The epizootiology of Marek's disease. 3. The interrelationship of virus pathogenicity, antibody and the incidence of Marek's disease.
Approximately 1000 day-old White Leghorn chickens were distributed into 5 pens in a brooder house and exposed to natural infection with Marek's disease virus (MDV). Observations were made on the inter-relationship between strains of MDV infecting the chickens, precipitating antibody, incidence of Marek's disease (MD), body weight, egg production, feed consumption and stress through movement. A wide variation in mortality from MD occurred between similar pens in the same brooding house. It was found that the sequence of infection and frequency of isolation of viruses of differing virulence varied from pen to pen and the mortality from MD was closely associated with these differences. Pen location did not affect any of the production parameters examined other than hen housed egg production. Infection with MDV was found to persist throughout the life of the chicken, however, the incidence of viraemia at 72 weeks of age was 60% of that at 10 weeks of age. Precipitating antibody was detected in the sera of most older chickens; however, no apparent differences could be observed in the incidence of precipitating antibody in chickens dying and surviving MDV infection when examined individually or on a pen basis. Chickens dying from MD tended to have an earlier and higher level of viraemia than those surviving infection with MDV. Movement of chickens to a rearing house at 8 weeks of age had little effect on the incidence of MD. It was concluded that this study confirmed the association between a widespread incidence of apathogenic virus and a low incidence of MD, and that the presence of such virus provided a protection against later challenge with pathogenic virus.
Jackson
C A
CA
Houghton Poultry Research Station, Houghton, Huntingdon, England.
Biggs
P M
PM
Bell
R A
RA
Lancaster
F M
FM
Milne
B S
BS