INTERACTION BETWEEN CHICKEN ANEMIA VIRUS AND LIVE NEWCASTLE-DISEASE VACCINE

Three groups of 150 SPF chickens were spray-vaccinated with live Newcastle disease La Sota-type vaccine (clone 30) at one day of age, and another three groups were NDV spray-vaccinated at 10 days of age. In each of the two series of NDV-vaccinated groups, one group also received at day-old 10(5) TCID50 of chicken anaemia virus (CAV) also and another group 10(5) TCID50 of CAV plus a low dose of virulent Marek's disease virus (MDV). After one week, chickens of the groups which had been NDV-vaccinated and CAV-infected at day-old, with or without MDV, showed severe respiratory distress, conjunctivitis, drooping wings and ruffled feathers. After two weeks, wet and inflamed eyes were observed. After three weeks the respiratory problems were overcome, but the entire group showed retarded growth as compared with the group which had received NDV vaccine only. The 'respiratory sounds' were milder in the chickens NDV-vaccinated at 10 days of age, about 10% of the chickens showing retarded growth. Mortality in CAV-infected chickens which had received NDV vaccine at day-old was above 30% at 4 weeks of age, and between 15 and 20% when NDV had been administered at the age of 10 days, and was 5% in the two NDC vaccine control groups. Decreased haematocrit levels were measured in all four CAV-infected groups at 14 days of age. In serum samples collected for 6 weeks at weekly intervals from chickens of the six groups, no differences were observed between HI antibody titres against NDV virus. Thus, dual infection with CAV and live NDV vaccine did not impair the humoral immune response against attenuated Newcastle disease vaccine.