Human WSN/33 Bioterror
Attack On US Swine In 2001?

Dr. Henry L. Niman, PhD
Recombinomics Commentary
The questions regarding if and when WSN/33 sequences made their way into swine in Korea are still being resolved. The WHO meeting today and tomorrow in Manila should resolve the "if" question. WHO has data for 11 WSN/33 H1 sequences from 2004 and 2005 swine in Korea, so there should be little doubt about the "if" question. WSN/33 is clearly in lung tissues of dead pigs in Korea in 2005. The genes were also in swine in 2004 as recombinants and reassortants with 2004 isolates of Korean H9N2.
The genetic composition of the 2005 isolates remain to be determined. There appear to be dual or triple infections because both H1 and H9 sequences have been detected from the same animal. The 2005 H9 sequences are closely related to the 2004 H9 sequences, which were found in both swine and chicken isolates. These sequences are distinct from 2003 H9 avian sequences in Korea, indicating the dual infections and associated recombination and reassortment were recent. In the 2004 isolates, there were sequences representing all 8 WSN/33 genes, but none of the isolates had the 3' half of PB2, which has a polymorphism at position 627 that is linked to increased virulence. It remains to be determined if the 2005 fatal infections include the 3' half of WSN/33 PB2.
However, the "when" question for WSN/33 remains undetermined. WSN/33 in the lab requires no helper virus. Its virulence and growth without adaptation are two features that make WSN/33 a popular lab virus. Therefore, it is likely that WSN/33 was introduced into the swine independent of the Korean H9N2 isolates. The WSN/33 sequences from 2004 swine are closely related to the WSN/33 sequences at GenBank. At Genbank there are related WS/33 and NWS/33 sequences, but the number of WSN/33 sequences, in the form of defective interfering sequences, is limited. Thus, it is difficult to determine the time and place of the infection of the swine.
There have been health problems with Korean swine for several years. Thus, if linked to WSN/33, then the WSN/33 would have predated the infections by 2004 Korean H9N2 isolates. As WHO noted in their non-press release on WSN/33, the H1N2 isolates detected on two Korean farms were triple reassortants and were closely related to H1N2 swine isolates in the United States. A 2002 Korean swine isolate had similar sequences, indicating that H1N2 infections had been in Korean swine for several years, and these infections were likely due to imported swine from the United States or Canada.
Since H1N2 isolates have been linked to isolates from swine in the United States in 2001, the possibility that the imported pigs also contained WSN/33 cannot be excluded.
The possibility of a bioterror attack on US swine in 2001 cannot be excluded by the above data.
Patricia A. Doyle, PhD
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