|GAUGER, PHILLIP - Iowa State University|
|MA, WENJUN - Non ARS Employee|
Submitted to: Influenza and Other Respiratory Viruses
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/4/2016
Publication Date: 4/5/2016
Publication URL: http://handle.nal.usda.gov/10113/62648
Citation: Balzli, C., Lager, K., Vincent, A., Gauger, P., Brockmeier, S., Miller, L., Richt, J.A., Ma, W., Suarez, D., Swayne, D.E. 2016. Susceptibility of swine to H5 and H7 low pathogenic avian influenza viruses. Influenza and Other Respiratory Viruses. 10(4):346-352.
Interpretive Summary: Influenza type A virus (IAV) can cause respiratory disease in people and other mammals (including horses, dogs, and pigs). In birds, IAV affects the intestinal tract with the severity of clinical disease dependent on specific characteristics of the virus, and the susceptibility of the avian species. Avian IAV can be divided into 16 different subtypes based on the hemagglutinin (HA) gene (HA1-HA16). The subtypes can be divided into two categories based on how sick chickens become following infection. Low pathogenic influenza viruses (LPAI) can infect chickens, but cause minimal disease. In contrast, high pathogenic influenza viruses (HPAI) kill most or all infected chickens. Although poultry are very susceptible to HPAI, many wild bird species infected with HPAI or LPAI are relatively resistant to disease making them ideal IAV carriers. The potential for LPAI to mutate into HPAI, and that some IAV subtypes can move or jump between species, further complicates the ecology and control of IAV. Swine have been described as an IAV mixing vessel because pigs can be infected with both avian and mammalian IAV. This can lead to a mixing of avian and mammalian genes which produces novel IAVs that could cause disease in swine, and possibly transfer to humans. The potential for swine to become infected with common avian IAV has been a concern and was the focus of this study. Following experimental inoculation, swine were susceptible to H5 and H7 LPAI viruses, but only minimal disease was detected and the experimentally-infected pigs did not transmit virus to others. In summary, there appears to be minimal health risk to swine exposed to common LPAI subtypes.
Technical Abstract: The ability of pigs to become infected with low pathogenic avian influenza (LPAI) viruses from an avian reservoir, and then generate mammalian adaptable influenza A viruses (IAVs) 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. The goal of this study was to assess susceptibility of pigs to LPAI viruses found within the United States, and their transmission potential to direct contacts. Pigs were inoculated with one of ten H5 or H7 LPAI selected from 7 different bird species to test the infectivity, virulence, pathogenesis, and potential to transmit virus to contact pigs for each LPAI strain. Nasal swabs and bronchoalveolar lavage fluid were collected from pigs post challenge to test for virus using RRT-PCR. Pigs were susceptible to infection with each of the LPAI viruses, however, 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 inoculated group were RRT-PCR positive in the lower respiratory tract (RRT-PCR positive lung lavage), 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. None of the LPAI viruses transmitted to contact pigs. Although LPAI strains from various bird populations within the United States were capable of infecting pigs, 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.