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
Citations
More filters
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)....
[...]
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]....
[...]
References
More filters
TL;DR: This island population seems to remain viable as a result of an extended breeding season and increased population densities in sites with summer or supplementary food, which provides a buffering effect against variations in natural food availability, and seems to be important for their long-term survival.
Abstract: The Channel Island of Jersey is 116 km2 but has only 540 ha of woodland distributed in 237 wooded fragments with mean size of 2.5 ha. Despite this, the island supports 300 to 600 red squirrels Sciurus vulgaris, a species that is under threat in mainland Britain from habitat fragmentation, disease and the spread of the alien grey squirrel S. carolinensis. Grey squirrels are not present on Jersey. Between 1994 and 1997, using trapping and tracking techniques, we studied how red squirrels survive on Jersey by focusing on three local populations in sites B, C and S with contrasting food availability. The primary squirrel foods at site B were autumn tree seeds, at site C autumn tree seeds and summer conifer cones, and at site S autumn tree seeds and ad libitum, year-round supplementary food provided by local people. The densities of squirrels in site C (mean over 3 years 0.97 ha−1) and site S (1.21 ha−1) were more than one and a half times that of site B (0.68 ha−1), which relied on autumn seeds. Body mass and condition, and early breeding (spring litters) were not affected by food availability although conception occurred as early as November, earlier than in mainland Britain. Less than 50% of females produced summer litters, and 88% of non-breeders did not receive supplementary food. Turnover rates were lowest and most stable in site B. Annual residency was not influenced by the size of the natural tree seed crop. Cat and road kills caused two out of three reported deaths. This island population seems to remain viable as a result of an extended breeding season and increased population densities in sites with summer or supplementary food. The results emphasize the beneficial effects of extra food provided by local people. This provides a buffering effect against variations in natural food availability, and seems to be important for their long-term survival.
46 citations
TL;DR: In this paper, the authors studied the host-pathogen dynamics of Squirrelpox virus (SQPV) disease in free-living red squirrels in the coniferous woodland of Thetford Chase, East Anglia.
Abstract: SUMMARY Squirrelpox virus (SQPV) causes a fatal disease in free-living red squirrels {Sciurus vulgaris) which has contributed to their decline in the United Kingdom. Given the difficulty of carrying out and funding experimental investigations on free-living wild mammals, data collected from closely monitored natural outbreaks of disease is crucial to our understanding of disease epidemiology. A conservation programme was initiated in the 1990s to bolster the population of red squirrels in the coniferous woodland of Thetford Chase, East Anglia. In 1996, 24 red squirrels were reintroduced to Thetford from Northumberland and Cumbria, while in 1999 a captive breeding and release programme commenced, but in both years the success of the projects was hampered by an outbreak of SQPV disease in which seven and four red squirrels died respectively. Valuable information on the host-pathogen dynamics of SQPV disease was gathered by telemetric and mark-recapture monitoring of the red squirrels. SQPV disease characteristics were comparable to other virulent poxviral infections: the incubation period was < 15 days; the course of the disease an average of 10 days and younger animals were significantly more susceptible to disease. SQPV disease places the conservation of the red squirrel in jeopardy in the United Kingdom unless practical disease control methods can be identified.
41 citations
Journal Article•
35 citations
"Study of squirrelpox virus in red a..." refers background in this paper
...It was suggested that since the grey squirrel normally appeared to be very resistant to this disease, the virus may be maintained in the grey squirrel population, from where it was transmitted to the more susceptible red squirrels (Duff et al., 1996)....
[...]
TL;DR: In this article, a series of index numbers have been calculated to show the distributional dynamics of the two species in Great Britain, using the established methodology of annual ornithological index numbers, and a new index, measuring the annual replacement of one species by the other species, indicates little overall change in England and Scotland, but a net advance of the gray squirrel in Wales.
Abstract: The invasion of Great Britain by the gray squirrel from America has posed many interesting problems in ecology and conservation (interactions with the native red squirrel) and in forest management (the gray squirrel severely damages young stands of deciduous trees). Since 1973, mapped data on the annual distribution of the two species in state-managed forests have been published by the Forestry Commission.
Using the established methodology of annual ornithological index numbers, series of index numbers have been calculated to show the distributional dynamics of the two species. In Great Britain as a whole there has been rather limited change over the 15-year period from 1973. However, this masks (1) the dramatic distributional decline in the red squirrel in Wales balanced by a modest expansion in Scotland, and (2) the substantial distributional increase in the gray squirrel in the small number of grid squares in Scotland in comparison with the relatively steady distribution in the large number of grid squares in England.
A new index, measuring the annual replacement of one species by the other species, indicates little overall change in England and Scotland, but a net advance of the gray squirrel in Wales. A series of Markovian matrices predicted that the red squirrel would persist in forests in Scotland and in some areas of England, but would be rare in Wales. Over Great Britain as a whole, the gray squirrel is likely to occur in about twice as many forest areas as the red squirrel.
Resumen: La invasion de la Gran Bretana por la ardilla gris proveniente de America ha planteado muchos problemas de interes en ecologia y conservacion (interaccion con la ardilla roja nativa) y en manejo forestal (la ardilla gris dana severamente parcelas jovenes de arboles caducifolios). Desde 1973 la comision forestal ha publicado mapas sobre la distribucion anual de las dos especies en bosques administrados por el estado.
Empleando la metodologia establecida de indices numericos ornitologicos anuales, se han calculado una serie de indices numericos para mostrar la dinamica de los cambios en la distribucion de las dos especies. A nivel de Gran Bretana ha habido solo un cambio limitado dentro del periodo de 15 anos desde 1973. Sin embargo, esto enmascara (1) la dramatica declinacion en la distribucion de la ardilla roja en Gales, compensado por una modesta expansion en Escocia, y (2) el substancial incremento en la distribucion de la ardilla gris en el reducido numero de cuadros en la reticula de Escocia, comparado con la relativa estabilidad de la distribucion en el gran numero de cuadros en la reticula de Inglaterra.
Un nuevo indice, que mide el remplazo anual de unu especie por la otra, indica poco cambio general en Inglaterra y Escocia, pero un avance neto de la ardilla gris en Gales. Una serie de matrices Markovianas predijeron que la ardilla persistiria en bosques de Escocia y en algunas areas de Inglaterra, pero que deberia ser rara en Gales. Sobre Gran Bretana en su conjunto, es probable que la ardilla gris se presente en aproximadamente el doble de areas forestales que la ardilla roja.
34 citations
TL;DR: There is increasing evidence that squirrel pox disease is the principal cause of the rapid decline of the red squirrel in England, but relatively little is known about other infectious agents that may adversely affect this endangered species.
Abstract: SIR, — There is increasing evidence that squirrel pox disease is the principal cause of the rapid decline of the red squirrel ( Sciurus vulgaris ) in England ([Rushton and others 2006][1]). However, relatively little is known about other infectious agents that may adversely affect this endangered
29 citations