Insights into the evolutionary history of an emerging livestock pathogen: porcine circovirus 2 - PubMed (original) (raw)

Insights into the evolutionary history of an emerging livestock pathogen: porcine circovirus 2

Cadhla Firth et al. J Virol. 2009 Dec.

Abstract

Porcine circovirus 2 (PCV2) is the primary etiological agent of postweaning multisystemic wasting syndrome (PMWS), one of the most economically important emerging swine diseases worldwide. Virulent PCV2 was first identified following nearly simultaneous outbreaks of PMWS in North America and Europe in the 1990s and has since achieved global distribution. However, the processes responsible for the emergence and spread of PCV2 remain poorly understood. Here, phylogenetic and cophylogenetic inferences were utilized to address key questions on the time scale, processes, and geographic diffusion of emerging PCV2. The results of these analyses suggest that the two genotypes of PCV2 (PCV2a and PCV2b) are likely to have emerged from a common ancestor approximately 100 years ago and have been on independent evolutionary trajectories since that time, despite cocirculating in the same host species and geographic regions. The patterns of geographic movement of PCV2 that we recovered appear to mimic those of the global pig trade and suggest that the movement of asymptomatic animals is likely to have facilitated the rapid spread of virulent PCV2 around the globe. We further estimated the rate of nucleotide substitution for PCV2 to be on the order of 1.2 x 10(-3) substitutions/site/year, the highest yet recorded for a single-stranded DNA virus. This high rate of evolution may allow PCV2 to maintain evolutionary dynamics closer to those of single-stranded RNA viruses than to those of double-stranded DNA viruses, further facilitating the rapid emergence of PCV2 worldwide.

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Figures

FIG. 1.

FIG. 1.

Bayesian maximum clade credibility phylogenetic tree of the full-genome sequences of PCV2. Tips are colored by the country of sampling, and the internal branches are colored based on the reconstructed ancestral state (country) as estimated by the reversible diffusion model. Tip times reflect the sampling time of the sequence in question (x axis). Numbers at the nodes indicate BPPs greater than 0.9. Disease status (when reported) is associated with each tip. The location of the branch leading to the primary PCV2b clade with a dN/dS ratio of >1 is indicated with an asterisk (*).

FIG. 2.

FIG. 2.

Tanglegram indicating the associations between each circovirus and its reservoir host. The numbers in smaller print at the nodes are BPPs, while the numbers in larger print indicate the divergence time for that node, as estimated from the literature (in millions of years ago, for hosts) or directly from the data (in ybp, for circoviruses). Values are shown for duck (DuCV), goose (GsCV), swan (MSwCV), gull (GuCV), columbid (CoCV), finch (FiCV), raven (RaCV), canary (CaCV), and starling (StCV) circoviruses in addition to PCVs.

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