| 词汇 | example_english_virulence |
| 释义 | Examples of virulenceThese examples are from corpora and from sources on the web. Any opinions in the examples do not represent the opinion of the Cambridge Dictionary editors or of Cambridge University Press or its licensors. Tuberculosis and typhus were not difficult to diagnose and there is no evidence that their autonomous virulence had declined. The usual argument is that cooperation consists in a reduction of virulence; in other words, avirulence is a cooperative restraint in host exploitation. Rather, virulence may also derive from toxin-mediated alteration of host immune responses prior to sepsis and toxaemia. Population studies demonstrate that the small amount of variation defines three clonal lineages where phenotypes such as virulence are associated with a single lineage. The ability to endocytose has been correlated with the virulence of the organism. Blood from mice which developed infections was passaged repeatedly through mice and then rats at 3 day intervals to increase virulence, before cloning in mice. The diversity among clusters may correspond to presence of these virulence factors. The ability of meningococcal strains to cause invasive disease and their subsequent virulence are variable. In a warmer climate, the agent might not be able to withstand the environmental changes, resulting in the decay of its virulence. Genes coding for metabolic functions or virulence factors are the main targets for producing safe vaccine strains. Specific virulence determinants that are required by strains to cause invasive diseases are unknown. Alternatively, while speculative, it is possible that all these strains are derived from the seventh-pandemic strain by the absence or loss of virulence genes. Other virulence factors include the ability to cause attaching-and-effacing lesions in the intestine and plasmid encoded haemolysins. All strains possessed the toxin genes and the other virulence factors investigated. The aim, therefore, was to determine if additional therapeutic antibiotic use was associated with changes in virulence gene prevalence. In the host, the parasite mediates its virulence in the presence of the natural gut flora and bacterial associates support in vitro growth. The relationship between adaptation to colonization and virulence of individual serotypes is not yet fully understood [36]. Virulence reduces parasite fitness by reducing the duration of infection. As gametocyte production and infectivity determine parasite fitness, understanding its relation to disease is crucial to understanding the epidemiological significance of parasite virulence. The patterns we offered for the evolution of virulence levels support two similar yet distinct hypotheses. The most common virulence characteristic in 99 strains was stx2, stx2c alone or with other stx (79 %). The most important one being the virulence of the material; unless the cattle are protected by chemoprophylaxis the majority would die. In this case, virulence might be ' coincidental ' to an adaptation to the colonic niche as has previously been suggested [41]. Virulence and transmissibility of pathogens : what is the relationship ? Resistance to diseases in natural systems is often heterogeneous within plant populations and dynamically coevolves with virulence genes in the pathogen population. The second part examines the genes involved within host-parasite interactions, with an emphasis on arms races between parasite infectivity and\\or virulence and host resistance. To understand the kind of selection pressure acting on resistance, infectivity and virulence, it is important to understand the specificity of the interaction. An interesting feature of the mite's pathogenicity is that virulence varies between and within geographical strains and can change rapidly within a few months. A correlated response of a parasite's virulence and life cycle to selection on its host's life history. Ectoparasite virulence is linked to mode of transmission. However, these studies measured virulence under standard laboratory conditions with excess food and limited competition. The contrast in virulence between normal and progenetic metacercariae is very revealing. The accuracy of these measurements of virulence was improved as the production laboratory's experience increased. The expectation now is an increase in virulence. Work to determine whether rashes are caused by particular vaccine variants that perhaps revert to virulence is currently ongoing. One gene, or set of genes, regulates the amount of antigen produced, which is reflected by the virulence of the infection. Likewise, one should also consider whether evolutionary changes in resistance, infectivity or virulence influence host-parasite population dynamics. However, if the magnitude of the group selection factor modulating the virulence of these viral populations is large enough, no significant change would be expected. The remaining three (nos. 10550/1, 15830, 18526) were negative for all the virulence genes assayed. Shared themes of antigenic variation and virulence in bacterial, protozoal and fungal infections. The bacterial flora of the intestine plays an important role in amoebic virulence. In summary, mixed-strain infections are likely to be important in the evolution and maintenance of virulence in schistosome infections of snails. In turn this worsening of economic conditions leads to increased virulence of the disease. Alternatively, the addition of chlortetracycline may have been associated with the change in the prevalence of the virulence genes. Further comparative analyses among clusters with identification of virulence factors are necessary. A close relationship between the combination of virulence genes and adherence properties was observed. With respect to the pathogenicity and virulence characteristics, only one isolate per animal was selected. The other serogroups are abundant in aquatic environments but do not possess the virulence genes necessary for causing the disease. The combination of all four virulence marker genes was most frequently found in isolates also carrying stx2. Interestingly, 41n4 % of all strains in this latter group carried none of the virulence markers examined. Strains can also differ greatly with regard to virulence. In this case, the expected response is a reduction in