- 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
- Please visit my "Emerging Diseases" message
board at: http://www.clickitnews.com/ubbthreads/postlist.php?
- Zhan le Devlesa tai sastimasa
- Go with God and in Good Health