Table of Contents
Influenza Research and Treatment
Volume 2011, Article ID 206975, 7 pages
Research Article

Experiences after Twenty Months with Pandemic Influenza A (H1N1) 2009 Infection in the Naïve Norwegian Pig Population

1Department of Laboratory Services, Norwegian Veterinary Institute, P.O. Box 750 Sentrum, 0106 Oslo, Norway
2Department of Health Surveillance, Norwegian Veterinary Institute, P.O. Box 750 Sentrum, 0106 Oslo, Norway
3Department of Control, Norwegian Food Safety Authority, Kyrkjevegen 332, 4325 Sandnes, Norway
4Norwegian Pig Health Service, Animalia, P.O. Box 396 Økern, 0513 Oslo, Norway
5Division of Infectious Disease Control, Department of Virology, Norwegian Institute of Public Health, P.O. Box 4404 Nydalen, 0403 Oslo, Norway

Received 15 September 2011; Revised 21 November 2011; Accepted 18 December 2011

Academic Editor: Montserrat Torremorell

Copyright © 2011 B. Gjerset et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


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.