Comparison of pre- and post-vaccination ovine Johne's disease prevalence using a Bayesian approach

Abstract

This study was conducted to evaluate the effectiveness of Gudair TM vaccine in decreasing the prevalence of shedding of Mycobacterium avium subsp. paratuberculosis (MAP) in flocks of varying initial prevalence. Thirty seven self-replacing Merino flocks from New South Wales and Victoria (Australia) that had been vaccinating lambs with Gudair TM for at least five years were enrolled in the study. These flocks had been tested prior to or at commencement of vaccination using pooled faecal culture, agar gel immunodiffusion or both tests. These prevaccination test results were used to estimate pre-vaccination prevalence. Post-vaccination prevalence was estimated from culture of usually 7 pools of 50 sheep collected from the enrolled flocks in [2008][2009], approximately five or more years after commencement of vaccination.A Bayesian model was developed to estimate and compare the pre-and postvaccination prevalences for the enrolled flocks. Apparent pre-and post-vaccination prevalences for flocks were modelled as functions of the true pre-and post-vaccination prevalences, respectively, and the sensitivities and specificities of the respective diagnostic tests. Logit-normal models were specified on pre-and post-vaccination true prevalences and were then used to make inferences about the median and 90 th percentile of the prevalence 2 distributions and their differences. Priors were mostly specified based on published literature or analysis of abattoir surveillance data for this population of flocks.The analysis found a significant decline in ovine Johne's disease prevalence from a pre-vaccination median prevalence of 2.72% [95% probability interval (PI): 1.40; 6.86%] to a post-vaccination median prevalence of 0.72% (0.39; 1.27%). However 30 of the 37 flocks still contained sheep that were shedding MAP in their faeces. The results suggest that vaccination with Gudair™ is usually effective in reducing the prevalence of faecal shedding but the response to vaccination is variable among flocks. This approach could be implemented in similar situations to compare prevalences where information from multiple diagnostic tests with varied sensitivities and specificities is available.

High-Throughput Direct Fecal PCR Assay for Detection of Mycobacterium avium subsp. paratuberculosis in Sheep and Cattle

“…mortality in adult sheep. An annual lamb vaccination program commenced in 2002 using the Gudair vaccine (Zoetis Australia), and by the time fecal samples for this study were collected from adult sheep (3 to 7 years of age) from 2009 to 2010, sheep in all age classes on each of the 12 properties had been vaccinated, with a drop in the prevalence of fecal shedders recorded compared to prevaccination prevalence (25).…”

Effectiveness of Gudair™ vaccine for the control of ovine Johne's disease in flocks vaccinating for at least 5 years

“…Prevalence estimates ordered into categories constituted the ordinal outcome variable. Further, a Bayesian model was developed to estimate and compare the pre‐ and post‐vaccination prevalences for the enrolled flocks (detailed data published elsewhere).…”

Molecular and histopathological evaluation of the efficacy of Saponifiedand Freund’s incomplete adjuvanted paratuberculosiskilled vaccine in murine model

“…Vaccination is the only possible way to control the disease by reducing the morbidity and mortality which in turn will reduce the economic losses associated with the disease (Dhand et al, 2013;Singh et al, 2013;Sohal et al, 2015).…”

“…Vaccination is regarded as the only cost effective method for controlling JD (Dhand et al, 2013;Sohal et al, 2015).). Vaccination reduces morbidity and mortality due to JD, reduces shedding of MAP in feces, improves clinical signs (reduces diarrhea and increases body weight), cures intestinal lesions and enhances flock immunity to JD (Singh et al, 2013).…”