Increased susceptibility of leukemia-infected chickens to Marek's disease.

Intramuscular (i.m.) injection of RAV-49 into 1--3 day-old chickens infected with Marek's disease herpes virus (MDHV) by contact led to exceedingly high rate of Marek's disease (MD) incidence. According to the data obtained in three experiments 52 out of 108 (48.1%) chickens fell ill in this group. While in the group uninfected with RAV-49 but contactly infected with MDV-Kekava there were only 11 out of 102, (10.7%) incidences. Simultaneous inoculations of RAV-49 and MDV had no effect on MD morbidity. Increased susceptibility of i.m. RAV-49-infected and contactly MDV-infected chickens to MD was abolished by simultaneous inoculation of RAV-49 and herpes virus of turkeys (HVT).