The H1N1 influenza A, or
swine flu, evolved and hopped to humans several months before public health
officials recognized the outbreak, according to a new analysis. Scientists also
said the virus's early incarnation was festering in pigs for years but went
undetected.
The work, published online
today in the journal Nature, highlights the need for systematic surveillance ofinfluenzain swine, the journal's publisher said in a statement, and it provides evidence
that new genetic elements in swine can result in the emergence of viruses with pandemic
potential in humans.
Reports this week indicate
the World Health Organization (WHO) is on
the verge of declaring the viral outbreak a full pandemic (currently the
agency ranks the outbreak as a level 5 on a six-point scale, indicating that a
pandemic is imminent and time is short to prepare mitigation measures).
It is known that flu
viruses evolve quickly. Two or more strains can get together in the body of
a human or other animal and swap genes to generate new strains. As an example,
one relatively benign strain that is able to infect humans might pass that
ability to a more deadly strain that had only been able to transmit between
pigs, thereby evolving into a new strain that is deadly and can pass between
humans.
Researchers do not yet know
exactly when, how or where the current strain developed.
For the new analysis, Andrew
Rambaut of the University of Edinburgh (Scotland) and his colleagues used evolutionary analysis to
estimate the timescale of the origins and the early development of the
epidemic. They think it was derived from several viruses circulating in swine,
and that the initial transmission to humans occurred several months before
recognition of the outbreak.
"Despite widespread
influenza surveillance in humans, the lack of systematic swine surveillance
allowed for the undetected persistence and evolution of this potentially
pandemic strain for many years," the researchers conclude.
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