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Searching For H5N1 LPAI Wild Bird Flu in Tomsk Russia
September 10, 2005
As reflected in several postings in this thread, including the above NPR program, there is an ongoing debate about the role of migratory birds in the dissemination of the highly pathogenic H5N1 strain which has been the causal agent of the pandemic in southeastern and central Asia, and particularly about their potential to spread the agent to other parts of the globe. The debate is related to the observations about the potential of the said strain to clinically affect -- and kill -- several species of migratory avians.
The above commentary by promed cites an ongoing debate, but there has been no evidence to support a debate. The recent transmission and transportation of highly pathogen H5N1 has been associated with the movement of migratory birds (see map). It seems that each time H5 is reported in these birds, or associated poultry, promed commentaries ask if the H5 is H5N1. The above commentary was in response to H5 being detected in a number of wild birds in Tomsk in southern Siberia.
Tomsk is adjacent to Novosibirsk, which was the epicenter of the H5N1 outbreak on southern Russia (see July map) and media reports suggested that H5N1 was present in Tomsk in July. More recent reports have indicated H5 antibodies were fund in wild birds in several regions of Tomsk, so there is little reason to suspect that the H5 antibodies are not related to H5N1. Although H5N2 or H5N3 have been isolated from southern Russia in the past (at Chany Lake or Primorie), all N serotypes reported this year have been N1 and all H5's that have been characterized and reported have been highly pathogenic with a multibasic cleavage site matching H5N1 from Asia.
An earlier promed commentary questioned whether the wild birds were victims. It seems that the working hypothesis is that the wild birds carry a LPAI H5, infect domestic poultry, and then HPAI H5 is isolated from infected poultry or other wild birds.
However, there has been no evidence for the LPAI at this time in the regions of H5N1 isolation. Each isolated reported from wild birds has been HPAI and indeed all reported isolates have been HPAI. If the wild birds are merely bringing LPAI sequences into the area, it is unclear how the exact match of the cleavage site is obtained. Generating an exact match via random mutation is unlikely, and generating it via recombination requires a parental sequences with the multibasic cleavage site. However, all multibasic cleavage sites have been in H5N1, so the promed commentaries remain curious.