Oral vaccination against coccidiosis: responses in strains of mice that differ in susceptibility to infection with Eimeria vermiformis.

Four strains of mice with different susceptibilities to Eimeria vermiformis were orally dosed with a crude antigen prepared from sporulated oocysts of the parasite, with or without cholera toxin as adjuvant. The effect on subsequent challenge infections depended on the resistance and susceptibility phenotypes of the host: oocyst production was reduced in susceptible C57BL/6 and NIH mice but increased in resistant BALB/c and C3H mice. Despite this contrast, no fundamental differences were detected between the immune responses of BALB/c and C57BL/6 mice, either to vaccination or after superimposed infection, but the suppressing and enhancing effects of vaccination were transmissible to naive recipients via suspensions of mesenteric lymph node cells. The results obtained are compared with those previously reported for parenterally immunized BALB/c and C57BL/6 mice.