Squirrelpox Research Articles

Immune interactions and heterogeneity in transmission drives the pathogen-mediated invasion of grey squirrels in the UK.

Mathematical models highlighted the importance of pathogen-mediated invasion, with the replacement of red squirrels by squirrelpox virus (SQPV) carrying grey squirrels in the UK, a well-known example. In this study, we combine new epidemiological models, with a range of infection characteristics, with recent longitudinal field and experimental studies on the SQPV dynamics in red and grey squirrel populations to better infer the mechanistic basis of the disease interaction. A key finding is that a model with either partial immunity or waning immunity and reinfection, where individuals become seropositive on the second exposure to infection, that up to now has been shown in experimental data only, can capture the key aspects of the field study observations. By fitting to SQPV epidemic observations in isolated red squirrel populations, we can infer that SQPV transmission between red squirrels is significantly (4×) higher than the transmission between grey squirrels and as a result our model shows that disease-mediated replacement of red squirrels by greys is considerably more rapid than replacement in the absence of SQPV. Our findings recover the key results of the previous model studies, which highlights the value of simple strategic models that are appropriate when there are limited data, but also emphasise the likely complexity of immune interactions in wildlife disease and how models can help infer disease processes from field data.

Significant differences in the caecal bacterial microbiota of red and grey squirrels in Britain.

Introduction. Red squirrel populations have declined in the UK since the introduction of the grey squirrel, due to resource competition and grey squirrels carrying a squirrelpox virus that is fatal to red squirrels.Hypothesis/Gap Statement. It is not known if the gut microbiota of the two species is similar and if this could impact the survival of red squirrels.Aim. The aim of this study was to profile the caecal microbiota of red and grey squirrels obtained opportunistically from a conservation programme in North Wales.Methodology. Bacterial DNA was extracted from ten red and ten grey squirrels and sent for 16S rRNA sequencing. Three samples from red squirrels returned less than 5000 reads, and so were not carried forward for further analyses.Results. Samples taken from the caeca of red squirrels had significantly lower bacterial diversity and a higher percentage of Bacilli bacteria when compared to samples from grey squirrels. When the abundance of bacterial groups across all levels of phylogenetic classifications was compared between the two groups of squirrels, grey squirrels had a higher abundance of bacteria belonging to the families S24-7, RF39 and Rikenellaceae. Escherichia coli with resistance to amoxicillin/clavulanic acid was identified in all samples. Cefotaxime resistance was identified in two samples from grey squirrels along with sulfamethoxazole/trimethoprim in one of these samples.Conclusion. Clear differences between the caecal microbiota of the two species of squirrel were identified, which could potentially impact their overall health and ability to compete for resources.

Opportunistic viral surveillance confirms the ongoing disease threat grey squirrels pose to sympatric red squirrel populations in the UK.

Red Squirrels United was a UK landscape-scale grey squirrel management programme undertaken between 2016 and 2020. A total of 11034 grey squirrels were removed by culling, with 1506 necropsied and 1405 suitable for adenovirus (AdV) or squirrelpox virus (SQPV) quantitative PCR (qPCR) analysis. Spleen, lip or hair were extracted, and DNA was isolated, with samples tested in duplicate by qPCR. Of 1378 tissue samples, 43% were positive for AdV and 10% for SQPV. Of 1031 hair samples, 11% were positive for AdV and 10% for SQPV. Overall, 762 of 1405 (54%) animals were positive for one or both viruses. Ad hoc sampling was undertaken from limited geographical areas but provided the only dataset from that period, instead of extrapolating from historical data. The grey squirrel is an asymptomatic reservoir host for AdV and SQPV. Interspecific infection transmission potential is demonstrated. Grey squirrel management by culling is essential for mainland red squirrel viability until other suitable management tools are available.

