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A method to determine the virulence of strains of Mycobacterium avium and related mycobacteria by measuring increases in spleen to body weight ratio (SBR) in C57 mice is described. Groups of 5 mice were inoculated with known numbers of viable mycobacteria and examined 100 days after inoculation. SBRs increased as the dose was increased and there were significant differences between some groups of mycobacteria but not between M. avium and M. paratuberculosis. Bacterial counts per g of spleen tissue were compared in infections with different species of mycobacteria. M. avium was present in the greatest numbers. High SBRs in mice indicated that strains were more likely to be pathogenic for chickens. © 1982.

Original publication




Journal article


Journal of Comparative Pathology

Publication Date





387 - 392