386,206 research outputs found
Within-Host Dynamics of Multi-Species Infections:Facilitation, Competition and Virulence
No full textHost individuals are often infected with more than one parasite species (parasites defined broadly, to include viruses and bacteria). Yet, research in infection biology is dominated by studies on single-parasite infections. A focus on single-parasite infections is justified if the interactions among parasites are additive, however increasing evidence points to non-additive interactions being the norm. Here we review this evidence and theoretically explore the implications of non-additive interactions between co-infecting parasites. We use classic Lotka-Volterra two-species competition equations to investigate the within-host dynamical consequences of various mixes of competition and facilitation between a pair of co-infecting species. We then consider the implications of these dynamics for the virulence (damage to host) of co-infections and consequent evolution of parasite strategies of exploitation. We find that whereas one-way facilitation poses some increased virulence risk, reciprocal facilitation presents a qualitatively distinct destabilization of within-host dynamics and the greatest risk of severe disease.</p
Host choice and host leaving in Rhopalosiphum padi (Hemiptera: Aphididae) emigrants and repellency of aphid colonies on the winter host
No full textHost choice and winter-host leaving in emigrants of bird cherry–oat aphid,
Rhopalosiphum padi (Linnaeus), were investigated in the laboratory. In settling
choice tests, emigrants collected from the winter host, Prunus padus, preferred this
plant over a summer host, oats. Emigrants which had left P. padus for up to 24 h
did not express a preference as a group, and those which had left for 24–48 h
preferred oats. Eighty seven percent of emigrants caged as fourth-instar nymphs
on P. padus leaves abandoned the host by the second day of adult life, and
apparently did not subsequently return to the leaf. In an olfactometer, P. padus
leaves which had supported spring generations of R. padi were repellent to
emigrants. Volatiles were entrained from uninfested and R. padi-infested P. padus
using cut twigs in the laboratory as well as intact twigs on a tree in the field.
Entrainment extracts from uninfested P. padus had no effect on emigrants in the
olfactometer, whereas those from twigs infested with nymphal emigrants were
repellent. The study indicates that in R. padi, host-alternation is driven by
behavioural changes which occur in individuals as well as between morphs
The fitness of African malaria vectors in the presence and limitation of host behaviour
No full text<p>Background
Host responses are important sources of selection upon the host species range of ectoparasites and phytophagous insects. However little is known about the role of host responses in defining the host species range of malaria vectors. This study aimed to estimate the relative importance of host behaviour to the feeding success and fitness of African malaria vectors, and assess its ability to predict their known host species preferences in nature.</p>
<p>Methods
Paired evaluations of the feeding success and fitness of African vectors Anopheles arabiensis and Anopheles gambiae s.s in the presence and limitation of host behaviour were conducted in a semi-field system (SFS) at Ifakara Health Institute, Tanzania. In one set of trials, mosquitoes were released within the SFS and allowed to forage overnight on a host that was free to exhibit natural behaviour in response to insect biting. In the other, mosquitoes were allowed to feed directly on from the skin surface of immobile hosts. The feeding success and subsequent fitness of vectors under these conditions were investigated on 6 host types (humans, calves, chickens, cows, dogs and goats) to assess whether physical movements of preferred host species (cattle for An. arabiensis, humans for An. gambiae s.s.) were less effective at preventing mosquito bites than those of common alternatives.</p>
<p>Results
Anopheles arabiensis generally had greater feeding success when applied directly to host skin than when foraging on unrestricted hosts (in five of six host species). However, An. gambiae s.s obtained blood meals from free and restrained hosts with similar success from most host types (four out of six). Overall, the blood meal size, oviposition rate, fecundity and post-feeding survival of mosquito vectors were significantly higher after feeding on hosts free to exhibit behaviour, than those who were immobilized during feeding trials.</p>
<p>Conclusions
Allowing hosts to move freely during exposure to mosquitoes was associated with moderate reductions in mosquito feeding success, but no detrimental impact to the subsequent fitness of mosquitoes that were able to feed upon them. This suggests that physical defensive behaviours exhibited by common host species including humans do not impose substantial fitness costs on African malaria vectors.</p>
The host of GRB 060206 : kinematics of a distant galaxy
No full textContext. GRB afterglow spectra are sensitive probes of interstellar matter along the line-of-sight in their host galaxies, as well as in intervening galaxies. The rapid fading of GRBs makes it very difficult to obtain spectra of sufficient resolution and S/N to allow for these kinds of studies.
