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Since 1997, there have been several occurrences of low pathogenicity avian influenza (LPAI) H5 and H7 viruses in Italy. Furthermore, H5N2 and H7N1 highly pathogenic (HP) AI viruses were responsible for two epidemics in poultry in 1997 and 1999–2000, respectively. In particular, in 1999–2000 H7N1 virus circulated as LPAI virus in the industrial sector for several months in the absence of control measures before turning into HPAI virus. This virus spread rapidly in the most densely populated poultry area (DPPA), involving over 16 million birds (Mannelli and others 2006). After this major epidemic, a risk-based surveillance system was implemented allowing for the early detection of LPAI-infected holdings and the enforcement of adequate measures to limit the spread of the viruses and the emergence of HPAI strains (Comin and others 2011).
This paper describes the origin and epidemiological features of an H7N7 HPAI virus epidemic that took place in the late summer of 2013.
An HPAI H7N7 virus was detected on August 14 in a holding housing 135,000 layers located in the Po river delta (province of Ferrara, Emilia Romagna Region). The holding comprised five sheds, of which the two outer ones (1 and 7, Fig 1) had external areas for free-range hens. Production data showed an initial increase in the mortality rate from 0.2 to 0.7 per cent in the outer sheds and from 0.2 to 0.9 per cent in the inner sheds (sheds 2, 4 and 5) in the week of July 22–28. A second peak was reported from August 7 to 12 accounting for a mortality of …