Age at Infection as a Key Predictor of Cyst Burden in Pigs Experimentally Infected with Taenia solium

Background: Taenia solium cysticercosis is a zoonotic parasitic disease with significant public health implications, particularly in endemic regions of low- and middle-income countries. In pigs, cyst burden varies widely, with most harboring fewer than 10 cysts and only a small fraction carrying high cyst loads. Age has been identified as a key factor influencing infection susceptibility. However, inconsistencies in previous studies have hindered clear characterization of infection patterns and immunity. In this study, we conducted controlled experiments involving the infection of pigs with T. solium eggs to evaluate the relationship between pig age and susceptibility to infection. Methods: A total of 52 pigs from northern Peru, aged 4 to 22 weeks, were experimentally infected with T. solium eggs to examine age-related differences in cyst burden. Pigs were housed individually under controlled conditions and fed commercial pig diets. Infections were administered using an esophageal catheter, delivering 20,000 T. solium eggs encapsulated in gelatin capsules. Six age groups were studied using a standardized egg pool to ensure consistency across infection rounds. After 10 weeks, necropsies were performed to count cysts in all muscles, the brain, and other organs. Weekly serological tests monitored seroconversion. Statistical models were used to analyze cyst counts and assess the effects of age and other predictors. Results: The number of live, degenerated, and total cysts was overdispersed making a negative binomial model the most suitable choice to represent the data and their dependence on age at infection. Younger pigs showed low median live cyst count, similar to older pigs, while median cyst burden increased in pigs infected at intermediate ages, around natural weaning age. The negative binomial regression showed that age and a covariate inversely related to age at infection were significantly associated with cyst count at necropsy. Other covariates such as pool viability and sex did not significantly affect model performance. Serological tests confirmed seroconversion in all pigs. Conclusions: Our results show that younger pigs display partial protection against the development of cysticerci compared to those infected at the natural weaning age (around 9 to 12 weeks of age). Additionally, infection susceptibility then decreases with age in a way that is consistent with previous literature hypothesizing near-complete resistance by one year of age.