Table of Contents
Influenza Research and Treatment
Volume 2011 (2011), Article ID 163745, 6 pages
Research Article

Clinical Impact of Infection with Pandemic Influenza (H1N1) 2009 Virus in Naïve Nucleus and Multiplier Pig Herds in Norway

1Norwegian School of Veterinary Science, Department of Production Animal Clinical Sciences, P.O. Box 8146, 0033 Oslo, Norway
2Department of Health Surveillance, Norwegian Veterinary Institute, P.O. Box 750, 0106 Oslo, Norway
3Department of Laboratory Services, Norwegian Veterinary Institute, P.O. Box 750, 0106 Oslo, Norway
4Norwegian Pig Health Service, Animalia, P.O. Box 396, 0513 Oslo, Norway

Received 14 September 2011; Revised 20 November 2011; Accepted 1 December 2011

Academic Editor: Montserrat Torremorell

Copyright © 2011 Carl Andreas Grøntvedt 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.


The Norwegian pig population has been free from influenza viruses until 2009. The pandemic influenza outbreak during the autumn 2009 provided an opportunity to study the clinical impact of this infection in an entirely naïve pig population. This paper describes the results of a case-control study on the clinical impact of pandemic influenza (H1N1) 2009 infection in the nucleus and multiplier herds in Norway. The infection spread readily and led to seroconversion of 42% of the Norwegian nucleus and multiplier herds within a year. Positive and negative herds were identified based on surveillance data from the Norwegian Veterinary Institute. Telephone interviews were conducted with pig herd owners or managers between November 2010 and January 2011. Pigs with clinical signs were reported from 40% of the case herds with varying morbidity and duration of respiratory disease and reduced reproductive performance. Clinical signs were reported in all age groups.