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Biomedical subjects

M Begon

Publications and source records attributed to M Begon.

At least 19 recordsLinked to original sources
PubMed2006

Plague metapopulation dynamics in a natural reservoir: the burrow system as the unit of study.

The ecology of plague (Yersinia pestis infection) in its ancient foci in Central Asia remains poorly understood. We present field data from two sites in Kazakhstan where the great gerbil (Rhombomys opimus) is the major natural host. Family groups inhabit and defend burrow systems spaced throughout the landscape, such that the host population may be considered a metapopulation, with each occupied burrow system a subpopulation. We examine plague transmission within and between family groups and its effect on survival. Transmission of plague occurred disproportionately within family groups although not all gerbils became infected once plague entered a burrow system. There were no spatial patterns to suggest that family groups in close proximity to infected burrow systems were more at risk of infection than those far away. At one site, infection increased the chances of burrow-system extinction. Overall, it is useful to consider the burrow system as the unit of study within a much larger metapopulation.

Animals↗
PubMed2006

Contrasting dynamics of Bartonella spp. in cyclic field vole populations: the impact of vector and host dynamics.

Many zoonotic disease agents are transmitted between hosts by arthropod vectors, including fleas, but few empirical studies of host-vector-microparasite dynamics have investigated the relative importance of hosts and vectors. This study investigates the dynamics of 4 closely related Bartonella species and their flea vectors in cyclic populations of field voles (Microtus agrestis) over 3 years. The probability of flea infestation was positively related to field vole density 12 months previously in autumn, but negatively related to more recent host densities, suggesting a dilution effect. The 4 Bartonella species exhibited contrasting dynamics. Only B. grahamii, showed a distinct seasonal pattern. Infection probability increased with field vole density for B. doshiae, B. taylorii and BGA (a previously unidentified species) and with density of coexisting wood mice for B. doshiae and B. grahamii. However, only the infection probability of BGA in spring was related to flea prevalence. B. doshiae and BGA were most common in older animals, but the other 2 were most common in non-reproductive hosts. Generally, host density rather than vector abundance appears most important for the dynamics of flea-transmitted Bartonella spp., possibly reflecting the importance of flea exchange between hosts. However, even closely related species showed quite different dynamics, emphasising that other factors such as population age structure can impact on zoonotic risk.

Animals↗
PubMed2006

A role for vector-independent transmission in rodent trypanosome infection?

Within host-pathogen systems where vector-borne transmission is the primary route of infection, little or no attention has been paid to the relative importance of secondary or alternative routes of transmission. Here, by contrast, we report the results from a controlled longitudinal field-scale experiment in which the prevalence of fleas (Siphonaptera) was manipulated and the occurrence and distribution of a flea-borne protozoan (Trypanosoma (Herpetosoma) microti) in a natural field vole (Microtus agrestis) population was monitored over a 2-year period. A non-systemic insecticide was applied to individual voles within two treatment grids and the prevalences of fleas and of T. microti were monitored on these and on two control grids. Blood samples were taken from all voles and PCR-based methods used to determine infection status. Insecticidal treatment was highly effective at reducing overall flea prevalence and recaptured animals (treated ca. 4 weeks previously) were very rarely infested (ca. 3%, compared with 50-70+% normally). On the other hand, the probability of trypanosome infection was reduced in treated animals on experimental grids to only around one-third of that normally observed. This suggests that direct, as opposed to flea-borne, transmission may not only occur, it may also be of epidemiological importance. The possibility that the importance of such transmission routes may have been underestimated in 'vector-borne' infections more generally is discussed.

Animals↗
PubMed2006

Effects of movement for estimating the hip joint centre.

Determination of the hip joint centre (HJC) using a functional approach requires access to the kinematics of various body postures. The present study aimed to determine the combined impact of the nature of the movement, its type and the number of cycles, on the accuracy of HJC estimation. Kinematics noise was modelled based on the deformation of hip and thigh clusters of seven subjects, while perfect ball-and-socket movements (used as reference) were calculated based on the movements of one of the subjects. The noise added to the reference kinematics allowed the simulation of 27 tests. Errors were defined as the Euclidean distance between the estimated and the reference HJC. A nested ANOVA and a multiple comparison procedures were performed on all errors. A test including 10 cycles of three different types of limited movements (flexion-extension, abduction-adduction and circumduction) yielded the greatest accuracy for estimating HJC (4.0+/-1.3 mm). Combining different types of movements allowed improving the accuracy. Given that noise increases as a function of the range of a motion, limited movements proved to be the most accurate; however, 10 cycles were required to achieve such results. For trials involving a single cycle, a large movement proved more efficient.

