At last, the controversial paper by Yoshihiro Kawaoka of theUniversity of Wisconsin-Madison on mammalian transmissibility ofH5N1 (bird flu) virus through genetic manipulation is publishedtoday (May 3) in Nature . The study looks at droplet transmission of the virus in a ferretanimal model. Ferrets are chosen for such studies as they are thebest animal models that mimic human influenza effects. The “principal scientific interest” of the study”arises from the small number [four] of mutations found to benecessary” to make it transmissible, notes the Editorialaccompanying the piece.
The findings also clearly indicate that theviruses have potential to cause a “human pandemic.” And it was precisely for this reason that the paper, which wassubmitted to the journal in August 2011, faced many hurdles. The USNational Science Advisory Board for Biosecurity (NSABB) wanted thejournal to publish only a redacted (censored) version as it fearedthat the details in the paper could be used by some people forengaging in bio-terrorism. The NSABB finally cleared the fullpublication of the paper in March end. The procedure Dr. Kawaoka first introduced four mutations into the viralhaemagglutinin (HA) protein of H5N1.
He then combined the H5N1virus with seven gene segments from the 2009 pandemic H1N1 (swineflu) virus. Genes of influenza virus strains from one source (man/animal)combining with another animal occurs continually in nature, and theresultant virus is called a reassortant influenza virus. The reassortant virus that Dr. Kawaoka and his team produced wascapable of droplet transmission. Parking Barrier Gates
It was able to replicate”efficiently” in ferrets but did not kill them. Also,the virus “preferentially recognised human-typereceptors.” It is worth noting that the binding of H5N1 virusto avian cells is very different from the way human influenza bindsto human cells. Occurs in nature “Natural emergence of an H5N1–H1N1 hybrid [reassortant]virus is plausible. Some H1N1 and H5N1 viruses readily swap geneswith one another in vitro , generating hybrid viruses, states a News and Views pieceaccompanying the paper. Parking Control Terminal
“Pandemic H1N1 viruses areestablished in pigs in many parts of the world, and H5N1 viruseshave been isolated from pigs, suggesting that opportunities existfor the viruses to combine in these animals.” Why the concern The team led by Dr. Kawaoka states that “recentstudies” have shown “high genetic compatibility”between the pandemic H1N1 virus and the avian H5N1 virus.”These two viruses have been isolated from pigs, which havebeen considered as ‘mixing vessels’ for the reassortment ofavian, swine and human strains,” they write. Their verypresence together in pigs provides an ideal opportunity fortransmissible H5N1 reassortants to emerge. Bird flu outbreaks in poultry occur quite frequently, and in someinstances, such as in Indonesia, Vietnam and Egypt, transmission tohumans has been reported. But H5N1 is yet to acquire the ability tobecome transmissible from one human to another. Barrier Gates
Humans “lack immunity” to H5N1 mutant viruses, andhence the possibility of a H5N1 pandemic cannot be ruled out. Henceit is “critical” to understand the “molecularchanges” that might take place in the viral haemagglutinin(HA) protein that will make H5N1 virus transmissible in humans,they note. The only way of staying prepared of such an eventuality is byknowing in advance the possible mechanism required for theemergence of such a strain. Though it is not clear if fourmutations alone would have made the avian H5N1 virus transmissible,the study provides a window to the several possibilities.