%0 Journal Article
%T Experiences after Twenty Months with Pandemic Influenza A (H1N1) 2009 Infection in the Na£¿ve Norwegian Pig Population
%A B. Gjerset
%A C. Er
%A S. L£¿tvedt
%A A. J£¿rgensen
%A O. Hungnes
%A B. Lium
%A A. Germundsson
%J Influenza Research and Treatment
%D 2011
%I Hindawi Publishing Corporation
%R 10.1155/2011/206975
%X Pandemic (H1N1) 2009 influenza A virus was detected in Norwegian pigs in October 2009. Until then, Norway was regarded free of swine influenza. Intensified screening revealed 91 positive herds within three months. The virus was rapidly transmitted to the susceptible population, including closed breeding herds with high biosecurity. Humans were important for the introduction as well as spread of the virus to pigs. Mild or no clinical signs were observed in infected pigs. Surveillance of SIV in 2010 revealed that 41% of all the Norwegian pig herds had antibodies to pandemic (H1N1) 2009 virus. Furthermore, this surveillance indicated that pigs born in positive herds after the active phase did not seroconvert, suggesting no ongoing infection in the herds. However, results from surveillance in 2011 show a continuing spread of the infection in many herds, either caused by new introduction or by virus circulation since 2009. 1. Introduction Swine influenza A viruses (SIVs) are enzootic in most European pig populations [1]. The SIV H1N1 and H3N2 subtypes have been circulating for more than 30 years, and the SIV subtype H1N2 has been circulating since it was first isolated in Great Britain in 1994 [2, 3]. In April 2009, a new influenza A virus of subtype H1N1 emerged in the human population in Mexico and the United States. This was a multiple reassortant virus containing genes from North American and Eurasian lineages [4, 5]. The virus spread rapidly across the world by human-to-human transmission. Human-to-pig transmission was first reported in Canada in late April 2009, then in European pig population in early September 2009, and has since been reported in several countries all over the world [6¨C9]. In October 2009, SIV was reported for the first time in Norway when an integrated pig herd tested positive for pandemic (H1N1) 2009 virus after showing mild clinical signs of respiratory disease [10]. The clinical picture of pandemic (H1N1) 2009 infections in experimentally and naturally infected pigs was described as mild respiratory illness, increased temperature, and decreased appetite [6, 11, 12]. In some infected herds, clinical signs were not detected [13]. Studies have shown that immunological na£¿ve pigs experimentally infected with pandemic (H1N1) 2009 virus could transmit the virus efficiently to other na£¿ve pigs [11, 14, 15]. Although pandemic (H1N1) 2009 virus contains gene segment genetically related to other swine influenza virus strains circulating in Europe and North America, it shows antigenetic differences in the major glycoproteins of the virus
%U http://www.hindawi.com/journals/irt/2011/206975/