Adult↗
PubMed2006

Sympatric Ixodes trianguliceps and Ixodes ricinus ticks feeding on field voles (Microtus agrestis): potential for increased risk of Anaplasma phagocytophilum in the United Kingdom?

The importance of wild rodents as reservoirs of zoonotic tick-borne pathogens is considered low in the United Kingdom because, in studies to date, those parasitized by exophilic Ixodes ricinus ticks carry almost exclusively larvae and thus have a minor role in transmission cycles. In a cross-sectional study, 11 (6.7%) of 163 field voles (Microtus agrestis) captured at field sites in Northern England were PCR-positive for Anaplasma phagocytophilum. The voles were found to act as hosts for both larval and nymphal I. ricinus and all stages of the nidicolous tick I. trianguliceps, and eight individuals were infested with ticks of both species at the same time. Two of 158 larval and one of 13 nymphal I. ricinus, as well as one of 14 larval and one of 15 nymphal I. trianguliceps collected from the rodents were PCR-positive. These findings suggest that habitats where field voles are abundant in the United Kingdom may pose a risk of A. phagocytophilum infection because (i) field voles, the most abundant terrestrial mammal in the United Kingdom, may be a competent reservoir; (ii) the field voles are hosts for both nymphal and larval ixodid ticks so they could support endemic cycles of A. phagocytophilum; and (iii) they are hosts for nidicolous I. trianguliceps, which may alone maintain endemic cycles, and exophilic I. ricinus ticks, which could act as a bridge vector and transmit infections to humans and domesticated animals.

Anaplasma phagocytophilum↗
PubMed2005

Disruption of a host-parasite system following the introduction of an exotic host species.

The potential of biological invasions to threaten native ecosystems is well recognized. Here we describe how an introduced species impacts on native host-parasite dynamics by acting as an alternative host. By sampling sites across an invasion front in Ireland, we quantified the influence of the introduced bank vole (Clethrionomys glareolus) on the epidemiology of infections caused by flea-transmitted haemoparasites of the genus Bartonella in native wood mice (Apodemus sylvaticus). Bartonella infections were detected on either side of the front but occurred exclusively in wood mice, despite being highly prevalent in both rodent species elsewhere in Europe. Bank vole introduction has, however, affected the wood mouse-Bartonella interaction, with the infection prevalence of both Bartonella birtlesii and Bartonella taylorii declining significantly with increasing bank vole density. Whilst flea prevalence in wood mice increases with wood mouse density in areas without bank voles, no such relationship is detected in invaded areas. The results are consistent with the dilution effect hypothesis. This predicts that for vector-transmitted parasites, the presence of less competent host species may reduce infection prevalence in the principal host. In addition we found a negative relationship between B. birtlesii and B. taylorii prevalences, indicating that these two microparasites may compete within hosts.

Animals↗
PubMed2005

Trypanosomes, fleas and field voles: ecological dynamics of a host-vector--parasite interaction.

To investigate the prevalence of a flea-borne protozoan (Trypanosoma (Herpetosoma) microti) in its field vole (Microtus agrestis) host, we monitored over a 2-year period a range of intrinsic and extrinsic parameters pertaining to host demographics, infection status and vector (flea) prevalence. Generalized Linear Mixed Modelling was used to analyse patterns of both flea and trypanosome occurrence. Overall, males of all sizes and ages were more likely to be infested with fleas than their female counterparts. Flea prevalence also showed direct density dependence during the winter, but patterns of density dependence varied amongst body mass (age) classes during the summer. Trypanosome prevalence did not vary between the sexes but was positively related to past flea prevalence with a lag of 3 months, with the highest levels occurring during the autumn season. A convex age-prevalence distribution was observed, suggesting that individuals develop a degree of immunity to trypanosome infection with age and exposure. An interaction between age and whether the individual was new or recaptured suggested that infected animals are less likely to become territory holders than their uninfected counterparts.

Animals↗
PubMed2002

Host specificity of Trypanosoma (Herpetosoma) species: evidence that bank voles (Clethrionomys glareolus) carry only one T. (H.) evotomys 18S rRNA genotype but wood mice (Apodemus sylvaticus) carry at least two polyphyletic parasites.

