A conceptual model of tuberculosis transmission risk in free-ranging bison herds of northern Canada

Abstract

Tuberculosis transmission in free-ranging bison of northern Canada is of significant concern to wildlife managers because of its effects on condition and mortality in bison herds and the potential for transmission to local hunters and neighbouring cattle populations. The chronic nature of tuberculosis combined with the gregarious behaviours of bison permit its persistence in free-ranging herds even at low densities, which makes disease eradication difficult without whole herd depopulation. The protection of remaining non-infected free-ranging bison populations is thus of paramount importance to the conservation of specific disease-free wild bison in northern Canada and to the economic stability of cattle farms. Detection of movements and removal of dispersing animals between spatially separated free-ranging populations reduces the potential for contact between bison populations and minimizes the probability of tuberculosis transmission. In this thesis, a conceptual model was developed to assess the potential for tuberculosis transmission between two infected bison herds (Nyarling River and Garden River) in Wood Buffalo National Park and the spatially separated, Mackenzie Bison herd in the Northwest Territories. This conceptual model identifies gaps in knowledge and highlights areas where research is required to ensure accurate evaluation of tuberculosis transmission risk in freeranging bison. The main finding was that the bison cohort representing the highest risk for tuberculosis transmission between spatially separated free-ranging herds is mature males. The propensity of mature males to make long-distance movements is also not fully understood and research to predict these movements would make a significant contribution to risk assessment and management planning to reduce the probability of contact between infected and non-infected bison populations.