The US Centers for Disease Control and Prevention (CDC) said that there is a “global need for more systemic surveillance of influenza viruses in pigs”, during a press briefing where they explained the findings of a recent study on the genetic and antigenetic properties of the new 2009 H1N1 swine flu virus.
The CDC led study was published online in the journal Science on 22 May and was the work of human and animal health scientists from the US, Mexico, the UK and the Netherlands.
According to the CDC, the study is the first to explain the history and evolution of the human and swine influenza viruses in North America and other areas of the world, as deduced from the detailed analysis of the antigenic and genetic characteristics of the new H1N1 viruses.
In a press briefing on Friday, senior author Dr Nancy Cox, who is director of the CDC’s influenza division said that the study reinforced the fact that:
“Swine are an important reservoir of influenza viruses with the potential to cause significant respiratory outbreaks or even a possible pandemic in humans.”
Cox praised the “excellent collaboration” that went into the study, and stressed the importance of the global co-operation that will be needed to fight the new H1N1 strain, for example by rapidly collecting and sharing specimens, without which it is not possible to understand the origin of the virus and how to stop it spreading and re-emerging.
For the study, the researchers sequenced the genomes of more than 70 samples of the new H1N1 taken from human patients diagnosed with the infection in the recent outbreaks, including 17 viruses isolated in Mexico and 59 viruses from 12 states in the United States.
The analysis showed that the new H1N1 virus likely originated in pigs because each of its genetic components closely corresponds to genes found in swine flu viruses, said Cox, who then highlighted the study’s main findings:
- The new H1N1 viruses are very alike in the way they react to antibodies, that is their antigenetic properties are similar. However, in this respect they are very different to human H1N1 viruses (like the seasonal flu virus), so this indicates that the seasonal flu vaccine will probably not protect against the new virus, a fact that the CDC announced last week.
- The fact the new H1N1 strains are very similar means that it will be much easier to come up with a new candidate virus for vaccine development (there are already reports that a lab has sent a sample candidate virus to the CDC). Cox said as far as they could tell, the new H1N1 swine flu viruses varied much less among themselves than say the typical seasonal flu viruses do.
- From their resistance patterns it appears that the new H1N1 viruses are sensitive to the neuraminidase inhibitors, but resistant to the M2 blockers or rimantidine (Flumadine) and amantadine (Symmetrel). This is important information for the development and use of antivirals.
- As revealed in previous press briefings, the new virus also contained clusters of gene segments that had not been seen in swine or human flu viruses before. A noticeable new feature was that two gene segments, one from a matrix protein and the other from a nerve gene, seemed to have come from Eurasian swine viruses not seen outside of Eurasia before.
- While the analysis shows that all gene segments came from swine flu viruses, it was not possible to say if the virus then went straight into humans or via an intermediate host, and if it did go via a host, then which animal that would be.
- Animal scientists all over the world, including colleagues from the US Department of Agriculture (USDA) are testing samples they have kept frozen for years to see if they can provide any missing links to this part of the puzzle. For instance, there might be intermediate versions of the virus that could help narrow down the time and place where the new virus emerged.
When asked if these findings mean that pig surveillance will now be as important as avian surveillance as far as flu virus monitoring was concerned, Dr Anne Schuchat, director of CDC’s national center for immunization and respiratory diseases, said:
“This really hits home how important it is for animal and human health to cooperate and collaborate.”
She said she and her colleagues at the CDC were very pleased at how the collaboration between animal and human health has improved, implying it was vital to continue this because as the past few decades have shown, “the animal-human interface is very important”.
“Antigenic and Genetic Characteristics of Swine-Origin 2009 A(H1N1) Influenza Viruses Circulating in Humans.”
Rebecca J. Garten, C. Todd Davis, Colin A. Russell, Bo Shu, Stephen Lindstrom, Amanda Balish, Wendy M. Sessions, Xiyan Xu, Eugene Skepner, Varough Deyde, Margaret Okomo-Adhiambo, Larisa Gubareva, John Barnes, Catherine B. Smith, Shannon L. Emery, Michael J. Hillman, Pierre Rivailler, James Smagala, Miranda de Graaf, David F. Burke, Ron A. M. Fouchier, Claudia Pappas, Celia M. Alpuche-Aranda, Hugo López-Gatell, Hiram Olivera, Irma López, Christopher A. Myers, Dennis Faix, Patrick J. Blair, Cindy Yu, Kimberly M. Keene, P. David Dotson, Jr., David Boxrud, Anthony R. Sambol, Syed H. Abid, Kirsten St. George, Tammy Bannerman, Amanda L. Moore, David J. Stringer, Patricia Blevins, Gail J. Demmler- Harrison, Michele Ginsberg, Paula Kriner, Steve Waterman, Sandra Smole, Hugo F. Guevara, Edward A. Belongia, Patricia A. Clark, Sara T. Beatrice, Ruben Donis, Jacqueline Katz, Lyn Finelli, Carolyn B. Bridges, Michael Shaw, Daniel B. Jernigan, Timothy M. Uyeki, Derek J. Smith, Alexander I. Klimov, and Nancy J. Cox.
Published Online May 22, 2009
Additional sources: CDC.
Written by: Catharine Paddock, PhD