Abstract
To eliminate onchocerciasis-associated morbidity, it is important to identify areas where there is still high ongoing Onchocerca volvulus transmission. Between 2015 and 2021, door-to-door surveys were conducted in onchocerciasis-endemic villages in Cameroon, the Democratic Republic of Congo (DRC), Nigeria, South Sudan, and Tanzania to determine epilepsy prevalence and incidence, type of epilepsy and ivermectin therapeutic coverage. Moreover, children aged between six and 10 years were tested for anti-Onchocerca antibodies using the Ov16 IgG4 rapid diagnostic test (RDT). A mixed-effect binary logistic regression analysis was used to assess significantly associated variables of Ov16 antibody seroprevalence. A high prevalence and incidence of epilepsy was found to be associated with a high Ov16 antibody seroprevalence among 6–10-year-old children, except in the Logo health zone, DRC. The low Ov16 antibody seroprevalence among young children in the Logo health zone, despite a high prevalence of epilepsy, may be explained by a recent decrease in O. volvulus transmission because of a decline in the Simulium vector population as a result of deforestation. In the Central African Republic, a new focus of O. volvulus transmission was detected based on the high Ov16 IgG4 seropositivity among children and the detecting of nodding syndrome cases, a phenotypic form of onchocerciasis-associated epilepsy (OAE). In conclusion, Ov16 IgG4 RDT testing of 6–10-year-old children is a cheap and rapid method to determine the level of ongoing O. volvulus transmission and to assess, together with surveillance for OAE, the performance of onchocerciasis elimination programs.
Highlights
Onchocerciasis, commonly known as river blindness, is caused by the filarial worm Onchocerca volvulus (O. volvulus) [1]
47,935 individuals from eight different onchocerciasis foci participated in the epilepsy door-to-door surveys and Ov16 rapid diagnostic test (RDT) were performed in 1821 children aged 6–10 years
Ivermectin coverage, and Ov16 RDT testing among 6–10-year-old children constitutes three important parameters to evaluate the performance of onchocerciasis-elimination programs and/or to identify sites where potentially such a program needs to be introduced
Summary
Onchocerciasis, commonly known as river blindness, is caused by the filarial worm Onchocerca volvulus (O. volvulus) [1]. It is estimated that 99% of the 20.9 million O. volvulus infected individuals live in 31 African countries [2]. Over 70% (14.6 million) of the O. volvulus infected individuals are considered to have onchocerciasis-induced skin disease and 5.5% (1.15 million) to have vision loss [3]. Accumulating evidence suggest that O. volvulus infection is able to trigger epilepsy in a manner that is dependent on the microfilarial (mf) load in the skin [4,5,6], so-called onchocerciasis-associated epilepsy (OAE) [7]. Onchocerciasis-elimination programs rely on community-directed treatment with ivermectin (CDTI) and vector control [3]. Using CDTI, the African Programme for Onchocerciasis Control (APOC) has successfully eliminated onchocerciasis as a public health problem in several African countries [3,8]. In some onchocerciasis-endemic areas in Africa there is still high ongoing O. volvulus transmission and a high prevalence of onchocerciasis-associated morbidity including OAE due to low CDTI coverage and in some areas resulting from CDTI interruptions during the periods of insecurity [7,9,10]
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