Calves shedding Mycobacterium avium subspecies paratuberculosis are common on infected dairy farms

Abstract

Mycobacterium avium subspecies paratuberculosis (MAP) causes Johne’s disease, a chronic progressive enteritis. It is generally assumed that calves rarely shed MAP bacteria and that calf-to-calf transmission is of minor importance. The objectives were 1) to estimate the prevalence of MAP-shedding young stock in MAP-infected dairy herds, and identify predictors for test-positive young stock; and 2) to estimate proportions of MAP-contaminated young stock group housing pens and air spaces, and furthermore, identify predictors for test-positive pens. Fecal samples were collected from 2606 young stock on 18 MAP-infected dairy farms. Environmental fecal samples were collected from all group-housing pens and dust samples were collected from all barns. All individual samples were analysed using IS900 and F57 qPCR; fecal samples positive by either PCR and all environmental and dust samples were cultured. Overall, 8.1, 1.2 and 2.0% of cattle were positive on IS900 qPCR, F57 qPCR and bacterial culture, respectively. Young stock housed on farms with culture-positive environmental samples collected from adult cow housing and manure storage had higher odds of testing IS900 qPCR-positive than young stock housed on farms with only negative environmental samples. Furthermore, 14% of collected environmental samples, but no dust samples, were test-positive. Age of cattle in the pen was a significant predictor for environmental sample results. Young stock excreted MAP bacteria in their feces which provided strong evidence for calves as sources of within-herd transmission of MAP on dairy farms known to be infected with this organism.Electronic supplementary materialThe online version of this article (doi:10.1186/s13567-015-0192-1) contains supplementary material, which is available to authorized users.

The isolation and molecular characterization of Mycobacterium avium subsp. paratuberculosis in Shandong province, China

“…Complete eradication of the disease from cattle, although desirable, is extremely difficult [ 20 ]. Vaccination can be effective to control clinical disease, reducing faecal shedding and increasing productivity but it does not completely eliminate infection [ 21 , 22 ].…”

Quantifying transmission of Mycobacterium avium subsp. paratuberculosis among group-housed dairy calves

“…A second solution would be regular and vigorous maintenance of a clean group-housed environment, in which contaminated material is removed and replaced with new bedding and base, and sides of the enclosure are disinfected. Additionally, young stock should be considered for inclusion of MAP testing in a herd testing program, as up to 2% of young stock on positive farms have been identified positively for MAP shedding [15]. Animals with positive fecal samples, or whose environment tests are positive for MAP, should be immediately removed from group-housing and monitored/tested in the future to determine infection status.…”

“…The primary route of MAP transmission is fecal–oral through contaminated feed, milk, water and the environment caused by infectious animals intermittingly shedding MAP in their feces [7–9]. To decrease transmission from cows to calves and limit exposure of young stock to MAP, calves are removed from adult cows as soon as possible after birth and placed in calf barns or pens [10, 11]; however, calves up to 1 year of age have demonstrated susceptibility to MAP infection and calves can begin fecal shedding of MAP bacteria as early as 2 weeks after exposure [12–15]. Therefore, separating calves from cows and subsequent group housing may not be an effective method for prevention of new infections in young stock.…”

Knowledge gaps that hamper prevention and control ofMycobacterium aviumsubspeciesparatuberculosisinfection

“…It was estimated that under the circumstances of the study, one MAP‐infected calf on average infected three other calves. Additionally, on 17 MAP‐infected dairy farms in Alberta, Canada, 3% of calves were shedding the bacterium, and on nine of these farms, MAP‐positive environmental samples were collected from young stock pens (Wolf, Orsel, De Buck, & Barkema, ). Due to acidified milk feeding and automatic milk feeders (Barkema et al., ), many dairy calves are group‐housed both before and after weaning.…”