Relative abundance of Mycobacterium bovis molecular types in cattle: a simulation study of potential epidemiological drivers
Date
2017-08-22
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Publisher
BMC
Abstract
Background: The patterns of relative species abundance are commonly studied in ecology and epidemiology to
provide insights into underlying dynamical processes. Molecular types (MVLA-types) of Mycobacterium bovis, the
causal agent of bovine tuberculosis, are now routinely recorded in culture-confirmed bovine tuberculosis cases in
Northern Ireland. In this study, we use ecological approaches and simulation modelling to investigate the
distribution of relative abundances of MVLA-types and its potential drivers. We explore four biologically plausible
hypotheses regarding the processes driving molecular type relative abundances: sampling and speciation;
structuring of the pathogen population; historical changes in population size; and transmission heterogeneity
(superspreading).
Results: Northern Irish herd-level MVLA-type surveillance shows a right-skewed distribution of MVLA-types, with a
small number of types present at very high frequencies and the majority of types very rare. We demonstrate that
this skew is too extreme to be accounted for by simple neutral ecological processes. Simulation results indicate that
the process of MVLA-type speciation and the manner in which the MVLA-typing loci were chosen in Northern
Ireland cannot account for the observed skew. Similarly, we find that pathogen population structure, assuming for
example a reservoir of infection in a separate host, would drive the relative abundance distribution in the opposite
direction to that observed, generating more even abundances of molecular types. However, we find that historical
increases in bovine tuberculosis prevalence and/or transmission heterogeneity (superspreading) are both capable of
generating the skewed MVLA-type distribution, consistent with findings of previous work examining the distribution
of molecular types in human tuberculosis.
Conclusion: Although the distribution of MVLA-type abundances does not fit classical neutral predictions, our
simulations show that increases in pathogen population size and/or superspreading are consistent with the pattern
observed, even in the absence of selective pressures acting on the system.
Description
Publication history: Accepted - 11 August 2017; Published online - 22 August 2017.
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Keywords
Bovine Tuberculosis, Multiple-locus variable number tandem repeats, Neutral theory of biodiversity, Species abundance distributions, Population genetics
Citation
Trewby, H., Wright, D. M., Skuce, R. A., McCormick, C., Mallon, T. R., Presho, E. L., Kao, R. R., Haydon, D. T. and Biek, R. (2017) ‘Relative abundance of Mycobacterium bovis molecular types in cattle: a simulation study of potential epidemiological drivers’, BMC Veterinary Research, 13(1). doi: 10.1186/s12917-017-1190-5.