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United States Department of Agriculture

Agricultural Research Service

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2012 Annual Report

1a. Objectives (from AD-416):
To assess the pathogenicity and infectivity of influenza vaccine reassortants and their respective parental wild type viruses for chickens. This includes: 1) determining in vivo pathotype of wild type and reassortant vaccine candidate strains in chickens, and 2) assess in vivo infectivity and pathogenicity in chickens using simulated natural route of exposure (intranasal).

1b. Approach (from AD-416):
The challenge studies will be conducted in BSL-3 Enhanced facilities. Four vaccine candidates will be tested per year using the below study design: 1) conducting in vivo pathotype of virus strains by intravenous testing in chickens using intravenous pathogenicity index, and 2) conducting in vivo infectivity and pathogenicity testing by intranasal inoculation of chickens and determining the ability for the virus to grow as evident by virus shedding for oropharynx and cloaca, and ability to cause disease by assessing clinical features, serological reaction and histopathological changes to various organs.

3. Progress Report:
This project is related to objective 5 of this in-house project: Develop new vaccine platforms designed to control and prevent avian influenza virus outbreaks. For FY2012, avian influenza virus strains previously attenuated by genetic engineering or reverse genetics (rg) by CDC were inoculated into chickens by intranasal and intravenous routes, aiming to test if the attenuation process was successful and if the vaccine viruses would not have a negative impact on animal agriculture. One rg candidate H9N2 vaccine virus and its parent H9N2 low pathogenicity avian influenza virus were tested. The rg vaccine virus was attenuated in chickens based on the inability to cause clinical signs or death in chickens after intravenous inoculation while the parent H9N2 virus caused mild respiratory disease. However both viruses were able to infect the birds and both viruses were shed, but only at low levels for the rg vaccine virus. Both viruses induced specific antibodies detected by agar gel immunodiffusion (AGID) in all the wild type virus intranasal inoculated birds, and 4 out of 8 for the recombinant vaccine inoculated chickens. The rg vaccine virus would have negligible negative impact on animal agriculture and can be pursued as potential human pandemic influenza vaccine strain.

4. Accomplishments

Last Modified: 10/19/2017
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