virulence. Therefore, differences in the virulence and propagation of different species were used to rate their efficacy. The matings of midges in the separate blocks would be strongly assortative for virulence against crop resistance genes. Hence, it is probable that virulence genes present in populations on non-cultivated grasses could be transferred into populations commonly found on crops. Similarly, the results could be explained by separate effects of genetic heterogeneity on parasite reproductive rate and virulence resulting in the statistical association seen. We investigated, for a snail-schistosome system, whether a conditional increase in replication rates occurred in mixed genotype infections and resulted in increased virulence. Nonetheless, the virulence differences it proposes may help explain the variation detected in host responses to trematode parasitism. However, one should keep in mind that strains that have undergone multiple passages in laboratory animals might have lost or changed their pathogenicity and virulence. There are several reasons why infection genetic diversity should increase virulence. Selection may act indirectly through statistical or physical associations of neutral markers with selected genes, such as genes directly involved in resistance or virulence. Ten clones, which had been preserved in liquid nitrogen, were chosen from the progeny of the 5th cross and analysed for virulence and antigenic type. Investigations into possible causes for the loss of virulence were undertaken. The mechanism of increased virulence following bacterial co-association is not well understood. They cannot be regarded as valid names, in the sense of scientific nomenclature, for virulence and immunity reactions are not adequate tests of specificity. However, the method does not give an indication on the virulence of the stabilates. After testing for virulence, immunogenicity and purity, suitable strains are preserved as master stabilates in liquid nitrogen. They then chose the first-degree vaccine and the second-degree vaccine according to the appropriate ratio of virulence to produce immunity without too much risk. All cytotoxic strains were adhesive, and therefore the simultaneous presence of these virulence factors confirms the role of such microorganisms as potential pathogens. Moreover, it highly increased its virulence with increasing nematode concentrations (up to 77% infected host larvae at 15.9 nematodes cmx2). Alternatively, three clades may have shared virulence genes originating from a common ancestor. If they did become arboviruses, would that prevent a predicted evolution toward lower virulence? There may be exchange of genetic material between clades conditioning for virulence to crops. However, other, as yet unidentified, virulence factors are likely to exist. A fourth key concern is how multiple infection with malaria parasites might modify virulence of infection. Adhesion is important not only for persistence and controlled migration of the pathogen, but also for the virulence of the parasite. Additionally, because virulence factors are not found in nonpathogenic bacteria, such therapies would not be expected to disrupt commensal bacteria. To date, a possible link between virulence and any particular strain pro®le has never been demonstrated. The species has low intrinsic pathogenicity but a number of putative virulence factors have been described [13, 14]. The strains harbouring these virulence characteristics formed separate clusters whereas the strains possessing stx1 alone did not. Parasites that infect their hosts horizontally as well as vertically are model organisms for the study of the evolution of virulence. We examined 10 parasite clones for their inhost growth rate, virulence, transmission potential and infection length when infecting nave and imi munized mice. Definitions of virulence, however, do differ across the literature. Unfortunately, the potential strain-specificity of parasite infectivity and virulence has not yet been so intensely investigated as has host resistance. Trade-offs may also be an important mechanism for the maintenance of genetic variation for resistance, infectivity and virulence in natural populations. In particular, the evolution of snail resistance and schistosome infectivity and virulence may offer the prospect of an insight into the genetics of adaptation. However, where parasites have a major effect on host population dynamics, coupled coevolution could still lead to spatio-temporal variation in resistance, infectivity and virulence. Parasites could evolve a genetically fixed virulence strategy appropriate for the frequency, and average genetic heterogeneity, of mixed infections in the population. Both strains have relatively low virulence with the animals surviving more than 30 days. The evolution of virulence in parasites and pathogens : reconciliation between two competing hypotheses. The mechanisms underlying virulence in malaria parasites are still poorly understood, despite their possible clinical importance. A number of possible relationships between multiplicity and virulence are conceivable and 4 distinct types of models have been considered in recent years. Table 2 shows the combination of virulence genes and the phenotypic characteristics of the strains of each serotype. The remaining 50 % included strains presenting different combinations of virulence factors or those lacking any virulence property. The peninsular and loyalist masses reacted with virulence against anyone suspect of sympathising with reformism and separatism. The gap in the virulence between the two vaccines used to produce artificial immunity had to be carefully regulated and stable. The graduation of vaccines implied the development of a scale of virulence. The relative virulence of the 2 clones is unaltered by dose and the more virulent clone is always more virulent. Aspects of pneumococcal infection including bacterial virulence, host response and vaccination. However, a small number of isolates were resistant to these drugs and most of them possessed virulence-related genes. These examples are from corpora and from sources on the web. Any opinions in the examples do not represent the opinion of the Cambridge Dictionary editors or of Cambridge University Press or its licensors. |
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