Eachfallas punctual and certain as the fall of the leaves of the trees,flu season falls on us. And as spring arrives, equally predictably, the season concludes. This cyclical pattern, common in temperate regions, is well known, but the forces that cause it have always been a matter of debate among scientists.
The thing isflu strains die every springand are they replaced by new strains from other parts of the world? Or rather it happens that during the summer a“Hidden Chain of Disease” Sowing Next Season’s Epidemic? A genetic analysis carried out by scientists at the University of Michigan, the Howard Hughes Medical Institute and Florida State University reveals that in the United Statesnot all flu strains die at the end of each winter: some migrate to South America and others migrate even further afield.
“The dominant view that has developed over the last three years or so is the hypothesis that holds thatthe strains that cause each flu season in temperate regions originate from China and Southeast Asia, where the influenza A virus is less seasonal“, explains Bedford, co-author of the study published in the journalPublic Library of Science Pathogens. He and his colleagues tested this hypothesis by analyzing the genetic sequences of virus fromflu a(H3N2) collected from patients around the world between 1988 and 2009, and building a “family tree” that shows the relationships between viruses. And they found that, instead of dying at the end of a flu season, many strains of the virus simply move to more favorable environments.
The results have implications for public health efforts aimed at fighting the disease. For example, the new knowledge that influenza migrates out of the United States suggests the advisability of agreater caution in the use of antiviral drugs that can promote the development of strains resistant to these drugs. If, as previously thought, these strains died at the end of the season, they would not be a problem, but their newly discovered ability to survive and circulate means that drug-resistant strains can spread from the United States to the entire world. Moreover, these findings also mean that vaccination programs outside of China and Southeast Asia can be effective in slowing the spread of influenza.
Researchers have also found thatSouth America gets almost all of its flu from North America. ? This would indicate that, instead of giving in South America the same vaccine that is distributed throughout the world, vaccines could be preferentially produced from the strains that were circulating in North America in the previous season. As we collect more data from other regions, this could be done for the whole world ?, suggests Bedford.
