Pathogenicity and antigenicity of eleven isolates of chicken anaemia agent (CAA)

Pathogenicity for chicks of 11 isolates of chicken anaemia agent (CAA) isolated in Japan was examined. Each strain produced aplastic anaemia in 100% of chicks when inoculated at 1 day of age with mortalities ranging from 20 to 90%. Incidence of anaemia in chicks inoculated at 7 days of age varied from 0 to 87.5% according to the isolates, but no chick died. The susceptibility of chicks at various ages against the G1 (Gifu-1) and A2 strains was compared. Both strains produced anaemia in 100% of the chicks when inoculated at 1, 2, 3 or 4 days of age. Half of the chicks inoculated with the A2 strain at 8 days of age showed anaemia, but none of those inoculated with the G1 strain did. No chick showed anaemia from either strain when inoculated at 14 days of age. The antigenicities of the isolates were compared by cross neutralisation and indirect immunofluorescent antibody methods. No serological distinction was recognised among the isolates.