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. 2023 Jan 24;54(1):4.
doi: 10.1186/s13567-022-01133-x.

Infectivity and transmissibility of an avian H3N1 influenza virus in pigs

Wojciech Stadejek  1 , Koen Chiers  2 , Kristien Van Reeth  3
Affiliations

Infectivity and transmissibility of an avian H3N1 influenza virus in pigs

Wojciech Stadejek et al. Vet Res. .

Abstract

In 2019 a low pathogenic H3N1 avian influenza virus (AIV) caused an outbreak in Belgian poultry farms, characterized by an unusually high mortality in chickens. Influenza A viruses of the H1 and H3 subtype can infect pigs and become established in swine populations. Therefore, the H3N1 epizootic raised concern about AIV transmission to pigs and from pigs to humans. Here, we assessed the replication efficiency of this virus in explants of the porcine respiratory tract and in pigs, using virus titration and/or RT-qPCR. We also examined transmission from directly, intranasally inoculated pigs to contact pigs. The H3N1 AIV replicated to moderate titers in explants of the bronchioles and lungs, but not in the nasal mucosa or trachea. In the pig infection study, infectious virus was only detected in a few lung samples collected between 1 and 3 days post-inoculation. Virus titers were between 1.7 and 4.8 log10 TCID50. In line with the ex vivo experiment, no virus was isolated from the upper respiratory tract of pigs. In the transmission experiment, we could not detect virus transmission from directly inoculated to contact pigs. An increase in serum antibody titers was observed only in the inoculated pigs. We conclude that the porcine respiratory tract tissue explants can be a useful tool to assess the replication efficiency of AIVs in pigs. The H3N1 AIV examined here is unlikely to pose a risk to swine populations. However, continuous risk assessment studies of emerging AIVs in pigs are necessary, since different virus strains will have different genotypic and phenotypic traits.

Keywords: Avian influenza; H3N1; explants; replication; swine; transmission.

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Conflict of interest statement

The authors declare that they have no competing interests.

Figures

Figure 1
Figure 1
Comparison of virus titers, expressed as log10 TCID50/mL, of A/chicken/Belgium/136/2019 (chB19) and A/swine/Missouri/A01410819/2014 (swMO14) in supernatant collected from inoculated nasal (NE), tracheal (TE), bronchial (BE) and lung (LE) explants at 1-, 24- and 48-hpi. Each value represents a mean virus titer of three replicates and bars represent the standard deviation. The chB19 experiment was performed twice with explants collected from two different pigs. The dashed line represents the detection limit (1 log10 TCID50/mL)
Figure 2
Figure 2
Microscopic lung lesions in chB19-inoculatedpigs with detectable virus (A), undetectable virus (B) and uninoculated control pigs (C). Inflammatory infiltration and slight cellular debris are seen in all groups. The extent of lesions in chB19-inoculated pigs never exceeded that of control pigs
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