The 1999-2000 avian influenza (H7N1) epidemic in Italy: veterinary and human health implications.

From the end of March to the beginning of December 1999, 199 outbreaks of low pathogenicity avian influenza (LPAI) were diagnosed in the Veneto and Lombardia regions, which are located in the northern part of Italy. The virus responsible for the epidemic was characterized as a type A influenza virus of the H7N1 subtype of low pathogenicity. On the 17th of December, highly pathogenic avian influenza (HPAI) was diagnosed in a meat turkey flock in which 100% mortality was observed in 72 h. The infection spread to the industrial poultry population of northern Italy including chickens, guinea-fowl, quail, pheasants, ducks and ostriches for a total of 413 outbreaks. Over 13 million birds were affected by the epidemic, which caused dramatic economic losses to the Italian poultry industry with severe social and economic implications. The possibility of H7 virus transmission to humans in close contact with the outbreaks was evaluated through a serological survey. Seven hundred and fifty nine sera were collected and tested for the detection of anti-H7 antibodies by means of the micro-neutralization (MN) and single radial haemolysis (SRH) tests. All samples resulted negative. A limited number of clinical samples were also collected for attempted virus isolation with negative results. Current European legislation considers LPAI and HPAI as two completely distinct diseases, not contemplating any compulsory eradication policy for LPAI and requiring eradication for HPAI. Evidence collected during the Italian 1999-2000 epidemic indicates that LPAI due to viruses of the H7 subtype may mutate to HPAI, and, therefore, LPAI caused by viruses of the H5 or H7 subtypes must be controlled to avoid the emergence of HPAI. A reconsideration of the current definition of avian influenza adopted by the EU, could possibly be an aid to avoiding devastating epidemics for the poultry industry in Member States.