BACKGROUND: In onchocerciasis endemic areas in Africa, heterogenous biting rates by blackfly vectors on humans are assumed to partially explain age- and sex-dependent infection patterns with Onchocerca volvulus. To underpin these assumptions and further improve predictions made by onchocerciasis transmission models, demographic patterns in antibody responses to salivary antigens of Simulium damnosum s.l. are evaluated as a measure of blackfly exposure. METHODOLOGY/PRINCIPAL FINDINGS: Recently developed IgG and IgM anti-saliva immunoassays for S. damnosum s.l. were applied to blood samples collected from residents in four onchocerciasis endemic villages in Ghana. Demographic patterns in antibody levels according to village, sex and age were explored by fitting generalized linear models. Antibody levels varied between villages but showed consistent patterns with age and sex. Both IgG and IgM responses declined with increasing age. IgG responses were generally lower in males than in females and exhibited a steeper decline in adult males than in adult females. No sex-specific difference was observed in IgM responses. CONCLUSIONS/SIGNIFICANCE: The decline in age-specific antibody patterns suggested development of immunotolerance or desensitization to blackfly saliva antigen in response to persistent exposure. The variation between sexes, and between adults and youngsters may reflect differences in behaviour influencing cumulative exposure. These measures of antibody acquisition and decay could be incorporated into onchocerciasis transmission models towards informing onchocerciasis control, elimination, and surveillance.

Biomedical and Public Health Research Unit CSIR Water Research Institute Accra Ghana

Centre for the Evaluation of Vaccinations Vaccine and Infectious Disease Institute University of Antwerp Wilrijk Belgium

Department of Parasitology Faculty of Science Charles University Prague Czech Republic

London Centre for Neglected Tropical Disease Research and Department of Pathobiology and Population Sciences Royal Veterinary College Hatfield United Kingdom

MRC Centre for Global Infectious Disease Analysis and London Centre for Neglected Tropical Disease Research Department of Infectious Disease Epidemiology School of Public Health Imperial College London London United Kingdom

Zeeman Institute for Systems Biology and Infectious Disease Epidemiology Research and School of Life Sciences University of Warwick Coventry United Kingdom

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