An inactivated vaccine against acquired Toxoplasma gondii infection in pigs as a tool to minimize the zoonotic transmission risk

Abstract

Toxoplasma gondii, a zoonotic protozoan parasite, represents a major threat to public health and food safety worldwide, particularly through the consumption of undercooked or raw pork containing tissue cysts. Controlling T. gondii infection in pigs is therefore critical to reduce zoonotic transmission. This study evaluated a novel inactivated vaccine formulated with antigens from the Type III TgPigSp1 isolate, comprising both tachyzoite and bradyzoite stages, and adjuvanted with Quil-A. Safety, immunogenicity, and efficacy were assessed first in a murine model as proof of concept and subsequently in piglets challenged with 1000 oocysts of the heterologous Type II-PRU TgShSp1 isolate. The vaccine showed no systemic adverse effects in either model, and an absence of local reactions was observed in piglets. In mice, vaccination elicited strong parasite-specific IgG responses and significantly reduced the parasite burden in brain and muscle tissues by more than 80%. In piglets, robust humoral and cellular immune responses were induced, as evidenced by elevated IgG and IFN-γ levels after the booster vaccination. Following challenge, the parasite load was reduced by ≥ 95% in target muscles, and viable T. gondii cysts were undetectable in at least 50% of vaccinated animals, as confirmed by bioassay. Molecular detection methods further supported the significant reduction in the parasite DNA content. These results indicate that this inactivated multistage vaccine represents a safe, immunogenic, and effective strategy to reduce tissue cyst formation and offer a promising tool within a One Health approach to improve food safety and reduce the burden of toxoplasmosis in both animal and human populations.