[Isolation of an avirulent strain of the chicken herpes virus type B]

Experiments were carried out to isolate type 'B' of the chicken Herpes virus on a farm for stock layers with a low level of losses due to Marek's disease. Seven virus isolates were obtained from 3-4-month-old White Leghorn poults via direct kidney cell cultures. One of them, named strain C-80, was studied in chick embryo fibroblast cultures, and egg cultures (Büllow's test) as well as biochemically, serologically, and through the electron microscope. Results made it reasonable to identify it as a chicken Herpes virus type 'B'. In vivo experiments with strain C-80 inoculated in day-old chicks at the rate of 15 x 10(3) PFU showed that it did not cause gross and microlesions in the nervous system and the parenchymal organs in the course of 18 weeks of observation. The immunogenic properties of strain C-80 were studied in 2250 day-old White Plymouth Rock chicks inoculated at the rate of 1360 PFU, kept in an infected environment together with as many as 4500 control birds immunized three times with a vaccine (obtained from a turkey Herpes virus) at 1500 PFU. Twenty-four weeks later the losses due to Marek's disease were 3.4 per cent in the test group, and 7.2 per cent in the control one. It is believed that strain C-80 is appropriate for the production of a vaccine against Marek's diseases--Rispens type. Further studies are being performed on the antigenic composition and the immunogenic properties as well as series of in vivo passages with regard to reversibility.