Short communication
Novel H1N2 swine influenza reassortant strain in pigs derived from the pandemic H1N1/2009 virus

https://doi.org/10.1016/j.vetmic.2010.12.011Get rights and content

Abstract

Swine influenza monitoring programs have been in place in Italy since the 1990s and from 2009 testing for the pandemic H1N1/2009 virus (H1N1pdm) was also performed on all the swine samples positive for type A influenza. This paper reports the isolation and genomic characterization of a novel H1N2 swine influenza reassortant strain from pigs in Italy that was derived from the H1N1pdm virus.

In May 2010, mild respiratory symptoms were observed in around 10% of the pigs raised on a fattening farm in Italy. Lung homogenate taken from one pig showing respiratory distress was tested for influenza type A and H1N1pdm by two real time RT-PCR assays. Virus isolation was achieved by inoculation of lung homogenate into specific pathogen free chicken embryonated eggs (SPF CEE) and applied onto Caco-2 cells and then the complete genome sequencing and phylogenetic analysis was performed from the CEE isolate.

The lung homogenate proved to be positive for both influenza type A (gene M) and H1N1pdm real time RT-PCRs. Virus isolation (A/Sw/It/116114/2010) was obtained from both SPF CEE and Caco-2 cells. Phylogenetic analysis showed that all of the genes of A/Sw/It/116114/2010, with the exception of neuraminidase (NA), belonged to the H1N1pdm cluster. The NA was closely related to two H1N2 double reassortant swine influenza viruses (SIVs), previously isolated in Sweden and Italy. NA sequences for these three strains were clustering with H3N2 SIVs. The emergence of a novel reassortant H1N2 strain derived from H1N1pdm in swine in Italy raises further concerns about whether these viruses will become established in pigs. The new reassortant not only represents a pandemic (zoonotic) threat but also has unknown livestock implications for the European swine industry.

Introduction

Influenza type A viruses are currently circulating in the European pig population with high prevalence of H1N1, H1N2 and H3N2 subtypes. In April 2009 a new virus, identified as pandemic H1N1/2009 strain of influenza A (H1N1pdm), was reported to have caused a human influenza outbreak in Mexico (Centers for Disease Control and Prevention, 2009a, pp. 400–402). By June 2009 the H1N1pdm had rapidly spread among humans, leading the WHO to the declaration of the first influenza pandemic of the 21st century (WHO, 2009c, phase of pandemic alert). The virus is a quadruple reassortant and contains mostly genes from the triple reassortant H1N1 viruses found in swine in North America as well as two genes, neuraminidase (NA) and matrix (M) from influenza viruses found in swine in Europe and Asia (Schnitzler and Schnitzler, 2009). In Italy, swine influenza monitoring programs, based on genome detection, virus isolation and sequencing of all respiratory forms, have been in place since the nineties, especially in North Italy where more than 75% of the swine industry is located. Responding to the emergence of the new pandemic virus and consequently to the recent reports on human to animal transmission (Hofshagen et al., 2009, OIE, 2009), testing for the H1N1pdm was also performed on all the swine samples which resulted positive to influenza type A. In the last two years, systematic virological surveillance of influenza viruses in pigs has led to the isolation of 67 swine influenza viruses (SIVs) belonging to the following subtypes: 24 H1N1, 25 H1N2, 18 H3N2 SIVs (Moreno et al., 2010a, p. 73), 2 H1N1pdm viruses (Moreno et al., 2010b, pp. 52–56) and one new reassortant strain derived from H1N1pdm. This paper reports the first isolation of a new H1N2 reassortant strain on an Italian pig farm. The molecular characterization and phylogenetic analysis of the new reassortant strain revealed that all the genes except the neuraminidase (NA) belonged to the H1N1pdm viruses and the NA gene was closely related to two H1N2 SIV strains, previously isolated in Sweden (A/Sw/Sweden/1021/2009) and Italy (A/sw/Italy/58769/2010).

Section snippets

Clinical samples

In May 2010, a clinical outbreak was reported on a pig fattening farm with 4000 heads located in the province of Mantua (North Italy). The clinical signs observed were coughing, dyspnoea, fever, anorexia and depression with 10% morbidity, 0.5% mortality. This farm used a continuous flow system of management with monthly introduction of animals and fortnightly departures to the slaughterhouse. SIV vaccination program had not been in place at the farm. One dead pig was submitted to the laboratory

Virus isolation and subtype determination

Lung homogenates from one pig carcase showing purple areas of consolidation in the apical lobes of the lungs, interlobular oedema, and fibrinous pleuritis resulted positive for influenza type A and H1N1pdm by real time RT-PCR assays. The clinical specimen was further inoculated in SPF CEE and onto Caco-2 cells for virus isolation.

The presence of influenza A and the H1N1pdm was detected on AF and Caco-2 CS by real time RT-PCRs. A multiplex RT-PCR specific for subtype determination was further

Discussion

The identification of the new H1N2 reassortant virus demonstrates once again the important role played by pigs as mixing vessels for animal and human influenza, providing a place for reassortment and host adaptation to take place. These results show that the introduction of H1N1pdm in the swine population has provided opportunities for reassortment with the risk that the H1N1pdm virus could alter transmissibility and increase virulence. The success of interspecies transmission of influenza

Conflicts of interest

All authors have declared that no conflicts of interest exist.

Acknowledgments

We would like to thanks Dr. Leonardo James Vinco and Manola Adella for excellent technical assistance. The study was partially funded by Network of Excellence for Epizootic Disease Diagnosis and Control (EPIZONE) an European Union funded research project officially started on 1st of June 2006 and supported by the European Union Sixth Research Framework Programme (http://www.epizone-eu.net).

References (28)

  • A. Moreno et al.

    Genetic evolution of Italian H1N2 swine influenza viruses during 1998–2009: presence of new reassortant strains, abstr. p. 73

  • A. Moreno et al.

    First pandemic H1N1 outbreak from a pig farm in Italy

    TOVJ

    (2010)
  • G. Neumann et al.

    Emergence and pandemic potential of swine-origin H1N1 influenza virus

    Nature

    (2009)
  • OIE, 2009. World Animal Health Information Database: follow up report (serial on the internet). Influenza A H1N1,...
  • Cited by (0)

    View full text