EFFECT OF MULTIPLE CELL-CULTURE PASSAGES ON THE BIOLOGICAL BEHAVIOR OF CHICKEN ANEMIA VIRUS

The Cux-1 isolate of chicken anaemia virus (CAV) was passaged over 320 times in Marek's disease virus transformed chicken lymphoblastoid (MD CC-MSB1) cells. Comparison of the infectivity titres of virus pools de rived from viruses that had received 0 (P0), 49 (P49), 170 (P170) and 320 (P320) passages in our laboratory indicated that the yields of inf ectious virus increased over 100-fold with passage number from P0 to P 170. P320 exhibited unusual cell culture growth characteristics in tha t, unlike its lower passage counterparts, virus-specific immunofluores cence (IF) and cytopathic effect were detected at very low levels at 2 days post infection, with an additional passage of infected cells int o fresh medium being required to produce high levels of infectious vir us. Experimental infection of 1-day-old SPF chicks showed that P170 an d P320 were substantially attenuated compared to P49 and a pathogenic, low-passage isolate used as control. When assessed by the indirect IF test, infection of 1-day-old chicks with the P49 and P170 isolates el icited similar levels of CAV-specific antibody to those elicited by in fection with the pathogenic, low-passage virus and higher than those e licited by infection with the P320 isolate. Experimental infection of 5-week-old chicks indicated that the attenuated P170 and P320 isolates invoked similar CAV-specific antibody levels to those invoked by the pathogenic P49 and control isolates.