Susceptibility of swine to H5 and H7 low pathogenic avian influenza viruses

Charles Balzli,Kelly Lager,David E Swayne,Wenjun Ma,Laura Miller,Juergen A Richt,Phillip Gauger,Amy Vincent,David Suarez,Susan Brockmeier

doi:10.1111/irv.12386

Abstract

BackgroundThe ability of pigs to become infected with low pathogenic avian influenza (LPAI) viruses and then generate mammalian adaptable influenza A viruses is difficult to determine. Yet, it is an important link to understanding any relationship between LPAI virus ecology and possible epidemics among swine and/or humans.ObjectivesAssess susceptibility of pigs to LPAI viruses found within the United States and their direct contact transmission potential.MethodsPigs were inoculated with one of ten H5 or H7 LPAI viruses selected from seven different bird species to test infectivity, virulence, pathogenesis, and potential to transmit virus to contact pigs through histological, RRT‐PCR and seroconversion data.ResultsAlthough pigs were susceptible to infection with each of the LPAI viruses, no clinical disease was recognized in any pig. During the acute phase of the infection, minor pulmonary lesions were found in some pigs and one or more pigs in each group were RRT‐PCR‐positive in the lower respiratory tract, but no virus was detected in upper respiratory tract (negative nasal swabs). Except for one group, one or more pigs in each LPAI group developed antibody. No LPAI viruses transmitted to contact pigs.Conclusions LPAI strains from various bird populations within the United States are capable of infecting pigs. Although adaptability and transmission of individual strains seem unlikely, the subclinical nature of the infections demonstrates the need to improve sampling and testing methods to more accurately measure incidence of LPAI virus infection in pigs, and their potential role in human‐zoonotic LPAI virus dynamics.

Highlights

Influenza A viruses (IAV) are members of the Orthomyxoviridae virus family and have a dynamic capacity to change host range and virulence through point mutations and reassortment of gene segments
Based on the hemagglutinin (HA) gene, there are 18 known IAV subtypes found in animals; 16 HA subtypes (H1–16) in the Class Aves, within which various aquatic birds act as reservoirs for these low pathogenicity avian influenza (LPAI) viruses, while two HA subtypes (H17-18) have been found only in the Class Mammalian, Order Chiropteran.[1,2]
A mild transient anorexia was recorded at 4–5 days post-infection (DPI) in the Waterfowl/H7N9, Turkey/H7N2, Swine/H1N1- and Emu/ H5N9-infected groups

Summary

Introduction

Influenza A viruses (IAV) are members of the Orthomyxoviridae virus family and have a dynamic capacity to change host range and virulence through point mutations and reassortment of gene segments. Influenza ecology is complex, involving transmission of distinct viruses among different species and classes of animals. Based on the hemagglutinin (HA) gene, there are 18 known IAV subtypes found in animals; 16 HA subtypes (H1–16) in the Class Aves, within which various aquatic birds act as reservoirs for these low pathogenicity avian influenza (LPAI) viruses, while two HA subtypes (H17-18) have been found only in the Class Mammalian, Order Chiropteran.[1,2] From the avian reservoirs, LPAI viruses and/or specific gene segments have crossed genera, families, orders, and even classes of animals with the pig emerging as a “mixing vessel” or bridging species for adaptation of novel IAVs to mammals, some leading to human infections and new endemic HA subtypes. It is an important link to understanding any relationship between LPAI virus ecology and possible epidemics among swine and/or humans

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