Poxviral Disease in Red Squirrels Sciurus vulgaris in the UK: Spatial and Temporal Trends of an Emerging Threat

Abstract

The squirrel poxvirus (SQPV) is the probable mediator of apparent competition between the introduced invading gray squirrel (Sciurus carolinensis) and the red squirrel (Sciurus vulgaris) in the UK, and modeling studies have shown that this viral disease has had a significant impact on the decline of the red squirrel in the UK. However, given our limited understanding of the epidemiology of the disease, and more generally the effects of invasive species on parasite ecology, there is a need to investigate the transmission dynamics and the relative pathogenicity of the virus between species. We aimed to increase our knowledge of these processes through an empirical study in which we: (i) used pathological signs and transmission electron microscopy (TEM) to diagnose SQPV disease in red squirrels found dead during scanning surveillance between 1993 and 2005; (ii) detected antibody to SQPV using an enzyme-linked immunosorbent assay (ELISA) in the same animals; and (iii) mapped cases of the disease, and the gray squirrel distribution, using a geographical information system. We analyzed the distribution of cases of SQPV disease according to woodland type, a measure of squirrel density. SQPV disease occurred only in areas of England also inhabited by seropositive gray squirrels, and as the geographical range of gray squirrels expanded, SQPV disease occurred in these new gray squirrel habitats, supporting a role for the gray squirrel as a reservoir host of the virus. There was a delay between the establishment of invading gray squirrels and cases of the disease in red squirrels which implies gray squirrels must reach a threshold number or density before the virus is transmitted to red squirrels. The spatial and temporal trend in SQPV disease outbreaks suggested that SQPV disease will have a significant effect on Scottish populations of red squirrels within 25 years. The even spread of cases of disease across months suggested a direct rather than vector-borne transmission route is more likely. Eight juvenile and sub-adult free-living red squirrels apparently survived exposure to SQPV by mounting an immune response, the first evidence of immunity to SQPV in free-living red squirrels, which possibly suggests a changing host-parasite relationship and that the use of a vaccine may be an effective management tool to protect remnant red squirrel populations.

Locating species range frontiers: a cost and efficiency comparison of citizen science and hair-tube survey methods for use in tracking an invasive squirrel

“…The eastern grey squirrel (Sciurus carolinensis), native to eastern North America, has been frequently introduced to locations worldwide (Bertolino 2009) where it often easily establishes (Wood et al 2007) to the detriment of native sciurid populations (Kenward and Holm 1993;Gurnell et al 2004b;Sainsbury et al 2008). The grey squirrel was introduced to one site in the Republic of Ireland in 1911 (Watt 1923;O'Teangana et al 2000a), via populations in Great Britain (Fig.…”

First report of Obeliscoides cuniculi in European brown hare (Lepus europaeus)

“…In some cases, the impact of the invasion by non-indigenous animal species on the environment is particularly severe for animal health, especially when mediated by the introduction of "new" pathogens (Stebbins 1992;Dobson 1996). A well-known example of this possibility is represented by the squirrel poxvirus, which played a clear role in the severe competition between the introduced invading grey squirrel (Sciurus carolinensis) and the native red squirrel (Sciurus vulgaris) in Europe (Sainsbury et al 2008). In Italy, one of the allochthonous invaders is the eastern cottontail (Sylvilagus floridanus) which was introduced illegally as game in France (1953), Italy (1966, Spain (1980) andSwitzerland (1982).…”

In This Issue

“…In a further example of disease emergence and population change, Sainsbury et al (2008) present their findings from research into the spatial and temporal trends of squirrel poxvirus infection in red squirrels (Sciurus vulgaris) in the UK. As gray squirrels (Sciurus carolinensis), introduced into central and southern England from 1876, have encroached on red squirrel populations, the transmission of squirrel poxvirus and the ensuing disease in red squirrels has given the gray squirrel a competitive advantage over the red squirrel, allowing the former to increase its geographic range rapidly through England and Wales over the last 100 years.…”