Wildlife disease elimination and density dependence

Abstract

Disease control by managers is a crucial response to emerging wildlife epidemics, yet the means of control may be limited by the method of disease transmission. In particular, it is widely held that population reduction, while effective for controlling diseases that are subject to density-dependent (DD) transmission, is ineffective for controlling diseases that are subject to frequency-dependent (FD) transmission. We investigate control for horizontally transmitted diseases with FD transmission where the control is via culling or harvest that is non-selective with respect to infection and the population can compensate through DD recruitment or survival. Using a mathematical model, we show that culling or harvesting can eradicate the disease, even when transmission dynamics are FD. Eradication can be achieved under FD transmission when DD birth or recruitment induces compensatory growth of new, healthy individuals, which has the net effect of reducing disease prevalence by dilution. We also show that if harvest is used simultaneously with vaccination, and there is high enough transmission coefficient, application of both controls may be less efficient than vaccination alone. We illustrate the effects of these control approaches on disease prevalence for chronic wasting disease in deer where the disease is transmitted directly among deer and through the environment.

Infection dynamics in frog populations with different histories of decline caused by a deadly disease

“…Pathogens with density-dependent transmission cannot reduce their host populations below a critical minimum size (Nokes 1992). In contrast, pathogens that have frequency-dependent transmission (Potapov et al 2012), or that can persist in another host species or the abiotic environment, are more likely to cause extinction. For example, transmission of the parapoxvirus from the introduced grey squirrel to the native red squirrel is eliminating the latter from the UK (Tompkins et al 2002).…”

“…The mode of transmission plays a critical role in whether or not pathogens can drive their host populations to extinction McCallum et al 2001;Potapov et al 2012). Pathogens with density-dependent transmission cannot reduce their host populations below a critical minimum size (Nokes 1992).…”

Familiarity Breeds Contempt: Combining Proximity Loggers and GPS Reveals Female White-Tailed Deer (Odocoileus Virginianus) Avoiding Close Contact With Neighbors

“…However, pathogen transmission rates are often high within social groups, which can decrease the likelihood of stochastic pathogen extinction early in an epizootic (Newman 2003;Krause et al 2007). Socially structured contact rates have been proposed as a mechanism for frequency-dependent disease transmission (McCallum et al 2001;Begon et al 2002), which can confound attempts to control disease (Potapov et al 2012). In extreme cases, frequency-dependent transmission could drive hosts extinct (e.g., devil facial tumor disease; McCallum et al 2009).…”

Roles of wildlife in epidemiology of rabies: A mini-review

“…The disease thereafter spread westward towards Western and Central Europe within a few years. In France and Northern Italy, however, foxes were treated with oral rabies vaccine which halted the spread of the disease (Wandeler, 2004;Potapov et al, 2012 …”