Indirect effects of pine marten recovery result in benefits to native prey through suppression of an invasive species and a shared pathogen

Invasive species pose a major threat to native species, both through direct interactions, such as competition for resources, and indirect interactions, such as when the invasive species acts as a reservoir host for a virulent pathogen. Recent research has indicated that the recovery of native predators can benefit native prey species that compete with invasive prey, in circumstances where predation is more pronounced on the naïve invasive species. We use the native red squirrel (Sciurus vulgaris), invasive grey squirrel (Sciurus carolinensis) and shared squirrelpox virus (SQPV) system in North Wales, UK, as a case study system to assess the impact of a recovering, native predator of both squirrel species, the pine marten (Martes martes), on community structure. We develop a stochastic, spatial model that represents the habitat structure, distribution, and connectivity in North Wales and models the interactions of red and grey squirrels, SQPV, and pine marten to examine the indirect effect of native predator recovery on competitively linked native-invasive prey species and a viral pathogen. Our model demonstrates the potential role of native predators in reversing the replacement of a threatened native prey through the regulation of the invasive prey species due to sustained predation, and the resultant extirpation of a viral pathogen, which otherwise catalyses the replacement of the native red squirrel by the invasive grey squirrel. Our findings have system specific applied conservation implications, but moreover demonstrate the critical role of native predators in mitigating the impacts of invasive species and, indirectly, the infectious diseases they harbour.

A systematic review into the suitability of urban refugia for the Eurasian red squirrel Sciurus vulgaris

Abstract Urban growth and intensification are projected to increase as the global human population increases. Historically, urban areas have been disregarded as suitable wildlife habitat, but it is now known that these areas can be biodiverse and that wildlife species can adapt to the environmental conditions. One such urban‐dwelling species is the Eurasian red squirrel Sciurus vulgaris, which has suffered population declines in several countries throughout its range in recent decades. The current published literature was systematically reviewed to determine whether or not urban habitats are suitable refugia for red squirrels, through identifying and discussing key topics regarding the urban ecology of red squirrels. Urban environments can support higher population densities of red squirrels than rural areas, probably due to the widespread and reliable provision of anthropogenic supplemental food alongside natural food sources. The availability and quality of urban greenspaces are important determinants of the suitability of urban habitats for red squirrels, as they provide natural food sources and nesting sites. Despite the barriers present in urban landscapes (e.g. roads), red squirrels can still disperse and maintain gene flow at the population level. Road traffic accidents appear to be a significant cause of mortality in some urban red squirrel populations, and seasonal peaks of mortality occur during the autumn months. Diseases (e.g. squirrelpox virus) can also be a significant cause of mortality, although effects differ between populations and depend on whether grey squirrels Sciurus carolinensis are present. Many of the predation events that affect red squirrels appear to be due to free‐ranging domestic and feral cats Felis catus, although there is currently little evidence to suggest that predation is a limiting factor for urban red squirrel populations. We conclude that urban areas can be suitable refugia for red squirrels, provided that high‐quality greenspaces are maintained. Mitigation measures may also be necessary to reduce population mortality and to prevent disease outbreaks.

Recalibrating risk: Implications of squirrelpox virus for successful red squirrel translocations within mainland UK

Recalibrating risk: Implications of squirrelpox virus for successful red squirrel translocations within mainland <scp>UK</scp>

Reinstating trophic cascades as an applied conservation tool to protect forest ecosystems from invasive grey squirrels (Sciurus carolinensis)

Red squirrel (Sciurus vulgaris) range within the United Kingdom (UK) has retracted significantly due to the spread of an Invasive Alien Species, the North American Eastern grey squirrel (Sciurus carolinensis). Where grey squirrels are sympatric, red squirrel populations decline through inter-specific competition and squirrelpox virus (SQPV) infection. Grey squirrel eradication from the island of Anglesey facilitated the complete restoration of native red squirrels. Although native species recovery delivered significant ecological and economic benefits, the eradication extended only to a narrow sea-channel boundary, across which grey squirrel dispersal continues to occur. Hence, the long-term sustainability of Anglesey's red squirrel population is vulnerable to grey squirrel re-establishment without continuous intervention. Recent research has demonstrated that as pine marten (Martes martes) landscape use intensity increases, so too does red squirrel occupancy, likely linked to parallel declines in grey squirrel occupancy. Restoration of this mustelid predator is a potential tool to deliver sustainable grey squirrel control by restoring a missing trophic component, depressing grey squirrel incursion rates onto Anglesey, reducing red squirrel exposure to SQPV. Recent UK pine marten translocations have sourced animals under licence from wild Scottish populations. We explore the alternative use of captive-bred founders, simultaneously introducing new genetic variability against a limited diversity within extant populations. A current conservation translocation is paired with an ongoing assessment of founder behaviour and ‘personality’ measured before release. We then highlight the multi-disciplinary approach to delivering applied red squirrel conservation programmes in the face of invasive species.

