GENETIC SUSCEPTIBILITY TO MAREKS-DISEASE VIRUS OF LOCAL CHICKENS IN TAIWAN

Marek's disease is a contagious disease in chickens caused by Marek's disease virus (MDV) infection. Invasion of very virulent MDV (vvMDV) w as considered to be a major cause of vaccine break, resulting in a lar ge economic loss in the poultry industry. Two strains of the vvMDV (st rains LTB-1 and LTS-1) have been reported in Taiwan, causing early mor tality and formation of lymphoid tumors in broilers and layers. In thi s study we report the susceptibility of local chickens in Taiwan to in oculation with strains LTB-1 and LTS-I at 1 day of age. Five lines of Taiwanese local chickens (lines B, D, L2, KM, and BG) were used to com pare the susceptibility to vvMDV. The chicks were inoculated via intra peritoneal route at 1 day of age. All MDV-inoculated chickens showed a trophy of various lymphoid organs. protection rests were also conducte d in local chickens, using vaccine of herpesvirus of turkey (HVT) at 1 day of age followed by vvMDV challenge at 10 days of age. Among the v accinated chickens, 0-20.0% showed early mortality, and tumor occurren ces in visceral organs and in peripheral nerves were 66.7%-100% and 0- 27.2%, respectively. From these results, it could be concluded that lo cal chickens in Taiwan have different susceptibilities to vvMDVs. Furt hermore, vaccination with HVT showed no protective effect against Taiw anese vvMDV isolate challenge in this experiment.