Scimex: An international study, which includes Australian researchers, has found that not all influenza viruses circulate around the world in the same way, with some preferring to hang around in localised regions for longer periods of time. The scientists report that influenza viruses that evolve quickly tend to move between regions and cause epidemics more frequently than those that don't, and say that the results will help health officials to better track the viruses in the future.
Not all seasonal influenza viruses circulate around the world in the
same way, a study published in Nature this week demonstrates. Compared
with A/H3N2, the most frequent and severe influenza subtype, A/H1N1 and B
viruses do not show the same degree of global movement but persist for
longer periods of time locally. Understanding the dynamics of influenza
viruses is an important scientific and public health challenge; the
latest research provides new insights on the circulation patterns of
A/H1N1 and B viruses, which have not been studied in as much detail as
the more common A/H3N2 viruses.
An analysis of nearly 10,000 seasonal human influenza virus sequences
over a 12-year period, performed by Colin Russell, Trevor Bedford, and
colleagues, reveals that A/H3N2 viruses move between regions more
frequently than A/H1N1 and B viruses. One reason for this variation may
be the rates at which these viruses evolve, the authors suggest. A/H3N2
viruses evolve relatively quickly and routinely infect people of all
ages, but A/H1N1 and B viruses evolve more slowly and mainly infect
children. As children travel long distances much less than adults this
factor may account for differences in the global circulation of viruses.
The slower rates of evolution of A/H1N1 and B viruses compared with
A/H3N2 viruses may also explain why A/H1N1 and B viruses cause fewer
major epidemics than A/H3N2 viruses.