|Torchetti, Mia - Diagnostic Virology Laboratory/ National Veterinary Services Laboratories|
Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 8/4/2013
Publication Date: 9/4/2013
Citation: Pantin Jackwood, M.J., Miller, P.J., Spackman, E., Swayne, D.E., Torchetti, M., Susta, L., Suarez, D.L. 2013. Pathogenesis and transmission of H7N9 influenza virus in poultry [abstract]. Abstracts for the Options for the Control of Influenza VIII Meeting, Cape Town, South Africa, September 4-10, 2013. p.6.
Technical Abstract: Background: The recent and ongoing outbreak of H7N9 influenza in China has resulted in many human cases with a high fatality rate. Poultry have been suspected as the source of infection based on sequence analysis and virus isolations from live bird markets; however it’s not clear which species of birds are most likely to be infected and shedding sufficient levels of virus to infect humans. In these studies we evaluated the potential role of different avian species in the epidemiology of H7N9 influenza, information that is vital for effective disease control. Materials and Methods: The pathogenesis of the human isolate A/Anhui/1/2013(H7N9) was determined in White Leghorn chickens (egg layer type), turkeys, Japanese quail, pigeons, Pekin ducks, Mallard ducks, Muscovy ducks, and Embden geese, by intranasal inoculation with 106 mean embryo infective doses (EID50) of the virus. In addition, three doses of virus was administered to groups of quail, pigeons and Pekin ducks (102, 104, or 106 EID50) and uninfected birds were added to each dose group to determine the transmission potential of the virus. Oropharyngeal (OP) and cloacal (C) swabs were collected at 2, 4, 6, 8, and 10 days post inoculation (dpi) from all birds to examine for virus shedding. Viruses recovered from infected birds were also sequenced. Results: Inoculation of the avian species examined with the H7N9 virus resulted in infection of all species but no clinical signs. Virus shedding in quail, chickens, turkeys, and Muscovy ducks was much higher and prolonged (= 10 dpi) than in the rest of the species (= 6 dpi). Quail effectively transmitted the virus to direct contacts but pigeons and Pekin ducks did not. In all species, virus was detected at much higher levels from OP swabs when compared to C swabs. The HA gene and part of the PB2 gene from selected virus positive OP swabs collected from chickens and quail were sequenced to examine for changes in the virus after passage in these species. All 8 samples examined had lysine at position 627 of the PB2 gene, similar to the parent human isolate. However, 3 amino acid differences were observed in the HA compared to A/Anhui/1/2013: N123D, N149D, and L217Q. The inoculum used in these experiments already contained D at position 123 and 149, but maintained the L at position 217. Four different combinations were observed in the infected birds indicating that most likely the inoculum had virus subpopulations that were selected after passage in birds. Conclusion: The H7N9 virus outbreak clearly has an important poultry component based on the sequence analysis and epidemiology of the virus, and these experimental studies corroborate that poultry species are important reservoirs of the virus. The high viral shedding from chickens, turkeys, quail and Muscovy ducks create a likely source of infection for humans. The high levels of viral replication in the upper respiratory tract and much lower levels in the intestinal tract is characteristic of poultry-adapted influenza viruses, and consequentially testing of bird species should preferentially be conducted with OP swabs for best sensitivity. As the H7N9 virus continues to circulate in poultry changes, including both mutations and possible reassortment with other influenza viruses, are expected to occur.