Abstract
ObjectiveA systematic review and meta-analysis of all available case-control studies on the relationship between onchocerciasis and epilepsy. Because age and level of onchocerciasis endemicity in the area of residence are major determinants for infection, an additional analysis was performed, restricted to studies achieving control of these confounding factors.Data sourcesMedical databases, the “African Neurology Database, Institute of Neuroepidemiology and Tropical Neurology, Limoges,” reference lists of relevant articles, commercial search engines, up to May 2012.MethodsWe searched for studies examining infection status with Onchocerca volvulus in persons with epilepsy (PWE) and without epilepsy (PWOE) providing data suitable for the calculation of pooled odds ratios (ORp) and/or standardized mean differences (SMD) using random-effects models.ResultsEleven studies providing data of qualitative skin biopsies for diagnosis of onchocerciasis were identified. Combined analysis on the total sample of 876 PWE and 4712 PWOE resulted in an ORp of 2.49 (95% confidence interval (95%CI): 1.61–3.86, p<0.001). When this analysis was restricted to those studies achieving control for age, residence and sex (367 PWE, 624 PWOE), an ORp of 1.29 (95% CI: 0.93–1.79; p = 0.139) was found. Presence of nodules for diagnosis of onchocerciasis was analyzed in four studies (225 PWE, 189 PWOE; ORp 1.74; 95%CI: 0.94–3.20; p<0.076), including two studies of the restricted analysis (106 PWE, 106 PWOE; ORp 2.81; 95%CI: 1.57–5.00; p<0.001). One study examined quantitative microfilariae counts in patients without preceding microfilaricidal treatment and demonstrated significantly higher counts in PWE than in PWOE.InterpretationOur results strengthen the hypothesis that, in onchocerciasis foci, epilepsy and infection with O. volvulus are associated. Analysis of indicators giving information on infection intensity, namely nodule palpation and quantitative microfilaria count in untreated patients, support the hypothesis that intensity of infection with O. volvulus is involved in the etiology of epilepsy.
Highlights
Onchocerciasis is a parasitic disease caused by infection with the nematode worm Onchocerca volvulus
A study was considered eligible if it made a comparison of O. volvulus infection status in a group of people with epilepsy (PWE) to that in a comparison group of people without epilepsy (PWOE), and if it reported data allowing for the calculation of an odds ratio (OR) with O. volvulus infection status considered as exposure and epilepsy as outcome and its 95% confidence intervals
The article by Konig et al [36] and the abstract by Schmutzhard et al [45] from the Morogoro focus in Tanzania reported information on O. volvulus infection status of persons with epilepsy (PWE) and controls only as pooled data, based on skin snip microscopy combined with the results of a polymerase chain reaction (PCR) method searching for O. volvulus specific DNA in the skin
Summary
Onchocerciasis is a parasitic disease caused by infection with the nematode worm Onchocerca volvulus. Infective larvae are transmitted through bites of flies of the genus Simulium which breed along fastflowing rivers throughout tropical Africa and some areas of Latin America and Yemen [1]. Whereas children in the first years of life are only exceptionally infected, the prevalence rises to virtually 100% in adults living in highly endemic areas, with usually a higher proportion in the male population [2,3,4]. N Intensity of exposure: In communities living in villages exposed to onchocerciasis, prevalence and intensity of infection increase with the proximity to the breeding places and the frequency of the bites of vector flies and the number of infective larvae transmitted per bite [5]. Usually specified as village of residence, is considered a valid indicator of intensity of exposure
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