Submitted to: Virology Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/19/2010
Publication Date: 11/19/2010
Publication URL: http://handle.nal.usda.gov/10113/61390
Citation: Spackman, E., Gelb, J., Preskenis, L., Ladman, B., Pope, C., Pantin Jackwood, M.J., Mckinley, E.T. 2010. The pathogenesis of low pathogenicity H7 avian influenza viruses in chickens, ducks and turkeys. Virology Journal. 7:331. Interpretive Summary: Avian influenza virus (AIV) of the H7 subtype typically causes mild disease in poultry, but it is not known how individual isolates affect different avian species. H7 AIV has also been a prominent type of AIV in the Northeast U.S., where live bird markets have served as a reservoir since 1994. The H7 strain of AIV has caused economically significant outbreaks in poultry in the Northeast and Mid-Atlantic U.S. numerous times since then. In order to determine if the ability of this strain to cause disease has changed since it emerged in 1994 12 isolates were evaluated for their ability to cause disease in chickens, turkeys and ducks. Eight of the isolates are from the live bird markets or related outbreaks in poultry and 4 isolates are from wild birds from the different regions of the U.S. This study showed that chickens and ducks rarely got sick at all, and when they did get sick it was with mild respiratory signs (e.g. sneezing, swollen sinuses). Turkeys got sick with most of the isolates and experienced more respiratory disease. Turkeys also shed virus as higher levels than chickens or ducks. The implications of the study are that turkeys are more susceptible to these strains and that virus control programs need to take into account that virus will spread more rapidly in turkeys than in the other species. Importantly, infection of turkeys will be easier to detect since they get sick and secrete more virus. Virus spread among chickens and ducks will be slower. Elucidating these species associated differences are crucial to developing effective control programs for different types of poultry.
Technical Abstract: Avian influenza (AI) viruses infect numerous avian species, and low pathogenicity (LP) AI viruses of the H7 subtype are typically reported to produce mild or subclinical infections in both wild aquatic birds and domestic poultry. However relatively little work has been done to compare LPAI viruses from different avian species for their ability to cause disease in white leghorn chickens, Pekin ducks and broad breasted white turkeys under the same conditions. In this study twelve H7 LPAI virus isolates from North America were each evaluated for their comparative pathogenesis in chickens, ducks, and turkeys. All 12 isolates were able to infect all three species at a dose of 106 50% egg infectious doses based on seroconversion. The severity of disease varied among isolate and species combinations, but there was a consistent trend for clinical disease to be most severe in turkeys where all 12 isolates induced disease and 9 viruses caused mortality. Turkeys also shed virus by the oral and cloacal routes at significantly higher titers than either ducks or chickens at numerous time points. Only 3 isolates induced observable clinical disease in ducks and only 6 isolates induced disease in chickens, which was generally very mild and no mortality was observed. Full genome sequence was completed for all 12 isolates and some isolates did have features consistent with adaptation to poultry (e.g. NA stalk deletions), however none correlated with disease severity. The data suggests that turkeys are more susceptible to clinical disease from H7 LPAI viruses that either chickens or ducks. However the severity of disease and degree of virus shed was not clearly correlated with any isolate or group of isolates, but relied on specific species and isolate combinations.