“Begging the Question”—Does Toxocara Infection/Exposure Associate with Multiple Sclerosis-Risk?

Abstract

Although the cause of multiple sclerosis (MS) is unclear, infectious agents, including some parasitic roundworms (nematodes), have been proposed as possible risk factors or contributors. Here, we conducted a systematic review and meta-analysis of published observational studies to evaluate whether there is a possible association between infection with, or exposure to, one or more members of the genus Toxocara (phylum Nematoda; superfamily Ascaridoidea) and MS. We undertook a search of public literature databases to identify relevant studies and then used a random-effects meta-analysis model to generate the pooled odds ratio (OR) and 95% confidence intervals (CIs). This search identified six of a total of 1371 articles that were relevant to the topic; these published studies involved totals of 473 MS patients and 647 control subjects. Anti-Toxocara IgG serum antibodies were detected in 62 MS patients and 37 controls, resulting in respective seroprevalences of 13.1% (95% CI: 8.2–20.3) and 4.8% (95% CI: 2.5–9.2), indicating an association (pooled OR, 3.01; 95% CI: 1.46–6.21). Because of the publication bias identified (six eligible studies), well-designed and -controlled studies are required in the future to rigorously test the hypothesis that Toxocara infection/exposure has an association with MS.

Case-Control Study to Assess the Association between Epilepsy and Toxocara Infection/Exposure

“…Although seroepidemiological studies suggest a relationship between Toxocara infection/exposure and epilepsy and other disorders, the pathogenic mechanisms underlying the neurological disorders are not well understood. One proposed mechanism relates to the migration of Toxocara larvae to, and through, the CNS [ 14 ], which may also account for other neuropsychiatric sequelae related to toxocariasis. Experimental studies in mice have revealed that Toxocara larvae can migrate in the tissues of the CNS for up to 28 days and survive for up to 2 years after infection [ 36 ].…”

“…MRI findings of neurotoxocariasis include subcortical, cortical or deep white-matter lesions with variable enhancement, which can associate with hydrocephalus, leptomeningeal or spinal cord involvement [ 13 ]. Findings from a range of epidemiological studies and meta-analyses [ 11 , 14 , 15 , 16 , 17 , 18 , 19 ] have indicated that Toxocara infection/exposure might play an under-appreciated role in inducing or contributing to neurological disorders, such as multiple sclerosis, schizophrenia, Parkinson’s, Alzheimer’s and/or epilepsy.…”

Helicobacter pylori infection and risk of multiple sclerosis: An updated meta‐analysis

“…8,9 Linked to the "hygiene hypothesis," it has been speculated that infection with particular microorganisms, particularly those occurring in childhood, may have a protective effect against allergic and autoimmune diseases. 10 In this regard, several studies have examined the possible involvement of infectious agents, such as Epstein-Barr virus and Toxocara spp., in promoting MS development, 8,[11][12][13] and others have suggested that parasites (e.g., Toxoplasma gondii, Necator americanus, and Trichuris suis) might prevent MS. [14][15][16] There is also been considerable debate as to whether Helicobacter pylori (H. pylori) is involved in development of MS or not. 17,18 H. pylori is a spiral-shaped, microaerophilic, gram-negative bacteria that colonizes the stomach of humans.…”

Translational Research of Zoonotic Parasites: Toward Improved Tools for Diagnosis, Treatment and Control

“…The wealth of literature published over recent decades requires critical systematic appraisals of information on NTDs. Taghipour et al [17] reviewed available medical literature to test a previous hypothesis of a possible association between Toxocara infection/exposure and multiple sclerosis (MS). Despite finding an association between anti-Toxocara IgG serum antibodies and MS in the published literature, the authors concluded that welldesigned and -controlled studies would be essential for a rigorous assessment of this association [17].…”

“…Taghipour et al [17] reviewed available medical literature to test a previous hypothesis of a possible association between Toxocara infection/exposure and multiple sclerosis (MS). Despite finding an association between anti-Toxocara IgG serum antibodies and MS in the published literature, the authors concluded that welldesigned and -controlled studies would be essential for a rigorous assessment of this association [17]. On a distinct topic, focused on the evaluation of the function of a par-ticular molecule, Mughal et al [18] characterised the right open reading frame protein kinase (Sj-riok-1) gene and its gene product (Sj-RIOK-1) in Schistosoma japonicum (a human blood fluke).…”