Assessment of exposure to influenza A viruses in pigs between weaning and market age

Juliana Bonin Ferreira,Robert Friendship,Zvonimir Poljak,Éva Nagy,Helena Grgić,Greg Wideman

doi:10.1186/s13567-021-00927-9

Juliana Bonin Ferreira, Robert Friendship + Show 4 more

Open Access

https://doi.org/10.1186/s13567-021-00927-9

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Abstract

Influenza A viruses (IAVs) are common causes of respiratory infection in pigs. The objective of this study was to characterize the circulation of IAVs between weaning and market age on the basis of development of antibody response and molecular epidemiology of detected viruses. Two batches of weaned pigs were followed in the nursery and finisher barns with a sample of 81 and 75 pigs. Nasal swabs and blood samples were collected from individual pigs for virological and serological analyses. A H3N2 subtype virus, of cluster IV, was detected in Study 1, with a maximum of 97.9% identity to HA gene of viruses previously isolated in Ontario. In Study 2, a H1N1 subtype virus, of 2009 H1N1 pandemic lineage, was detected, with a maximum of 97.8% identity to HA gene of viruses previously isolated in Ontario. On the basis of HA gene, it was observed that pigs were being detected with the same virus over time. The existence of antibody titers for IAV other than the isolated one confirmed that more than one subtype can circulate in the same population. In Study 1, pigs with higher numbers of IAV detection had lower serological titers for the same virus that was confirmed to circulate in the nursery (P < 0.01). Thorough knowledge of all endemic viral strains is fundamental for development of infection and disease control, particularly in complex production systems. This may include consideration of sampling and testing strategies which could detect circulation of all IAV variants, even if they have low prevalence.

Highlights

Influenza, an enzootic disease in many pig populations, is caused by influenza virus type A [1]
To expand our understanding of the development of antibodies to specific Influenza A viruses (IAVs) and what the factors might be to trigger the response, we combined repeated sampling and laboratory findings based on the combination of serological testing based on multiple influenza virus variants of the three common subtypes, including viruses detected in this specific barn
All viruses in Study 1 were typed as H3N2 subtype and all were within a minimum of 99.7% identity of HA gene, these viruses were obtained from the same animals that were repeatedly positive on virus isolation

Summary

Introduction

An enzootic disease in many pig populations, is caused by influenza virus type A [1]. Prevalence of exposure at the herd level is generally very high. Herd-level point prevalence of exposure has been estimated at 83% and 43% in Ontario sow and finisher herds, respectively [2]; and above 90% in sow herds in Belgium and Germany [3]. Recent studies showed that swine influenza viruses can persist within a farm, causing two distinct outbreaks [7]. Recurrent infections with influenza A viruses in nursery pigs have been reported under field conditions in two different studies [1, 8]. Several studies have reported exposure of pigs to more than a single strain or subtype, either cumulatively or concurrently

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