Modeling the Occurrence of Mycobacterium avium subsp. paratuberculosis in Bulk Raw Milk and the Impact of Management Options for Exposure Mitigation

Abstract

Mycobacterium avium subsp. paratuberculosis (MAP) is the causal agent of paratuberculosis (Johne's disease) in cattle and other farm ruminants. The potential role of MAP in Crohn's disease in humans and the contribution of dairy products to human exposure to MAP continue to be the subject of scientific debate. The occurrence of MAP in bulk raw milk from dairy herds was assessed using a stochastic modeling approach. Raw milk samples were collected from bulk tanks in dairy plants and tested for the presence of MAP. Results from this analytical screening were used in a Bayesian network to update the model prediction. Of the 83 raw milk samples tested, 4 were positive for MAP by culture and PCR. We estimated that the level of MAP in bulk tanks ranged from 0 CFU/ml for the 2.5th percentile to 65 CFU/ml for the 97.5th percentile, with 95% credibility intervals of [0, 0] and [16, 326], respectively. The model was used to evaluate the effect of measures aimed at reducing the occurrence of MAP in raw milk. Reducing the prevalence of paratuberculosis has less of an effect on the occurrence of MAP in bulk raw milk than does managing clinically infected animals through good farming practices.

Modeling the Effect of Direct and Indirect Contamination of On-Farm Bulk Tank Milk with Mycobacterium avium subsp. paratuberculosis

“…The low median concentration of MAP in bulk tank milk was similar to other models (Weber et al, 2008;Boulais et al, 2011). However, the stochastic model enabled infrequent but plausible case scenarios, such as a herd containing a few cows shedding extreme amounts of MAP in feces.…”

“…Previous models for MAP in bulk tank milk have mainly focused on clinically affected animals with obvious high concentrations of MAP in feces and rarely discuss the role of cows in earlier stages of infection (Nauta and van der Giessen, 1998;Weber et al, 2008;Boulais et al, 2011). Taking one step further, a model should also be able to assess the effect of differences in infection prevalence and herd sizes on the level of contamination.…”

Comparison among the Quantification of Bacterial Pathogens by qPCR, dPCR, and Cultural Methods

“…This is particularly relevant for some pathogens characterized by slow cultural growth rates (e.g., MAP), but generally, rapidity can be advantageous for detection and quantification of all pathogens. In this regard, some risk models have already been proposed for MAP (Nauta and van der Giessen, 1998; Boulais et al, 2011), F. tularensis (Wood et al, 2014) and L. monocyotogenes (Halder et al, 2010). …”

A screening sampling plan to detect Mycobacterium avium subspecies paratuberculosis-positive dairy herds

“…Moreover, our results confirm those of Slana et al (2012), who reported no association between within-herd prevalence and frequencies of MAP-positive ILMF in herds. No studies are available on the factors affecting ILMF positivity, but studies on BTM showed that milk contamination is more related to the presence of clinical or subclinical high shedders (Sweeney et al, 1992;Boulais et al, 2011;Khol et al, 2013) and milking hygiene (Jayarao et al, 2004) labor intensive for farmers, especially in large herds. In Italy, an ELISA milk test performed using the ID Screen Paratuberculosis indirect confirmation test in the public laboratory of the National Reference Centre for Paratuberculosis costs €2.54, whereas PCR costs €26.40, meaning that the complete SSP tested in this study cost €57.88 for each farm.…”