Long-term detection of Mycobacterium avium subspecies paratuberculosis in individual and bulk tank milk from a dairy herd with a low prevalence of Johne’s disease

Abstract

Mycobacterium avium ssp. paratuberculosis (MAP) causes Johne's disease (JD) in ruminants and is shed into the milk of infected cows, which contributes to the controversial discussion about a possible link between MAP and Crohn's disease in humans. The aim of the study was to investigate the risk for the entry of MAP in the food chain via milk from dairy farms with subclinical JD. Therefore, the occurrence of MAP in the milk of a dairy herd with a low prevalence of JD was studied in single and bulk tank milk samples over a period of 23 mo and compared with MAP shedding into feces. Milk, fecal, and blood samples were taken from all cows older than 1.5 yr of age at the beginning and the end of the trial and analyzed for MAP or specific antibodies. In addition, 63 cows (33 MAP infected and 30 MAP noninfected) were selected for monthly sampling. Raw and pasteurized bulk tank milk samples were collected on a monthly basis. The milk samples were tested for MAP by real-time quantitative PCR (qPCR), and the fecal samples were tested for bacterial shedding by qPCR or solid culture. Based on the results of the herd investigations, the prevalence of cows shedding MAP was around 5%; no cases of clinical JD were observed during the study period. The results of the ELISA showed high variation, with 2.1 to 5.1% positive milk samples and 14.9 to 18.8% ELISA-positive blood samples. Monthly milk sampling revealed low levels of MAP shedding into the individual milk samples of both MAP-infected and noninfected cows, with only 13 cows shedding the bacterium into milk during the study period. Mycobacterium avium ssp. paratuberculosis was not detected by qPCR in any raw or pasteurized bulk tank milk sample throughout the study. A significant positive association could be found between MAP shedding into milk and feces. From the results of the present study, it can be concluded that MAP is only shed via milk in a small proportion of cows with subclinical JD for a limited period of time and is diluted below the detection level of qPCR within the bulk tank milk of these herds. These findings indicate that dairy herds subclinically infected with JD pose only a minor source for human MAP consumption with milk and milk products.

Effects of subclinical Mycobacterium avium ssp. paratuberculosis infection on some physiological parameters, health status and production in dairy cows

“…The bulk tank milk positivity, as detected by PCR, varies among studies (Sweeney et al, 2012). Khol et al (2013) found no MAP-positive bulk tank milk samples in their study, while others reported a rate similar to our results (3.4%; Beaver et al, 2016), or even as high as 52% positive samples (Stabel et al, 2002).…”

A review of paratuberculosis in dairy herds — Part 1: Epidemiology

“…The same study reported that the level shed in milk was also influenced by the stage of lactation, with the highest levels present in the first 60 days-in-milk and negligible shedding in mid and late lactation (Stabel et al, 2014). In another longitudinal study, only a small proportion of subclinically infected cows were found to shed MAP in milk (Khol et al, 2013). On a commercial farm, colostrum is frequently contaminated with faecal material (McAloon et al, 2016a).…”

Knowledge gaps that hamper prevention and control ofMycobacterium aviumsubspeciesparatuberculosisinfection

“…This testing identifies herds with moderate (>5% within-herd milk ELISA positive) to high (>8% withinherd milk ELISA positive) prevalence (Serraino et al, 2014). This test is not sensitive enough to detect low prevalence herds (Jayarao et al, 2004;Khol et al, 2013;Van Weering et al, 2007) or to monitor subtle changes in within-herd prevalence over time.…”