Limits...
Host resistance, population structure and the long-term persistence of bubonic plague: contributions of a modelling approach in the Malagasy focus.

Gascuel F, Choisy M, Duplantier JM, Débarre F, Brouat C - PLoS Comput. Biol. (2013)

Bottom Line: Although bubonic plague is an endemic zoonosis in many countries around the world, the factors responsible for the persistence of this highly virulent disease remain poorly known.By combining deterministic and stochastic analyses of this model, and including sensitivity analyses, we show that (i) endemicity is favoured by intermediate host population sizes, (ii) in large host populations, the presence of resistant rats is sufficient to explain long-term persistence of plague, and (iii) the metapopulation structure of susceptible host populations alone can also account for plague endemicity, thanks to both subdivision and the subsequent reduction in the size of subpopulations, and extinction-recolonization dynamics of the disease.In the light of these results, we suggest scenarios to explain the localized presence of plague in Madagascar.

View Article: PubMed Central - PubMed

Affiliation: IRD, CBGP (UMR IRD/INRA/CIRAD/MontpellierSupAgro), Montferrier-sur-Lez, France. fanny.gascuel@college-de-france.fr

ABSTRACT
Although bubonic plague is an endemic zoonosis in many countries around the world, the factors responsible for the persistence of this highly virulent disease remain poorly known. Classically, the endemic persistence of plague is suspected to be due to the coexistence of plague resistant and plague susceptible rodents in natural foci, and/or to a metapopulation structure of reservoirs. Here, we test separately the effect of each of these factors on the long-term persistence of plague. We analyse the dynamics and equilibria of a model of plague propagation, consistent with plague ecology in Madagascar, a major focus where this disease is endemic since the 1920s in central highlands. By combining deterministic and stochastic analyses of this model, and including sensitivity analyses, we show that (i) endemicity is favoured by intermediate host population sizes, (ii) in large host populations, the presence of resistant rats is sufficient to explain long-term persistence of plague, and (iii) the metapopulation structure of susceptible host populations alone can also account for plague endemicity, thanks to both subdivision and the subsequent reduction in the size of subpopulations, and extinction-recolonization dynamics of the disease. In the light of these results, we suggest scenarios to explain the localized presence of plague in Madagascar.

Show MeSH

Related in: MedlinePlus

Equilibrium states for a susceptible host metapopulation composed of (a) 2 subpopulations, (b) 4 subpopulations and (c) 25 subpopulations (deterministic analysis).Total carrying capacity =  rats. Other parameter values are given in Table 1. Stable equilibrium states: (,) in black, (,) in dark grey and (,) in light grey.
© Copyright Policy
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC3649974&req=5

pcbi-1003039-g003: Equilibrium states for a susceptible host metapopulation composed of (a) 2 subpopulations, (b) 4 subpopulations and (c) 25 subpopulations (deterministic analysis).Total carrying capacity =  rats. Other parameter values are given in Table 1. Stable equilibrium states: (,) in black, (,) in dark grey and (,) in light grey.

Mentions: The threshold transmission parameter is plotted as a horizontal black line in Figures 1, 2 and 3; its values match with the values of obtained by numerical simulations (Figure 1). However, as already mentioned, the condition does not imply long-term persistence: Figure 1 shows that the equilibrium states with disease persistence (,) disappears when increases further above the critical transmission threshold , especially for large host populations. For rats and values of just above , strong oscillations of the number of rats occur in each class, with low values between the peaks (Supporting Figures S4 and S5, ). For higher values of , no oscillations happen but an epidemic wave decimates the host population (Supporting Figure S4, ): both the disease and the rat population therefore go extinct.


Host resistance, population structure and the long-term persistence of bubonic plague: contributions of a modelling approach in the Malagasy focus.

Gascuel F, Choisy M, Duplantier JM, Débarre F, Brouat C - PLoS Comput. Biol. (2013)

Equilibrium states for a susceptible host metapopulation composed of (a) 2 subpopulations, (b) 4 subpopulations and (c) 25 subpopulations (deterministic analysis).Total carrying capacity =  rats. Other parameter values are given in Table 1. Stable equilibrium states: (,) in black, (,) in dark grey and (,) in light grey.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3649974&req=5

pcbi-1003039-g003: Equilibrium states for a susceptible host metapopulation composed of (a) 2 subpopulations, (b) 4 subpopulations and (c) 25 subpopulations (deterministic analysis).Total carrying capacity =  rats. Other parameter values are given in Table 1. Stable equilibrium states: (,) in black, (,) in dark grey and (,) in light grey.
Mentions: The threshold transmission parameter is plotted as a horizontal black line in Figures 1, 2 and 3; its values match with the values of obtained by numerical simulations (Figure 1). However, as already mentioned, the condition does not imply long-term persistence: Figure 1 shows that the equilibrium states with disease persistence (,) disappears when increases further above the critical transmission threshold , especially for large host populations. For rats and values of just above , strong oscillations of the number of rats occur in each class, with low values between the peaks (Supporting Figures S4 and S5, ). For higher values of , no oscillations happen but an epidemic wave decimates the host population (Supporting Figure S4, ): both the disease and the rat population therefore go extinct.

Bottom Line: Although bubonic plague is an endemic zoonosis in many countries around the world, the factors responsible for the persistence of this highly virulent disease remain poorly known.By combining deterministic and stochastic analyses of this model, and including sensitivity analyses, we show that (i) endemicity is favoured by intermediate host population sizes, (ii) in large host populations, the presence of resistant rats is sufficient to explain long-term persistence of plague, and (iii) the metapopulation structure of susceptible host populations alone can also account for plague endemicity, thanks to both subdivision and the subsequent reduction in the size of subpopulations, and extinction-recolonization dynamics of the disease.In the light of these results, we suggest scenarios to explain the localized presence of plague in Madagascar.

View Article: PubMed Central - PubMed

Affiliation: IRD, CBGP (UMR IRD/INRA/CIRAD/MontpellierSupAgro), Montferrier-sur-Lez, France. fanny.gascuel@college-de-france.fr

ABSTRACT
Although bubonic plague is an endemic zoonosis in many countries around the world, the factors responsible for the persistence of this highly virulent disease remain poorly known. Classically, the endemic persistence of plague is suspected to be due to the coexistence of plague resistant and plague susceptible rodents in natural foci, and/or to a metapopulation structure of reservoirs. Here, we test separately the effect of each of these factors on the long-term persistence of plague. We analyse the dynamics and equilibria of a model of plague propagation, consistent with plague ecology in Madagascar, a major focus where this disease is endemic since the 1920s in central highlands. By combining deterministic and stochastic analyses of this model, and including sensitivity analyses, we show that (i) endemicity is favoured by intermediate host population sizes, (ii) in large host populations, the presence of resistant rats is sufficient to explain long-term persistence of plague, and (iii) the metapopulation structure of susceptible host populations alone can also account for plague endemicity, thanks to both subdivision and the subsequent reduction in the size of subpopulations, and extinction-recolonization dynamics of the disease. In the light of these results, we suggest scenarios to explain the localized presence of plague in Madagascar.

Show MeSH
Related in: MedlinePlus