The temporal relationship between onchocerciasis and epilepsy: a population-based cohort study

Background Many studies have suggested that onchocerciasis might be associated with epilepsy. Therefore, we did a cohort study to assess the incidence of epilepsy relative to Onchocerca volvulus skin microfilarial density (MFD) measured during childhood and to assess the possibility of a temporal relationship. Methods During onchocerciasis surveys undertaken in 25 villages in Cameroon during 1991-93, we measured MFD in individuals aged 5 years or older. In 2017, we revisited seven of these villages. With a standardised five-item questionnaire, we collected information on the occurrence of epilepsy in 856 individuals who were aged 5-10 years in 1991-93, and had MFD determined during the original surveys. We did multivariable analyses to assess the overall incidence and incidence ratios taking into account age, sex, individual MFD in 1991-93, and onchocerciasis endemicity level in the village. Findings In 2017, we obtained data on the history of epilepsy for 85% (729 of 856) of individuals. Among these individuals, we classified 60 as being suspected cases of epilepsy. The overall incidence of epilepsy was 350 per 100 000 person-years (95% CI 270-450). The adjusted incidence ratio for developing epilepsy was 7.07 (95% CI 0.98-51.26; p=0.0530) in individuals with initial MFD of one to five microfilariae per skin snip (mf per snip), 11.26 (2.73-46.43) in individuals with six to 20 mf per snip, 12.90 (4.40-37.83) in individuals with 21-50 mf per snip, 20.00 (3.71-108.00) in individuals with 51-100 mf per snip, 22.58 (3.21-158.56) in individuals with 101-200 mf per snip, and 28.50 (95% CI 3.84-211.27; 13=0.0010) in individuals with more than 200 mf per snip, compared with that of individuals without detectable densities of skin microfilariae. Interpretation Individual O volvulus MFD in childhood was associated with the risk of either seizures or epilepsy in an onchocerciasis focus in Cameroon. This temporal relationship suggests a potential causal link between onchocerciasis and epilepsy. Copyright (C) 2018 Elsevier Ltd. All rights reserved.