Aims. We investigate the state and properties of the interstellar medium in the host of GRB060206 at z = 4.048 with a detailed study of groundstate and finestructure absorption lines in an early afterglow spectrum. This allows us to derive conclusions on the nature and origin of the absorbing structures and their connection to the host galaxy and/or the GRB.
Methods. We used early (starting 1.6 h after the burst) WHT/ISIS optical spectroscopy of the afterglow of the gamma-ray burst GRB060206 detecting a range of metal absorption lines and their finestructure transitions. Additional information is provided by the afterglow lightcurve. The resolution and wavelength range of the spectra and the bright afterglow have facilitated a detailed study and
fitting of the absorption line systems in order to derive column densities. We also used deep imaging to detect the host galaxy and probe the nature of an intervening system at z = 1.48 seen in absorption in the afterglow spectra.
Results. We detect four discrete velocity systems in the resonant metal absorption lines, best explained by shells within and/or around the host created by starburst winds. The finestructure lines have no less than three components with strengths decreasing from the redmost components. We therefore suggest that the finestructure lines are best explained as being produced by UV pumping from which follows that the redmost component is the one closest to the burst where Nv was detected as well. The host is detected in deep HST imaging with F814WAB = 27.48 ± 0.19 mag and a 3σ upper limit of H = 20.6 mag (Vega) is achieved. A candidate counterpart for the intervening absorption system is detected as well, which is quite exceptional for an absorber in the sightline towards a GRB
afterglow. The intervening system shows no temporal evolution as claimed by Hao et al. (2007, ApJ, 659, 99), which we prove from our WHT spectra taken before and Subaru spectra taken during those observations
Responses of a bacterial pathogen to phosphorus limitation of its aquatic invertebrate host
No full textHost nutrition is thought to affect the establishment, persistence, and severity of pathogenic infections. Nutrient-deficient foods possibly benefit pathogens by constraining host immune function or benefit hosts by limiting parasite growth and reproduction. However, the effects of poor elemental food quality on a host's susceptibility to infection and disease have received little study. Here we show that the bacterial microparasite Pasteuria ramosa is affected by the elemental nutrition of its aquatic invertebrate host, Daphnia magna. We found that high food carbon : phosphorus (C: P) ratios significantly reduced infection rates of Pasteuria in Daphnia and led to lower within-host pathogen multiplication. In addition, greater virulent effects of bacterial infection on host reproduction were found in Daphnia-consuming P-deficient food. Poor Daphnia elemental nutrition thus reduced the growth and reproduction of its bacterial parasite, Pasteuria. The effects of poor host nutrition on the pathogen were further evidenced by Pasteuria's greater inhibition of reproduction in P-limited Daphnia. Our results provide strong evidence that elemental food quality can significantly influence the incidence and intensity of infectious disease in invertebrate hosts
Host specificity and genetics of host resistance in the "Daphnia-Pasteuria" host-parasite system
No full textAntagonistic coevolution plays an important role in a large number of evolutionary and ecological phenomena. Furthermore, according to the Red Queen Theory coevolution between hosts and their parasites may explain the maintenance of sexual reproduction and genetic variation, pertinent issues in evolutionary biology. For antagonistic coevolution to lead to negative frequency dependent selection, preserve genetic variation and select for sexual reproduction parasites need to have high host specificity and this specificity has to have a simple genetic basis. In this thesis I investigate these two criteria in the Daphnia-Pasteuria system. Daphnia magna and its bacterial pathogen Pasteuria ramosa have become one of the prime model systems for antagonistic coevolution between hosts and parasites and one of the few systems with empirical evidence consistent with antagonistic coevolution by frequency dependent selection.
In the first chapter I show that specificity in the Daphnia-Pasteuria system is much stronger than previously reported. By using a novel technique I obtain single genotypes (clones) from the unculturable P. ramosa. Infections with these single parasite genotypes either result in hosts that are fully resistant or in hosts that are fully susceptible. High specificity for just some genotypes of D. magna as found in the first chapter contrast with reports from infections in natural populations which suggested that P. ramosa has a broad host range and is able to simultaneously infect highly diverged species of Daphnia. In the second chapter I address this apparent controversy. My findings of a controlled infection experiment with multiple host species and parasite lineages suggest that P. ramosa is a species complex consisting of multiple morphologically cryptic species each highly specialized for some genotypes within their host species. In addition I find that although infection does only occur in native host-parasite combinations, attachment of spores to the host esophagus, a necessary step in the infection process is conserved and polymorphic between highly diverged species of Daphnia. In chapters 3 & 4 I investigate the genetic basis of the observed specificity. Using a large array of crosses and two parasite genotypes I find that resistance is coded for by a single Mendelian inherited locus with three alleles with an allele hierarchy. An alternative, but more complex, explanation for our results is based on two closely linked diallelic loci with interlocus epistasis.
