An Interactive Tool to Inform Johne’s Disease Control in Beef Herds: What to Test, When and How Often

Background

Johne’s disease is a chronic, incurable enteric disease of ruminants caused by the bacteria Mycobacterium avium spp. paratuberculosis (or MAP). It is an animal welfare concern and results in significant economic losses in affected beef herds. There is concern that the risk of Johne’s disease in beef herds is increasing in part because of rapidly increasing herd sizes and herd dispersals.
Johne’s disease is particularly challenging to manage because infected animals can spread the disease to other cattle for months or even years before they show clinical signs. Tests to detect infected animals are also limited in their accuracy, especially in the early stages of disease. The best control option in beef herds is the identification and removal of cows that are shedding MAP before they contaminate the calving area and infect young stock. Testing is a significant investment of time and money, and testing options are limited to testing individual animals utilizing cultures and PCR of fecal samples and serum ELISAs.

Objectives

• To develop a web-based interactive tool to inform Johne’s disease testing options in individual cow-calf herds.

What They Did

Canadian surveillance data, including regional research, was incorporated into a dynamic risk model developed to simulate different options for managing Johne’s disease transmission and control in a cow-calf herd. An agent-based model was customized to reflect western Canadian herds and further developed into an interactive web-based tool that can be used by veterinarians and producers to help inform choice of test (ELISA, PCR, pooled PCR), risk-based testing strategies, and frequency of testing for control of Johne’s in individual beef herds. The resulting tool accounts for the imperfect nature of the tests and the role of chance in disease transmission. The model can be adapted as further data is collected.

What they learned

The dynamic risk assessment tool constructed as part of this project is unique in that it is built on production, disease and testing data from Canadian beef herds. The resulting cloud-based simulation tool is available on www.beefresearch.ca in two forms with a user guide and short how-to videos. A basic version allows veterinarians and producers to explore the customizable options and get an idea of how different choices might impact the long-term disease trajectory and costs to their herd in terms of disease control, culling and replacement costs relative to testing efforts. The tool allows the user to customize their herd size and composition, replacement strategy, and starting prevalence of Johne’s in the herd. The user can pick what tests they want to use, how often they want to test, what age of animals they want to test and whether they want to target specific risk groups. The user can also evaluate the potential impact of other disease management options.

The second version of the tool has a slightly less intuitive user interface but does allow the user more options for customizing the outputs to their particular herd. More importantly, the second version provides users with a platform to run the scenarios they want to test many times (10 to 30 for example) to assess the expected variation in the results due to chance, the variability in how this disease progresses, and the uncertainty related to test performance. It provides graphics to compare the results across different testing and management scenarios. It is also possible to save the inputs and outputs from each model for further analysis.

What it means

Johne’s disease requires renewed attention from cow-calf producers, especially seed-stock suppliers and anyone considering herd expansion.
This tool is not intended to predict what will happen in an individual herd nor to provide specific recommendations on what an individual producer should do to manage this disease. However, it does help organize information and navigate a very complex problem.
This tool will help veterinarians and beef cattle producers compare the relative costs and benefits of different disease management options in the face of uncertainty, using research from Canadian beef herds integrated into an applied learning tool for disease management.