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H5N1 Bird Flu Reassortants In India
August 1, 2006
Sequences of the NA and M gene from two isolates from India, A/chicken/Navapur/Maharashtra/India/7966/2006(H5N1) and A/chicken/Navapur/Maharashtra/India/7972/2006(H5N1 have been deposited at GenBank. The two sets of sequences are identical. A partial HA sequence from one of the above isolates has been published previously and was found to be a Qinghai H5N1 bird flu strain.
The above M sequences are also closely related to previously described Qinghai strains. However, the NA sequences are virtually identical to A/Hatay/2004(H5N1), a chicken isolate from Vietnam. The two sequences from India differ from the Hatay sequence by a single nucleotide, indicating the two isolates from India are reassortants with at least two Qinghai genes (HA and M) and one Clade 1 gene from Vietnam (NA).
Recently an H5N1 and H9N2 NS gene sequence from Israel were released and the H5N1 and one of the H9N2 sequences were identical, indicating the H9N2 isolate was also a reaassortant with at least one Qinghai gene.
Thus, the recent data indicates dual infections between Qingahi H5N1 and H9N2 found in Israel or clade 1 H5N1 from Vietnam have produced reassortants involving Qinghai genes or isolates.
A recent report by authors from the CDC indicated that H5N1 reassorted with H3N2 huamn geens did not produce reassortants that were evolutionarily fit. The reassortants had either poorer replication in culture or were not transmissible in ferrets. However, the detection of human H5N1 from Indonesia in the upper respiratory tracty of the ferrets indicated that H5N1 was becoming more dangerous to mammals without reassortment with human genes or acquisition of changes in the receptor binding domain.
The latest data from India indicate H5N1 is evolving via reassortment with avian H5N1, but not via reassortment with mammalian genes. However, sequence analysis demonstrates the acquisition of mammalian polymorphisms via recombination.
The analysis of newly acquire polymorphisms in the Qinghai strain also provides evidence from evolution via recombination. The recent reassortments point toward dual infections with Qinghai H5N1 and other avian H5N1's or H9N2;s. These dual infections can lead to further evolution by recombination, which is the primary means of H5N1 rapid evolution.