|Van Kessel, Jo Ann|
Submitted to: Joint Meeting of the ADSA, AMSA, ASAS and PSA
Publication Type: Abstract Only
Publication Acceptance Date: 2/17/2006
Publication Date: 7/9/2006
Citation: Hovingh, E., Whitlock, R.H., Sweeney, R.W., Fyock, T., Wolfgang, D.R., Smith, J., Schukken, Y.H., Van Kessel, J.S. 2006. Identification and implications of map supershedders. Joint Meeting of the ADSA, AMSA, ASAS and PSA, Minneapolis, MN, July 9-13, 2006. Interpretive Summary:
Technical Abstract: The objective of this research was to determine the range of colony-forming units (cfu) per gram of Mycobacterium avium paratuberculosis (MAP) in manure from cows previously classified as heavy shedders, and the role of these animals in Johne’s Disease (JD) in dairy herds. Cattle are typically classified as light, moderate or heavy shedders based on the number of MAP colonies seen on Herrold’s egg yolk media (HEYM). Laboratories routinely report the number of cfu up to 70 per HEYM tube. (Seventy cfu corresponds to an estimated 1,470 MAP cfu per gram of manure.) Counts above 70 are reported as ‘too numerous to count’ and these cows are classified as heavy shedders. Preliminary investigation found that 1:100 and 1:1,000 dilutions of feces from heavy shedders were appropriate for enumerating the actual concentration of MAP in these samples. Subsequently, more than 200 fecal samples from animals currently identified as heavy shedders were diluted and cultured on HEYM. Supershedders (SS) were defined as animals that had manure with more than 10,000 cfu/gm. Culture results on diluted samples demonstrated that a substantial proportion of heavy shedders were SS, with some animals exceeding 1,000,000 MAP cfu/gm. Whole herd cultures from 4 herds found that 10% to 15% of all culture positives were SS. Not all of these SS cattle demonstrated clinical signs of JD at the time of sampling. It was calculated that SS cattle shedding the highest concentration of MAP were shedding more cfu than 2,000 moderate or 20,000 light shedders. Subsequent culture in one herd after the removal of a SS identified up to 15 animals that were potential false positives on the previous culture. This study has demonstrated the previously undocumented presence of MAP supershedders. The results suggest that SS contribute disproportionately to the herd environmental bioburden and the exposure of uninfected animals to MAP organisms. The data also suggest that the bioburden in herds with a SS present may contribute to herdmates being incorrectly identified as culture positive. Identification and removal of SS animals is likely to be a a critical component of a JD control and management program.