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Forum: Problem

19 November 2006

aurora – at 14:45

Any ideas what would happen if this connected met up with H5N1?

Flu :: Novel H3N1 Swine Influenza Virus Identified in Pigs in Korea

For the first time, researchers from the U.S. and abroad have identified the H3N1 swine influenza virus in domestic pigs in Korea. They report their findings in the November 2006 issue of the Journal of Clinical Microbiology.

A highly infectious respiratory pathogen, the H3N1 influenza A virus is a new genetic reassortment of influenza viruses first identified in pigs in the U.S. in 2004. The virus can be found in birds and mammals (including humans and pigs), but is not generally transmissible between birds and humans. Pigs are believed to be susceptible to both origins resulting in them being deemed “mixing vessels” for the virus and ultimately reinforcing concerns of zoonosis and pandemic outbreaks.”

snip

“Further testing confirmed the H3N1 viruses presenting were reassortments of an H3 human-like virus and other genes from swine influenza viruses and that pig-to-pig and farm-to-farm transmission had occurred…”

http://tinyurl.com/yg2lr5

aurora – at 14:46

I’m sorry. That’s supposed to be “H3N1 in swine. Problem?”

anon_22 – at 15:25

It doesn’t have to connect with H5N1. Not all viruses have to reassort with H5N1 to cause problems.

This H3N1 needs watching. I haven’t been able to get the full paper yet, but it looks to me like a virus fully adapted to swine in the internal gene has picked up a human HA which pigs have no immunity to. This is the equivalent in pigs of what a human pandemic could look like, assuming it acquires sufficient ability to transmit between pigs ie R0>1.

Remember that historically there has been far more instances of human flu viruses infecting swine than swine viruses infecting humans. I’m not sure we know why, but that’s been the pattern.

Depending on the rest of the internal genes, at first look this virus in itself should not be a worry for significant human infections. Of course, flu viruses change constantly and no one can tell, but we would be more worried if it was the other way round, ie a virus with human adapted internal genes acquiring swine or other surface HA for which humans have no immunity.

I’ll post some more when I get a chance to see the full paper.

references:

Olsen et al, J Virology 2000, Virologic and serologic surveillance for human, swine and avian influenza virus infections among pigs in the north-central United States

Olsen, 2002 Virus Research, The emergence of novel swine influenza viruses in North America

Karasin et al, 2006 J Clin Microbio. Identification of Human H1N2 and Human-Swine Reassortant H1N2 and H1N1 Influenza A Viruses among Pigs in Ontario, Canada (2003 to 2005)

This last paper is free. The following table is from this paper, and shows the kind of reassortments that happen.

anon_22 – at 15:31

As an aside, notice that in the above table, all the swine sequences that have acquired human genes, in whatever combination, always includes a human PB1.

This mirrors the 2 human pandemics of 1957 to 68, where the circulating human seasonal strain picked up new surface genes PLUS a new PB1. We don’t know exactly why, but it could be that the PB1 gene is the target of immune responses, so that over time, an ‘old’ PB1 no longer has the competitive advantage that a novel PB1 would have.

It is also likely that a new PB1 would be responsible for an increase in virulence of the new reassortant, but since it adapts (or degrades) fairly quickly, the virulence of the new strain drops relatively quickly. So the PB1 could be partly responsible for the reduction in virulence in the subsequent waves of a pandemic till the virus just becomes like other seasonal strains.

Mary in Hawaii – at 16:10

What precisely is the PB1 gene, is it also found in avian influenza viruses, and might it have anything to do with the seeming difficulty (mentioned in the Oct 23 WHO research rept)in producing sufficient antibodies against H5N1?

anon_22 – at 19:24

Mary in Hawaii – at 16:10 What precisely is the PB1 gene, is it also found in avian influenza viruses, and might it have anything to do with the seeming difficulty (mentioned in the Oct 23 WHO research rept)in producing sufficient antibodies against H5N1?

PB1 is one of several gene segments that code for the proteins of the polymerase complex, a group of proteins important for replication, pathogenesis, host immune response etc. The exact function of each is still not clear.

I am guessing that you are referring to the WHO saying that for some unknown reason, it’s been quite hard to make vaccines for H5N1 which produces sufficient antibody levels. I haven’t seen anything that links PB1 to it specifically.

Cygnet – at 19:54

Speculation — Is this what was killing pigs in China?

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