An improved method for the isolation and identification of bluetongue virus by intravenous inoculation of embryonating chicken eggs

Abstract

Twenty-eight samples from suspected field cases of bluetongue were titrated simultaneously in embryonating chicken eggs by the intravenous and by the yolk sac routes of inoculation. Type 16 virus was isolated from all the 28 samples inoculated intravenously. When they were inoculated into the yolk sac 19 samples tested were positive and 9 were negative. The highest titre of the virus in the intravenously inoculated eggs was 10 5·0 chicken embryo LD 50 per 0·1 ml. The highest titre in the yolk sac was 10 1·7 C.E. LD 50 0·1 ml . Those samples which had a titre of 10 2·7 C.E. LD 50 0·1 ml . or lower after intravenous inoculation were negative by the yolk sac method. When the first egg passages were titrated simultaneously by the intravenous and yolk sac routes the difference between the LD 50 titres of the virus in the intravenous and yolk sac inoculated eggs respectively was 3 logs. Embryo mortality following the intravenous inoculation was one hundred per cent. in the first egg passage. The time required for isolation and typing of the virus when this route was used was 10 days. When the yolk sac was used the mortality did not reach one hundred per cent. until the sixth or seventh consecutive egg passage. The time required for isolation and typing of the virus when this route was employed was 7 to 8 weeks.