Immunity against reinfection in pigs following Taenia solium infection and a quantitative dose-response model

Background: Taenia solium is a zoonotic parasite causing significant health and economic burdens, with complex transmission dynamics requiring improved control strategies. Methods: This study investigates the effect of T. solium infection and reinfection on cyst development in pigs and evaluates how acquired immunity constrains parasite burden. A total of 116 pigs were purchased from commercial farms in northern Peru and housed in pathogen-free facilities under controlled conditions. Of these, 110 pigs were allocated to 18 experimental groups to (1) evaluate the impact of infection and reinfection with varying doses of T. solium eggs and (2) generate a model to predict the number of live cysts produced, given the dose and age at infection. Gravid proglottids collected from human cases of T. solium taeniasis were used to prepare egg pools, ensuring viability consistency. Infections were administered orally using gelatin capsules via esophageal catheterization, followed by necropsy 10 weeks after the final infection event to quantify cysts. A negative binomial regression model was used to analyze cyst burden dependence on infection dose, past infection, age, and other factors. Results: No statistically significant differences in cyst counts were observed between pigs infected once and those that were reinfected, regardless of the initial dose (as low as 100 eggs) or reinfection dose (up to 20,000 eggs). This finding highlights that infection results in strong acquired immunity, effectively blocking subsequent infections. A quantitative dose-response model suggests that the relationship between egg dose and the number of viable cysts is best described by a power relationship. Combining data from single-infection and reinfected pigs into a unified model improved prediction precision. Finally, incorporating age at infection results in a model of the number of viable cysts in pigs depending on dose and age that combines acquired and innate immunity effects, i.e. changes in susceptibility with age. Conclusions: Initial exposure to T. solium eggs induces strong acquired immunity in pigs, effectively preventing reinfection. Our quantitative dose-response model predicting live cyst counts based on egg dose and pig age offers valuable insights for integrating immunity processes into models of T. solium transmission.