Impacts of deer herd management practices on bovine Tuberculosis (bTB)

A computer model was developed to evaluate the impact of practices such as baiting and vaccination on eradication of bTB in the wild deer population of northeast Michigan.

In January, Dr. Dave Ramsey of theArthur Rylah Institute of Australia presented the findings of his work with the Michigan Department of Natural Resources (MDNR) on the predictions of bovine Tuberculosis (bTB) persistence at a meeting of the Michigan Natural Resources Commission.

The model tested the impacts of changes in hunting kill rate, whether or not deer are baited and the impact of vaccination of deer. Vaccination was modeled even though it would be years before any potential field use is approved.

Some of the predictions from the model are disease prevalence in the wild deer population and probability of eradication. The current scenario was compared to predicted results from applied management practices.

Findings include:

  • If baiting is allowed, then at least a doubling of current harvest rates is required to eradicate bTB within 30 years.
  • With no baiting, there is an 80% probability of eradication by increasing the harvest rate 50%. However, there is no chance of the disease eradication at that increased harvest rate if baiting is continued.
  • Annual vaccination only (with 90% of the population exposed to vaccine) with no increase in harvest will only eradicate bTB within 30 years if baiting is eliminated.
  • An increase in harvest by 25% plus annual vaccination and elimination of baiting will eradicate bTB within 30 years.
  • If bTB is eliminated in an area, and one positive deer enters the area, the disease is 6 times more likely to be established if baiting occurs during the hunting season.

The model clearly shows the negative impact of baiting on the eradication of bTB from the wild whitetail deer population. This epidemiological model of bTB in deer was spatially explicit, that is, it was able to account for spatial variation in bTB occurrence and the application of management. The model is also stochastic, and therefore, able to address uncertainty around the effects of management. The model simulates behavior of individual deer.

There will be further work with the model to look at transmission to cattle and the impact of management practices.

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