Based on the parsimony principle, this outbreak therefore probably corresponds to a single expanding population originating from a single introduction in the Belgrade area.
Estimates of effective population size, R e, using various S 0 values for all Victoria (A ) and Yamagata (C ) lineage viruses isolated in Australia and for the largest monophyletic group of Victoria (B ) viruses in Australia that clearly represent a single introduction.
These molecular investigations demonstrated a unique strain of LCMV, 201202467, in facility A mice, which suggests a single introduction and transmission event throughout the breeding facility.
If there had been a single introduction, individuals in the introduced populations would represent a monophyletic group; the single introduction hypothesis can be rejected based on the relationships of group A and B haplotypes in the multilocus network.
Even though the paucity of human viruses sampled is a limitation in this study, the data suggest a single introduction of human viruses into swine followed by transmission within and between swine farms for >4 months.
Even with no intervention, the finding that R 0 = 1.14 indicates that the chance that a single introduction would result in any further spread is ≈12%.
This phylogeography pattern is consistent with a single introduction of this lineage in the country, followed by dispersal of the ancestral population toward West and South, with progressively derived local populations of B. anthracis strains.
Since this cluster of Bangladeshi clade 2.3.2.1 viruses is very homogenous (i.e., it always has the same virus pattern in all trees) and shows that all isolates included have the same ancestors, this may be a sign of a single introduction of clade 2.3.2.1 in 2011 into the geographic region of Bangladesh, India and Nepal and ongoing evolution within the region that is supported by poultry movement.
High levels of genetic diversity in the early process of invasion may result from a single introduction of a large number of individuals or from multiple introductions from genetically divergent source populations (Sakai et al. 2001; Allendorf and Lundquist 2003).
Therefore, WNV may have circulated silently in the western Mediterranean region, establishing an endemic cycle after a single introduction.
