A comparison of sporozoite transport after homologous and heterologous challenge in chickens immunized with the Guelph strain or the Florida strain of Eimeria maxima

The two strains of Eimeria maxima, Guelph and Florida, used in this study were previously shown to only partially cross-protect immunologically with respect to lesion scores, weight gains and feed conversions after heterologous challenge. In this paper, we provide evidence that this partial lack of cross-protection is manifested at the level of sporozoite transport. In birds immunized and challenged with the homologous strain, sporozoites accumulated in the lamina propria and were blocked from further movement into the crypts by 72 h post-challenge, unlike the situation observed in naive birds. Fewer than 5% of sporozoites were found in the crypts by 72 h post-challenge. In immunized birds challenged with the heterologous strain, fewer sporozoites reached the crypts than in naive birds but at least four times as many sporozoites successfully migrated to the crypts, when compared with birds challenged with the homologous strain. The degree of cross-protection afforded by the heterologous strain as measured by sporozoite transport success was not equally reciprocal. Received: 26 June 2000 / Accepted: 8 August 2000