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The scientific view of the pandemic (H1N1) 2009 virus outbreak

By Dr Jim Robinson, on behalf of the Pig Vetirinary Society
It has been difficult for many of the public to maintain a cool head amongst the media hype and scare stories concerning “swine flu”. The authoritative voices of WHO, OIE and FAO, the bodies that are respected as the international receivers and interpreters of all information concerning serious diseases, both human and animal, have too often been drowned out by the sensational and selective reporting that motivates the lay press.As the present epidemic of a new human Type A influenza virus (that shares some genes with the classical H1N1 virus causing swine flu) started to spread through the world and qualified for “pandemic “ status, a joint article was written and published for the enlightenment of the public, to set the matter factually and soberly in proportion.
The following extracts have been selected as relevant for readers of Porcus, with acknowledgements to:

  • ProMED-mail the electronic reporting journal of the International Society for Infectious Diseases (ISID),
  • The South African Veterinary Association for permission to edit and use the WHO article “Widespread, Rapid Emergence of Novel Influenza A H1N1 among Humans “
  • WHO Global Alert and Response (GAR) reports
  • OIE  reports
  • FAO Animal Production And Health Division

The name of the disease
This is officially as at the head of this article, namely:  pandemic (H1N1) 2009 virus.
It is not a disease of swine and the two incidents of the virus being isolated from pigs are not an indication of a threat to the pig industry.
History of the pandemic
In April 2009, several cases of human illness caused by a novel strain of Influenza A H1N1 were reported from the United States and Mexico. When compared with historical information on genetic sequences of influenza viruses, this novel influenza strain had never before been described.  Since then the number of laboratory confirmed cases has increased to over 94 000 in 134 countries, with 429 deaths, as reported by GAR on 6th July.
(It should be noted that in the same 10-week time period, it is probable that 105 000 people will have died of HIV/Aids, and 82000 of what is now called “seasonal flu”, while an average of 120 children die of malaria every hour).
The rate of spread appears to be rapid and is, compared with the times of previous pandemics, but this is not surprising in a global village where there are over 1 billion air passengers moving between towns, countries and continents every year, or over 2 million every day.
The viruses
The emergence of this novel influenza strain in humans has brought renewed attention on classical swine influenza. Swine influenza is caused by type A orthomyxoviruses. Subtypes are characterised by the two major surface glycoproteins, hemagglutinin (H) and neuraminidase (N).  Respiratory illness in pigs, consistent with what is now described as swine influenza, first appeared in several countries in different parts of the world in 1918. The “classical” swine influenza virus, also classified as influenza A H1N1, was first isolated in 1930 in North America, established itself in pig populations worldwide, and remained essentially unchanged for decades.
Influenza viruses generally prefer a specific host species, although the pig is unique in that it can be easily infected with influenza A viruses from swine, humans, or birds, or combinations of these viruses that are called “reassortant strains”.
The most common subtypes of influenza virus in swine are classical H1N1, H1N2, and H3N2. Currently, various “avian-like”, reassortant (e.g., swine-human), or triple reassortant (e.g., swine-human-avian) influenza viruses are circulating among swine populations worldwide.
Implications for human/pig cross-infection
In response to the emerging human epidemic, and potential for a pandemic, OIE made it a priority to consistently communicate with partners and stakeholders using the best science available at that time. As soon as the novel virus emerged in humans, OIE made an official statement on the A H1N1 influenza like human illness in Mexico and the USA, which included the clear point that the disease in humans should not be called swine influenza.
OIE clearly stated its position on safety of international trade of pigs and products of pig origin, and strongly counselled against the culling of pigs as a disease control measure in response to the presence of the novel virus. OIE made a joint statement with FAO, WHO, and WTO on the novel influenza A H1N1 and the safety of pork, which included a clear message that pork and pork products handled in accordance with hygienic practices are not a source of infection.
OIE has also outlined a scientific agenda in response to emergence of this new influenza strain. OIE will be collaborating with FAO, with the support of World Bank, on a project to update and enhance biosecurity guidance in the context of this new influenza strain that will also include the protection of swine from humans potentially infected with influenza. In all activities, OIE has stressed the critical importance of a One World One HealthTM approach and is extensively collaborating with WHO, FAO, and other joint animal-human health partners.
There remain many questions about the pandemic H1N1 strain. Based on the historic emergence of epidemic or pandemic strains in humans, it is likely that the continued circulation of this virus among humans could lead to more pig infections. Additional information is needed on whether infection in pigs with this novel virus causes disease and spreads within swine populations in a similar fashion to “classical swine influenza”. If this virus continues circulating among humans, how feasible or necessary will it be to prevent this new influenza from becoming a virus circulating in the pig population?
Summary
Pandemic (H1N1) 2009 is a new virus from a group of unstable RNA viruses, which has spread to many countries, causing a relatively mild human disease in nearly all cases.
It is related to the classical swine influenza virus but has recombinant elements of avian and human strains, making it genetically unique.
The anxiety of the media to compete for public attention has led to the “swine flu” misnomer and erroneous perception that it is a zoonotic disease.  The inclination of this family of viruses to mutate makes predictions concerning its infectivity and pathogenicity uncertain, but this has always been the case with influenza type A viruses.
Consumers need to be reassured, repeatedly, that there is no danger of catching flu from eating pork.

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