Schistosoma mansoni Worm Infection Regulates the Intestinal Microbiota and Susceptibility to Colitis.

Infection with parasite helminths induces potent modulation of the immune system of the host. Epidemiological and animal studies have shown that helminth infections can suppress or exacerbate unrelated autoimmune, allergic, and other inflammatory disorders. There is growing evidence that helminth infection-mediated suppression of bystander inflammatory responses is influenced by alterations in the intestinal microbiome modulating metabolic and immune functions of the infected host. We analyzed the fecal microbiota of mice infected with adult male Schistosoma mansoni worms, which are less susceptible to experimental colitis, and male- and female-worm-infected mice, which are highly sensitive to colitis. While both groups of infected mice developed a disrupted microbiota, there were marked alterations in mice with male and female worm infections. Antibiotic-treated recipients that were cohoused with both types of S. mansoni worm-infected mice acquired a colitogenic microbiome, leading to increased susceptibility to experimental colitis. Following anthelmintic treatment to remove worms from worm-only-infected mice, the mice developed exacerbated colitis. This study provides evidence that adult male S. mansoni worm infection modulates the host's immune system and suppresses bystander colitis while limiting dysbiosis of the host's intestinal microbiome during infection.