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

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

Implications of squirrelpox virus for successful red squirrel translocations within mainland UK

AbstractRemnant red squirrel populations in the UK mainland are threatened by squirrelpox viral disease and the reservoir of the squirrelpox virus, the invasive grey squirrel, is expanding its range. Until this threat can be effectively mitigated, there is a high risk from disease outbreaks, following proposed conservation translocation of red squirrels.

Poxvirus, red and grey squirrel dynamics: Is the recovery of a common predator affecting system equilibria? Insights from a predator-prey ecoepidemic model

In Europe, the Eastern grey squirrel is an allochthonous species causing severe impacts on the native red squirrel. The invasive species establishes complex relationships with the native one, out-competing it through resource and disease-mediated competition. However, recent research shed light on the potential role of a predator, the pine marten, in reversing the outcome of the competition between squirrels. Here, we investigate this hypothesis developing a one predator-two prey ecoepidemic model, including disease (squirrel poxvirus) transmission. We assess the equilibria of the dynamical system and investigate their sensitivity to ecosystem parameters changes through numerical simulations. Our analysis reveals that the system is more likely to evolve toward points where the red squirrels thrive than toward a disease-and-red-squirrels-free point. Although the disease is likely to remain endemic in the system, the introduction of the pine marten destabilizes previous equilibria, favouring the native squirrel and facilitating wildlife managers in their efforts to protect it. Nevertheless, the complete eradication of grey squirrels could be achieved only for specified values of the predation rates and pine marten carrying capacity. The active management of grey squirrel populations remains therefore necessary to try to eradicate the invader from the system.

The drivers of squirrelpox virus dynamics in its grey squirrel reservoir host

Many pathogens of conservation concern circulate endemically within natural wildlife reservoir hosts and it is imperative to understand the individual and ecological drivers of natural transmission dynamics, if any threat to a related endangered species is to be assessed. Our study highlights the key drivers of infection and shedding dynamics of squirrelpox virus (SQPV) in its reservoir grey squirrel (Sciurus carolinensis) population. To clarify SQPV dynamics in this population, longitudinal data from a 16-month mark-recapture study were analysed, combining serology with real-time quantitative PCR to identify periods of acute viraemia and chronic viral shedding. At the population level, we found SQPV infection prevalence, viral load and shedding varied seasonally, peaking in autumn and early spring. Individually, SQPV was shown to be a chronic infection in >80% of grey squirrels, with viral loads persisting over time and bouts of potential recrudescence or reinfection occurring. A key recurring factor significantly associated with SQPV infection risk was the presence of co-infecting squirrel adenovirus (ADV). In dual infected squirrels, longitudinal analysis showed that prior ADV viraemia increased the subsequent SQPV load in the blood. However, there was a strong, negative association between prior ADV viraemia and subsequent SQPV shedding from the forearm, probably caused by ADV prolonging the SQPV acute viraemic phase, so delaying onset of the chronic shedding phase, and thereby altering viral shedding patterns over the time scales examined here. Hence, co-circulating ADV infection may be involved in mediating both the quantitative levels of SQPV infection and the timing and degree of subsequent infectiousness of grey squirrels.

First report of dermatophilosis in wild European red squirrels (Sciurus vulgaris)

The carcases of two wild red squirrels (Sciurus vulgaris) from Anglesey, North Wales, which had severe skin lesions, were presented to the Animal and Plant Health Agency. One was found...

Assessing a potential non-invasive method for viral diagnostic purposes in European squirrels.

