European Surveillance Network for Influenza in Pigs : Surveillance Programs, Diagnostic Tools and Swine Influenza Virus Subtypes Identified in 14 European Countries from 2010 to 2013

Swine influenza causes concern for global veterinary and public health officials. In continuing two previous networks that initiated the surveillance of swine influenza viruses (SIVs) circulating in European pigs between 2001 and 2008, a third European Surveillance Network for Influenza in Pigs (ESNIP3, 2010-2013) aimed to expand widely the knowledge of the epidemiology of European SIVs. ESNIP3 stimulated programs of harmonized SIV surveillance in European countries and supported the coordination of appropriate diagnostic tools and subtyping methods. Thus, an extensive virological monitoring, mainly conducted through passive surveillance programs, resulted in the examination of more than 9 000 herds in 17 countries. Influenza A viruses were detected in 31% of herds examined from which 1887 viruses were preliminary characterized. The dominating subtypes were the three European enzootic SIVs: avian-like swine H1N1 (53.6%), human-like reassortant swine H1N2 (13%) and human-like reassortant swine H3N2 (9.1%), as well as pandemic A/H1N1 2009 (H1N1pdm) virus (10.3%). Viruses from these four lineages co-circulated in several countries but with very different relative levels of incidence. For instance, the H3N2 subtype was not detected at all in some geographic areas whereas it was still prevalent in other parts of Europe. Interestingly, H3N2-free areas were those that exhibited highest frequencies of circulating H1N2 viruses. H1N1pdm viruses were isolated at an increasing incidence in some countries from 2010 to 2013, indicating that this subtype has become established in the European pig population. Finally, 13.9% of the viruses represented reassortants between these four lineages, especially between previous enzootic SIVs and H1N1pdm. These novel viruses were detected at the same time in several countries, with increasing prevalence. Some of them might become established in pig herds, causing implications for zoonotic infections

Overview of RT-PCR techniques and pig sera used by 15 ESNIP3 partners for detection and preliminary subtyping of influenza A viruses in pig samples (rt = real-time; conv. = conventional; n.a. = not applicable; CA = Cotes d'Armor; Fin = Finistere; Eng = England; Calif = California; Scot = Scotland; Neth = Netherlands; It = Italy).

<p>Virus strains marked with an asterisk (*) were used to produce sera belonging to the ESNIP3 reference panel.</p>a<p>Since end 2012 (used during the third yearly period of the project).</p><p>Overview of RT-PCR techniques and pig sera used by 15 ESNIP3 partners for detection and preliminary subtyping of influenza A viruses in pig samples (rt =  real-time; conv. =  conventional; n.a. =  not applicable; CA =  Cotes d'Armor; Fin = Finistere; Eng =  England; Calif =  California; Scot =  Scotland; Neth =  Netherlands; It = Italy).</p

Number of investigated and positive herds obtained in each country by the different partners, in the three 12-month periods of the ESNIP3 program as well as in total from November 2010 to October 2013.

<p>Percentages of positive herds and total numbers of viruses that were subtyped in the context of the passive surveillance are also given. When several partners were involved in the surveillance in a country, individual numbers are indicated in grey.</p><p>Number of investigated and positive herds obtained in each country by the different partners, in the three 12-month periods of the ESNIP3 program as well as in total from November 2010 to October 2013.</p

Number of viruses identified within the different haemagglutinin and neuraminidase subtypes and lineages in 14 countries from November 2010 to October 2013.

<p>Number of viruses identified within the different haemagglutinin and neuraminidase subtypes and lineages in 14 countries from November 2010 to October 2013.</p