Focal, seasonal and behavioural patterns of infection and transmission of Schistosoma haematobium in a farming village at the Volta Lake, Ghana.

Integrated sampling for human prevalence, intensity, and incidence of Schistosoma haematobium, as well as for human water contact and snail distribution and density was carried out in the Volta lake farming village of Agbenoxoe at various times between 1978 and 1980. Nuclepore filters were used for determining egg output. Snail sampling was by the man-time method. A new system of recording human water contact was introduced for the peculiar condition at Agbenoxoe. Results indicated significant focality of infection and transmission in the compact village, concentration in the 5- to 19-year-old age group, and distinct seasonality of transmission. Water contact was frequent but of short duration. Only a few children under the age of 5 entered the water, and age-specific curves for duration of water contact paralleled the curve for geometric mean of egg counts (log10 of eggs + 1) for males and the prevalence curve for females. Water contact for males was of longer duration than for females and included more time playing and wading. These activities probably accounted for the much higher incidence and prevalence rates recorded for males over females in the village. The concentration of infection, transmission, and water contact in the 5- to 19-year-old age groups at Agbenoxoe and villages like it supports a control strategy of treating only this age span with drugs.