Onchocerciasis in the Northern Province of Sierra Leone

The new town of Lunsar near the Marampa mines was investigated by taking a 4% clinical sample derived from a 10% sample census. The population of the town at 31 July 1959 was 9,540 and the clinical sample comprised 380 persons. 4 villages situated between 7 and 20 miles from Lunsar were examined, the total population being seen in 3, and a half sample taken of a fourth, a total of 1,010 persons. Persons in the two areas were examined for onchocerciasis, a skin biopsy being performed on 91·6% of persons in Lunsar and 76·3% of persons in the villages, the difference being due to the large number of infants in the villages. The rates for onchocerciasis positive cases were 54·5% for males and 44·5% for females in Lunsar, and 40·8% for males and 52·0% for females in the villages. Villages near to the Rokel river, the breeding place of Simulium damnosum, had higher rates for onchocerciasis, varying from 65·9% at Mawulay-Mamanso to 38·5% at Kamasundu. The rates can be arranged in descending order in relation to the distance from the river. On using direct standardization because of the differences in population structure between the town and the villages, it is seen that the rates for the combined villages were higher than that of the town. The town had lower standardized rates than a village equidistant from Simulium breeding places. Urban life may to some extent protect from infection.