Onchocerciasis hyperendemic in the Unturan Mountains: the value of recombinant antigens in describing a new transmission area in southern Venezuela

A recently described hyperendemic onchocerciasis area, located in the Untur an Mountains (between the Siapa and Orinoco basins) of southern Venezuela w as studied using a cocktail of 3 low molecular weight onchocercal recombina nt antigens (OvMBP/10, OvMBP/11, and OvMBP/29). The resulting seroepidemiol ogical data were compared with those from a hypoendemic community (Altamira ) situated in the northern coastal mountain range. Parasitological (skin bi opsy) and serological (enzyme-linked immunosorbent assay, ELISA) methods fo r the specific diagnosis of Onchocerca volvulus in these 2 very different e ndemic areas were, respectively, 88% and 96% sensitive in Unturan, and 57% and 91% sensitive in Altamira. The mean microfilarial load, the mean optica l density (OD), and the seropositivity rates all increased significantly wi th age in both communities. The serological variables (mean OD and prevalen ce of anti-O. volvulus antibodies) were both significantly higher in Untura n than in Altamira for children and young adults (aged <25 years), although above this age no differences between communities were detected. Seropreva lence had already reached 50% in the under 15 year-olds examined at Unturan but was just 5% at Altamira for the same age-class. The prevalence of spec ific antibodies (mainly a marker of exposure to risk of infection) exceeded 85% in the remaining age-categories at the hyperendemic area. This is in a greement with the high community microfilarial load recorded in Unturan (>2 0 mf/mg) and the presence of sclerosing keratitis and hanging groin, sugges ting that onchocerciasis is a public health problem in this community. The ELISA test used here, based on a cocktail of 3 low molecular weight onchoce rcal recombinant antigens, appears, therefore, to constitute a practical to ol for the description of endemicity levels in remote areas, particularly g iven the fact that finger-prick blood samples are routinely taken from chil dren in the Upper Orinoco region for surveys of malaria incidence. Such stu dies could aid in defining the true extent of the Amazon focus (still unkno wn) and providing priority indicators for the selection of communities wher e onchocerciasis control programmes should be implemented.