1. Controlling persistent infectious disease in wildlife populations is an on-going challenge for wildlife managers and conservationists worldwide.

2. Here, we develop a dynamic pathogen transmission model capturing key features of M. ovipneumoniae infection, a major cause of population declines in North American bighorn sheep (Ovis canadensis). We explore the effects of model assumptions and parameter values on disease dynamics, including density versus frequency dependent transmission, the inclusion of a carrier class versus a longer infectious period, host survival rates, disease-induced mortality and recovery rates, and the epidemic growth rate.

3. We compare the effectiveness of a suite of management actions following an epidemic, including test-and-remove, depopulation-and-reintroduction, range expansion, herd augmentation, and density reduction.

4. Our results suggest that test-and-remove, depopulation-and-reintroduction, and range expansion have the potential to facilitate recovery of persistently infected bighorn sheep herds post-epidemic. By contrast, augmentation could lead to worse outcomes than those expected in the absence of management. Management that improves host survival or reduces disease-induced mortality are also likely to improve population size and persistence of chronically infected herds.

5. Dynamic transmission models like the one employed here offer a structured, logical approach towards exploring hypotheses and can serve as a basis for planning field experiments and adaptive management. Models should be used iteratively with the field empirical approaches to triangulate on better approaches to wildlife management.

Data were gathered by Idaho Department of Fish and Game, Oregon Department of Fish and Wildlife, and Washington Department of Fish and Wildlife as part of the Hells Canyon Bighorn Sheep Initiative, under the coordination of E. Frances Cassirer. Field efforts consisted of at least biweekly (and often higher-resolution) aerial or ground survey of instrumented bighorn sheep ewes in the Hells Canyon system (specific herds indiciated in the Herd field). Dates of birth (DayInYear_birth) were taken to be the midpoint of the last survey of a ewe without a lamb and the first survey in which she had a lamb each year, unless lambs were clearly less than 72 hours old upon first observation. Lamb mortalities are recorded in the DayInYear_death field (the midpoint between the last observation the lamb was seen alive and the first observation in which it was not observed).

More details can be found in: 

Cassirer, E.F., Plowright, R.K., Manlove, K.R., Cross, P.C., Dobson, A.P., Potter, K.A. and Hudson, P.J., 2013. Spatio‐temporal dynamics of pneumonia in bighorn sheep. Journal of Animal Ecology, 82(3), pp.518-528.

and

Cassirer, E.F., Manlove, K.R., Plowright, R.K. and Besser, T.E., 2017. Evidence for strain‐specific immunity to pneumonia in bighorn sheep. The Journal of Wildlife Management, 81(1), pp.133-143.