LitCovid-sentences  

PMC:7551987 / 1862-7699 JSONTXT 3 Projects

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Id Subject Object Predicate Lexical cue
T11 0-2 Sentence denotes 1.
T12 3-15 Sentence denotes Introduction
T13 16-145 Sentence denotes Interactions between the life history of a pathogen and the environment in which it is embedded drive the evolution of virulence.
T14 146-298 Sentence denotes These interactions thus dictate both the experience of disease at the individual host level and the shape of disease dynamics in host populations [1,2].
T15 299-446 Sentence denotes The nature of the interaction between virulence and transmission has been the object of both theoretical and empirical examination [2,3,4,5,6,7,8].
T16 447-617 Sentence denotes Free-living survival, here defined as the ability of a pathogen to persist outside of its host, is one of many transmission life-history traits associated with virulence.
T17 618-724 Sentence denotes The relationship between the two varies between host–pathogen types and different environments [4,8,9,10].
T18 725-847 Sentence denotes Several hypotheses serve as the canon in the evolution of virulence, theorizing its relationship with transmission traits.
T19 848-1200 Sentence denotes The Curse of the Pharaoh hypothesis—Named after a tale about a mythical curse that torments individuals who dig up tombs of Egyptian pharaohs [11]—Suggests that, if a parasite has high free-living survival, then it is far less dependent on its host for transmission and, consequently, will have no evolutionary incentive to decrease virulence [2,4,12].
T20 1201-1390 Sentence denotes The potential negative fitness consequences of killing hosts rapidly (being highly virulent) can be counteracted by persisting in the environment until the arrival of new susceptible hosts.
T21 1391-1590 Sentence denotes Any presumptive selection on beneficence may be relaxed: parasites can detrimentally affect the health of hosts at no cost to transmission because most of their life cycle is spent outside of a host.
T22 1591-1732 Sentence denotes Previous studies support a positive correlation between free-living survival and mortality per infection (a common proxy for virulence) [13].
T23 1733-1888 Sentence denotes Alternatively, the “tradeoff” hypothesis suggests that there is some intermediate level of parasite virulence [3,6,14] that is optimal for a given setting.
T24 1889-2009 Sentence denotes In this scenario, too high a virulence kills the host and parasite and too low a virulence leads to failure to transmit.
T25 2010-2232 Sentence denotes Applying this hypothesis specifically to free-living survival would suggest that selection for increased free-living survival should come at the expense of virulence (producing a pathogen that is less harmful to the host).
T26 2233-2375 Sentence denotes Mechanistically, as a consequence of increased adaptation to a nonhost environment, a virus may be less fit to replicate inside a host [9,15].
T27 2376-2522 Sentence denotes For example, a more robust viral capsid may help to survive harsh environmental conditions but may make it more difficult to package RNA/DNA [15].
T28 2523-2710 Sentence denotes More generally, the tradeoff hypothesis can be framed in the context of a life-history tradeoff: investment in certain parts of the life cycle often comes at the expense of others [2,16].
T29 2711-2858 Sentence denotes Theoretical studies have explored varying evolutionary relationships between heightened virulence and extreme pathogen longevity [4,5,12,17,18,19].
T30 2859-2979 Sentence denotes One critical component of these studies revolves around whether virulence evolves independently of free-living survival.
T31 2980-3330 Sentence denotes For example, some models have argued [4] that pathogen virulence is independent of survival under a set of conditions: when the host–pathogen system is at an equilibrium (evolutionary and ecological), if host density fluctuates around an equilibrium, or if turnover of the infected host population is fast relative to the pathogen in the environment.
T32 3331-3580 Sentence denotes However, if the host–pathogen system is at disequilibrium and if the dynamics of propagules in the environment are fast compared to the dynamics of infected hosts, then virulence is, as hypothesized, an increasing function of propagule survival [4].
T33 3581-3847 Sentence denotes Kamo and Boots [17] examined this hypothesis by incorporating a spatial structure in the environment using a cellular, automata model and found that, if virulence evolution is independent of transmission, then long-lived infective stages select for higher virulence.
T34 3848-4080 Sentence denotes However, if there is a tradeoff between virulence and transmission, there is no evidence for the Curse of the Pharaoh hypothesis, and in fact, higher virulence may be selected for by shorter rather than long-lived infectious stages.
T35 4081-4194 Sentence denotes Further, the evolution of high virulence does not have to occur solely through a transmission–virulence tradeoff.
T36 4195-4380 Sentence denotes Day [18] demonstrated how pathogens can evolve high virulence and even select for traits to kill the host (e.g., toxins) if pathogen transmission and reproductive success are decoupled.
T37 4381-4465 Sentence denotes These studies emphasized the context-dependence of virulence–survival relationships.
T38 4466-4660 Sentence denotes Understanding where in the relationship between virulence and survival a given pathogen population exists may allow one to understand how virus evolution will manifest at the level of epidemics.
T39 4661-4857 Sentence denotes In this study, we examine the epidemic consequences of different virulence–survival relationships—Positive and negative correlation—In a viral disease with an environmental transmission component.
T40 4858-5189 Sentence denotes In order to measure how pathogen survival influences disease dynamics, we included an environmental compartment in our model, which represents contaminated environments that act as a reservoir for persisting pathogens, causing disease spread when they come in contact with susceptible individuals (infection via “fomites”) [20,21].
T41 5190-5355 Sentence denotes We find that the identity of the virulence–free-living survival relationship (e.g., positive vs. negative) has distinct implications for how an epidemic will unfold.
T42 5356-5491 Sentence denotes Some, but not all, features of an outbreak are dramatically influenced by the nature of the underlying virulence–survival relationship.
T43 5492-5650 Sentence denotes This indicates that signatures for evolution (adaptive or other) in a pathogen population will manifest more conspicuously in certain features of an outbreak.
T44 5651-5837 Sentence denotes We reflect on these findings in light of their theoretical implications on the evolution and ecology of infectious disease and for their potential utility in public health interventions.