Paratuberculosis

Project entitled:

Working for More Effective Control and a Better Understanding of Bovine Paratuberculosis

Summary

Paratuberculosis is an insidious, contagious enteric disease caused by the intracellular bacterium Mycobacterium avium ssp. paratuberculosis (MAP). It is difficult to control, and can cause major economic losses when it infects a herd. This study aims to 1) facilitate the identification of herds affected by bovine paratuberculosis by validating a standardized method and 2) study the inflammatory and genetic markers associated with bovine paratuberculosis to better understand the evolution of this incurable disease.

For the first part, environmental samples from 24 farms as well as individual samples (serum [ELISA] and faeces [CFI]) from all adult cows were collected in summer and fall. The two sites most frequently identified as positive were boots (summer 15% and fall 12.5%) and the pit (summer 9.5% and fall 10.4%). The combination of samples from the pit and scourer and comparing the group of sick cows and the group of lean cows correctly identified all (8/8) positive farms upon ENV testing. When compared with the CFI, the ENV correctly identified 72% (95% CI: 43.4–90.3%) of positive herds. Our results suggest that the performance of the ENV was similar to that of the CFI and ELISA in identifying Quebec dairy herds in stall housing infected with MAP.

For the second part, the inflammatory profile of infected cows was studied. Although the so-called Th1 cellular immune response is effective in infancy during the silent infection period, this type of defense against intracellular pathogens wanes during the subclinical stage as the disease progresses. MAP thwarts its host’s immunological vigilance in some cows, which explains why antibodies against it are developed in such a delayed way (ELISA serum is still negative). The profiles are varied and do not always fit with the theorem that says that cows first have a Th1 response which, as the disease evolves, is replaced by a humoral response (Th2) manifested through a positive result in the ELISA test. Our analysis allowed us to characterize the inflammatory state in cows suffering from paratuberculosis and identify a genetic pattern associated with variations in the gene for osteopontin, a cytokine under study which is linked with chronic diseases.