Reciprocal heterologous protection between Trichinella spiralis and Toxoplasma gondii concurrently present in experimental murine models.

Mixed parasitic infections have been long seen as a double impact on the host. In this study a different view of polyparasitism is demonstrated. The influence of the immunological environments created by two biologically different parasites on the pathogenesis of each other was evaluated. Swiss albino mice were sequentially infected with the intracellular protozoan Toxoplasma gondii (acute and latent), which elicits a T-helper 1 (Th1)-polarized immune response and the helminth parasite Trichinella spiralis, whose infection is predominated by a Th2 response. The results show a significant heterologous protection from one parasite towards the other. There was a highly significant lower Trichinella muscle larvae burden in mixed infection group compared to single Trichinella infection, in spite of delayed intestinal adult worm expulsion in the mixed infection group. A highly significant lower burden of T. gondii brain cysts in mixed infection compared to single latent Toxoplasma infection was also demonstrated. Concerning the anti-Toxoplasma antibody response, there was a significant lower levels in the latent Toxo-Trich. group compared to the group of latent toxoplasmosis only. These significant lower antibody titers were reproducible by two different assays; dye test and direct agglutination test.