Modelling the spatial dynamics of parapoxvirus disease in red and grey squirrels: a possible cause of the decline in the red squirrel in the UK?

Abstract

Summary1. A stochastic individual-based model for simulating the dynamics of an infectious disease in sympatric red and grey squirrel populations is described. The model simulates the spread of parapoxvirus between squirrels in fragmented populations based on the dispersal of infected animals, the probability of encounters between individuals, exposure to the virus and subsequent mortality. 2. The disease model was integrated with a spatially explicit population dynamics model that simulated red and grey squirrel populations in real landscapes, using habitat information held in a geographical information system. Latin hypercube sampling was used to create a range of realistic life-history and infection scenarios and the model was used to investigate the dynamics of red and grey squirrels in Norfolk between 1966 and 1980. 3. The model predicted that parapoxvirus, like interspeci®c competition, could have led to the extinction of the red squirrel in Norfolk. The results suggest that the red squirrel±grey squirrel±parapoxvirus interaction represents a system of apparent competition mediated by an infectious agent, as seen in other interactions between resident and exotic species. 4. The need for further epidemiological research on the virus is emphasized. We believe that the combined eects on disease transmission of habitat, behaviour and grey squirrels acting as reservoir hosts will lead to a patchy prevalence and sporadic incidence of parapoxvirus disease in red squirrels and a more rapid local replacement by grey squirrels. 5. These results have implications for conservation management of the red squirrel in the UK. Schemes in which animals are translocated or given supplementary feeding may enhance disease spread by bringing infected animals into contact with others.

Parapoxvirus causes a deleterious disease in red squirrels associated with UK population declines

“…A related observation is that the viruschallenged red squirrel with the lowest initial antibody response (lowest by 48%; figure 4) was the individual in which disease development was fastest, being the first to reach a clinical score of eight points (figure 3b). These observations suggest that the development and application of a red squirrel vaccine against parapoxvirus, as has been discussed in the literature (Rushton et al 2000;Sainsbury et al 2000), has a good chance of conferring a high degree of immunity to the disease caused by the virus and may thus be an essential management tool in the effort to conserve the remaining UK red squirrel populations.…”

“…When the introduced host acts as a reservoir population from which infection can 'spill-over' to sympatric wildlife, pathogens, which would otherwise fail to persist, may instead cause the extinction of susceptible host populations (Tompkins et al 2000). Such a scenario is believed to describe the action of parapoxvirus in squirrels (Rushton et al 2000;Sainsbury et al 2000).…”

Feeding of grey squirrels (Sciurus carolinensis) with the contraceptive agent DiazaCon™: effect on cholesterol, hematology, and blood chemistry

“…In areas where both species are present, grey squirrels raid red squirrel caches of seed, leading to reduced reproductive and juvenile recruitment rates for red squirrels (Wauters et al 2002;Gurnell et al 2004). Grey squirrels also carry Squirrelpox virus, which is lethal to red squirrels but has little effect on grey squirrels (Rushton et al 2000;Sainsbury et al 2000;Tompkins et al 2002;Thomas et al 2003;McInnes et al 2006). Grey squirrels also cause bark stripping damage to trees (Kenward 1983;Rowe & Gill 1985;Dagnall et al 1998), and this can have serious economic impacts as well as influence woodland composition (Mayle et al 2009).…”

Temporal Pattern of Africanization in a Feral Honeybee Population From Texas Inferred From Mitochondrial Dna

“…Biotic factors (e.g. diseases, parasites) can aggravate the pace and extension of replacement, indirectly by altering the nature of interactions between invading and invaded taxa (McNeil et al 2003), and directly by causing losses in the resident population (Calvo-Ugarteburu and McQuaid 1998;Rushton et al 2000).…”