Infectious Disease · Medical Literature
Toxocara infection in children with asthma: a systematic review and meta-analysis.
Abstract
Evidence linking zoonotic nematode Toxocara and asthma is mounting in children. We aimed to estimate the pooled prevalence of Toxocara seropositivity in asthmatic children and quantify the association. We searched PubMed, Embase and Web of Science for studies (through 18 June 2025) reporting Toxocara seropositivity in asthmatic children. A random effects model was used to estimate pooled seroprevalence and odds ratios (ORs). Heterogeneity was explored using τ2, I2 and Cochran's Q test, subgroup analyses, meta-regression and sensitivity analysis. Publication bias assessment (Egger's test, funnel plots, trim and fill) and risk of bias evaluation (Newcastle-Ottawa Scale) was performed. Twenty-six studies comprising 3246 asthmatic children were included, of which 7 were high-quality studies. Pooled Toxocara seropositivity among asthma was 22% (95% confidence interval 16 to 29) with significant country-wise heterogeneity. In 23 studies comparing cases and controls, asthmatic children had significantly higher odds of Toxocara seropositivity (pooled OR 2.56, p<0.0001), with significant variation by geographic region (p<0.0001) and asthma case definitions (p=0.0004), with stronger associations observed in studies using rigorous definitions such as the Global Initiative for Asthma criteria. Sensitivity analyses showed that while the direction of association remained consistent, the magnitude was influenced by a few outlier studies. There is a significant association between Toxocara seropositivity and childhood asthma; however, the strength of this association should be interpreted cautiously due to heterogeneity, potential cross-reactivity in serological assays and methodological differences across studies. Prospective longitudinal studies and randomized controlled trials evaluating the impact of antiparasitic treatment are needed to clarify temporal relationships and establish causality.
Clinical relevance
Among children with asthma, what is the pooled prevalence of Toxocara seropositivity, and is Toxocara seropositivity independently associated with increased odds of asthma compared to non-asthmatic controls? __SNAPSHOT__ {"studyDesign":"Systematic review with meta-analysis (random-effects model); includes case-control and prevalence studies","setting":"International; multi-country data aggregated from PubMed, Embase, and Web of Science (search date through 18 June 2025)","sampleSize":"26 studies comprising n=3,246 asthmatic children; 23 studies included a case-control comparison (control group sizes not reported in abstract)","population":"Children with asthma; age ranges and specific inclusion criteria for individual primary studies not detailed in abstract; geographic variation present across included studies","intervention":"Toxocara seropositivity (anti-Toxocara IgG antibody detection, consistent with visceral/occult toxocariasis exposure)","comparator":"Non-asthmatic controls (in 23 of 26 included studies); 3 studies appear to report seroprevalence only without a control arm","primaryOutcome":"Pooled prevalence of Toxocara seropositivity in asthmatic children; pooled odds ratio (OR) for Toxocara seropositivity in asthmatic children vs. controls","followUp":"Not applicable (cross-sectional seroprevalence and case-control designs); temporal relationship between infection and asthma onset not reported","fundingSource":"Not reported in abstract"}
Key findings
Twenty-six studies (n=3,246 asthmatic children) were included. The pooled prevalence of Toxocara seropositivity among asthmatic children was 22% (95% CI: 16%–29%), with significant country-level heterogeneity (statistical measure not specified beyond τ², I², and Cochran's Q testing). In 23 studies with case-control designs, asthmatic children had significantly higher odds of Toxocara seropositivity compared to controls (pooled OR 2.56; p<0.0001). Confidence intervals for the OR were not reported in the abstract. NNT/NNH cannot be calculated from available data. Significant effect modification was observed by geographic region (p<0.0001) and by asthma case definition (p=0.0004), with the abstract indicating stronger associations under certain conditions (text truncated; full subgroup results not available). Only 7 of 26 studies were rated as high-quality by the Newcastle-Ottawa Scale. Publication bias was assessed using Egger's test, funnel plots, and trim-and-fill methods; results of these assessments are not described in the available abstract text. Adverse events are not applicable to this observational meta-analysis.
Practice implications
This meta-analysis establishes a statistically significant association between Toxocara seropositivity and asthma in children (pooled OR 2.56, p<0.0001), with approximately 1 in 5 asthmatic children in pooled studies being seropositive. However, several critical limitations preclude causal inference: (1) All primary studies are cross-sectional or case-control in design, making it impossible to determine whether Toxocara infection precedes asthma onset, co-occurs, or represents reverse causation (e.g., eosinophilic airway inflammation heightening serologic cross-reactivity). (2) Substantial heterogeneity across geographic regions and case definitions limits generalizability to any single clinical population. (3) Only 7/26 primary studies were rated high-quality, introducing meaningful risk of bias across the evidence base. (4) The abstract is truncated, meaning subgroup and sensitivity analysis results, publication bias conclusions, and meta-regression findings are unavailable for review. (5) Populations underrepresented include children from high-income, low-endemicity settings, where the clinical relevance is likely lower. The findings are most applicable to children in regions with higher Toxocara endemicity (e.g., Latin America, Eastern Europe, parts of Africa and Asia). This summary is based on the abstract only; full-text review is required before applying findings to clinical decision-making. __LIMITATIONS__ Cross-sectional and case-control designs preclude causal or temporal inference between Toxocara exposure and asthma development.,Only 7 of 26 included studies were rated high-quality on the Newcastle-Ottawa Scale, indicating elevated risk of bias across the evidence base.,Significant unexplained heterogeneity by geographic region and asthma case definition substantially limits pooled estimates.,Asthma case definitions varied across primary studies, introducing heterogeneity in the outcome itself.,Serologic cross-reactivity between Toxocara and other helminths may lead to misclassification of exposure.,The abstract is truncated; subgroup analysis results, meta-regression outputs, and publication bias conclusions are unavailable, preventing full methodological appraisal.,Control group sizes and matching criteria are not reported, making it impossible to assess selection bias in the case-control comparisons.,Confounding by socioeconomic status, pet ownership, geographic exposure, and atopic predisposition is not addressed in the abstract.,Confidence intervals for the pooled OR are not reported in the abstract, limiting precision assessment.,Funding source is not reported, precluding conflict-of-interest evaluation. __BOTTOM_LINE_CATEGORY__ promising_but_preliminary __BOTTOM_LINE__ This systematic review and meta-analysis of 26 studies found that approximately 22% of asthmatic children are seropositive for Toxocara, with a pooled OR of 2.56 (p<0.0001) for seropositivity compared to non-asthmatic controls. However, all included studies are observational, quality is highly variable, and substantial geographic and definitional heterogeneity prevents causal conclusions. Routine Toxocara serologic screening in asthmatic children should not be adopted based on this evidence alone; rather, testing may be considered in children with poorly controlled asthma, peripheral eosinophilia, or relevant exposure history in endemic regions, pending prospective longitudinal data.