Protecting chickens against Marek's disease under laboratory conditions by the administration of Marvak, a Czechoslovak produced vaccine and vaccine imported from East Germany

Laboratory trials were conducted to compare the efficiency of two vaccines against Marek's disease (MD) on the basis of the dynamics of post-vaccination viraemia and by means of a challenge test. Two groups of the HX-SL hybrid layers, each containing 40 birds, were vaccinated with the MARVAK cellular vaccine manufactured in Czechoslovakia (100 PFU per chick) or with the Insel Riems vaccine manufactured in the GDR (1000 PFU per chick). In weekly intervals, half the birds of each group were tested for post-vaccination viraemia and the other half, including 20 non-vaccinated birds, were infected by contact with the pathogenic virus of MD from the second day of age. The viraemia in the birds vaccinated with MARVAK culminated in the third week of age when it reached the average value of 25 PFU/10(7) leucocytes; later on, by the eighth week of age, it decreased to 0.62 PFU/10(7) leucocytes. The maximum number of viraemic chicks was found in the third and fourth week of age (80%); on an average it ranged from 60%. The average viraemia in the chickens treated with the vaccine from the GDR ranged from 1.6 to 3.6 PFU/10(7) leucocytes in the second to eighth week of age. A 100% positivity of the tested birds was found in the sixth week of age; it ranged around 70% on an average. In all the challenged groups of birds the precipitation antigen of Marek's disease was detected in feather follicles already 14 weeks from contact infection.(ABSTRACT TRUNCATED AT 250 WORDS)