Unraveling Resistance and Susceptibility to Johne’s Disease

Project Overview

Mycobacterium avium subsp. paratuberculosis (MAP) causes Johne’s disease, which is responsible for substantial economic losses in the dairy industry. This research investigated the host genetic and epigenetic variations associated with susceptibility and tolerance to Johne's disease. They also examined the diversity of MAP genetics and the host-pathogen dynamics responsible for disease progression in cows infected with MAP.

What Did the Research Team Do?

Collected samples from 3,300 cows from 22 dairy herds in the provinces of Ontario and Quebec and identified inter-herd transmission patterns using whole-genome-sequencing as an epidemiological tool to validate cow movement as the cause of inter-herd disease transmission.
 
Collected samples from 67 cows in these 22 herds to look at the variability of MAP strains.
 
Within four dairy herds, further investigated 14 cows shedding MAP to identify if multiple MAP strains were infecting a single infected animal and if microevolution of MAP was occurring.
 
Developed a multiplex-PCR test for Johne’s disease with greater sensitivity than the currently available commercial kits.

What Did the Research Team Find?

• Identification of genetic markers associated with the susceptibility of developing Johne’s disease.
• Epigenetic variations associated with susceptibility of Johne's disease.
• Cows can be infected with multiple strains of MAP and the strain of MAP can evolve within the cow.
• MAP strains differ substantially between farms. This variability may explain differences in the severity of Johne’s disease that may be present on farms.
• This information can be used to explain differences observed between the spread of MAP and clinical signs associated with a MAP infection, such as long-lasting diarrhea, progressive weight loss, decreased milk production, and increased culling and mortality.
• Evaluated the efficacy of a new quantitative polymerase chain reaction (qPCR) technology used for detecting MAP infection.

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