Epidemiology of squirrelpox virus in grey squirrels in the UK

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.

Capturing red squirrels (Sciurus vulgaris) on camera: A cost-effective approach for monitoring relative abundance and habitat preference

Effective methods for monitoring animal populations are crucial for species conservation and habitat management. Motion-activated cameras provide an affordable method for passively surveying animal presence across the landscape but have mainly been used for studying large-bodied mammals. This paper explores the relative abundance and habitat preferences of red squirrels (Sciurus vulgaris) in coniferous forests using cameras and live trapping. The study was conducted in two forests (Newborough and Pentraeth) on Anglesey, North Wales, with a total of 50 sampling locations across four habitat categories. Detailed woodland structure and composition data were gathered around each sampling location. We found a strong positive correlation between the number of individual red squirrels live trapped over 10 days with the number of camera images of squirrels recorded during a previous 5-day period. The time interval between camera deployment and the first recorded image of a red squirrel showed a significant negative correlation with the number of individuals live trapped. Red squirrel relative abundance was negatively related to forest canopy openness, while the presence of Scots pine and increased tree species diversity were positively associated with the relative abundance of squirrels. There was also a strong site difference with lower relative abundance at Newborough compared with Pentraeth, which likely reflects the heavy thinning of mature forest at Newborough reducing tree crown connectivity. The results show that remotely activated cameras are an effective method for monitoring red squirrel populations across varying animal densities. The cameras also provided crucial information on red squirrel habitat preferences that can aid in woodland management and conservation efforts. Cameras have great potential to collect data on the population status of other small mammals, but it is essential that these methods are validated on a species-by-species basis.

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

BACKGROUND

Red Squirrels United was a UK landscape-scale grey squirrel management programme undertaken between 2016 and 2020.

METHODS

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.

RESULTS

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.

LIMITATIONS

Ad hoc sampling was undertaken from limited geographical areas but provided the only dataset from that period, instead of extrapolating from historical data.

CONCLUSIONS

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.

Dermatologic Aspects of Zoo Mammal Medicine

The article deals with the primary aspects of how to maintain healthy integument in zoo mammals and in particular why husbandry-related health problems can occur in general in a zoologic setting. While working with these species we are often faced with diagnostic challenges, which may include a general approach (often requiring anesthesia or medical training), lack of "normal" references, and difficulties, especially if the cutaneous signs are not a primary ailment, but a manifestation of a generalized disease (eg, immune-suppression). The different etiologies of skin problems are discussed with clinical examples.

Interactions between native and invasive species: A systematic review of the red squirrel-gray squirrel paradigm

The eastern gray squirrel (Sciurus carolinensis) has been labeled as one of the 100 worst invasive alien species by the IUCN. In Europe, the species has been introduced to Britain, Ireland and Italy, and its subsequent spread has resulted in wide-scale extinction of native Eurasian red squirrels (Sciurus vulgaris) from the areas colonized by the gray squirrel. This replacement of a native by an alien competitor is one of the best documented cases of the devastating effects of biological invasions on native fauna. To understand how this replacement occurs, we present a systematic review of the literature on competition and interactions between red and gray squirrels. We describe the patterns of red and gray squirrel distribution in those parts of Europe where gray squirrels occur and summarize the evidence on the different processes and mechanisms determining the outcome of competition between the native and alien species including the influence of predators and pathogens. Some of the drivers behind the demise of the red squirrel have been intensively studied and documented in the past 30 years, but recent field studies and mathematical models revealed that the mechanisms underlying the red-gray paradigm are more complex than previously thought and affected by landscape-level processes. Therefore, we consider habitat type and multi-species interactions, including host-parasite and predator-prey relationships, to determine the outcome of the interaction between the two species and to better address gray squirrel control efforts.

