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

Abstract

A recently described hyperendemic onchocerciasis area, located in the Unturán Mountains (between the Siapa and Orinoco basins) of southern Venezuela was studied using a cocktail of 3 low molecular weight onchocercal recombinant antigens (OvMBP/10, OvMBP/11, and OvMBP/29). The resulting seroepidemiological data were compared with those from a hypoendemic community (Altamira) situated in the northern coastal mountain range. Parasitological (skin biopsy) and serological (enzyme-linked immunosorbent assay, ELISA) methods for the specific diagnosis of Onchocerca volvulus in these 2 very different endemic areas were, respectively, 88% and 96% sensitive in Unturán, and 57% and 91% sensitive in Altamira. The mean microfilarial load, the mean optical density (OD), and the seropositivity rates all increased significantly with age in both communities. The serological variables (mean OD and prevalence of anti-O. volvulus antibodies) were both significantly higher in Unturán than in Altamira for children and young adults (aged < 25 years), although above this age no differences between communities were detected. Seroprevalence had already reached 50% in the under 15 year-olds examined at Unturán but was just 5% at Altamira for the same age-class. The prevalence of specific antibodies (mainly a marker of exposure to risk of infection) exceeded 85% in the remaining age-categories at the hyperendemic area. This is in agreement with the high community microfilarial load recorded in Unturán (> 20 mf/mg) and the presence of sclerosing keratitis and hanging groin, suggesting that onchocerciasis is a public health problem in this community. The ELISA test used here, based on a cocktail of 3 low molecular weight onchocercal recombinant antigens, appears, therefore, to constitute a practical tool for the description of endemicity levels in remote areas, particularly given the fact that finger-prick blood samples are routinely taken from children in the Upper Orinoco region for surveys of malaria incidence. Such studies could aid in defining the true extent of the Amazon focus (still unknown) and providing priority indicators for the selection of communities where onchocerciasis control programmes should be implemented.

Human infection patterns and heterogeneous exposure in river blindness

“…Most models focus on onchocerciasis in West Africa (13)(14)(15)(16)(17), with some models focusing on Latin America (19), but few attempt to bring epidemiological commonalities and differences into a single and coherent mathematical framework (29). Age-specific exposure to vector bites (13)(14)(15)(16), operation of parasite-related human mortality (13,15), and parasite-induced immunosuppression (12,17,26) are among the mechanisms put forward to explain observed departures Observations of ABR and L3 load are independent from the data to which the model has been fitted. of O. volvulus patterns from predictions generated by simple immigration-death models (7).…”

“…Cross-sectional surveys of skin mf load (mf per mg of skin) were conducted before introduction of mass ivermectin treatment in 37 Sudan savannah (Mboum and Dourou) villages of the Vina du Nord valley in northern Cameroon (23), Mayan populations living in nine coffee fincas of central Guatemala (24), and 21 Yanomami communities of the Venezuelan Upper Orinoco basin (12,25,26). The number of people (and percentage of the total population) examined was, respectively, 5,040 (50%), 872 (76-99%), and 995 (70%).…”

“…O. volvulus has been shown to reduce host immunological responsiveness to parasite-specific and other antigens (reviewed in ref. 38), and it has been proposed that age-and͞or parasite-specific immunosuppression may be responsible for increasing parasite loads with host age (12,17). Models have been developed that make the rate of parasite establishment an increasing function of already established worms to fit adult worm nodulectomy data (8,17,28).…”

Pathological Impact and Disease Burden of Human Onchocerciasis in Endemic Areas of Delta State, Nigeria

“…The area to be skin snipped was first, carefully swabbed with methylated spirit [11] and two bloodless skin-snips were taken from each subject from the left iliac crest and shoulder with the aid of a corneo-sclera biopsy punch (2mm or 4mm bite), manufactured by surgitrac co. Ltd, 1902, Global trade center, 15, Wingkin Road, Kwai Chung, Hong Kong. This is because the iliac crest is recognized as having the greatest diagnostic potential for 0. volvulus in Nigeria [12].…”

Human Onchocerciasis in the Amazonian Area of Southern Venezuela: Spatial and Temporal Variations in Biting and Parity Rates of Black Fly (Diptera: Simuliidae) Vectors

“…The results presented here form part of a more extensive study in southern Venezuela with the purpose of obtaining entomological, parasitological, and clinical indicators appropriate to the evaluation of onchocerciasis endemicity and severity, and for epidemiological modeling (Botto et al 1997(Botto et al , 1999Basáñ ez et al 1998, Basáñ ez andBoussinesq 1999;Vivas-Martṍnez et al 1998, 2000a, 2000b. The entomological component of this project aimed at quantifying, before and during mass ivermectin distribution, the spatial and seasonal variations of various components of vectorial capacity: biting rate on humans, parity rate, vector competence, and vector survival, as well as natural infection levels in the less studied species of the Amazonian area, namely, S. oyapockense s.l.…”