PATHOGENICITY OF CHICKEN ANEMIA VIRUS (ISOLATE-10343) FOR YOUNG AND OLDER CHICKENS

One-day-old chicks, inoculated intramuscularly (i.m.) with the chicken anaemia virus (CAV) isolate 10343, showed depression of body weight g ain and anaemia, particularly between days 14 and 21 post-inoculation (p.i.). The weights of thymus and bursa were substantially reduced com pared to controls at days 14 and 21 p.i. The histological lesions dete cted in thymus, bursa, spleen and liver were similar in frequency at d ays 14 and 21 p.i. Eosinophilic intranuclear inclusion bodies, lymphoc yte depletion, and focal necrosis were detected in the thymus, spleen, bursa and liver of more than 50% of the inoculated chicks at days 14 and 21 p.i. Focal necrosis and vacuolar degeneration in the liver, as well as apoptosis in different organs were more evident at days 14 and 21 p.i. Ten-week-old broiler breeders, inoculated i.m, with isolate 1 0343 showed pathological changes that were less severe than the change s shown by 1-day-old chicks. No anaemia could be detected in this grou p. However, severe thymus atrophy, and histological lesions in bursa, spleen, and liver, were also evident at days 14 and 21 p.i. in some of the inoculated birds. Viral detection by immunofluorescence using a m onoclonal antibody revealed a wide distribution of the CAV isolate. CA V antigen was detected until day 21 p.i, in thymus, spleen, bursa and liver. According to the severity of the lesions shown by 1-day-old chi cks, the length of the period in which CAV antigen could be detected i n tissues, and the fact that CAV isolate 10343 was capable of inducing disease in 10-week-old chickens, it seems that this CAV isolate may b e particularly virulent.