Monitoring of squirrelpox in Scotland’s red squirrels (Sciurus vulgaris) – identification of a sentinel case in a naïve population?

IIntroduction: Following their introduction to the UK, grey squirrels (Sciurus carolinensis) have substantially expanded their range, bringing grey squirrels into conflict with native British red squirrels (Sciurus vulgaris). This has resulted in decreases in red squirrels, which is partly related to the introduction of squirrelpox virus (SQPV), the causative agent of squirrelpox (SQPx), for which grey squirrels act as a reservoir host.

Materials and methods: An ongoing national surveillance programme identified SQPV on both tail hair and whiskers from a red squirrel, submitted from Perth and Kinross (Central Scotland) in September 2020 by opportunistic sampling. This was the most northerly identification of SQPx to date and may represent a sentinel case of the northerly spread of SQPx. Antibody ELISAs were used to assess the seroconversion in Central Scotland compared with endemic areas (Dumfries and Galloway) to the south and naïve areas (Highlands) to the north.

Results: All red squirrels submitted during 2019 and 2020 from these three areas were assessed, which identified seroconversion only within Dumfries and Galloway (ie, the historically endemic area). Nested PCRs are currently being used to assess the SQPV exposure within this trial area.

Conclusions: This potential identification of SQPx in Perth and Kinross is concerning. Should SQPx become established, this may have a substantial impact on local red squirrel numbers. This may also facilitate spillover and further northerly spread into other naïve areas, perhaps including northern red squirrel strongholds. Further work is required to fully characterize this population and sentinel case.