Assessment of live candidate vaccines for paratuberculosis in animal models and macrophages.

Mycobacterium avium subsp. paratuberculosis (basonym M. paratuberculosis) is the causative agent of paratuberculosis, a chronic enteritis of ruminants. To control the considerable economic effect that paratuberculosis has on the livestock industry, a vaccine that induces protection with minimal side effects is required. We employed transposon mutagenesis and allelic exchange to develop three potential vaccine candidates, which were then tested for virulence with macrophages, mice, and goats. All three models identified the WAg906 mutant as being the most attenuated, but some differences in the levels of attenuation were evident among the models when testing the other strains. In a preliminary mouse vaccine experiment, limited protection was induced by WAg915, as evidenced by a reduced bacterial load in spleens and livers 12 weeks following intraperitoneal challenge with M. paratuberculosis K10. While we found macrophages and murine models to be rapid and cost-effective alternatives for the initial screening of M. paratuberculosis mutants for attenuation, it appears necessary to do the definitive assessment of attenuation with a ruminant model.