Modeling management strategies for chronic disease in wildlife: predictions for the control of respiratory disease in bighorn sheep

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.