The emergence of wildlife disease and the application of ecology

Since most emerging diseases are zoonotic infections derived from wildlife, they can be considered invasive species that exploit a new habitat. In this paper we consider emerging diseases as interspecifi c transmission events, but the fi tness of the invading parasite is determined by the success of subsequent dispersal (transmission) to new resource- rich patches (susceptible hosts) and sustaining the chain of transmission. Successful invasion does not depend simply on invading a closely related host species but on the number of times invasion is attempted and the size of the individual dose. Successful invasion also depends on the presence of competitors and release from host immunity. In epidemiology, the likelihood of invasion is usually mea sured as R0, the average number of infected individuals established within the new host species when an infectious individual is introduced into a population of susceptible hosts. Likelihood of per sis tence, on average, will fall with R0, although a longer period of infectiousness will increase per sis tence even if R0 remains the same. Estimates of R0 generally make assumptions about the average case, yet there is increasing evidence that in many parasitic diseases, infectiousness and susceptibility may covary, such that just a few individuals may be responsible for much of the transmission; these individuals are sometimes referred to as superspreaders. In the control of emerging infections in wildlife, stopping interspecifi c spillover through culling or vaccination may be useful in some situations but can also lead to increased rates of transmission. We suggest that the identifi cation and treatment of superspreaders and other features that infl uence R0 can provide a novel way of controlling spillover events and preventing epidemics of emerging diseases.