RESEARCH ARTICLE z r

P.O. Box 750, 0106 Oslo, Norway Full list of author information is available at the end of the articleRespiratory diseases in pigs are serious concerns for pig producers worldwide because they cause substantial eco-nomic losses from increased mortality, reduced feed effi-ciency and growth rate, increased time to reach market weight, increased carcass condemnation at slaughter and costs of treatment and vaccination [1]. Among the many respiratory pathogens in pigs, swine influenza viruses (SIVs) are ubiquitous in intensive pig farming, and can April 2009, a new influenza A virus, named influenza A (H1N1)pdm09 emerged in North- and South-America. It spread rapidly in humans and pigs and soon became endemic in pig populations worldwide including Norway [5-7]. Like other SIVs, this A(H1N1)pdm09 virus spreads easily between pigs and can cause acute respiratory dis-ease [8-10] characterized by high fever, depression, loss of appetite, tachypnoea, abdominal breathing and cough-ing [7]. Uncomplicated SIV infections cause low mortal-ity (usually less than 1%), but morbidity can reach 100% * Correspondence