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December 8, 2004
1933 Human Sequences in 2004 Swine on Farm
Here is some additional background on the WSN/33 sequences in 2004 swine from Korea. I have confirmed that the sequences were from pigs on a farm(s). There are 6 isolates with human sequences. Two are H1N1 and 7 of the 8 genes are closely related to WSN/33. The other 4 are H9N2 and have 5,4,4,or 3 human genes. All of the human genes are greater than 99% homologous with WSN/33, but virtually all have some differences with WSN/33 and each other. There is high degree of fidelity in the avian sequences, suggesting that the differences with WSN/33 are not simply sequencing errors.
Although the human genes are very closely related to WSN/33, there seem to be too many differences for the changes to be due to lab contamination of the swine samples. However, I do not know of an independent confirmation of the sequences nor do I know of any recent human H1N1 cases with WSN/33 sequences. WHO has been alerted to the possibility that these pigs in South Korea may contain sequences very closely related to the 1933 human sequence, WSN/33. The isolates not only have reassorted genes, but they also have recombined genes, both between WSN/33 and avian sequences as well as between two distinct avian sources.