Surveillance for Onchocerciasis-Associated Epilepsy and OV16 IgG4 Testing of Children 6–10 Years Old Should Be Used to Identify Areas Where Onchocerciasis Elimination Programs Need Strengthening

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.

Assessing Onchocerca volvulus Intensity of Infection and Genetic Diversity Using Mitochondrial Genome Sequencing of Single Microfilariae Obtained before and after Ivermectin Treatment

“…A recent study concluded that today, Simulium dentulosum appears to be the main vector of human onchocerciasis in the area, and that Simulium vorax may be a secondary vector [ 42 ]. Ov16 IgG4 antibody positivity, determined with the Ov16 IgG4 Bioline rapid diagnostic test [ 43 , 44 , 45 , 46 ], between 2016 and 2018 was 0% (0/55) among 6-year-old and 7.1% (13/182) among 7–10-year-old children in the Logo Health zone [ 47 ]. In contrast, the Ov16 seroprevalence, determined with the same rapid test in an area in Maridi close to the blackfly breeding site, was 40% among children 3–6 years old and 66.7% among children 7–9 years old [ 48 ].…”

Identification of the onchocerciasis vector in the Kakoi-Koda focus of the Democratic Republic of Congo

“…less than 20% nodule prevalence by REMO). However, the recent change of objective from onchocerciasis control to elimination of transmission requires new epidemiological mapping (known as 'elimination mapping', using OV-16 serology) so that 'Transmission Zones' (TZs) can be properly defined and CDTI can be extended into hypo-endemic areas [24][25][26]. A TZ is defined as "a geographical area where transmission of Onchocerca volvulus occurs by locally breeding vectors and which can be regarded as a natural ecological and epidemiological unit for interventions" [26].…”

Identification of the onchocerciasis vector in the Kakoi-Koda focus of the Democratic Republic of Congo

“…less than 20% nodule prevalence by REMO). However, the recent change of objective from onchocerciasis control to elimination of transmission requires new epidemiological mapping (known as ‘elimination mapping’, using OV-16 serology) so that ‘Transmission Zones’ (TZs) can be properly defined and CDTI can be extended into hypo-endemic areas (WHO, 2016; WHO-OTS, 2018; Dusabimana et al, 2022). A TZ is defined as “ a geographical area where transmission of Onchocerca volvulus occurs by locally breeding vectors and which can be regarded as a natural ecological and epidemiological unit for interventions ” (WHO, 2016).…”