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Changes in Within-Flock Prevalence of Mycobacterium Avium Paratuberculosis Shedding Following Vaccination
Project OJD.033 was a longitudinal observational study examining the efficacy of GudairTM in decreasing the prevalence of shedding of infectious organisms following the commencement of vaccination in flocks varying in initial OJD prevalence. Twelve flocks were examined over a 6 year period, 3 with high, 5 with medium and 4 with low OJD prevalence at the commencement of the study. Changes in the prevalence of shedding as the proportion of vaccinates in the flock increased were estimated and it was found that vaccinates had significantly lower prevalence of shedding than unvaccinated sheep (0.63% versus 1.66%; P<0.001). However a significant observation was that at the final sampling when all adult sheep had been vaccinated as lambs, a total of 10 of the 11 flocks still in the study had sheep with detectable shedding, ranging from 0.13% to 1.29%. The persistence of shedding for an extended period following onset of vaccination presents a risk for spread and recrudescence of OJD. It is recommended that the study be continued for a further 3 rounds of testing to provide additional data on the rate of decline of shedding in flocks now composed entirely of ‘second generation vaccinates’. This will assist sheep producers to assess the risks of ceasing vaccination and purchasing vaccinated re-stocker sheep.
This page was last updated on 23/08/2017
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