Cowpox virus infection in natural field vole Microtus agrestis populations: delayed density dependence and individual risk

Abstract

Summary 1.Little is known about the dynamics of pathogen (microparasite) infection in wildlife populations, and less still about sources of variation in the risk of infection. Here we present the first detailed analysis of such variation. 2. Cowpox virus is an endemic sublethal pathogen circulating in populations of wild rodents. Cowpox prevalence was monitored longitudinally for 2 years, in populations of field voles exhibiting multiannual cycles of density in Kielder Forest, UK. 3. The probability that available susceptible animals seroconverted in a given trap session was significantly positively related to host density with a 3-month time lag. 4. Males were significantly more likely to seroconvert than females. 5. Despite most infection being found in young animals (because transmission rates were generally high) mature individuals were more likely to seroconvert than immature ones, suggesting that behavioural or physiological changes associated with maturity contribute to variation in infection risk. 6. Hence, these analyses confirm that there is a delayed numerical response of cowpox infection to vole density, supporting the hypothesis that endemic pathogens may play some part in shaping vole cycles.

Statistical analysis of an endemic disease from a capture–recapture experiment

“…Finally, males were found to be more susceptible to infection than females. This is in broad agreement with [5]. Also wood mice were found to be more susceptible to infection than bank voles.…”

Host–pathogen time series data in wildlife support a transmission function between density and frequency dependence

“…We explored the effects of fitting a variety of seasonal loss terms that, for simplicity, ignored the likelihood that there is a minimum infection period before recovery, beyond which there is variation in the time taken to recover (12,13). This leads us to expect that the average per capita recovery rate will be low when the infected population is made up of a greater proportion of newly infected individuals (when the infected subpopulation is growing fastest) and will be high when it is mostly made up of individuals that have been infected for a relatively long period (when the infected subpopulation is shrinking fastest).…”

“…S1 for all 4 sites). Most individuals in this system become infected with cowpox virus before or soon after reproductive maturity, remain infected for Ϸ28 days, and thereafter recover and stay immune for life (12,13).In common with most host-pathogen interactions, we have very little information about the important physiological, behavioral, and environmental factors that determine how the disease is transmitted in this system. Cowpox is thought to be transmitted only through direct contact (14), implying that the rate of contacts may be a major determinant of the infection dynamics.…”

“…S1 for all 4 sites). Most individuals in this system become infected with cowpox virus before or soon after reproductive maturity, remain infected for Ϸ28 days, and thereafter recover and stay immune for life (12,13).…”

The Common Shrew (Sorex araneus): A Neglected Host of Tick-Borne Infections?

“…During the study period, approximately 2.3 times as many field voles were caught, countering the higher prevalence of A. phagocytophilum recorded in shrews, and this difference is likely to be even greater in peak vole years when densities can reach 600 per hectare (Burthe et al 2006). This suggests that higher numbers of infected or infective voles may be present than shrews.…”