Research Article: Toxoplasmosis and Epilepsy — Systematic Review and Meta Analysis

Date Published: February 19, 2015

Publisher: Public Library of Science

Author(s): Edgard B. Ngoungou, Devender Bhalla, Amandine Nzoghe, Marie-Laure Dardé, Pierre-Marie Preux, Rima McLeod.

Abstract: BackgroundToxoplasmosis is an important, widespread, parasitic infection caused by Toxoplasma gondii. The chronic infection in immunocompetent patients, usually considered as asymptomatic, is now suspected to be a risk factor for various neurological disorders, including epilepsy. We aimed to conduct a systematic review and meta-analysis of the available literature to estimate the risk of epilepsy due to toxoplasmosis.MethodsA systematic literature search was conducted of several databases and journals to identify studies published in English or French, without date restriction, which looked at toxoplasmosis (as exposure) and epilepsy (as disease) and met certain other inclusion criteria. The search was based on keywords and suitable combinations in English and French. Fixed and random effects models were used to determine odds ratios, and statistical significance was set at 5.0%.Principal findingsSix studies were identified, with an estimated total of 2888 subjects, of whom 1280 had epilepsy (477 positive for toxoplasmosis) and 1608 did not (503 positive for toxoplasmosis). The common odds ratio (calculated) by random effects model was 2.25 (95% CI 1.27–3.9), p = 0.005.ConclusionsDespite the limited number of studies, and a lack of high-quality data, toxoplasmosis should continue to be regarded as an epilepsy risk factor. More and better studies are needed to determine the real impact of this parasite on the occurrence of epilepsy.

Partial Text: Epilepsy is a major chronic neurological disorder that affects about 70 million people worldwide [1]. However, its importance goes beyond mere numbers [2]. Most of its burden is felt in low- and middle-income tropical countries, where a number of infections that are important risk factors for epilepsy, are predominantly reported [3–5]. Parasitic infections are important causes of epileptic seizures or epilepsy, among other neurological and mental health conditions [6,7]. Infection with Toxoplasma gondii (T. gondii) in particular is reported to affect one-third of the world’s population, mainly in the low- and middle-income countries [8,9]. Certain currently available data strongly suggest the possibility of a relationship between toxoplasmosis and epilepsy [6] [10], although results to the contrary have also appeared [11]. Therefore, we conducted a systematic review and meta-analysis of published data to estimate the risk of epilepsy due to toxoplasmosis.

The results of the search are presented in Fig. 1. Five databases (Pubmed, ScienceDirect, Refdoc, IENT and Ingentaconnect), two journals (Médecine/Sciences, PlosOne) and Google search gave a total of 684 articles. Of these, 301 were cited more than once. Of the remaining 383 articles on toxoplasmosis and epilepsy, 372 articles were eliminated on the basis of title as either non-epidemiological or in a language other than English or French. The remaining 11 articles were read as abstracts, and one was excluded because its full text was not accessible. Furthermore, two were literature reviews [12] [13], one was a meta-analysis [10] and one was an epidemiological study that did not meet our inclusion criteria i.e. no control group [14]. The references of the review articles and meta-analysis did not add any new articles. Lastly, six studies were retained [2] [11] [3,15] [16] [17] [18], from Israel, USA, Turkey, Iran and various countries of sub-Saharan Africa. Interestingly, no studies were from Latin America, Europe, or most of Asia, table 1.

We conducted a systematic review and meta-analysis of literature primarily to estimate the relationship between chronic toxoplasmosis and epilepsy. Our literature search was comprehensive as different databases and specific journals were searched, including those in the French language to avoid any publication bias. However, this search might have excluded important studies published exclusively in other languages. The last meta-analysis on this subject, conducted in 2007, [10] included only three studies, whereas ours identified six, table 1.



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