The strongest evidence for host specificity of mammalian trypanosomes comes from parasites of the subgenus Trypanosoma (Herpetosoma). Laboratory studies have shown that T. (Herpetosoma) species will not infect an alternative host. However, this has not been demonstrated in wild populations. We screened 560 bank voles (Clethrionomys glareolus) and 148 wood mice (Apodemus sylvaticus) for trypanosomes by PCR amplification of the 18S rRNA gene. In total, 109 (19%) bank voles and 12 (8%) wood mice were infected. A HaeIII restriction site was discovered that could be used to discriminate between T. (H.) evotomys of the bank vole and T. (H.) grosi of the wood mouse. All the parasites in the bank voles were identified as T. (Herpetosoma) evotomys by RFLP-PCR. Out of the 12 wood mouse infections 10 were due to T. grosi. Two of the wood mice were infected with parasites with a novel genotype that was most similar to those of T. evotomys and T. microti of voles. Fifty-six fleas collected from the rodents were also screened for trypanosomes; 9 were infected with T. evotomys and 1 with T. grosi. One of the fleas infected with T. evotomys was collected from a wood mouse.

Animals↗
PubMed2002

A clarification of transmission terms in host-microparasite models: numbers, densities and areas.

Transmission is the driving force in the dynamics of any infectious disease. A crucial element in understanding disease dynamics, therefore, is the 'transmission term' describing the rate at which susceptible hosts are 'converted' into infected hosts by their contact with infectious material. Recently, the conventional form of this term has been increasingly questioned, and new terminologies and conventions have been proposed. Here, therefore, we review the derivation of transmission terms, explain the basis of confusion, and provide clarification. The root of the problem has been a failure to include explicit consideration of the area occupied by a host population, alongside both the number of infectious hosts and their density within the population. We argue that the terms 'density-dependent transmission' and 'frequency-dependent transmission' remain valid and useful (though a 'fuller' transmission term for the former is identified), but that the terms 'mass action', 'true mass action' and 'pseudo mass action' are all unhelpful and should be dropped. Also, contrary to what has often been assumed, the distinction between homogeneous and heterogeneous mixing in a host population is orthogonal to the distinction between density- and frequency-dependent transmission modes.

Disease Transmission, Infectious↗
PubMed2002

New world origins for haemoparasites infecting United Kingdom grey squirrels (Sciurus carolinensis), as revealed by phylogenetic analysis of bartonella infecting squirrel populations in England and the United States.

Phylogenetic analyses of bartonella have suggested divergence between bartonellae that infect mammals native to the Old and New Worlds. We characterized bartonella isolated from Eastern grey squirrels (Sciurius carolinensis) in the United States and from grey and red squirrels (Sciurus vulgaris) in the United Kingdom by nucleotide sequence comparison (gltA and groEL). Isolates from grey squirrels in the United States and the United Kingdom were identical, and most similar to Bartonella vinsonii, a species associated with New World rodents. A single and novel bartonella genotype was obtained from all 12 red squirrel isolates. Although grey squirrels were first introduced into the United Kingdom over 125 years ago, they continue to be infected solely by the bartonella associated with grey squirrels native to the United States. These results illustrate that exotic species may be accompanied by the introduction and maintenance, over many generations, of their microparasites.

Animals↗
PubMed2001

The impact of specialized enemies on the dimensionality of host dynamics.

Although individual species persist within a web of interactions with other species, data are usually gathered only from the focal species itself. We ask whether evidence of a species' interactions be detected and understood from patterns in the dynamics of that species alone. Theory predicts that strong coupling between a prey and a specialist predator/parasite should lead to an increase in the dimensionality of the prey's dynamics, whereas weak coupling should not. Here we describe a rare test of this prediction. Two natural enemies were added separately to replicate populations of a moth. For biological reasons that we identify here, the prediction of increased dimensionality was confirmed when a parasitoid wasp was added (although this increase had subtleties not previously appreciated), but the prediction failed for an added virus. Thus, an imprint of the interactions may be discerned within time-series data from component species of a system.

Animals↗
PubMed2001

Longitudinal monitoring of the dynamics of infections due to Bartonella species in UK woodland rodents.

Blood samples were repeatedly collected from 12 sympatric woodland rodents over a 12-month period and DNA extracts from each were incorporated into a bartonella-specific PCR targeting a fragment of the 16S/23S rRNA intergenic spacer region (ISR). The composition of each amplicon was analysed using restriction enzyme analysis (REA) and base sequence comparison. Bartonella DNA was detected in 70 of 109 samples. Eleven samples contained DNA derived from more than one strain. Sequence analysis of 62 samples found 12 sequence variants (ISR genotypes) that were provisionally assigned to 5 different species, 2 of which were newly recognized. Up to five different species were detected in each animal. On about two-thirds of occasions, a species detected I month was not there the next, but never was a genotype superseded by another of the same species. However, a genotype could be re-encountered months later in the same animal, even if interim samples contained other genotypes. Our results suggest that although most animals are bacteraemic most of the time, specific infections are often superseded and that a complex and dynamic epidemiology of bartonella bacteraemias exists in woodland rodents.

