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Early in 2012 fattening pigs in a pig holding in northern Baden-Württemberg developed serious respiratory disease. After detecting Influenza A specific RNA by Real time-RT-PCR in the lung of an euthanized pig, virus isolation was achieved in embryonated chicken eggs. The haemagglutination-inhibition (HI) test performed on this isolate showed a reaction with H1N1 specific serum, so the strain was initially characterised as subtype H1N1. However, serum samples from convalescent pigs of the same stock four and six weeks later did not show any antibodies to H1N1 in HI test. However, using an ELISA, selected serum samples showed positive reactions against the highly conserved nucleocapsid protein. Performing an HI test using the isolated virus as antigen, significantly positive titers between 1:80 and 1:160 were obtained. The virus isolate was finally identified by molecular methods as a subtype H1pdmN2, a reassortant between the human pandemic (pdm) subtype H1N1/2009 virus and a swine influenza virus of the subtype HxN2.

Influenza A viruses are maintained as a quasispecies cloud in several natural host reservoirs of avian as well as mammalian species. Accidental host exposure, selection and further adaptation of individual influenza A viruses during sporadic trans-species transmission may eventually lead to the establishment of new, stably circulating lineages in a new, possibly mammalian, host species. Given a high transmissibility of such a virus and a susceptible, immunologically naive population, pandemic spread of such viruses within a short time may ensue. In April 2009, a novel multi-reassortant influenza A virus of subtype H1N1 has emerged and regionally spread in humans in Mexico and the United States causing flu-like symptoms. Until June 2009 increasing levels ofa multiregional, global spread of this virus prompted the WHO to raise the pandemic alert to the highest level. Data from experimental infections in pigs as well as experience from natural outbreaks in swine farms world-wide have shown that porcine populations are fully susceptible to the new virus and are able to sustain uninterrupted transmission chains. A broad front incursion of the new human pandemic virus into the porcine population would have a significant negative impact on measures to restrict further spread of the virus in the human population.Therefore, sensitive tools for monitoring and detection of such an incursion in a timely manner are mandatory. We have developed two real-time RT PCRs which are specific for the hemagglutinin gene of the novel A/H1N1 virus and which allow detection of infected pigs with high sensitivity.These PCRs may become useful tools in future surveillance programmes.

Aquatic wild birds constitute the natural reservoir of influenza A viruses. Under appropriate selection pressure these viruses display a remarkable genetic flexibility which is based on their high mutation rate. At least 16 subtypes of the viral hemagglutinin glycoprotein (HA) und 9 of the viral neuraminidase (NA) are distinguishable as a result of natural evolution. Due to the segmentation of the viral genome, genetic reassortments and, thus, a theoretically unrestricted combination of HA and NA subtypes is possible. Transspecies-specific transmissions of viruses from the natural reservoirs to mammals (horses, swine, humans) led to the establishment of several influenza virus lineages which are circulating stably and independently from the previous reservoir. Introduction of viruses featuring new HA/NA combinations into immunologically naive populations can cause rapid and widespread, even pandemic, dissemination of such viruses. The (highly pathogenic avian influenza, HPAI). These mutants constitute the causative agents of classical fowl plague. HPAI viruses of subtypes H5 and H7 generally share a polybasic endoproteolytical cleavage site in the HA protein which allows for systemic replication in the avian host. Subtype H5 and H7 viruses which are maintained in the natural reservoir hosts, in contrast, are of low pathogenicity (LPAI) and harbour monobasic HA cleavage sites restricting their tissue tropism to epithelia of the respiratory and gastronintestinal tracts. This context forms the basis of all legal measures targeting the monitoring, prevention and eradication of HPAIV and LPAIV of subtypes H5 and H7 in poultry. Results of such measures in Germany in 2008 are presented and discussed.