Detection of Mycobacterium avium subspecies paratuberculosis in the saliva of dairy cows: A pilot study

Johne's disease (JD) is a production limiting, intestinal disease of ruminants that is caused by Mycobacterium avium subsp. paratuberculosis (MAP). Transmission of MAP occurs predominately through feces, colostrum and milk. Since other intestinal bacteria can be found in saliva, it possible that saliva might serve as a previously overlooked route of MAP transmission. Therefore, the objective of this study was to investigate whether MAP is present in the saliva of cows. Methods were validated using MAP K10 spiked saliva samples of cows from a voluntary JD control program level 4 herd and applied to saliva and fecal samples of cows from a known infected herd. The matched pairs of saliva and feces were analyzed for MAP with PCR and culture. Fourteen of the twenty-six sampled cows were saliva positive by conventional PCR. The fecal samples of 10 and 6 cows were positive by realtime PCR and MAP culture, respectively. Overall there was a poor agreement between saliva and fecal PCR results for MAP (kappa 0.24). This is the first study that detected MAP in the saliva of cows. The finding needs further investigation to identify the source of MAP in saliva and to quantify the role of this newly identified route of MAP emission for the transmission of MAP infections on farm.