Evaluating the importance of within- and between-host selection pressures on the evolution of chronic pathogens

Coombs, Daniel; Gilchrist, Michael A.; Ball, Colleen L.

doi:10.1016/j.tpb.2007.08.005

Cited by 128 publications

(111 citation statements)

References 62 publications

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“…In general terms, we predict that a parasite may be selected for in the environment if it provides protection from a more virulent pathogen. The competitive advantage we observed for a low-cost (that is, low-virulence) parasitic element provides a valuable contrast to studies that predict or demonstrate an increase in virulence under competitive pressure for other parasites (Kover et al, 1997;Kover and Clay, 1998;Kerr et al, 2006;Coombs et al, 2007;Bull and Ebert, 2008). We postulate that the importance of vertical transmission and the resistance of the infected host to superinfection are key factors that support a competitive reduction in virulence in our system.…”

Section: Discussionmentioning

confidence: 56%

Competition favours reduced cost of plasmids to host bacteria

2009

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Conjugative plasmids of Gram-negative bacteria have both vertical and horizontal modes of transmission: they are segregated to daughter cells during division, and transferred between hosts by plasmid-encoded conjugative machinery. Despite maintaining horizontal mobility, many plasmids carry fertility inhibition (fin) systems that repress their own conjugative transfer. To assess the ecological basis of self-transfer repression, we compared the invasion of bacterial populations by fin þ and fin À variants of the plasmid R1 using a computational model and co-culture competitions. We observed that the fin þ variant had a modest cost to the host (measured by reduction in growth rate), while the fin À variant incurred a larger cost. In simulations and empirical competitions the fin À plasmid invaded cultures quickly, but was subsequently displaced by the fin þ plasmid. This indicated a competitive advantage to reducing horizontal transmission and allowing increased host replication. Computational simulations predicted that the advantage associated with reduced cost to the host would be maintained over a wide range of environmental conditions and plasmid costs. We infer that vertical transmission in concert with competitive exclusion favour decreased horizontal mobility of plasmids. Similar dynamics may exert evolutionary pressure on parasites, such as temperate bacteriophages and vertically transmitted animal viruses, to limit their rates of horizontal transfer.

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Section: Discussionmentioning

confidence: 56%

Competition favours reduced cost of plasmids to host bacteria

2009

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“…Much of the work to date has been motivated by the withinhost dynamics of HIV infection ( Nowak & May 2000;Perelson 2002), but the interest in influenza and other acute infections is allowing mathematical models to be developed for a range of other diseases (Baccam et al 2006;Heffernan & Keeling 2008). It is to be hoped that incorporating such mechanisms into epidemiological models will allow for greater insights into issues such as repeat infections, partial immunity, cross-reaction between strains, heterogeneous response to infection and transmission-virulence trade-offs (Gilchrist & Coombs 2006;Read & Keeling 2006;Coombs et al 2007) for general models. This merging of scales is also clearly necessary if epidemiology and public-health modelling are to exploit the wealth of new genetic and molecular information available on many pathogens.…”

Section: Discussionmentioning

confidence: 99%

“…This framework allows one to explicitly determine parameters of the between-host model from the behaviour of the within-host model-and hence predict the transmission consequences of waning immunity. Previous studies have used nested models to link within-host and epidemiological characteristics to study the relationship between transmission and virulence (Sasaki & Iwasa 1991;Antia et al 1994;Ganusov et al 2002;Gilchrist & Sasaki 2002;André et al 2003;Krakauer & Komarova 2003;Alizon & Van Baalen 2005;Gilchrist & Coombs 2006;Read & Keeling 2006;Coombs et al 2007), while other studies have developed immunoepidemiological models, where the classes of hosts are delineated by immune or infection status (Kostova 2005;Vickers & Osgood 2007;Cornell et al 2008;Mitchell et al 2008). However, with the exception of a select few (e.g.…”

Section: Introductionmentioning

confidence: 99%

Implications of vaccination and waning immunity

Heffernan

Keeling

2009

Proc. R. Soc. B.

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For infectious diseases where immunization can offer lifelong protection, a variety of simple models can be used to explain the utility of vaccination as a control method. However, for many diseases, immunity wanes over time and is subsequently enhanced (boosted) by asymptomatic encounters with the infection. The study of this type of epidemiological process requires a model formulation that can capture both the withinhost dynamics of the pathogen and immune system as well as the associated population-level transmission dynamics. Here, we parametrize such a model for measles and show how vaccination can have a range of unexpected consequences as it reduces the natural boosting of immunity as well as reducing the number of naive susceptibles. In particular, we show that moderate waning times (40-80 years) and high levels of vaccination (greater than 70%) can induce large-scale oscillations with substantial numbers of symptomatic cases being generated at the peak. In addition, we predict that, after a long disease-free period, the introduction of infection will lead to far larger epidemics than that predicted by standard models. These results have clear implications for the long-term success of any vaccination campaign and highlight the need for a sound understanding of the immunological mechanisms of immunity and vaccination.

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“…The within-and between-host dynamics have been studied for several infectious diseases using the nested models (e.g. [7,9,[11][12][13][14][15][16]25]). However, to the best of our knowledge, no existing work has attempted to address the coupled within-and between-host dynamics of cholera (a severe water-borne gastroenteric disease caused by the bacterium Vibrio cholerae), despite the fact that a large body of work has been devoted to its population level modelling (e.g.…”

Section: Introductionmentioning

confidence: 99%

Disease dynamics in a coupled cholera model linking within-host and between-host interactions

Wang

2016

Journal of Biological Dynamics

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A new modelling framework is proposed to study the within-host and between-host dynamics of cholera, a severe intestinal infection caused by the bacterium Vibrio cholerae. The within-host dynamics are characterized by the growth of highly infectious vibrios inside the human body. These vibrios shed from humans contribute to the environmental bacterial growth and the transmission of the disease among humans, providing a link from the within-host dynamics at the individual level to the between-host dynamics at the population and environmental level. A fast-slow analysis is conducted based on the two different time scales in our model. In particular, a bifurcation study is performed, and sufficient and necessary conditions are derived that lead to a backward bifurcation in cholera epidemics. Our result regarding the backward bifurcation highlights the challenges in the prevention and control of cholera. ARTICLE HISTORY

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Evaluating the importance of within- and between-host selection pressures on the evolution of chronic pathogens

Cited by 128 publications

References 62 publications

Competition favours reduced cost of plasmids to host bacteria

Competition favours reduced cost of plasmids to host bacteria

Implications of vaccination and waning immunity

Disease dynamics in a coupled cholera model linking within-host and between-host interactions

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