First Pandemic H1N1 Outbreak from a Pig Farm in Italy

The first outbreak of the pandemic H1N1 virus in a swine breeder farm in Italy in November 2009 was reported. Clinical signs observed in sows included fever, depression, anorexia and agalactia, while in piglets diarrhoea and weight loss. The morbidity in sows was approximately 30% and the accumulated mortality rate was similar with those usually reported in piggeries (<10%). Virus was isolated from piglets (A/Sw/It/290271/09) and the sequencing of the whole genome was then performed. Comparison with all (H1N1)v sequences available in GenBank shows A/Sw/It/290271/09 three unique amino-acid (aa) changes in PB2 (S405T), PB1 (K386R) and PA (K256Q), not yet associated to any well characterized phenotype markers of Influenza viruses. All eight aa at positions representing the so-called species specific swine-human signatures, found in both swine and in the pandemic H1N1v, are also present. The M2 protein displays the C55F and the PA protein the S409N substitutions, both corresponding to enhanced transmission phenotype markers. Phylogenetic analysis showed that the virus was genetically related to the pandemic H1N1 virus. In addition, serological samples were collected from 40 sows, of which 20 resulted positive to the pandemic H1N1 virus by HI test proving a virus circulation in the farm.