Studies on the dynamics of transmission of onchocerciasis in a Sudan-savanna area of North Cameroon IV. The different exposure to Simulium bites and transmission of boys and girls and men and women, and the resulting manifestations of onchocerciasis.

The sojourn times of the human population were monitored over one year at 12 sites in the vicinity of three villages in the Cameroon Sudan-savanna, where the Onchocerca volvulus transmission potentials had been measured one year previously. Boys stayed longer outside the villages, and were exposed 2.1 to 2.7 times more than girls to transmission of onchocerciasis, whereas the exposure of men was similar or only moderately higher than the exposure of women. In boys, the onset of infections and ocular lesions was earlier and the average microfilarial density at the buttock (2.2, 9.4 and 79.3 mff snip-1) was much higher than in girls (0.1, 5.8 and 42.2 mff snip-1 at the three villages respectively). These differences were maintained in the adult population, where the average microfilarial density was 52.3, 80.4 and 183.1 mff snip-1 in men and 15.6, 49.6 and 114.7 mff snip-1 in women. Ocular lesions due to onchocerciasis were found in 5, 13 and 55% of the male population in the three villages, as compared with 2, 3 and 8% of the female population. There was a close relationship between the degree of exposure to the transmission of disease and the resulting microfilarial load in the skin which was not different for the two sexes, and a similar trend was seen for the occurrence of ocular lesions due to onchocerciasis. The influence of an early and heavy infection on the evolution of disease manifestations is discussed.