The FAO’s recent EMPRES briefing on swine influenza provides a useful history of swine influenza, from the paper Swine influenza: a zoonosis, by Paul Heinen, an excellent primer on the virus.
I’ve added some additional detail and comments to this history, largely informed by Bruce Janke’s 2008 presentation to the USDA’s APHIS.
Events in 1998, 2001, 2009 of particular relevance to the 2009 outbreak of swine-origin H1N1 influenza A in humans are emphasised.
(For emerging news, comment, science, argument and counter-argument on the 2009 H1N1 outbreak, see the Tracing Paper’s Novel H1N1 flu virus, pigs, farms and pork: an evolving round-up.)
A brief history of swine influenza, from 1918 to 2009
| 1918 | SI H1N1 described in north central USA, Hungary, and China. May have been cause of human pandemic, which resulted in 20-40 million human deaths. (Or may have originated in birds before spreading to humans and pigs. Janke says SI “entered swine population in 1918″) |
| 1930 | Shope isolated influenza virus from pigs. The prototype classic SI H1N1 strain (A/Swine/Iowa/30) transmitted experimentally to pigs. |
| 1941 | SI recognised in Europe and disappeared. |
| 1970 | Transmission of human H3N2 virus to pigs. Avian like H3N2 in pigs in Asia. |
| 1976 | Classical H1N1 reappears in European pigs. Janke says “SIV remained unique (a few exceptions) to the US until 1976 when exported to Italy” |
| 1977 | Human H3N2 virus isolated from pigs in Colorado in 1977 (no disease). (Janke) |
| 1979 | Introduction of whole H1N1 virus from birds to pigs. Antigenically distinguishable from classical strains. Still circulating in 2002. |
| 1984 | Reassortment between human H3N2 and avian H1N1 in swine resulting in reassortant H3N2 virus with avian internal gene segments. H3N2 strains first associated with respiratory epizootics. Still circulating in 2002. |
| 1986 | Classical H1N1 reappears in UK, similar to classical H1N1 in continental Europe. |
| 1987 | Reassortant H3N2 associated with respiratory epizootics in UK. Related to A/Port Chalmers/73 (H3N2). |
| 1989 | Avian like SI H1N1 is dominant and widespread in Europe. |
| 1992-1993 | Avian like H1N1 strains widespread in UK. |
| 1993 | Infection of children with reassortant H3N2 virus from pigs. Isolation of avian like swine H1N1 virus from a pneumonia patient in the Netherlands. |
| 1994 | H1N2 first isolated in pigs in UK, and later also in Belgium. Human avian reassortant virus. |
| 1992-1998 | H3N1 (H3 human, N1 swine) and H1N7 (H1 human, N7 equine) also occurred in swine in the UK but failed to spread. |
| 1998 | H9N2 in pigs and humans in Asia. Apparently an avian virus that has adapted to pigs. |
| 1998 | For first time, H3N2 viruses cause severe disease in N. America. Viruses are triple (avian / human / classical swine) reassortants, distinct from earlier strains and European strains.
Janke provides additional detail: H1N2 identical to H3N2, but with H1HA from classical swine H1N1, also isolated. |
| 1998-1999 | Continued Introduction of Human H3N2 into Swine • H3 & N2 from 1995 human virus (Cluster I – TX 98) • H3 & N2 from 1997 human virus (Cluster II – CO 99) • H3 & N2 from 1996 human virus (Cluster III – IL 99, OK 99) (Janke) |
| from 1998 | Reassortment of co-circulating H1N1 and H3N2 yielding 2nd generation reassortant H1N2, composed of: - Classic swine: H1, NP, M, NS - Human: N2, PB1 - Avian: PA, PB2 (Janke) |
| 1999 | Single case of isolation of avian H4N6 from pigs with pneumonia in Canada. |
| 2001 | Webby isolates 2nd generation reassortant (rH1N1): • H1N1 isolates with classic SI H1 and N1 and internal genes of H3N2 - Classic swine: H1, N1, NP, M, NS - Human: PB1 - Avian: PA, PB2 • rH1N1 retrospectively found to have displaced classical H1N1 almost immediately (Janke) |
| 2002 | Situation in Europe: avian like H1N1, and reassortant human like H3N2 and H1N2. In North America: classical swine H1N1, triple reassortant H3N2. |
| 2004 | 2nd generation reassortant H3N1 identified in MN and IA. Late identification suggests this combination is not as stable and efficient (Janke) |
| 2006 | H2N3 SI isolated from US pigs with clinical respiratory disease. Triple reassortant virus similar to most current SIVs: H2, N3 avian origin; PA more recent avian origin. First report of H2 virus in mammals since H2N2 human pandemic virus in 1957. (Janke) |
| 2008 | Current US SI viruses: Classic swine H1N1, H3N2 (triple reassortant), H1N2 (2nd generation), H3N1 (2nd generation), Reassortant H1N1, Reassortant human H1N1, H1N2 (Janke) |
| 2009 | Reassortant H1N1 appears in humans in Mexico and US, transmissable between humans and spreading to other regions. Genetic composition: - Swine (North America): H1, NP, NS - Swine (Europe): N1 - Swine (Eurasia): M - Avian (North America): PA, PB2 - Human (1993 H3N2 strain): PB1 (Source: Wikipedia 5/5/2009) (Compare 2001 2nd generation reassortant (rH1N1)H1N1 isolate: |
One Comment
I’m amazed to see swine flu was absent from Europe for 35 years till 1976. Was its reappearance caused or aided by the spread of factory farming??