Dissertation•
Study of squirrelpox virus in red and grey squirrels and an investigation of possible routes of transmission
30 Jun 2012-
TL;DR: The role of disease in the decline of the red squirrel in the UK .. 17 and the role of the host in poxvirus pathogenesis: host tropism .......................... 32 are examined.
Abstract: ................................................................................................................................. 10 CHAPTER 1 .......................................................................................................................... 12 INTRODUCTION ................................................................................................................. 12 1.1 History of squirrels in the UK ................................................................................... 12 1.1.1 Grey squirrels in the UK pre-1930 ................................................................. 12 1.1.2 Red squirrels in the UK pre-1930 .................................................................. 14 1.1.3 Distribution of red and grey squirrels in the UK post-1930 ........................... 15 1.1.4 Evidence of the role of disease in the decline of the red squirrel in the UK .. 17 1.1.5 Pox disease in red squirrels ............................................................................ 18 1.2 Poxviruses ................................................................................................................. 21 1.2.1 Taxonomic structure of Poxviridae ................................................................ 22 1.2.2 Virion morphology and structure ................................................................... 23 1.2.3 Genome features of poxviruses ...................................................................... 25 1.2.4 Poxvirus replication ....................................................................................... 27 1.2.5 Immunopathogenesis of poxvirus infection ................................................... 29 1.2.6 The role of the host in poxvirus pathogenesis: host tropism .......................... 32 1.2.7 Transmission of poxviruses ........................................................................... 33 1.3 Poxvirus infection in lagomorphs and rodents .......................................................... 35 1.3.1 Myxoma virus ................................................................................................ 35 1.3.2 Shope fibroma virus ....................................................................................... 36 1.3.3 Cowpox virus ................................................................................................. 36 1.3.4 Monkeypoxvirus ............................................................................................ 38 1.3.5 Squirrel fibroma virus .................................................................................... 39 1.3.6 Squirrelpox virus ............................................................................................ 41 1.4 Aim of the thesis ....................................................................................................... 42 CHAPTER 2 .......................................................................................................................... 44 MATERIALS AND METHODS ........................................................................................... 44 2.1 Centrifuges and Common reagents ........................................................................... 44 2.2 Sample storage .......................................................................................................... 44 2.3 Virology .................................................................................................................... 44
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TL;DR: Variation in tissue specific detection rates suggests that previous long-term surveillance of adenovirus in wild grey squirrels focussing on blood samples may have significantly underestimated true infection rates.
Abstract: Squirrel pox virus (SQPV) and adenovirus produce pathological disease in native red squirrels ( Sciurus vulgaris ). SQPV in particular is a significant factor in regional population declines and is generally prevalent in the UK's introduced grey squirrel ( Sciurus carolinensis ) population as an asymptomatic infection. Despite the role of the grey squirrel as a virus reservoir and potential inter-specific infection pathways being highlighted, there remains a paucity of field study data with known relative inter-specific infection rates and quantified frequency of interactions. Intriguingly, whilst captive zoological red squirrel collections are often present within woodland habitat containing wild grey squirrels, clinical pox cases are rarely observed unless red squirrels are released from the enclosures. In 2011 we monitored grey squirrel activity on an enclosure containing red squirrels. Grey squirrels were present for a cumulative total of 47.5 minutes within the twenty four hours of observation. A range of behaviours were recorded including feeding, and instances where discarded food fell into the red squirrel enclosures below. We interpret the value of these observations in the context of published theories of viral transmission. The local grey squirrels were subsequently culled and tested for evidence of both historical and current SQPV and adenovirus infections. Polymerase Chain Reaction (PCR) assays did not amplify adenovirus DNA from grey squirrel blood samples, but positive results were recorded in faeces (3/18, 17%) and (10/18, 56%) in parallel spleen samples from the same animals. This variation in tissue specific detection rates suggests that previous long-term surveillance of adenovirus in wild grey squirrels focussing on blood samples may have significantly underestimated true infection rates. Enzyme-Linked Immunosorbent Assay (ELISA) tests revealed exposure to SQPV by antibody presence in 33% of the animals. Additionally, 22% of the animals contained detectable levels of both viruses. In parallel with laboratory and field studies in 2011, we collated historical unpublished reports and archived data from a range of UK squirrel collections and highlight some key cases of infection. We recommend that further behavioural and viral screening studies are focussed within scenarios where captive red squirrels are sympatric with wild grey squirrels. Download the complete issue.
14 citations
Cites methods from "Study of squirrelpox virus in red a..."
...Separately, blood samples were analysed using an ELISA for detection of antibodies against SQPV (Sainsbury et al., 2000), and skin samples used for detection of SQPV DNA by PCR (following Fiegna 2012)....
