Gene swapping by flu viruses

MORE VIRULENT: If H1N1 virus swaps genes with a bird flu, the progeny can be more virulent than the two parental strains.  

The H1N1 flu virus that set off the 2009 pandemic could create yet more trouble. Research from a Chinese group has indicated that if this virus were to swap genes with a bird flu virus circulating in poultry, it can produce progeny that easily infect laboratory mice and are more virulent than the two parental strains.

When two strains of bird flu infect the same host, they can readily swap genes, a process known as reassortment. The 2009 H1N1 pandemic virus was itself a triple reassortant, with its genes drawn from bird, human and animal strains.

This mix of genes created a virus that readily infected humans, was easily transmitted from one person to another, and to which most people had no immunity.

The preceding three flu pandemics that occurred during the 20{+t}{+h} century were also produced by viruses that had undergone reassortment.

In research being published this week in the journal Proceedings of the National Academy of Sciences (PNAS), a team of scientists led by Jinhua Liu of the China Agricultural University in Beijing used laboratory techniques to create viruses with various combinations of genes drawn from the avian H9N2 virus and the pandemic H1N1.

Some 73 different reassortant viruses that replicated well in cultured cells were then tested on mice. Eight of those viruses were found to be more virulent than either of the parental strains, producing severe pneumonia in the animals.

Pigs, a mixing vessel

The worry is that such reassortment could take place in pigs, which have long been considered a ‘mixing vessel' as they can be infected by human as well as bird flu viruses.

The H1N1 virus that caused the 2009 pandemic seems to have undergone reassortment in pigs before making the leap to humans. The viruses that caused the previous three pandemics too appear to have been in some mammalian host, which may well have been the pig, before causing disease in humans.

There is already evidence that the 2009 H1N1 pandemic virus is infecting pigs and swapping genes with other flu viruses.

In a paper published in the journal Science last year, Vijaykrishna Dhanasekaran and others reported a novel reassortant virus that had been isolated from pigs in an abattoir in Hong Kong in January 2010. The reassortant virus combined genes from the H1N1 pandemic virus and a H1N2 virus. Swine infected with the new virus showed only mild illness.

It was not yet possible to predict what subtype of the flu virus would cause the next pandemic, said Dr. Vijaykrishna in an email.

Although more attention was paid to the H5N1 bird flu, the latest PNAS study clearly highlighted the fact that other flu subtypes that were circulating in poultry had the potential to start future pandemics.

The H9N2 virus, which had become the “underdog of avian influenza study,” had been detected virtually in every country in Asia. Studies showed that it had become endemic in poultry in East and South-East Asia (including China), India, Pakistan and some West Asian countries, he added.

Sustained transmission of avian viruses in pigs increased the possibility of mammalian adaptation, thereby increasing the risk of such a virus emerging in humans, observed Dr. Vijaykrishna. As such, it was very important to monitor the flu viruses that were circulating in pigs.

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Printable version | May 18, 2021 1:58:24 PM |

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