The dynamics of disease mediated invasions by hosts with immune reproductive tradeoff

The modern world involves both increasingly frequent introduction of novel invasive animals into new habitat ranges and novel epidemic-causing pathogens into new host populations. Both of these phenomena have been well studied. Less well explored, however, is how the success of species invasions may themselves be affected by the pathogens they bring with them. In this paper, we construct a simple, modified Susceptible-Infected-Recovered model for a vector-borne pathogen affecting two annually reproducing hosts. We consider an invasion scenario in which a susceptible native host species is invaded by a disease-resistant species carrying a vector-borne infection. We assume the presence of abundant, but previously disease-free, competent vectors. We find that the success of invasion is critically sensitive to the infectivity of the pathogen. The more the pathogen is able to spread, the more fit the invasive host is in competition with the more vulnerable native species; the pathogen acts as a ‘wingman pathogen,’ enhancing the probability of invader establishment. While not surprising, we provide a quantitative predictive framework for the long-term outcomes from these important coupled dynamics in a world in which compound invasions of hosts and pathogens are increasingly likely.

An Opportunistic Assessment of the Impact of Squirrelpox Disease Outbreaks upon a Red Squirrel Population Sympatric with Grey Squirrels in Wales

Simple Summary

In Europe, squirrelpox virus is carried by non-native grey squirrels and spread into native red squirrel populations. The virus causes a large proportion of infected red squirrels to die and contributes to local declines and the replacement by grey squirrels. There are relatively few published studies quantifying the impact of disease amongst red squirrels. We present findings from a short-term study in north Wales, United Kingdom.

Abstract

Native red squirrels (Sciurus vulgaris) persisted in the coastal mainland woodlands of northern Gwynedd whilst sympatric with an invasive grey squirrel (Sciurus carolinensis) population suppressed by culling. Squirrelpox disease in the red squirrel population was recorded in 2017 and 2020/21. An autumn 2020 outbreak was associated with only 17.4% of animals caught and marked in the preceding June known to be present in March 2021. Despite an opportunistic data collection lacking the rigour of empirical experimental design, we observed low local survival rates similar to previously published accounts reported during major squirrelpox outbreaks. The use of a conservation dog to detect red squirrel carcasses resulted in positive detection and confirmation of a temporal and spatial expansion of one disease outbreak. The study is the first in Wales to use conservation dogs and the findings reinforce the vital strategic importance of geographical isolation reducing sympatry of red with grey squirrels in European regions where the introduced congener is a source of the squirrelpox infection.

Disease transmission and introgression can explain the long-lasting contact zone of modern humans and Neanderthals

Neanderthals and modern humans both occupied the Levant for tens of thousands of years prior to the spread of modern humans into the rest of Eurasia and their replacement of the Neanderthals. That the inter-species boundary remained geographically localized for so long is a puzzle, particularly in light of the rapidity of its subsequent movement. Here, we propose that infectious-disease dynamics can explain the localization and persistence of the inter-species boundary. We further propose, and support with dynamical-systems models, that introgression-based transmission of alleles related to the immune system would have gradually diminished this barrier to pervasive inter-species interaction, leading to the eventual release of the inter-species boundary from its geographic localization. Asymmetries between the species in the characteristics of their associated ‘pathogen packages’ could have generated feedback that allowed modern humans to overcome disease burden earlier than Neanderthals, giving them an advantage in their subsequent spread into Eurasia.

Modern humans and Neanderthals coexisted in the Levant for tens of thousands of years before modern humans spread and replaced Neanderthals. Here, Greenbaum et al. develop a model showing that transmission of disease and genes can explain the maintenance and then collapse of this contact zone.

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.

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.

European red squirrel population dynamics driven by squirrelpox at a gray squirrel invasion interface