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Journal Article•
2 citations
09 Nov 2017
TL;DR: A model combining disease and competition is proposed and study how a disease affects the two competing species (article III), and it is shown that infection of the superior competitor enables the inferior competitor to coexist, either as a stable steady state or limit cycle.
Abstract: A community is a collection of populations of different species living in the same geographical area. Species interact with each other in the community and this interaction affects species distribution, abundance, and even evolution [5]. Species interact in various ways, for instance through competition, predation, parasitism, mutualism, and commensalism. Mutualism is an interaction between individuals of different species in which both individuals benefit. Examples include plants and nitrogen fixing bacteria, pollination of flowering plants by an insect, lichen between a species of algae and fungus [53]. Commensalism is a type of relationship among organisms in which one organism is benefited while the other organism is neither benefited nor harmed. For example, some birds live among cattle to eat the insects stirred up by the cows. Predation is an interaction in which one organism consumes either all or part of another living organism (the prey), causing direct negative effect on the prey [6]. The individuals of one species is benefited while individuals of the other species is harmed. Parasitism is considered as a special case of (or analogous to) predation [47]. Individuals compete with each other for limited resources. This is a negativenegative interaction, that is, each individual adversely affects another. Historically, competition has been viewed as an important species interaction. Now, competition is recognized as one of many interacting factors that affect community structure. We have two focuses in this thesis. One focus is analyzing the dynamical behaviors of the discretization systems of the Lotka-Volterra predator-prey model. It is well known that the dynamics of the logistic map is more complex compared with logistic differential equation. Period doubling and the onset of chaos in the sense of Li-York occur for some values. Inspired by this, we analyze the dynamical behaviors of the discretization systems of the Lotka-Volterra predator-prey model (articles I and II). In article I, we show that the system undergoes fold bifurcation, flip bifurcation and Neimark-Sacker bifurcation, and has a stable invariant cycle in the interior of R + for some parameter values. In article II, we show that the unique positive equilibrium undergoes flip bifurcation and Neimark-Sacker bifurcation. Moreover, system displays much interesting dynamical behaviors, including period-5, 6, 9, 10, 14, 18, 20, 25 orbits, invariant cycles, cascade of period-doubling, quasi-period orbits and the chaotic sets. We emphasize that the discretization of continuous models (articles I and II) are not acceptable as a derivation of discrete predator-prey models [26]. A discrete predatorprey model is also formulated in Section 2. We analyze the dynamics (articles I and II) from the mathematical point of view instead of biological point of view. The other focus is disease-competition in an ecological system. We propose a model combining disease and competition and study how a disease affects the two competing species (article III). In our model, we assume that only one of the species is susceptible to an SI type disease with mass action incidence, and that infected individuals do not reproduce but suffer from additional disease induced death. We further assume that infection does not reduce the competitive ability of the infected. We show that infection of the superior competitor enables the inferior competitor to coexist, either as a stable steady state or limit cycle. In the case where two competing species coexist without the disease, the introduction of disease is partially determined by the basic
1 citations
Cites background from "Study of squirrelpox virus in red a..."
...Similar considerations can also play a role in the competition between native red squirrels in Britain and introduced grey squirrel, via the action of a shared viral infection, which was highly pathogenic to the resident species [17]....
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References
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TL;DR: It is shown that parapoxvirus is likely to have played a crucial role in the red squirrel decline even though the prevalence of infection is low, and conservationists should pay particular attention to pathogens, even when they occur at low prevalence.
Abstract: Although a parapoxvirus harmful to red squirrels is present in UK squirrel populations it has not been considered a major cause of red squirrel decline, and replacement by the introduced grey squirrel, mainly because diseased individuals are rarely observed. By developing a generic model we show that parapoxvirus is likely to have played a crucial role in the red squirrel decline even though the prevalence of infection is low. Conservationists are quite rightly concerned with the invasion of exotic organisms such as the grey squirrel. Our work emphasizes that they, along with other ecologists, should pay particular attention to pathogens, even when they occur at low prevalence.
331 citations
Book•
01 Jan 1995
302 citations
TL;DR: In this paper, the authors validate the potential role of the parapoxvirus in the red squirrel and prove that the virus is highly pathogenic in red squirrel while having no detectable effect on grey squirrel health.
Abstract: The disease implications of novel pathogens need to be considered when investigating the ecological impact of species translocations on native fauna. Traditional explanations based on competition or predation may often not be the whole story. Evidence suggests that an emerging infectious disease, caused by a parapoxvirus, may be a significant component of the impact that the introduced grey squirrel has had on UK red squirrel populations. Here we validate the potential role of parapoxvirus by proving that the virus is highly pathogenic in the red squirrel while having no detectable effect on grey squirrel health.
