Risk factors for Toxoplasma gondii seropositivity in the Old Order Amish

Abstract

Toxoplasma gondii (T. gondii) is an important human disease-causing parasite. In the USA, T. gondii infects >10% of the population, accrues economic losses of US$3.6 billion/year, and ranks as the second leading culprit of foodborne illness-related fatalities. We assessed toxoplasmosis risk among the Old Order Amish, a mostly homogenous population with a high prevalence of T. gondii seropositivity, using a questionnaire focusing on food consumption/preparation behaviours and environmental risk factors. Analyses were conducted using multiple logistic regression. Consuming raw meat, rare meat, or unpasteurised cow or goat milk products was associated with increased odds of seropositivity (unadjusted Odds Ratios: 2.192, 1.613, and 1.718 , respectively). In separate models by sex, consuming raw meat, or consuming unpasteurised cow or goat milk products, was associated with increased odds of seropositivity among women; washing hands after touching meat with decreased odds of seropositivity among women (adjusted OR (AOR): 0.462); and cleaning cat litterbox with increased odds of seropositivity among men (AOR: 5.241). This is the first study to assess associations between behavioural and environmental risk factors and T. gondii seropositivity in a US population with high seroprevalence for T. gondii. Our study emphasises the importance of proper food safety behaviours to avoid the risk of infection.

Keywords: Amish; Toxoplasma gondii; food safety.

Fig. 1.

Toxoplasma gondii life cycle: The definitive felid hosts, including house cats (1), uptake the Toxoplasma gondii parasite through ingestion of tissue oocysts (5) from infected intermediates, such as rodent and bird prey, or other sources, including water (4a). Following uptake, the definitive felid hosts shed unsporulated oocysts for up to 3 weeks through feces (2), contaminating water, soil, kitty litter, and food sources (3) of intermediate hosts/sources (4a/4b). The unsporulated oocysts distributed through the definitive felid host feces take 1 to 5 days to become infective. Intermediates include the definitive felid host prey, human food sources, water, and soil (4b). Humans can contract infection through intake of contaminated food or water; contact with contaminated soil or kitty litter; blood transfusions or organ transplants; or maternal to fetal (vertical/placental) transmission.