Infectious disease introduced by non-native species is increasingly cited as a facilitator of native population declines, but direct evidence may be lacking due to inadequate population and disease prevalence data surrounding an outbreak. Previous indirect evidence and theoretical models support squirrelpox virus (SQPV) as being potentially involved in the decline of red squirrels (Sciurus vulgaris) following the introduction of the non-native gray squirrel (Sciurus carolinensis) to the United Kingdom. The red squirrel is a major UK conservation concern and understanding its continuing decline is important for any attempt to mitigate the decline. The red squirrel–gray squirrel system is also exemplary of the interplay between infectious disease (apparent competition) and direct competition in driving the replacement of a native by an invasive species. Time series data from Merseyside are presented on squirrel abundance and squirrelpox disease (SQPx) incidence, to determine the effect of the pathogen and the non-native species on the native red squirrel populations. Analysis indicates that SQPx in red squirrels has a significant negative impact on squirrel densities and their population growth rate (PGR). There is little evidence for a direct gray squirrel impact; only gray squirrel presence (but not density) proved to influence red squirrel density, but not red squirrel PGR. The dynamics of red SQPx cases are largely determined by previous red SQPx cases, although previous infection of local gray squirrels also feature, and thus, SQPV-infected gray squirrels are identified as potentially initiating outbreaks of SQPx in red squirrels. Retrospective serology indicates that approximately 8% of red squirrels exposed to SQPV may survive infection during an epidemic. This study further highlights the UK red squirrel – gray squirrel system as a classic example of a native species population decline strongly facilitated by infectious disease introduced by a non-native species. It is therefore paramount that disease prevention and control measures are integral in attempts to conserve red squirrels in the United Kingdom.

Novel host-related virulence factors are encoded by squirrelpox virus, the main causative agent of epidemic disease in red squirrels in the UK

Squirrelpox virus (SQPV) shows little evidence for morbidity or mortality in North American grey squirrels (Sciurus carolinensis), in which the virus is endemic. However, more recently the virus has emerged to cause epidemics with high mortality in Eurasian red squirrels (S. vulgaris) in Great Britain, which are now threatened. Here we report the genome sequence of SQPV. Comparison with other Poxviridae revealed a core set of poxvirus genes, the phylogeny of which showed SQPV to be in a new Chordopoxvirus subfamily between the Molluscipoxviruses and Parapoxviruses. A number of SQPV genes were related to virulence, including three major histocomaptibility class I homologs, and one CD47 homolog. In addition, a novel potential virulence factor showing homology to mammalian oligoadenylate synthetase (OAS) was identified. This family of proteins normally causes activation of an endoribonuclease (RNaseL) within infected cells. The putative function of this novel SQPV protein was predicted in silico.

Squirrelpox virus: assessing prevalence, transmission and environmental degradation

Red squirrels (Sciurus vulgaris) declined in Great Britain and Ireland during the last century, due to habitat loss and the introduction of grey squirrels (Sciurus carolinensis), which competitively exclude the red squirrel and act as a reservoir for squirrelpox virus (SQPV). The disease is generally fatal to red squirrels and their ecological replacement by grey squirrels is up to 25 times faster where the virus is present. We aimed to determine: (1) the seropositivity and prevalence of SQPV DNA in the invasive and native species at a regional scale; (2) possible SQPV transmission routes; and, (3) virus degradation rates under differing environmental conditions. Grey (n = 208) and red (n = 40) squirrel blood and tissues were sampled. Enzyme-linked immunosorbent assay (ELISA) and quantitative real-time polymerase chain reaction (qPCR) techniques established seropositivity and viral DNA presence, respectively. Overall 8% of squirrels sampled (both species combined) had evidence of SQPV DNA in their tissues and 22% were in possession of antibodies. SQPV prevalence in sampled red squirrels was 2.5%. Viral loads were typically low in grey squirrels by comparison to red squirrels. There was a trend for a greater number of positive samples in spring and summer than in winter. Possible transmission routes were identified through the presence of viral DNA in faeces (red squirrels only), urine and ectoparasites (both species). Virus degradation analyses suggested that, after 30 days of exposure to six combinations of environments, there were more intact virus particles in scabs kept in warm (25°C) and dry conditions than in cooler (5 and 15°C) or wet conditions. We conclude that SQPV is present at low prevalence in invasive grey squirrel populations with a lower prevalence in native red squirrels. Virus transmission could occur through urine especially during warm dry summer conditions but, more notably, via ectoparasites, which are shared by both species.