Animals↗
PubMed2000

Invasion sequence affects predator-prey dynamics in a multi-species interaction.

Ecologists seek to understand the rules that govern the assembly, coexistence and persistence of communities of interacting species. There is, however, a variety of sequences in which a multi-species community can be assembled--unlike more familiar one- and two-species systems. Ecological systems can exhibit contrasting dynamics depending on initial conditions, but studies have been focused on simple communities initiated at different densities, not on multi-species communities constructed in different sequences. Investigations of permanence and convergence in ecological communities have been concerned with the flux of whole species (presence or absence) but have not addressed the central issues concerning the dynamics exhibited by individual species in particular interactions. Here we examine data for replicated three-species systems and demonstrate that the dynamic trajectories of both a predator and its prey within the system are determined by the sequence in which it is constructed, and that for one construction-sequence alternative dynamic patterns are possible.

Animals↗
PubMed2000

Subtyping of uncultured bartonellae using sequence comparison of 16 S/23 S rRNA intergenic spacer regions amplified directly from infected blood.

This study aimed to assess the usefulness of a PCR-based approach to the detection and differentiation of Bartonella strains in infected blood. The conservation of potential genus-specific PCR primer hybridisation sites within the 16 S/23 S rRNA gene intragenic spacer regions of Bartonella species was confirmed following sequence analysis of the intragenic spacer regions of four previously untested species. The extent of intra-species variation within the specific amplicons was assessed by comparison of sequences obtained from 17 strains of four Bartonella species. Eight sequence variants were obtained. Each species for which multiple strains were tested possessed at least two intragenic spacer regions variants, but the differences between these strains were markedly less than those observed inter-species. Sequence analysis was performed on 60 amplicons obtained from blood pellets collected from woodland rodent communities in which bartonella infections were known to be highly prevalent. Twelve variants were encountered, only five of which had been found among the studied isolates. Partial intragenic spacer region amplification followed by product sequence analysis offers a potentially sensitive and totally transferable means of inter- and intra-species differentiation of Bartonella strains, and its use in this study has broadened our knowledge of the genotypic spectrum of bartonellae associated with natural infections among UK woodland rodents.

Animals↗
PubMed2000

A longitudinal study of an endemic disease in its wildlife reservoir: cowpox and wild rodents.

Cowpox is an orthopoxvirus infection endemic in European wild rodents, but with a wide host range including human beings. In this longitudinal study we examined cowpox in two wild rodent species, bank voles Clethrionomys glareolus and wood mice Apodemus sylvaticus, to investigate the dynamics of a virus in its wild reservoir host. Trapping was carried out at 4-weekly intervals over 3 years and each animal caught was uniquely identified, blood sampled and tested for antibodies to cowpox. Antibody prevalence was higher in bank voles than in wood mice and seroconversion varied seasonally, with peaks in autumn. Infection was most common in males of both species but no clear association with age was demonstrated. This study provides a model for studying other zoonotic infections that derive from wild mammals since other approaches, such as one-off samples, will fail to detect the variation in infection and thus, risk to human health, demonstrated here.

Animals↗
PubMed1999

Transmission dynamics of a zoonotic pathogen within and between wildlife host species.

The transmission dynamics of the cowpox virus infection have been quantified in two mixed populations of bank voles (Clethrionomys glareolus) and wood mice (Apodemus sylvaticus), through analyses of detailed time-series of the numbers of susceptible, infectious and newly infected individuals. The cowpox virus is a zoonosis which circulates in these rodent hosts and has been shown to have an adverse effect on reproductive output. The transmission dynamics within species is best described as frequency dependent rather than density dependent, contrary to the 'mass action' assumption of most previous studies, both theoretical and empirical. Estimation of a transmission coefficient for each species in each population also allows annual and seasonal variations in transmission dynamics to be investigated through an analysis of regression residuals. Transmission between host species is found to be negligible despite their close cohabitation. The consequences of this for the combining ability of hosts as zoonotic reservoirs, and for apparent competition between hosts, are discussed.

Animals↗