Impact of a Bi-annual CDTI on the Incidence of Epilepsy in an Onchocerciasis-endemic Area

Overview

Onchocerciasis is a neglected tropical disease associated with epilepsy, particularly in areas of high Onchocerciasis volvulus transmission. Onchocerciasis-associated epilepsy is characterised by seizures that start between the ages of five to 18 years. The tropical disease can be controlled through community-directed treatment with ivermectin (CDTi). Mahenge, in Tanzania, had a high prevalence of onchocerciasis and epilepsy despite more than 20 years of annual CDTi. Hence, the Tanzanian Neglected Tropical Diseases Control Programme has switched from annual to bi-annually CDTi since 2019. After this switch, the CDTi coverage increased and was sustained in both ivermectin rounds in 2021, and the number of new epilepsy cases decreased. The latter were persons who did not take ivermectin the year they had the first seizures. Hence, all ivermectin-eligible children at risk of onchocerciasis should take ivermectin at least annually. Overall, increasing the frequency and coverage of the CDTi programme should be considered in onchocerciasis-endemic areas with a high prevalence of epilepsy.

Background: Community-directed treatment with ivermectin (CDTi) is used to eliminate onchocerciasis. However, despite 25 years of annual CDTi in Mahenge, Tanzania, the prevalence of onchocerciasis and onchocerciasis-associated epilepsy remained high in certain rural villages. Therefore, in 2019, bi-annual CDTi was introduced in the area. This study assessed the impact of the programme on the incidence of epilepsy in four villages. Methodology: Door-to-door epilepsy surveys were conducted prior to (2017/18) and after (2021) implementing bi-annual CDTi. All household members were screened for epilepsy symptoms using a validated questionnaire, and suspected cases were examined by a medical doctor to confirm/reject the diagnosis of epilepsy. The prevalence and annual incidence of epilepsy, including nodding syndrome, were calculated with 95% Wilson confidence intervals with continuity correction. The latter was also done for CDTi coverage in 2021.