Effects of Toxoplasma gondii (Gleadle strain) on the host-parasite relationship in trichinosis.

The effects of concurrent infection with Toxoplasma gondii on the host-parasite relationship in trichinosis were studied. Infected mice showed a delay in expulsion of Trichinella spiralis adults from the gut. Persisting adult female worms were fecund but the numbers of larvae recovered from the muscles were not increased. Increased resistance to the systemic phase of trichinosis was shown by reduced numbers of muscle larvae after intravenous injection of newborn larvae in animals with toxoplasmosis as compared with control mice. There were no differences in small bowel pathology of trichinous mice with and without toxoplasmosis but inflammation around muscle cysts of T. spiralis was reduced in mice with toxoplasmosis. The eosinophilia which normally develops in mice with trichinosis was suppressed by concurrent toxoplasmosis. Trichinella infection did not alter the numbers of T. gondii cysts recovered from the brain 4 weeks after infection. It is suggested that the delay in expulsion of adult worms, decrease in muscle inflammation around T. spiralis cysts, and inhibition of eosinophilia result from immune suppression, while the reduction in numbers of muscle larvae after intravenous injection of newborn larvae reflects enhanced nonspecific resistance to infection in toxoplasmosis.