Pangloss revisited: a critique of the dilution effect and the biodiversity-buffers-disease paradigm

The twin concepts of zooprophylaxis and the dilution effect originated with vector-borne diseases (malaria), were driven forward by studies on Lyme borreliosis and have now developed into the mantra "biodiversity protects against disease". The basic idea is that by diluting the assemblage of transmission-competent hosts with non-competent hosts, the probability of vectors feeding on transmission-competent hosts is reduced and so the abundance of infected vectors is lowered. The same principle has recently been applied to other infectious disease systems--tick-borne, insect-borne, indirectly transmitted via intermediate hosts, directly transmitted. It is claimed that the presence of extra species of various sorts, acting through a variety of distinct mechanisms, causes the prevalence of infectious agents to decrease. Examination of the theoretical and empirical evidence for this hypothesis reveals that it applies only in certain circumstances even amongst tick-borne diseases, and even less often if considering the correct metric--abundance rather than prevalence of infected vectors. Whether dilution or amplification occurs depends more on specific community composition than on biodiversity per se. We warn against raising a straw man, an untenable argument easily dismantled and dismissed. The intrinsic value of protecting biodiversity and ecosystem function outweighs this questionable utilitarian justification.

How Does Biodiversity Influence the Ecology of Infectious Disease?

Over the past years, biodiversity has been reduced on an unprecedented scale, while new infectious diseases are emerging at an increasing rate. Greater overall biodiversity could lead to a greater diversity of hosts and thus of pathogens. Yet disease regulation – due to the buffering role of host diversity – is considered to be one of the services provided by biodiversity. In this chapter, we ask how biodiversity is linked to infectious disease. First, we investigate the influence of the biodiversity of pathogens. We highlight that the number of pathogen species is not well known but that new findings are facilitated by the rapid expansion of molecular techniques. We show that, although there is a trend to find higher pathogen richness toward the equator, identifying a global pattern between the richness of all pathogen species and their latitudinal distribution is challenging. We emphasize that pathogen intraspecific diversity is a crucial factor in disease emergence and allows pathogens to adapt to the selective pressures they face. In addition, the selective pressure acting on hosts due to parasite, and reinforced by parasite diversity within hosts seems to be a major evolutionary and ecological force shaping hosts biodiversity. Second, we investigate how the diversity of hosts influences infectious disease ecology. For multi-host diseases, a change in host species richness or abundance can modify the dynamics of local infectious diseases by either reducing (“dilution effect”) or increasing (“amplification effect”) the risk of transmission to the targeted host species. The underlying hypothesis is that, the competence of reservoirs varies according to the host species. The dilution effect has been demonstrated mainly through theoretical work and there have been only few case studies. Regarding the genetic diversity of host, an important issue is: to what extent does a reduction of this diversity impact the ability of the host population to response to infectious diseases? Third, we rapidly examine the role of biodiversity in the treatment of infectious diseases. To conclude, we consider that the consequences of the loss of species biodiversity on infectious diseases is still largely unknown, notably due to the lack of knowledge on the dynamics of host-pathogen relationships, especially at the population and at the community level.. We highlight that work on multi-host/ ulti-pathogen systems should be fostered and that new approaches, such as metagenomic investigations that does not require a priori assumptions, are promising to describe a community of pathogens and their interactions.

Spatio-temporal dynamics of bumblebee nest parasites (Bombus subgenus Psythirus ssp.) and their hosts (Bombus spp.)

1. A 39-year bumblebee data base was used to study the codistribution of six cuckoo bumblebees in the subgenus Psythirus of Bombus (hereafter called Psythirus) and their free-living bumblebee hosts in the British Isles. 2. A model of nest parasitism predicted host threshold densities and stable deterministic dynamics, with fluctuations only emerging as a result of environmental or demographic stochasticity. 3. Standardized transects indicated that variation in total number of records could be largely attributed to variation in observer effort; analyses were therefore carried out using relative abundance. 4. Spatially, parasite-free zones were evident in areas of low host abundance, but the host threshold for parasite presence differed among species and locations. 5. Temporally, the relative numbers of the parasite and host species remained relatively constant, except that the nest parasite P. campestris declined significantly since 1990. 6. There were consistent negative effects of the parasitic species on the numbers of hosts in the following year, and this pattern was seen over large geographic areas. 7. The spatio-temporal patterns confirmed a high degree of host specificity, except that P. campestris may be parasitizing not only B. pascuorum but also other species in the subgenus Thoracobombus.