Abstract
Live vaccines for chicken coccidiosis using British or American strains of Eimeria are likely to be commercially available soon. To assess their potential usefulness in other countries, it is necessary to know the full extent of intra-specific antigenic differences, especially by comparing strains from widely separated geographical areas. Isolates of Eimeria acervulina, E. tenella, E. maxima, E. brunetti and E. necatrix were made from gut scrapings of birds at post-mortem in Bangladesh. Similar isolates of E. acervulina and E. tenella were made in Britain. For detailed study, 10 strains were derived from single oocyst infections of E. acervulina (5 Bangladesh, 2 England) and E. tenella (2 Bangladesh, 1 England). The biological, morphometric, isoenzyme and immunological compared.
characteristics of these strains were Regression of width on length and analysis of deviance some intra-specific morphological differences in E. acervulina. With one exception, strains within species were not different in pathogenicity or prolificity. Analysis of six isoenzymes revealed two zymodemes for E. acervulina and one for E. tenella. Polyclonal chick antibodies in serum and bile were totally cross-reactive between strains, but IgG isotype, though not IgA, showed a degree of species-specificity. A bank of 8 anti-E. tenella mouse monoclonal antibodies did not discriminate between In vivo E. tenella strains in immunofluorescence assays. cross-protection studies revealed intra-specific antigenic differences in E. acervulina on the basis of oocyst output but not weight gain. Two antigenically distinct which were also distinguishable by GPI isoenzyme mobility,
This
used to produce a genetically recombinant line which possessed hybrid isoenzyme characteristics. recombinant line conferred absolute protection against challenge with either of the two parental strains. tenella, intra-specific differences were observed both on the basis of oocyst output and weight gain when homologous immunity was complete by the criterion of weight gain but incomplete by oocyst output. In chicks solidly immune to homologous challenge by both criteria, heterologous immunity was almost complete. These results, using strains from widely separated geographical areas, confirm that there is a very limited degree of heterogeneity between strains of avian Eimeria. They suggest that intra-specific antigenic differences in E. acervulina and E. tenella from the United Kingdom and from Bangladesh will be of minor significance if chicks are solidly immune to homologous challenge. However, because it is difficult to develop complete immunity in young chicks, the intra-specific differences observed in this study need to be considered in immunoprophylaxis, especially of caecal coccidiosis. The possibility of using recombinant lines as master strains has been demonstrated.