Introduced Canadian Eastern grey squirrels: squirrelpox virus surveillance and why nothing matters.

Squirrelpox virus (SQPV), an unapparent infection of the Eastern grey squirrel (Sciurus carolinensis), is considered to be mediating the ecological replacement of the Eurasian red squirrel (Sciurus vulgaris) in the United Kingdom (UK) and Ireland. Evidence suggests that the Eastern grey squirrel is the natural reservoir host of SQPV and therefore there is considerable concern amongst conservationists that when translocated out of its natural range in North America, the Eastern grey squirrel could pose a similar threat to encountered indigenous squirrel populations. Serum samples collected from Eastern grey squirrels from British Columbia (BC), Canada, an introduced population derived from squirrels translocated at the beginning of the 20th Century, were surveyed for evidence of antibodies against SQPV. None of the 130 samples tested had antibodies to the virus, contrasting with 15 out of 19 (79%) positive serum samples collected from Ontario, a population within the natural range of the Eastern grey squirrel. We conclude that BC is currently free of SQPV and that to maintain the virus-free status further translocations of grey squirrels from their native range should be prevented. A comprehensive study of the founding population and comparison with the other populations in BC, including broad epidemiological surveillance for the virus is recommended as an early warning for potential incursions of the virus and the threats that this may pose.