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Characterize recent isolates of avian influenza virus from Vietnam: 1) Sequencing of strains of avian influenza virus in Vietnam to identify what viruses are circulating in Vietnam; 2) Antigenic analysis of selected viruses to provide information for vaccine selection and 3) Modifying high pathogenicity avian influenza (HPAI) viruses using reverse genetics to low pathogenic viruses so they can be handled at BSL2 (this requires animal testing to assure that the viruses are non-pathogenic).
APPROACH: Representative isolates will be sent from the National Center of Veterinary Diagnosis in Hanoi. The viruses will be fully sequenced and based on the phylogenetic analysis, isolates will be selected for biological and antigenic comparison. The hemagglutinin gene will be cloned and placed in either deoxyribonucleic acid (DNA) vaccine vectors or in a reverse genetics constructed virus and inoculated in chickens to get immune serum that will be compared with H5 standards by hemagglutination inhibition analysis. This information will provide a prediction of antigenic differences among the Vietnamese isolates. Additionally, selected isolates will be used for biological assessment in ducks for pathogenic potential. Using the sequence, antigenic and biological information, two or more isolates will be selected as challenge strains for vaccine efficacy studies. Available commercial vaccines and autogenous vaccines made from the challenge viruses will be used to vaccinate both chickens and ducks. After 3 weeks the antibody response will be measured and the birds challenged with the Vietnamese highly pathogenic avian influenza viruses. The vaccine efficacy will be evaluated by measuring morbidity, mortality, and virus shedding. The serologic response before and after challenge will also be evaluated using both homologous and heterologous antigen to evaluate the immune response in conjunction with the challenge data. The results of these experiments will be used to advise the FAS, APHIS, and Vietnamese officials on whether available vaccines are still providing adequate levels of protection from viruses circulating in their country.