Viral infections globally threaten wild and captive mammal populations, with surveillance options limited by a lack of non-invasive diagnostics; especially when infection is asymptomatic in nature. We explored the potential for hair samples collected from red (Sciurus vulgaris) and grey (Sciurus carolinensis) squirrels to provide a means of screening for adenovirus (ADV) and squirrelpox virus (SQPV) using evolving polymerase chain reaction (PCR) assays. An initial pilot study phase utilised samples opportunistically harvested from grey squirrels controlled in Gwynedd, United Kingdom (UK). The screening of 319 grey squirrel carcasses revealed 58% spleen ADV DNA qPCR and 69% SQPV antibody enzyme linked immunosorbent assay (ELISA) positives. We developed new nested ADV and SQPV qPCRs and examined tail hair samples from a sub-set of 80 of these 319 sampled squirrels and these assays amplified ADV and SQPV DNA in a higher proportion of animals than the original qPCR (94% and 21% respectively). Tail hair samples obtained from six Cumbrian red squirrels which had died from squirrelpox disease also revealed 100% SQPV and 50% ADV DNA positive by the nested qPCR assays. These findings indicate enhanced sensitivity for the new platform. The integration of this non-invasive approach in assessing viral infection has wide application in epidemiological studies of wild mammal populations, in particular, during conservation translocations, where asymptomatic infections are of concern.

Conservation of genetic uniqueness in remaining populations of red squirrels (Sciurus vulgaris L.) in the South of England.

The Eurasian red squirrel (Sciurus vulgaris) is an emblematic species for conservation, and its decline in the British Isles exemplifies the impact that alien introductions can have on native ecosystems. Indeed, red squirrels in this region have declined dramatically over the last 60 years due to the spread of squirrelpox virus following the introduction of the gray squirrel (Sciurus carolinensis). Currently, red squirrel populations in Britain are fragmented and need to be closely monitored in order to assess their viability and the effectiveness of conservation efforts. The situation is even more dramatic in the South of England, where S. vulgaris survives only on islands (Brownsea Island, Furzey Island, and the Isle of Wight). Using the D‐loop, we investigated the genetic diversity and putative ancestry of the squirrels from Southern England and compared them to a European dataset composed of 1,016 samples from 54 populations. We found that our three populations were more closely related to other squirrels from the British Isles than squirrels from Europe, showed low genetic diversity, and also harbored several private haplotypes. Our study demonstrates how genetically unique the Southern English populations are in comparison with squirrels from the continental European range. We report the presence of four private haplotypes, suggesting that these populations may potentially harbor distinct genetic lineages. Our results emphasize the importance of preserving these isolated red squirrel populations for the conservation of the species.

Mortalities, amyloidosis and other diseases in free-living red squirrels (Sciurus vulgaris) on Jersey, Channel Islands

Between 2007 and 2014, 337 free-living red squirrels (Sciurus vulgaris) on Jersey, Channel Islands, were examined post mortem as part of a mortality and disease surveillance scheme. Road traffic accidents...

Disease, invasions and conservation: no evidence of squirrelpox virus in grey squirrels introduced to Italy

AbstractNative red squirrels Sciurus vulgaris in Great Britain and Ireland are threatened by alien grey squirrels S. carolinensis through exploitation competition and spillover of squirrelpox virus (SQPV). By accelerating the replacement of red squirrels by the invader, SQPV represents a fundamental factor to consider when planning management and conservation strategies. In mainland Europe, grey squirrels introduced to Italy threaten the survival of the whole continental red squirrel population, but no extensive surveys for SQPV presence have been carried out in the region. We therefore investigated SQPV infection in north Italian grey squirrel populations through a combination of serological and molecular methods. Firstly, we analysed sera from 285 individuals through an enzyme‐linked immunosorbent assay (ELISA) to detect antibodies against SQPV. Secondly, a PCR designed to amplify a segment of the G8R SQPV gene was carried out on DNA extracted from swabs and skin tissue samples from a second set of 66 grey squirrels. ELISA tests identified four reactors (1.4%), but the subsequent PCR survey did not detect any SQPV DNA. Based on the low prevalence observed and on PCR results, we believe that the four suspected positives were the result of an ELISA cross‐reaction following exposure to another pox virus. Considering sample size and performances of the two methods, confidence of freedom from SQPV resulted above 99.9%. However, because of the severe impact of SQPV on red squirrels, we recommend the implementation of a passive surveillance plan for the early detection of an SQPV emergence in continental Europe.

Berlin Squirrelpox Virus, a New Poxvirus in Red Squirrels, Berlin, Germany.

