Chesnais CB, et al. - Researchers investigated if a temporal link exists between onchocerciasis and epilepsy. They evaluated the Onchocerca volvulus skin microfilarial density (MFD) measured during childhood relative to the incidence of epilepsy. In Cameroon, they observed the risk of either seizures or epilepsy was correlated to individual O volvulus MFD in childhood. A temporal link was observed that was suggestive of a potential causal link between onchocerciasis and epilepsy.

Methods

• Researchers measured MFD in individuals aged 5 years or older during onchocerciasis surveys conducted in 25 villages in Cameroon during 1991–1993; 7 of these villages were revisited in 2017.
• In 856 individuals who were aged 5–10 years in 1991–1993 and had MFD determined during the original surveys, epilepsy occurrence was determined via a standardized five-item questionnaire.
• The overall incidence and incidence ratios were evaluated in multivariable analyses taking into account age, sex, individual MFD in 1991–1993, and onchocerciasis endemicity level in the village.

Results

• For 85% (729 of 856) of individuals, history of epilepsy was collected in 2017; of those, 60 were classified as being suspected cases of epilepsy.
• The observed overall incidence of epilepsy was 350 per 100,000 person-years (95% CI 270–450).
• For developing epilepsy, the observed adjusted incidence ratio 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; p=0.0010) in individuals with more than 200 mf per snip, vs those without detectable densities of skin microfilariae.