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Novel H5N1 Wild Bird Flu Recombinants in the Ukraine
December 23, 2005
The latest OIE report from the Ukraine describes a number of H5N1 outbreaks on the Crimea peninsula. Samples were sent to Russia and England for independent confirmation. Reports from both agencies indicated H5N1 that was closely related to the strain linked to wild birds at Qinghai Lake, Novosibirsk, Mongolia, Kazakhstan, Turkey, Romania, Croatia, and Tula.
The HA cleavage site identified in England was GERRRKKR which matched the cleavage site in isolates from the above locations. However, the cleavage site identified by Russia was RERRRKKR which matches the cleavage site of the 1996 Guangdong goose as well as most of the H5N1 isolates from Asia.
This is the first report of that cleavage site in H5N1 isolates outside of Asia and is probably the basis of the Ukranian announcement that the H5N1 on the Crimea peninsula was unique.
This result indicates H5N1 continues to evolve via recombination and is similar to the evolution of HA sequences of 2005 H5N1 isolates from northern Vietnam. Those isolates had a clade 1, Z genotype, genetic background, but had acquired a cleavage site found in China and Japan, which was the Asian sequence minus an R (RERRKKR).
A multi-basic HA cleavage site is the hallmark signature of HPAI in H5 and H7, and the sequence identified by Russia is widespread in Asia. Its presence in wild bird flu in Europe marks an additional first for H5N1 as it expands its global reach. This expansion has led reports of novel HA cleavage sites, and the latest data shows that these cleavage sites can appear on H5N1 with different genetic backgrounds.
The rapid genetic evolution of H5N1, coupled with its expanded global reach, increases the likelihood of recombinations that will generate H5N1 that is more efficiently transmitted from human-to-human.