Near Berlin, Germany, several juvenile red squirrels (Sciurus vulgaris) were found with moist, crusty skin lesions. Histology, electron microscopy, and cell culture isolation revealed an orthopoxvirus-like infection. Subsequent PCR and genome analysis identified a new poxvirus (Berlin squirrelpox virus) that could not be assigned to any known poxvirus genera.

Enhancement of wildlife disease surveillance using multiplex quantitative PCR: development of qPCR assays for major pathogens in UK squirrel populations.

Rapid development in polymerase chain reaction (PCR) technology has revolutionised the speed and accuracy of many diagnostic assays. However, comparatively few wildlife epidemiological studies use quantitative PCR (qPCR) for pathogen detection, even fewer employ an internal control, to ensure confidence in negative results, and PCR’s ability to multiplex and therefore detect several targets in a single reaction is underutilised. Here, we describe the development of two multiplex qPCR assays for the red and grey squirrel that detect the pathogens squirrelpox virus (SQPV) and adenovirus in squirrels (SADV), both of which cause mortality in the red squirrel. Both assays use a section of the squirrel phosphoglycerate kinase gene as an endogenous internal control that identifies and compensates for both, inadequate sampling or PCR inhibition. Tests on infected squirrel tissue demonstrate that simple swab samples (particularly from distal antebrachial skin) are sufficient to detect and identify the relative quantity of SQPV DNA in both squirrel species, while rectal swabs and blood cell pellets can be used to reliably indicate SADV infection. These assays are sensitive and specific with an endogenous internal control providing confidence in negative results and allowing comparison across laboratories. Using such assays should prove advantageous in wildlife studies with limited resources while allowing the maximum data yield.Electronic supplementary materialThe online version of this article (doi:10.1007/s10344-016-1031-z) contains supplementary material, which is available to authorized users.

Modelling disease spread in real landscapes: Squirrelpox spread in Southern Scotland as a case study

There is increasing evidence that invading species can gain an advantage over native species by introducing novel disease. A clear understanding of the role of disease in the expansion of introduced and invading species is therefore essential for the conservation of native species. In this study we focus on the case study system of the UK red and grey squirrel system in which disease-mediated competition has facilitated the replacement of red squirrels by greys. We modify a deterministic model of the squirrel system in which the competition and infection dynamics are well understood to produce a stochastic model which includes a realistic representation of the heterogeneous habitat in Southern Scotland. The model is used to examine the potential spread of infection (squirrelpox virus) through the squirrel system and to examine the impact of conservation measures that control grey squirrel numbers in an attempt to contain disease spread. The results have direct implications for conservation management and we discuss how they have helped shape current and future policy for red squirrel conservation in Scotland. The methods in this study can be readily adapted to represent different systems and since the stochastic population and disease dynamics are underpinned by classical deterministic modelling frameworks the results are applicable in general.

Host-pathogen dynamics of squirrelpox virus infection in red squirrels (Sciurus vulgaris)

To improve our understanding of squirrelpox virus (SQPV) infection in the susceptible host, three red squirrels were challenged with wild-type SQPV via scarification of the hind-limb skin. All squirrels seroconverted to the infection by the end of the experiment (17 days post-challenge). Challenged animals suffered disease characterised by the development of multiple skin and oral lesions with rapid progression of skin lesions at the infection site by day 10 post-challenge. No internal pathological changes were found at post-mortem examination. A novel SQPV Taqman® Real-time PCR detected viral DNA from multiple organs, with the largest amounts consistently associated with the primary and secondary skin and oral lesions where viral replication was most likely occurring. Immunohistochemistry clearly detected viral antigen in the stratified squamous epithelium of the epidermis, tongue and the oropharyngeal mucosa-associated lymphoid tissue and was consistently associated with histological changes resulting from viral replication. The lack of internal pathological changes and the detection of relatively low levels of viral DNA when compared with primary and secondary skin lesions argue against systemic disease, although systemic spread of the virus cannot be ruled out. This study allowed a comprehensive investigation of the clinical manifestation and progression of SQPV infection with a quantitative and qualitative analysis of virus dissemination and shedding. These findings suggest two separate routes of SQPV transmission under natural conditions, with both skin and saliva playing key roles in infected red squirrels.