By IANS
Washington : It has been a mystery why unusually severe epidemics of influenza occur from time to time, when illness and mortality rates exceeded standard epidemic levels.
Researchers now claim to have an answer: human influenza viruses tend to exchange genetic material – or re-assort themselves – producing new hybrids that are the reason behind the heavy toll.
And this nothing new – re-assortment of the influenza A virus has been recurring throughout its evolutionary history, says a study published in the open-access journal, PLoS Pathogens.
Researchers at Pennsylvania State University relied on evolutionary analysis of influenza viruses from 1918 to 2005 to study seasonal epidemics with unusually high mortality.
They specifically found that the severe influenza epidemics of 1947 and 1951 were caused when two human influenza viruses of the same H1N1 strain, producing new hybrid viruses in both cases.
The standard model of human influenza virus evolution holds that such major pandemics, the largest of which occurred in 1918, are caused by hybridisation between human and avian influenza viruses.
But seasonal influenza epidemics do not involve such hybridisation.
These new findings suggest that the evolution of seasonal influenza is more complex than previously thought, generating genetically novel viruses with the potential to ignite major epidemics.