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Keeping track of swine influenza viruses
  1. Les Sims, BVSc (Hons), MANZCVSc, MRCVS
  1. Asia Pacific Veterinary Information Services, PO Box 55, Montmorency, Victoria 3094, Australia
  1. E-mail: apvis{at}

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IN 2009, the world witnessed the rapid global spread of an influenza A virus of the H1N1 subtype (A[H1N1]pdm09) through the human population. Although this virus was not identified in animals before its emergence in human beings, genetic studies strongly suggest that pigs were the putative host species (Smith and others 2009). Subsequently, the reverse process occurred as A(H1N1)pdm09 transmitted back from human beings into and within the global pig population.

The effects of this virus on pigs and the ease with which it then spread in pig populations are described by Williamson and colleagues (2012) in the paper summarised on p 271 of this week's issue of Veterinary Record. This study describes the detection of A(H1N1)pdm09 on 17 farms, the epidemiology of the disease and the clinical signs in pigs on these sites. It demonstrates that, in some cases, the virus apparently transmitted from infected breeding herds, displaying no or few clinical signs, to other farms that purchased piglets from these farms. In 10 cases, the source of infection was not determined. Outbreaks were studied in depth on two farms on which transmission occurred between batches of pigs held in different locations on the same premises.

This paper provides a timely reminder of three important issues regarding influenza viruses at the human-animal interface. These are: the importance of active surveillance for detecting influenza viruses in animal populations; the limits of farm biosecurity measures in preventing transmission of influenza viruses …

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