Combating highly pathogenic avian influenza: Novel vaccination strategies using recombinant live avian viral vaccine vectors

Combating highly pathogenic avian influenza: Novel vaccination strategies using recombinant live avian viral vaccine vectors. Avian influenza (AI) viruses (or the 'avian flu' as it is commonly called) naturally exist in wild birds such as waterfowl and shore birds where the virus is highly diverse and generally not pathogenic. These low pathogenic avian influenza (LPAI) viruses routinely cross over from the wild-bird reservoir and infect domestic poultry, frequently becoming highly pathogenic viruses (HPAI), which are extremely dangerous to commercial poultry and are occasionally fatal to humans. In the recent outbreaks of HPAI viruses of H5 and H7 subtypes in many parts of the world, including the EU, more than 200 million domestic poultry have either died or been culled, impecting huge socio-economic costs. The current epidemic of HPAI H5N1 originating from south East Asia and recently transmitted over long distances via migratory birds is unprecedented. The magnitude of risk that migratory birds are posing to the United Kingdom and other EU countries is not clear, however, there is growing evidence (recent death of migratory swan by H5N1 in Fife, Scotland) suggesting that the prevention and control of AI disease outbreak in poultry and other captive birds will be a major challenge for many years to come. To date the main strategy for controlling HPAI in domestic poultry in UK and in some other countries has been eradication of the virus by large scale culling of infected and contact flocks. However, the current world-wide epidemic has severely affected the economies of developed as well as developing countries. Therefore, for ethical, ecological and economic reasons, it is no longer considered acceptable to control and eradicate AI mainly by the mass killing of animals. As a result the European Parliament, the World Organization for Animal Health (OIE) and Food and Agriculture Organization (FAO) have allowed not only emergency vaccination, following disease outbreak, but also preventive vaccination as an additional tools for the control of AI. Currently, the available AI inactivated vaccines are produced in embryonated eggs and have several disadvantages. We propose to develop novel vaccines using some of the state of the art biotechnological tools. These will allow the administration of live viral vaccines as single injection either at hatch or into eggs before they hatch (in ovo vaccination). These new improved vaccines will be safe, effective and economical, and above all protect the commercial poultry and other domestic birds from disease and dissemination of AI viruses into the environment, consequently preventing AI virus spread, averting the looming global pandemic threat.

We propose to use novel approaches for AI vaccination using recombinant herpesvirus of turkey (HVT) and avian infectious bronchitis virus (IBV) as vaccine vectors that express protective haemagglutinin (HA) and neuraminidase (NA) antigens of avian influenza virus. Since these vaccine constructs will express only selected AI antigen, vaccinated birds can be unambiguously differentiated from those infected with the field virus. These virus vectors have several distinct advantages: (1) they are extensively used as live virus vaccines. (2) they induce immunity following in ovo vaccine application. (3) it is relatively easy to generate new vaccines from the specific field isolates. Recombinant HVT and IBV vectors will be generated by cloning HA and NA genes (the multiple basic amino acids at the HA1 & HA2 cleavage sites will be deleted) from the HPAI viruses, [A/os/Italy 984/00 (H7N1) and A/ty/Turkey/1/05 (H5N1)], into the HVT and IBV genomes using in house derived reverse genetics systems. We plan to generate a panel of recombinant viruses (1) HVT/H7/N1 (2) HVT/H5/N1 (3) IBV/H7 (4) IBV/H5 (5) IBV/N1 for use as potential vaccine candidates. The recombinant viruses will be evaluated for expression of the AI-derived HA and NA genes in cell culture and in ovo. Selected viruses will be used in homologous virus challenge studies in chickens for comparison with commercially available inactivated vaccines. The protection parameters of the vaccines candidates will be assessed by comparing the immune responses, mortality rates, morbidity and shedding of AI virus from the challenged birds. The data obtained from these experiments will enable us to select the most effective vaccine candidate providing protection against challenge with HPAI AI virus and decrease in excretion of the AI virus. Ultimately, we anticipate that these novel AI vaccines will be used in the eradication of AI by the control of disease and reduction of viral load in the environment.