Proceedings of the 10th International Colloquium on Paratuberculosis

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Development <strong>of</strong> new live vaccines for paratuberculosis
Desmond M Collins, Gabriella M Scandurra, Ge<strong>of</strong>frey W de Lisle
AgResearch, National Centre for Biosecurity and Infectious Disease, Wallaceville, Upper Hutt, New Zealand
Control <strong>of</strong> paratuberculosis would be greatly facilitated by <strong>the</strong> availability <strong>of</strong> effective vaccines. However,
despite 80 years <strong>of</strong> vaccine development and use, current paratuberculosis vaccines provide only limited
protection, <strong>of</strong>ten cause unacceptable lesions at <strong>the</strong> site <strong>of</strong> inoculation, and interfere with diagnostic tests for
bovine tuberculosis. In order to develop vaccine candidates, mutants <strong>of</strong> Mycobacterium avium subsp. paratuberculosis
(MAP) were produced by random transposon mutagenesis and specific gene inactivation by allelic
exchange. Cytokine responses, levels <strong>of</strong> apoptosis and survival <strong>of</strong> selected mutants were assessed in bovine
macrophages, and virulence <strong>of</strong> <strong>the</strong> mutants was determined in mice and goats. Levels <strong>of</strong> apoptosis varied and
correlated with MAP strain virulence. All three models identified <strong>the</strong> same mutant (WAg906) as being <strong>the</strong> most
attenuated vaccine candidate, but some differences in <strong>the</strong> levels <strong>of</strong> attenuation were evident amongst <strong>the</strong>
models when testing <strong>the</strong> o<strong>the</strong>r strains. While we found macrophages and murine models to be rapid and cost
effective alternatives for <strong>the</strong> initial screening <strong>of</strong> MAP mutants for attenuation, <strong>the</strong> results correlated imperfectly
with those from <strong>the</strong> goat model, indicating <strong>the</strong> importance <strong>of</strong> assessing <strong>the</strong> virulence <strong>of</strong> likely vaccine candidates
in ruminants. Interestingly, ano<strong>the</strong>r mutant (WAg915) that was less attenuated than WAg906, showed
<strong>the</strong> greatest vaccine potential in a preliminary vaccine experiment, as animals vaccinated with WAg915 had <strong>the</strong>
lowest counts in <strong>the</strong> spleen and liver for <strong>the</strong> virulent MAP challenge strain.
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