Pigs are known to be susceptible to influenza A viruses of most haemagglutinin subtypes although only three serotypes, H1N1, H3N2 and H1N2, predominantly infect and cause clinical disease in pigs worldwide including the UK. Swine 'flu' is usually regarded as an endemic disease, epidemics may result when infection occurs in an immunologically naive population or through exacerbation by a variety of factors such as poor husbandry, secondary bacterial or viral infections and cold weather. Serosurveillance results in the UK indicated that more >50% of adult pigs had been infected with one or more influenza A viruses [1]. As part of this review of the swine influenza surveillance data from 1991-2006 we describe the submission rates and the frequency of positive virus isolations. Between 1998-2006 demographic analysis has also been performed including; submission and positive proportion per pig population, geographical distribution, seasonality, pig age, clinical signs and inter-current disease. In addition, the genetic evolution of UK isolates (HA & NA genes) in relation to those in continental Europe has been analysed.
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