In conclusion both my findings on host specificity and the genetics of host resistance suggest that Daphnia and Pasteuria have the potential to undergo antagonistic coevolution by negative frequency dependent selection. Furthermore, the finding that genetics of resistance in Daphnia are consistent with a matching allele model will allow the Daphnia-Pasteuria system to become a powerful tool for empirical testing of population level predictions of this model. Indeed, the Daphnia-Pasteuria system could be used to experimentally test for negative frequency dependent selection, the maintenance of genetic variation and the notion that antagonistic coevolution may favor genetic mixing
Which morphological characteristics are most influenced by the host matrix in downy mildews? : A case study in Pseudoperonospora cubensis
No full textBefore the advent of molecular phylogenetics, species concepts in the downy mildews, an economically important group of obligate biotrophic oomycete pathogens, have mostly been based upon host range and morphology. While molecular phylogenetic studies have confirmed a narrow host range for many downy mildew species, others, like Pseudoperonospora cubensis affect even different genera. Although often morphological differences were found for new, phylogenetically distinct species, uncertainty prevails regarding their host ranges, especially regarding related plants that have been reported as downy mildew hosts, but were not included in the phylogenetic studies. In these cases, the basis for deciding if the divergence in some morphological characters can be deemed sufficient for designation as separate species is uncertain, as observed morphological divergence could be due to different host matrices colonised. The broad host range of P. cubensis (ca. 60 host species) renders this pathogen an ideal model organism for the investigation of morphological variations in relation to the host matrix and to evaluate which characteristics are best indicators for conspecificity or distinctiveness. On the basis of twelve morphological characterisitcs and a set of twelve cucurbits from five different Cucurbitaceae tribes, including the two species, Cyclanthera pedata and Thladiantha dubia, hitherto not reported as hosts of P. cubensis, a significant influence of the host matrix on pathogen morphology was found. Given the high intraspecific variation of some characteristics, also their plasticity has to be taken into account. The implications for morphological species determination and the confidence limits of morphological characteristics are discussed. For species delimitations in Pseudoperonospora it is shown that the ratio of the height of the first ramification to the sporangiophore length, ratio of the longer to the shorter ultimate branchlet, and especially the length and width of sporangia, as well as, with some reservations, their ratio, are the most suitable characteristics for species delimitation
Host sexual dimorphism and parasite adaptation
No full textIn species with separate sexes, parasite prevalence and disease expression is often different between males and females. This effect has mainly been attributed to sex differences in host traits, such as immune response. Here, we make the case for how properties of the parasites themselves can also matter. Specifically, we suggest that differences between host sexes in many different traits, such as morphology and hormone levels, can impose selection on parasites. This selection can eventually lead to parasite adaptations specific to the host sex more commonly encountered, or to differential expression of parasite traits depending on which host sex they find themselves in. Parasites adapted to the sex of the host in this way can contribute to differences between males and females in disease prevalence and expression. Considering those possibilities can help shed light on host-parasite interactions, and impact epidemiological and medical science
Donor mesenchymal stem cells trigger chronic graft-versus-host disease following minor antigen-mismatched bone marrow transplantation
No full textChronic graft-versus-host disease (cGVHD) is a complication after minor antigen mismatched bone marrow transplantation (BMT) characterized by an autoimmune-type reaction in various organs. Aberration in T cell regulation is involved, with donor mesenchymal stem cells (MSCs) playing a possible role in immunomodulation. In a minor-antigen mismatched mouse BMT model, transplantation of mismatched, but not syngeneic MSCs triggered the onset of cGVHD, and was associated with fibrosis, increased IL-6 secretion, decreased Foxp3+ regulatory T cells and increased Th17 in the peripheral blood. Mismatched MSCs alone were sufficient to induce cGVHD, while removal of donor MSCs rescued mice from cGVHD. RAG2 knockout recipient mice did not suffer cGVHD, indicating that host T cells were involved. Residual host-derived T cells were significantly higher in cGVHD patients compared to non-cGVHD patients. In conclusion, donor MSCs react with residual host T cells to trigger the progression of cGVHD
Host-nested parasite unit.
No full textParasite growth is unlimited (bacteria, phage), as long as the habitat nourishes it. Once the host loses the ability to nourish the parasites, they are condemned to perish. The association of a dedicated hyperparasite (phage) with a given parasite (bacteria) forming nested parasite pairs is a very effective and robust taming strategy for a parasitized host (both populations fluctuate around their equilibria). (DOCX)</p
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