested that the transmission of S. haematobium was increased when the canals contained shallow stagnant water, when the temperature was above 26 degrees C, and when the site was frequented by small children (particularly boys aged 5-15), for swimming. Our data suggest that at any site the transmission period is short and seasonal.