Association between Toxocara spp. seropositivity and cognitive outcomes in older adults: a cross-sectional analysis of the amirkola health and ageing project

BACKGROUND: Human evidence regarding the association between Toxocara exposure and cognitive function in older adults remains limited and derives largely from U.S. population-based studies, with heterogeneous findings across cognitive domains. Evidence from non-Western older populations is scarce. We therefore examined the association between Toxocara spp. seropositivity and MMSE-based cognitive outcomes among older adults participating in the Amirkola Health and Ageing Project (AHAP) in northern Iran. METHODS: This population-based cross-sectional study included adults aged ≥60 years who participated in phase 3 of AHAP during 2023-2024. Anti-Toxocara IgG antibodies were measured by enzyme-linked immunosorbent assay. Cognitive function was assessed using the Mini-Mental State Examination (MMSE), with cognitive impairment defined as an MMSE score <22 based on Iranian validation data. Logistic regression was used to examine MMSE-defined cognitive impairment, and upper-censored Tobit regression was used to evaluate continuous MMSE scores. RESULTS: Among 1,559 participants tested for Toxocara, seroprevalence was 44.7% (95% CI, 42.3-47.2%). The analytic sample included 1,453 participants with serological and MMSE data; 223 (15.3%; 95% CI, 13.5-17.3%) had cognitive impairment. In the fully adjusted model, Toxocara seropositivity was not significantly associated with MMSE-defined cognitive impairment (OR=1.31; 95% CI, 0.84-2.06; P=0.231). Similarly, in the fully adjusted Tobit model, the estimated marginal effect of Toxocara seropositivity on the observed MMSE score was -0.16 points (95% CI, -0.51 to 0.18; P=0.356). CONCLUSIONS: We found no statistically significant evidence of an association between Toxocara seropositivity and MMSE-based cognitive outcomes in older adults; however, modest associations cannot be excluded. Longitudinal studies using domain-specific cognitive assessments are needed.