Genetic and Antigenic Evolution of Swine Influenza Viruses in Europe and Evaluation of Their Zoonotic Potential

Abstract

Swine influenza is a highly contagious respiratory viral infection of pigs that has become enzootic in areas densely populated with pigs. Like other influenza A viruses, swine influenza virus (SIV) is genetically unstable and able to accumulate antigenic drifts and/or antigenic shifts. The pig is susceptible to both avian and human influenza viruses and can serve as an intermediate host in influenza virus ecology. Zoonotic agents may emerge in pigs following the modification of an established swine strain, adaptation of a strain of avian origin to the mammalian host, or reassortment between human and avian influenza viruses. Three different subtypes, H1N1, H3N2 and H1N2, are at present circulating in Europe. They differ from those found in North America and Asia and various lineages can be distinguished within each subtype. To date, European SIVs have not produced a global outbreak of influenza in humans but sporadic cases of SIV infection have been reported. This review presents a historical record of the genetic and antigenic evolution of SIVs in Europe. Our present understanding of the transmission of European SIVs from pigs to other animal species and to humans, together with the factors that limit inter-species transmission, is described.

Influenza A virus infection of healthy piglets in an abattoir in Brazil: animal-human interface and risk for interspecies transmission

“…The primary route of virus transmission is via pig-to-pig contact resulting in nasopharyngeal routes of infection following nasal viral secretions that are disseminated through droplets or aerosols. Coughing, nasal discharge, fever, lethargy, difficulty in breathing, depressed appetite and reproductive disorders have been associated with different influenza A virus subtype infections throughout the world (Kuntz-Simon & Madec 2009). Close contact between pigs, stress, meteorological and environmental factors have been shown to contribute to influenza virus spread (Brown 2000, Williamson et al 2012).…”

First isolation and identification of H1N1 swine influenza viruses in Colombian pig farms

“…Based on antigenic differences in the surface glycoproteins, hemagglutinin (HA) and neuralminidase (NA), influenza A viruses are further classified into 16 HA and 9 NA subtypes [8,9]. Although other subtypes have been identified, the influenza A virus sub-types H1N1, H1N2 and H3N2 are the most prevalent in pig populations worldwide [7,10] The pig industry in Colombia has grown about 30% during the last decade. With a swine population close to four million heads, located in four geographical regions it is one of the major contributors to the GDP of the country (ICA, 2012).…”

“…Swine influenza is caused by Influenza A virus, a member of the Orthomyxoviridae family. Influenza A viruses have been isolated from different species including, humans, pigs, horses, dogs, sea mammals and birds [7,8] between others. The virus has a single-stranded RNA segmented genome.…”

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

“…In the epidemic form, the clinical picture is usually characterised by a sudden onset of fever, coughing, sneezing, nasal discharge, breathing difficulty (tachycardia or dysponoea), lethargy, anorexia, and decreased appetite (22). The virus quickly moves through all phases of a farm with rapid recovery, if there are no complicating factors, such as secondary bacterial infections, which occur very often and exacerbate the clinical signs (11,13). Morbidity rates can reach 100% of the population, while mortality rates are generally low (around 1%-4%) (22).…”

“…Two forms of SI occur in swine: epidemic and endemic (11,22). In the epidemic form, the clinical picture is usually characterised by a sudden onset of fever, coughing, sneezing, nasal discharge, breathing difficulty (tachycardia or dysponoea), lethargy, anorexia, and decreased appetite (22).…”