Review of Epidemiological Studies Searching for a Relationship between Onchocerciasis and Epilepsy

Abstract

A review and a meta-analysis of the available epidemiological literature for evidence of an association between onchocerciasis infection and epilepsy were carried out. We used EMBASE (1974–2002), MEDLINE (1966–2002), and PASCAL (1987–2002) databases and relevant journals and bibliographies. We limited our analysis to the epidemiological studies, where the status regarding onchocerciasis infection and epilepsy was available for each subject. Nine African studies were included. The common relative risk estimated by the random-effects model was 1.21 (95% CI 0.99–1.47; p = 0.06). The meta-analysis did not show any difference according to the onchocerciasis endemicity level and the African areas. Our results do not allow to conclude for an association between Onchocerca volvulus infection and epilepsy. However, the results are nearly significant. Further research is needed in this neglected subject, in particular for the better understanding of the neurological pathogenicity in onchocerciasis.

Association Between Onchocerciasis and Epilepsy in the Itwara Hyperendemic Focus, West Uganda: Controlling for Time and Intensity of Exposure

“…Because the rate of infection with O. volvulus in a representative sample of the general population was not assessed with this study, Ovuga and others 6 consistently did not subject their results to additional statistical analysis. Despite these limitations, the review of the study by Druet-Cabanac and others 5 constructed a risk ratio from the data of Ovuga and others 6 by relating the rate of infection with O. volvulus of epilepsy patients to the rate found in the non-epilepsy patients reported in the article. However, the majority of these people without epilepsy was affected by the mentioned Nakalanga syndrome, which again, has been found to be associated with onchocerciasi s .…”

“…2,3,11,14,15 The use of these highly selected patients as a comparison group has to be considered inappropriate for the determination of a risk ratio, and the study by Ovuga and others 6 did not qualify for inclusion in the meta-analysis of Druet-Cabanac and others. 5 So far, only two studies have been published on the relationship between onchocerciasis and epilepsy using a clearly matched case-control design. Both of these studies, DruetCabanac and others 4 in a meso-endemic area in the Central African Republic and Boussinesq and others 3 in a hyperendemic area in Cameroon, found a slightly higher rate of microfilaridermia in epilepsy patients compared with matched controls, although this was not statistically significant.…”

“…1 Although some reports using a casecontrolled approach seem to corroborate the results of prevalence studies, 2-4 a more comprehensive review on controlled studies searching for a relationship between onchocerciasis and epilepsy concluded that the link between the two entities still remains controversial. 5 Ovuga and others 6 reported on the frequent occurrence of epilepsy in the Kyarusozi subcounty close to the Itwara forest, West Uganda, an area known to be highly endemic for onchocerciasis. 7 Two years later, a second study conducted in the same area found an elevated prevalence of epilepsy of 8% in a village hyperendemic for onchocerciasis compared with a low prevalence of epilepsy of 0.2% in a nearby hypoendemic village.…”

“…7 Two years later, a second study conducted in the same area found an elevated prevalence of epilepsy of 8% in a village hyperendemic for onchocerciasis compared with a low prevalence of epilepsy of 0.2% in a nearby hypoendemic village. 8 When data of both these studies were included in the cited review by Druet-Cabanac and others, 5 a contradictory result was observed. Although Kipp and others 8 found a high risk ratio of 6.5 (95% confidence interval [CI] = 3.0-15.0), suggesting a significant positive association between epilepsy and onchocerciasis, the risk ratio of 0.84 (95% CI = 0.74-0.95) derived from the data of Ovuga and others 6 indicated a clearly negative association ( Table 1 ).…”

MRI findings in people with epilepsy and nodding syndrome in an area endemic for onchocerciasis: An observational study

“…7,8 In African areas affected by onchocerciasis, some studies suggest a connection with epilepsy, [9][10][11][12][13][14] while others do not. [15][16][17] Overall a link between the two diseases seems possible, 18,19 but is far from being established. Latest results on NS from South Sudan indicate that in some villages significantly more children with NS are infested with O. volvulus compared to healthy controls, whereas in other villages no difference could be found between cases and controls.…”