Increased risk of A(H1N1)pdm09 influenza infection in UK pig industry workers compared to a general population cohort

Abstract

BackgroundPigs are mixing vessels for influenza viral reassortment, but the extent of influenza transmission between swine and humans is not well understood.ObjectivesTo assess whether occupational exposure to pigs is a risk factor for human infection with human and swine‐adapted influenza viruses.Methods UK pig industry workers were frequency‐matched on age, region, sampling month, and gender with a community‐based comparison group from the Flu Watch study. HI assays quantified antibodies for swine and human A(H1) and A(H3) influenza viruses (titres ≥ 40 considered seropositive and indicative of infection). Virus‐specific associations between seropositivity and occupational pig exposure were examined using multivariable regression models adjusted for vaccination. Pigs on the same farms were also tested for seropositivity.ResultsForty‐two percent of pigs were seropositive to A(H1N1)pdm09. Pig industry workers showed evidence of increased odds of A(H1N1)pdm09 seropositivity compared to the comparison group, albeit with wide confidence intervals (CIs), adjusted odds ratio after accounting for possible cross‐reactivity with other swine A(H1) viruses (aOR) 25·3, 95% CI (1·4–536·3), P = 0·028.ConclusionThe results indicate that A(H1N1)pdm09 virus was common in UK pigs during the pandemic and subsequent period of human A(H1N1)pdm09 circulation, and occupational exposure to pigs was a risk factor for human infection. Influenza immunisation of pig industry workers may reduce transmission and the potential for virus reassortment.

Zoonotic Potential of Influenza A Viruses: A Comprehensive Overview

“…Interestingly, few human infections were reported due to rearing or culling of farmed animals. Several serological surveillance studies have shown that zoonotic IAV infections are more frequent in workers of poultry and pig farms [ 156 , 157 , 158 ]. Moreover, AIV infection of humans (e.g., hunters) through the direct contact with wild birds is an additional risk factor [ 159 , 160 ].…”

Interspecies Transmission of Reassortant Swine Influenza A Virus Containing Genes from Swine Influenza A(H1N1)pdm09 and A(H1N2) Viruses

“…This virus incorporates the genes encoding the envelope glycoproteins, HA and NA, from a European swine H1N2 subtype (which themselves derive from human-origin strains) and the remaining gene cassette encoding the internal proteins from swine-origin pandemic 2009 strains (8). Serologic assessment of potential exposure of pig industry workers in the United Kingdom to swine viruses during 2009-2010 showed that antibodies to H1N2 swine IAVs were present in 24% of persons, and this prevalence was increased relative to a comparator population (24). Because the potential risks associated with a novel combination of gene segments in the H1N2r isolate were unknown, we investigated the pathogenesis and infection dynamics of this virus in pigs, the natural host, and in ferrets, which are widely established as an animal model for investigating influenza and pandemic risk in humans (25,26).…”

A Single Amino Acid at Position 431 of the PB2 Protein Determines the Virulence of H1N1 Swine Influenza Viruses in Mice

“…Since 2009, genetic reassortment among the pandemic 2009/H1N1 virus, EA H1N1, and other swine H1N1, H1N2, and H3N2 viruses was detected repeatedly in pigs (13)(14)(15)(16)(17)(18)(19)(20). Notably, sporadic human infections of endemic and novel reassortant SIVs (21)(22)(23)(24)(25)(26)(27) and the seropositivity of at-risk populations, such as swine workers (28)(29)(30), underscore the importance of influenza surveillance in pigs.…”