Submitted to: Avian Diseases
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/13/1995
Publication Date: N/A
Citation: N/A Interpretive Summary: Marek's disease causes extensive losses in broiler and layer chickens. This disease is controlled by vaccines, but current vaccines are not fully effective. Also, the best of the current vaccines contain live cells and must be stored at very low temperatures in expensive containers. This work describes the further characterization of vaccines made by recombinant DNA technology from fowlpox virus. The fowlpox virus can be engineered to express genes from Marek's disease virus and thus become a vaccine. Although several genes from Marek's disease were tested in fowlpox virus, only one, glycoprotein B, caused chickens with antibodies to resist the disease. Furthermore, glycoprotein B from a certain group of serotype 1 Marek's disease virus was more protective than those from other groups. Finally, the protection produced by the vaccine composed of fowlpox virus with glycoprotein B was increased when this vaccine was used in combination nwith another, older vaccine for Marek's disease called turkey herpesvirus. The protection by the combination was greater than the protection by either component alone. The amount of the protection by the new combination vaccine was roughly similar to that of existing vaccines and suggests that this type of vaccine may ultimately help the poultry industry in their efforts to provide effective control for Marek's disease.
Technical Abstract: Recombinant fowlpox viruses (rFPV) were constructed to express genes from serotype 1 Marek's disease virus (MDV) coding for glycoproteins gB1, gC, and gD and tegument proteins UL47 and UL48, as well as genes from serotype 2 and 3 MDV coding for glycoprotein B (gB2 and gB3). These rFPVs, alone and in various combinations, including combinations of FPV/gBs with turkey herpesvirus (HVT), were evaluated for ability to protect maternal antibody positive (ab+) and negative (ab-) chickens against challenge with highly virulent MDV isolates. The protective efficacy was also compared to that of prototype Marek's disease (MD) vaccines. No protection was induced in ab+ chickens by rFPV expressing gC, gD, UL47, or UL48. In contrast, the rFPV/gB1 construct protected about 23% of ab+ chickens against MDV challenge compared to 26% for cell-associated HVT. Levels of protection by rFPV/gBs of different MDV serotypes was highest for gB1, intermediate for gB2, and lowest for gB3. When rFPV/gB1 was combined with cell-associated HVT, protection was enhanced by an average of 138% compared to the best component monovalent vaccine and the mean level of protection was 59% compared to 67% for the HVT + SB-1 bivalent vaccine. Relatively high protection (50%) and enhancement (200%) was also observed between rFPV/gB1 and cell-free HVT. Levels of protection by rFPV/gB1 alone or by bivalent rFPV/gB1 + cell-associated HVT were similar to those of conventional cell-associated MD vaccines. However, the bivalent rFPV/gB1 + cell-free HVT vaccine was clearly more protective than cell-free HVT alone and, thus, may be the most protective, entirely cell-free MD vaccine thusfar described.