Location:2011 Annual Report
1a. Objectives (from AD-416)
Characterize avian influenza viruses circulating in Vietnam, select representative isolates, and perform vaccine efficacy studies with these isolates. The goal is to provide scientific data to allow the determination of the best vaccine and vaccination protocols to be used as part of the vaccine program to be used in the country. The specific objectives are: 1) Sequence analysis of recent avian influenza (AI) viruses from Vietnam to identify what is circulating in the country; 2) Antigenic analysis of selected viruses to provide information for vaccine selection; 3) Vaccine efficacy studies using available commercial vaccines with representative strains to identify vaccines that provide clinical protection and reduce viral shedding to the greatest degree in chickens and ducks.; 4) Studies evaluating the effects of maternal immunity on vaccination. This is an important issue, especially in ducks, since vaccination at the hatchery would be an ideal solution for increasing vaccination of all birds, as opposed to the twice yearly campaigns that leave large gaps in coverage.
1b. Approach (from AD-416)
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 effect of maternal immunity on the response to vaccination in chickens and ducks will be evaluated by passive antibody transfer studies.
3. Progress Report
This research is related to inhousoe objective 2: Develop vaccines that effectively stop outbreaks, allow differentiation from natural infection, and can be administered in a cost effective manner. The pathogenicity of H5N1 highly pathogenic avian influenza (HPAI) Vietnam viruses from three different hemagglutinin (HA) clades (1, 2.3.4, and 7) was evaluated in chickens and ducks. HA clade 7 viruses have been reported to be less pathogenic in birds in Vietnam, and was in fact less pathogenic in our studies than the other two viruses from clades 1 and 2.3.4, which were very virulent for both chickens and ducks, as previously studied viruses from Vietnam. The HA clade 7 virus did not produce disease in ducks, however did produce disease in chickens, which could be a concern because the ducks could be healthy carriers and spread these viruses among other poultry species. Vaccine efficacy studies using available commercial vaccines with representative strains help identify vaccines that provide clinical protection and reduce viral shedding to the greatest degree in chickens and ducks. The protection conferred by two commercial inactivated vaccines currently used in Vietnam (Re-1 and Re-5) to protected ducks against H5N1 HPAI was also evaluated. Both vaccines conferred good protection against mortality to ducks challenged with two recent H5N1 HPAI viruses from 2010.