Virological Surveillance and Preliminary Antigenic Characterization of Influenza Viruses in Pigs in Five European Countries from 2006 to 2008

Abstract

This study presents the results of the virological surveillance for swine influenza viruses (SIVs) in Belgium, UK, Italy, France and Spain from 2006 to 2008. Our major aims were to clarify the occurrence of the three SIV subtypes - H1N1, H3N2 and H1N2 - at regional levels, to identify novel reassortant viruses and to antigenically compare SIVs with human H1N1 and H3N2 influenza viruses. Lung tissue and/or nasal swabs from outbreaks of acute respiratory disease in pigs were investigated by virus isolation. The hemagglutinin (HA) and neuraminidase (NA) subtypes were determined using standard methods. Of the total 169 viruses, 81 were classified as 'avian-like' H1N1, 36 as human-like H3N2 and 47 as human-like H1N2. Only five novel reassortant viruses were identified: two H1N1 viruses had a human-like HA and three H1N2 viruses an avian-like HA. All three SIV subtypes were detected in Belgium, Italy and Spain, while only H1N1 and H1N2 viruses were found in UK and Northwestern France. Cross-hemagglutination inhibition (HI) tests with hyperimmune sera against selected older and recent human influenza viruses showed a strong antigenic relationship between human H1N1 and H3N2 viruses from the 1980s and H1N2 and H3N2 human-like SIVs, confirming their common origin. However, antisera against human viruses isolated during the last decade did not react with currently circulating H1 or H3 SIVs, suggesting that especially young people may be, to some degree, susceptible to SIV infections.

First Isolation of the H1N2 Swine Influenza Virus in Polish Pig Farm

“…According to Kyriakis et al (12) 48.3% of SIV isolated from 2006 to 2008 in European countries were identified as H1N1, 21.3% as H3N2, and 29.6% as H1N2. Regionally, all three SIV subtypes were isolated from pigs in Belgium, Italy, and Spain, while no H3N2 virus was found in UK and France (4,5,11,12,15,30).…”

“…All three SIV subtypes are currently circulating in swine populations worldwide; however, the origin and genetic and antigenic composition of the strains differ significantly between continents (4,10,12,26,30,32,33). In Europe, the H1N1 SIV having an entirely avian genome is predominant (4,15,26,31).…”

“…On the basis of the results of serological and virological monitoring studies it can be stated that infection is more frequent than an acute disease (12,14). The disease is highly contagious and therefore it is considered as a herd disease (11,12,14,22,31). The susceptibility of infected pigs to SIV-induced signs and lesions correlates with the age of the animals and depends on the superior response to the virus.…”

Influenza Virus Infection in Pigs

“…In 1979, there was avian influenza virus H1N1 (avian-like), which quickly replaced cH1N1 virus, becoming the dominant strain and subsequently undergoing a reassortment with the human H3N2 virus, resulting in virus HA gene containing the and NA of human origin and the internal genes from avian origin (Castrucci et al, 1993). From the 90s, H1N2 viruses emerged containing different combinations of genes (Balint et al, 2009;Kyriakis et al, 2009). Most swine IAV circulating in Europe are also found in Asia, but there are several viral strains that are found only in Asia.…”

Scientific opinion on the possible risks posed by the influenza A (H3N2v) virus for animal health and its potential spread and implications for animal and human health

“…Most human cases have been associated with direct exposure to pigs. Kyriakis et al, 2011;Kyriakis et al, 2013).…”