| Avian influenza (AI) is a major disease of domesticated poultry. Effective methods for the prevention and control of AI are presently not available. During this dissertation research, we tested the hypothesis that a recombinant herpes virus of turkeys (HVT) expressing the AI virus nucleoprotein (NP) gene will engender a cross-protective immune response against the Al virus. To test this hypothesis, studies were designed to develop, characterize and evaluate a live recombinant vaccine for the prevention of Al infection in poultry. The (NP) gene was inserted into the HVT genome through the process of in vivo homologous recombination. Southern blot hybridization confirmed the specific integration of foreign DNA, further validated by PCR and nucleotide sequence analyses. The expression of (NP) from the recombinant HVT (rHVT-NP) was evaluated by immunofluorescence staining and western blot analysis.; Next, the rHVT-NP virus construct was evaluated as a, live vaccine for protection of SPF chickens against challenge with a mild nephropathogenic strain of AL The results of these investigations show that the pathologic lesions were significantly attenuated in rHVT-NP vaccinated chickens as compared with control groups. Kidneys were significantly (p < 0.05) less affected in chickens that were vaccinated with rHVT-NP as compared with the control groups on days 5 and 7 post-challenge. The spleen and bursa also showed significantly (p < 0.05) less severe gross lesions relative to the control groups at 5 and 11 days post-challenge, respectively. Consistent with these findings, significantly lower proportion of birds vaccinated with rHVT-NP were virus positive in various organs. For example, bursal tissues of the rHVT-NP immunized group showed significantly lower proportion (p < 0.05) of chicks positive for AI as compared with the controls. They also showed a marginally significant (p = 0.057) reduction in the proportion of birds with the Al virus in kidney tissues as compared with the controls.; Together, the results of this dissertation research show that rHVT-NP has the potential of providing partial broad spectrum protection against mildly pathogenic AI strains. Since low and mildly pathogenic AI is an ongoing problem, a vaccine capable of providing broad-spectrum immunity is likely to reduce economic losses associated with AI outbreaks. |
