Prevalence of onchocerciasis and epilepsy in a Tanzanian region after a prolonged community-directed treatment with ivermectin

Journal article

Introduction: Epidemiological evidence suggests that Onchocerca volvulus is associated with epilepsy, although the exact pathophysiological mechanism is unknown. Mahenge is an endemic focus of onchocerciasis, with the longest-running ivermectin treatment intervention in Tanzania. We assessed the prevalence of onchocerciasis and epilepsy after 25 years of control using ivermectin. Methods: This was a population-based cross-sectional study in 34 villages in Mahenge in 2021. Community health workers conducted door-to-door household surveys to enumerate the population and screen for individuals suspected of epilepsy using a standardised questionnaire. Trained physicians confirmed epilepsy. Children aged 6–11 years were screened for onchocerciasis antibodies using the Ov16 rapid test. Villages were stratified into three altitude levels (low [<400], medium [400–950], and high [>950 meters above sea level]) as a proxy for rapids, which black flies favour for breeding sites. Incidence of epilepsy was estimated as a ratio of new cases in the year preceding the survey per 100,000 population. Results: 56,604 individuals (median age 20.2 years, 51.1% females) were surveyed. Onchocerciasis prevalence in children was 11.8% and was highest in villages at medium (21.7%) and lowest in low altitudes (3.2%), p<0.001. Self-reported use of ivermectin was 88.4%. Epilepsy prevalence was 21.1 (95%CI: 19.9–22.3) cases per 1000 persons and was highest in medium (29.5%) and lowest in the lowlands (12.7%). The odds ratio (OR) of having epilepsy was significantly higher in females (OR = 1.22, 95%CI: 1.08–1.38), middle altitudes (OR = 2.34 [95%CI: 2.04–2.68]), and in individuals positive for OV16 (OR = 1.98 [95%CI:1.57–2.50]). The incidence of epilepsy a year before the survey was 117 (95%CI: 99.7–160.4) cases per 100,000 person-years. Conclusion: Despite ivermectin use for 25 years, the prevalence of onchocerciasis and epilepsy remains high. It is crucial to strengthen bi-annual ivermectin treatment and initiate interventions targeting vectors to control onchocerciasis and epilepsy in the area.

Authors: Mushi, VP; Bhwana, D; Massawe, IS; Makunde, W; Sebukoto, H

• Publication status: Published
• Peer review status: Peer reviewed
• Publisher: Public Library of Science
• Journal: PLoS Neglected Tropical Diseases
• Volume: 18
• Issue: 9
• Article number: e0012470
• Publication date: 2024-09-06
• Acceptance date: 2024-08-18
• DOI: 10.1371/journal.pntd.0012470
• EISSN: 1935-2735
• Language: English