A quick fuse and the emergence of Taura syndrome virus

Over the last two decades, Taura syndrome virus (TSV) has emerged as a major pathogen in penaeid shrimp aquaculture and has caused substantial economic loss. The disease was first discovered in Ecuador in 1991, and the virus is now globally distributed with the greatest concentration of infections in the Americas and Southeast Asia. To determine the evolutionary history of this virus, we constructed a phylogeny containing 83 TSV isolates from 16 countries sampled over a 16-year period. This phylogeny was inferred using a relaxed molecular clock in a Bayesian Markov chain Monte Carlo framework. We found phylogenetic evidence that the TSV epidemic did indeed originate in the Americas sometime around 1991 (1988-1993). We estimated the TSV nucleotide substitution rate at 2.37 x 10(-3) (1.98 x 10(-3) to 2.82 x 10(-3)) substitutions/site/year within capsid gene 2. In addition, the phylogeny was able to independently corroborate many of the suspected routes of TSV transmission around the world. Finally, we asked whether TSV emergence in new geographic locations operates under a quick fuse (i.e. rapid appearance of widespread disease). Using a relaxed molecular clock, we determined that TSV is almost always discovered within a year of entering a new region. This suggests that current monitoring programs are effective at detecting novel TSV outbreaks.