Submitted to: Society for Tropical Veterinary Medicine
Publication Type: Abstract Only
Publication Acceptance Date: 6/13/2005
Publication Date: 6/27/2005
Citation: Bublot, M., Pritchard, N., Swayne, D.E., Selleck, P., Audonnet, J.C., Mickle, T.R. 2005. Development and use of fowl pox vectored vaccines for avian influenza. In: Proceedings of the Society for Tropical Veterinary Medicine. 8th Biennial Conference, June 30-July 1, 2005, Hanoi, Vietnam. 2005 CD-ROM.
Technical Abstract: Inactivated vaccines are the most widely used vaccines in avian influenza (AI) controlled vaccination programs but there is currently no serology test commercially available that can differentiate infected from vaccinated birds (DIVA test). TROVAC AI H5, a fowlpox recombinant expressing the hemagglutinin of an H5 isolate, has received a conditional license in US in 1998 and is used since then in Mexico, Guatemala and El Salvador. More than one billion doses of TROVAC AI H5 have been used so far with no reported adverse reactions. This vaccine protects chickens against mortality and morbidity and significantly decreases shedding after challenge with a wide panel of H5-subtype AI strains. It was recently found to provide 100% protection against mortality/morbidity induced by challenge with recent Asian highly pathogenic H5N1 isolates and reduced challenge virus shedding from respiratory and gastrointestinal tracts by 2.5-4.5log10 of virus. TROVAC AI H5 is fully active in maternal antibody positive 1 day old broiler chickens from breeder hens vaccinated with killed AI and/or fowlpox. However, after placement of chickens in the field, fowlpox vaccination or natural infection interferes with TROVAC AI-induced immunity. Vaccinated birds with TROVAC AI H5 will develop antibodies detectable by the HI test using the appropriate antigen. However, they will not produce antibodies against matrix/nucleoprotein detectable by common serological tests such as AGP and ELISA, which therefore can be used as DIVA tests. Another advantage of TROVAC AI H5 over inactivated vaccine is that it is fully efficacious when administered once in one day-old bird, and it is compatible with Marek's disease vaccination. Trovac AI H5 provides protective immunity for at least 20 weeks. A priming with fowlpox recombinant followed by a boost with an inactivated regimen may also be used to get optimal immunity. These features make TROVAC AI H5 the ideal vaccine to be used in hatcheries. The fowlpox vector technology can be used for the rapid production of an emergency vaccine. Once the sequence of the Asian H5N1 HA gene was available, a fowlpox vector expressing a modified synthetic HA gene was generated in less than four months without having to manipulate the HPAI virus. Fowlpox recombinant viruses expressing the hemagglutinin of H7 avian influenza isolates belonging to each of the three lineages of H7 subtype (Eurasian, American and Australian) were also generated. A study comparing the efficacy of these 3 vaccine candidates against an Eurasian HPAI H7N1 challenge has shown that only the fowlpox recombinant expressing the Eurasian HA type provided sufficient protection against the Eurasian HPAI challenge. This finding contrasts with the wide protection provided by AI H5 fowpox recombinant.