The geographical distribution of Onchocerca volvulus infection in Liberia

The survey carried out for the assessment of onchocerciasis prevalence in Liberia from 1968 to 1971 covered about 1% of the rural population. From 10.885 persons examined parasitologically, 38% were carriers of microfilariae of O. volvulus in the skin, and an additional 6.8% carried nodules but no mf. One or more onchocercal nodules were prevalent in a total of 27% of the population. Geographic and sex differences were observed as well as several different patterns of increasing age. A description of the geographic distribution patterns is given but evaluation of population clusters classified by overall endemicity is considered more profitable for analyses of parasitological and clinical lesions related to the transmission of the filarial infection. Regional differences of the age-adjusted mf-rates ranging from 0 to 78% prevalence were obtained from the analysis of 121 communities throughout the country. The general onchocerciasis distribution pattern showed the highest endemicity in the western part of the country with a general decline towards hypoendemic condition in the Eastern regions. Exceptions were found in that sizable pockets of high transmission activity seems to exist in Eastern Liberia near the coast and also in Central Liberia.