Swine Influenza Virus Antibodies in Humans | CDC EID

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Volume 17, Number 3–March 2011
Research
Swine Influenza Virus Antibodies in Humans, Western Europe, 2009
Nancy A. Gerloff, Jacques R. Kremer, Emilie Charpentier, Aurélie Sausy, Christophe M. Olinger, Pierre Weicherding, John Schuh, Kristien Van Reeth, and Claude P. Muller

Author affiliations: Centre de Recherche Public de la Santé/Laboratoire National de Santé, Luxembourg, Grand-Duchy of Luxembourg (N.A. Gerloff, J.R. Kremer, E. Charpentier, A. Sausy, C.P. Muller); Laboratoires Réunis, Junglinster, Luxembourg (C.M. Olinger, J. Schuh); Health Directorate, Luxembourg (P. Weicherding); and Ghent University, Ghent, Belgium (K. Van Reeth)

Suggested citation for this article

Abstract
Serologic studies for swine influenza viruses (SIVs) in humans with occupational exposure to swine have been reported from the Americas but not from Europe. We compared levels of neutralizing antibodies against 3 influenza viruses—pandemic (H1N1) 2009, an avian-like enzootic subtype H1N1 SIV, and a 2007–08 seasonal subtype H1N1—in 211 persons with swine contact and 224 matched controls in Luxembourg. Persons whose profession involved contact with swine had more neutralizing antibodies against SIV and pandemic (H1N1) 2009 virus than did the controls. Controls also had antibodies against these viruses although exposure to them was unlikely. Antibodies against SIV and pandemic (H1N1) 2009 virus correlated with each other but not with seasonal subtype H1N1 virus. Sequential exposure to variants of seasonal influenza (H1N1) viruses may have increased chances for serologic cross-reactivity with antigenically distinct viruses. Further studies are needed to determine the extent to which serologic responses correlate with infection.

Pandemic (H1N1) 2009 influenza virus resulted from genetic reassortment between at least 2 swine influenza viruses (SIVs) (1). Hemagglutinin (HA) of this novel subtype H1N1 virus is similar to that of classical swine influenza virus and the triple reassortant subtype H1N1 viruses that are endemic in swine populations in North America. At the time of its detection in humans, pandemic (H1N1) 2009 virus had never been detected in swine populations anywhere, but it is believed to have circulated undetected in regions with little or no surveillance for influenza viruses in swine. Because this virus has not been reported by the European Surveillance Network for Influenza in Pigs (www.esnip.ugent.be) since the network's inception in 2001, it was most likely absent in swine in western Europe. By the end of 2009, pandemic (H1N1) 2009 virus infection of swine had been reported in Norway (2); sporadic cases have been reported in a few other European countries (e.g., Germany, Italy, Denmark) (3). The swine were probably infected by contact with infected humans, whereas transmission from swine to humans has not yet been documented. Pandemic (H1N1) 2009 virus is the first swine-origin virus that is readily transmitted between humans (4).

Human infections with SIVs are rare. During 1958–2005, only 50 cases of zoonotic infections were reported; most were in persons who had contact with swine (5). Limited secondary transmission to close contacts has been reported but appears to be rare, and to our knowledge, sustained human-to-human transmission of enzootic SIVs has never been noted (6). Some serologic studies suggest that persons who work with swine are at increased risk for zoonotic infection with SIVs (7–12).

The predominant subtype H1N1 SIVs in Europe were introduced from wild ducks to swine in 1979 and have an entirely avian-derived genome (13–15). These viruses are designated as avian-like viruses and are antigenically distinct from subtype H1N1 SIVs in North America and from pandemic (H1N1) 2009 virus. Few cases of human infection with these avian-like swine subtype H1N1 viruses have been reported; chains of transmission have not been found (5,9,15), and no serologic studies have provided indirect evidence of transmission of SIVs to humans in Europe (15).

Studies in the United States, United Kingdom, and Finland found antibodies against pandemic (H1N1) 2009 virus in elderly persons (16–18). These antibodies can be explained by antigenic evolution of seasonal human influenza (H1N1) viruses that are derived from the 1918 pandemic virus (such as the classical swine influenza [H1N1] virus) but have undergone greater antigenic drift than the swine virus (19). Antigenically, the influenza (H1N1) viruses that circulated among humans before the 1950s are probably more closely related to the classical swine virus and thus to the pandemic (H1N1) 2009 virus than to contemporary human subtype H1N1 viruses. We investigated whether persons whose professions involve contact with swine (swine workers [SWs]) have neutralizing antibodies against 3 influenza viruses: pandemic (H1N1) 2009 virus, a European avian-like subtype H1N1 SIV, and a 2007–08 seasonal influenza subtype H1N1 (seasonal influenza) virus.


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Suggested Citation for this Article
Gerloff NA, Kremer JR, Charpentier E, Sausy A, Olinger CM, Weicherding P, et al. Swine influenza virus antibodies in humans, western Europe, 2009. Emerg Infect Dis [serial on the Internet]. 2011 Mar [date cited].
http://www.cdc.gov/EID/content/17/3/403.htm

DOI: 10.3201/eid1703100581


Comments to the Authors
Please use the form below to submit correspondence to the authors or contact them at the following address:

Claude P. Muller, Institute of Immunology, CRP-Santé/LNS, 20A, Rue Auguste Lumière, L-1950 Luxembourg; email: claude.muller@lns.etat.lu