High prevalence of epilepsy in two rural onchocerciasis endemic villages in the Mahenge area,Tanzania,after 20 years of community directed treatment with ivermectin

Background:Epilepsy is a neurological disorder with a multitude of underlying causes,which may include infection with Onchocerca volvulus,the parasitic worm that causes human onchocerciasis.A survey carried out in 1989 revealed a high prevalence of epilepsy(1.02%overall,ranging from 0.51 to 3.71%in ten villages)in the Mahenge area of Ulanga district,an onchocerciasis endemic region in south eastern Tanzania.This study aimed to determine the prevalence and incidence of epilepsy following 20 years of onchocerciasis control through annual community directed treatment with ivermectin(CDTI).Methods:The study was conducted in January 2017 in two suburban and two rural villages in the Mahenge area.Door-todoor household visits were carried out by trained community health workers and data assistants to screen for persons suspected of having epilepsy,using a standardised questionnaire.Persons with suspected epilepsy were then interviewed and examined by a neurologist for case verification.Onchocerciasis associated epilepsy was defined as epilepsy without an obvious cause,with an onset of seizures between the ages of 3-18 years in previously healthy children.In each village,fifty males aged≥20 years were tested for onchocerciasis antibodies using an OV16 rapid test and were examined for presence of onchocerciasis nodules.Children aged 6-10 years were also tested using OV16 tests.Results:5117 individuals(median age 18.5 years,53.2%female)from 1168 households were screened.244(4.8%)were suspected of having epilepsy and invited for neurological assessment.Prevalence of epilepsy was 2.5%,with the rural villages having the highest rate(3.5%vs 1.5%),P<0.001.Overall incidence of epilepsy was 111 cases(95%CI:73-161)per 100000 person-years,while that of onchocerciasis associated epilepsy was 131(95%CI:70-223).Prevalence of OV16 antibodies in adult males and among children 6-10 years old was higher in rural villages than in suburban villages(76.5%vs 50.6,and 42.6%vs 4.7%respectively),(P<0.001),while overall prevalence of onchocerciasis nodules was 1.8%.Conclusions:This survey revealed a high prevalence and incidence of epilepsy in two rural onchocerciasis endemic villages in the Mahenge area.Despite 20 years of CDTI,a high prevalence of OV16 antibodies in children aged 6-10 years suggests on-going O.volvulus transmission.Reasons for the persistence of on-going parasite transmission in the Mahenge area need to be investigated.

Onchocerciasis-associated epilepsy:another piece in the puzzle from the Mahenge mountains, southern Tanzania

In a study from the onchocerciasis-endemic area of Mahenge in southern Tanzania,Mmbando et al.[Inf Dis Poverty.2018,7:64]demonstrate that in four selected villages the overall epilepsy prevalence was high,and significantly more elevated in the two villages of higher onchocerciasis endemicity compared to those of lower endemicity.This is replicating earlier findings from many other areas of tropical Africa.The authors are also providing data indicating that in the Mahenge focus,the prevalence of nodding syndrome may be related to that of onchocerciasis in the same way as epilepsy in general.The application of a clinical case definition for onchocerciasis-associated epilepsy(OAE)as used in the study of Mmbando et al.[Inf Dis Poverty.2018;7:64]faces some difficulties;indeed,its precision in discerning cases of OAE from epilepsy due to other etiologies is not known,and it does not allow for a specific diagnosis in the individual patient.Because an operational surveillance tool for assessing the number of patients in the population could mean substantial advance for better estimating the burden of OAE,the proposed definition should be tried in different settings and its performance reviewed in the process.