184 citations
"Study of squirrelpox virus in red a..." refers background in this paper
...…the work of several authors it has been generally accepted that this ecological replacement of red squirrels by the greys is most likely to be pathogen-mediated (Gurnell et al., 2006; Rushton et al., 2006; Sainsbury & Ward, 1996; Sainsbury et al., 1997; Tompkins et al., 2002; Tompkins et al., 2003)...
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...However, whilst the grey 43 squirrel does not show any apparent clinical signs of the disease, red squirrels suffer disease severe enough to cause high mortality in the wild (Tompkins et al., 2002)....
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...Furthermore, experimental infection studies have confirmed that both grey and red squirrels can be infected with the virus (Thomas et al., 2003; Tompkins et al., 2002)....
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...The macroscopic lesions induced by SQPV are characterised by erythematous exudative dermatitis and ulceration with some lesions covered by haemorrhagic scabs (Tompkins et al., 2002; Scott et al., 1981a)....
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...It was considered severe enough to suggest that red squirrels, infected in the wild, may not be expected to survive (Thomas et al., 2003; Tompkins et al., 2002) a suggestion that had previously been made (Sainsbury & Gurnell 1995; Sainsbury et al., 1997)....
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TL;DR: Analysis of the incidence of disease and changes in distribution of the two species in Cumbria, from 1993 to 2003 and the predictions of an individual-based (IB) spatially explicit disease model simulating the dynamics of both squirrel species and SQPV in the landscape show grey squirrels increased whilst red squirrels declined.
Abstract: Red squirrels are declining in the United Kingdom. Competition from, and squirrel poxvirus (SQPV) disease carried by, grey squirrels are assumed to be determining the decline. We analyse the incidence of disease and changes in distribution of the two species in Cumbria, from 1993 to 2003 and compare these to the predictions of an individual-based (IB) spatially explicit disease model simulating the dynamics of both squirrel species and SQPV in the landscape. Grey squirrels increased whilst red squirrels declined over 10 years. The incidence of disease in red squirrels was related to the time since grey squirrels arrived in the landscape. Analysis of rates of decline in red squirrel populations in other areas showed that declines are 17–25 times higher in regions where SQPV is present in grey squirrel populations than in those where it is not. The IB model predicted spatial overlap of 3–4 years between the species that was also observed in the field. The model predictions matched the observed data best when contact rates and rates of infection between the two species were low. The model predicted that a grey squirrel population control of >60% effective kill was needed to stop the decline in red squirrel populations in Cumbria.
153 citations
"Study of squirrelpox virus in red a..." refers background in this paper
...Squirrelpox virus (SQPV) has had a significant impact on this decline and it is thought to be the major factor in competition between the native red squirrel and the introduced North American grey squirrel (Sciurus carolinensis) (Rushton et al., 2006)....
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...The results suggested that in areas of interaction between 21 red and grey squirrels, where virus was present, the observed decline in the red squirrel population was 17-25 times more rapid than in areas where no virus was present (Rushton et al., 2006)....
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...…the work of several authors it has been generally accepted that this ecological replacement of red squirrels by the greys is most likely to be pathogen-mediated (Gurnell et al., 2006; Rushton et al., 2006; Sainsbury & Ward, 1996; Sainsbury et al., 1997; Tompkins et al., 2002; Tompkins et al., 2003)...
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TL;DR: The results suggest that reductions in energy availability can impair humoral immunity in seasonally breeding rodent species, prairie voles and Siberian hamsters.
Abstract: Mounting an immune response requires substantial energy, and it is well known that marked reductions in energy availability (e.g. starvation) can suppress immune function, thus increasing disease susceptibility and compromising survival. We tested the hypothesis that moderate reductions in energy availability impair humoral immunity. Specifically, we examined the effects of partial lipectomy (LIPx) on humoral immunity in two seasonally breeding rodent species, prairie voles (Microtus ochrogaster) and Siberian hamsters (Phodopus sungorus). Animals received bilateral surgical removal of epididymal white adipose tissue (EWATx), inguinal white adipose tissue (IWATx) or sham surgeries and were injected with the antigen keyhole limpet haemocyanin (KLH) either four or 12 weeks after surgery. In prairie voles, serum anti-KLH immunoglobulin G (IgG) did not differ significantly at four weeks. At 12 weeks, serum IgG was significantly reduced in IWATx, but not EWATx animals, compared with sham-operated animals. In Siberian hamsters, both IWATx and EWATx animals reduced serum IgG at four weeks. At 12 weeks, EWATx hamsters displayed a significant compensatory increase in IWAT pad mass compared with sham-operated hamsters, and serum IgG no longer differed from sham-operated animals. There was no significant increase in EWAT in IWATx hamsters compared with sham animals and IgG remained significantly reduced in IWATx hamsters. These results suggest that reductions in energy availability can impair humoral immunity.
134 citations