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: Recommendations are that care should be taken to release translocated animals in similar habitat to their origin, and that grey squirrels should be excluded from future release areas until red squirrels have settled and, before biodiversity is reduced by landscape management for red Squirrels, more research is needed to determine whether interactions with grey Squirrels or differential predation will ultimately displace red squirrelS in conifers.
Abstract: Fourteen radio-tagged red squirrels were released in pine woodland containing grey squirrels. Movements of the squirrels were related to the tree species of the donor site. Survival after release was lower than for the grey squirrels: of 11 red squirrels that survived at least a week, only three survived more than three months and none for four months. More than half were eaten or cached by predators, mainly foxes; an experiment with grey squirrel carcasses indicated that they had been killed, not scavenged after death. Hypertrophied adrenals, disease and loss of weight indicated stress as another factor in the deaths. Data on overlap of core ranges, and reluctance of red squirrels to enter traps used by grey squirrels in the mixed population, indicated interference competition between the two species, with grey squirrels possibly dominant. We recommend: (i) that care should be taken to release translocated animals in similar habitat to their origin; (ii) that grey squirrels should be excluded from future release areas until red squirrels have settled and, before biodiversity is reduced by landscape management for red squirrels; (iii) more research to determine whether interactions with grey squirrels or differential predation will ultimately displace red squirrels in conifers.
71 citations
TL;DR: Comparative sequence analysis of two other genes suggests that the squirrel virus represents a previously unrecognized genus of the chordopoxvirus, which is similar to that found in other parapoxviruses.
Abstract: A parapoxvirus has been implicated in the decline of the red squirrel in the United Kingdom. Virus was isolated from an outbreak of lethal disease in red squirrels in the north-east of England. Experimental infection of captive-bred red squirrels confirmed that this virus was the cause of the severe skin lesions observed. Electron microscopic examination of the virus showed that it had a morphology typical of parapoxviruses whilst preliminary sequence data suggested a genomic G+C composition of approximately 66 %, again similar to that found in other parapoxviruses. However Southern hybridization analysis failed to detect three known parapoxvirus genes, two of which have been found so far only in the genus parapoxvirus. Comparative sequence analysis of two other genes, conserved across the eight recognized chordopoxvirus genera, suggests that the squirrel virus represents a previously unrecognized genus of the chordopoxvirus.
66 citations
TL;DR: Analysis of serum from British woodland rodents failed to find any evidence of SQPV infection in wood mice or bank voles, but for the first time serum samples from grey squirrels in the USA were found to contain antibody against SQPK, confirming that it partitions on its own in a separate clade of the poxviruses.
Abstract: The genome of a virulent squirrelpox virus (SQPV) isolate was characterized in order to determine its relationship with other poxviruses. Restriction enzyme analysis suggested a genome length of approximately 158 kb, whilst sequence analysis of the two ends of the genome indicated a G + C composition of approximately 66 %. Two contiguous stretches of 23 and 37 kb at the left-hand and right-hand ends of the genome, respectively, were sequenced allowing the identification of at least 59 genes contained therein. The partial sequence of a further 15 genes was determined by spot sequencing of restriction fragments located across the genome. Phylogenetic analysis of 15 genes conserved in all the recognized genera of the subfamily Chordopoxvirinae confirmed that the SQPV does not group within the family Parapoxvirinae, but instead partitions on its own in a separate clade of the poxviruses. Analysis of serum from British woodland rodents failed to find any evidence of SQPV infection in wood mice or bank voles, but for the first time serum samples from grey squirrels in the USA were found to contain antibody against SQPV.
65 citations
"Study of squirrelpox virus in red a..." refers background in this paper
...The squirrelpox virus genome has an even higher G + C content of ~66% (McInnes et al., 2006)....
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...Although SQPV has never been isolated from grey squirrels in the USA, serological 42 samples collected from North America have tested positive for antibodies against SQPV (McInnes et al., 2006)....
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...SQPV is the sole member of an unclassified genus which seems to be genetically related to the Parapoxvirus genus and Molluscum contagiousum virus genus (McInnes et al., 2006)....
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TL;DR: It is suggested that reductions in energy availability lead to impairments in humoural immunity and that leptin can serve as a neuroendocrine signal between body fat and immunity regulating humoural immune responses.
Abstract: Mounting an immune response requires a relatively substantial investment of energy and marked reductions in energy availability can suppress immune function and presumably increase disease susceptibility. We have previously demonstrated that a moderate reduction in energy stores via partial surgical lipectomy (LIPx) impairs humoural immunity of Siberian hamsters ( Phodopus sungorus ). Here we tested the hypothesis that LIPx-induced decreases in immunity are mediated by changes in the adipose tissue hormone leptin. Hamsters received bilateral surgical removal of inguinal white adipose tissue (IWATx) or sham surgeries (Sham). Half the animals in each group received osmotic minipumps containing murine leptin (0.5 μl h −1 for 10 days) whereas the remaining animals received minipumps containing vehicle alone; all animals were subsequently challenged with the novel antigen keyhole limpet haemocyanin (KLH). In general, serum leptin and anti-KLH antibodies were significantly correlated with one another with higher levels generally indicating enhanced immunity. In addition, IWATx hamsters had significantly lower serum anti-KLH IgG compared with sham animals. Exogenous leptin, however, attenuated LIPx-induced immune suppression but did not affect humoural immunity in sham animals. These results suggest that reductions in energy availability lead to impairments in humoural immunity and that leptin can serve as a neuroendocrine signal between body fat and immunity regulating humoural immune responses.
63 citations
TL;DR: The threats posed by parapoxvirus infection, metabolic bone disease and coccidiosis to the reintroduction of red squirrels into Thetford Chase were investigated by making blood biochemical, radiological and parasitological examinations on the squirrels before they were released and on resident squirrels.
Abstract: The threats posed by parapoxvirus infection, metabolic bone disease and coccidiosis to the reintroduction of red squirrels into Thetford Chase were investigated by making blood biochemical, radiological and parasitological examinations on the squirrels before they were released and on resident squirrels. Red squirrels found dead in Thetford Chase were examined post mortem by parasitological, electron microscopical and radiological techniques. Parapoxvirus infection was the probable cause of death of two red squirrels. Parapoxvirus infection may be a significant threat to remnant populations of red squirrels in England, and to the success of conservation measures.
52 citations
"Study of squirrelpox virus in red a..." refers background in this paper
...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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