Disease and causes of mortality in red squirrel populations

The major infectious disease threatening the red squirrel population in Europe is undoubtedly squirrelpox virus (SQPV) infection. However, red squirrels can be affected by a wide range of other infectious and non-infectious diseases, some of which have the potential to have a significant influence on red squirrel populations. The presence of a wide range of parasites, viruses, bacteria, fungi and protozoa has been reported in a variety of studies on red squirrels, some of which have been associated with overt disease, and some for which the significance of infection is unclear. In addition to the impact of natural predation, competition with grey squirrels and other factors such as weather and food abundance on survival rates and population dynamics, red squirrels are subject to anthropogenic causes of premature or unnatural mortality, such as road traffic collisions, predation from pet cats and dogs, electrocution and rodenticide toxicity. Other non-infectious causes include starvation, extreme cold weather, failure to thrive after weaning, nutritional disease, neoplasia and stress after relocation. Ongoing surveillance into causes of mortality and investigations of the emergence of new or previously undescribed infectious diseases are a vital part of the conservation effort for this species.