Persistent infection with chicken anaemia virus and some effects of highly virulent infectious bursal disease virus infection on its persistency

Chicken anaemia virus (CAV) infectivity and the effect of highly virulent infectious bursal disease virus (hvIBDV) infection on CAV'S infectivity were examined in chickens inoculated with CAV or inoculated dually with CAV and hvIBDV. Five chickens inoculated dually with hvIBDV at 35 days old and then with CAV at 40 days old exhibited no clinical signs of disease, but showed atrophic bursae of Fabricius when necropsied 4 weeks later. Upon examining the chickens at 7 days postinoculation (dpi) with CAV, it was found that hvIBDV infection had inhibited production of virus neutralising (VN) antibody to CAV, and that it was possible to recover CAV from plasma of these chickens. Although VN antibody to CAV appeared after 14 dpi, CAV was recovered from blood cells (Bcs) at high titres ranging from 10(2.5) to 10(5.5) TCID50/0.1 ml, 7 to 28 dpi in IBDV-induced immunosuppressed chickens. In addition, CAV was sporadically recovered, using rectal swabs, from the dually inoculated chickens at low titers, ranging from 10(1.0) to 10(2.0) TCID50/0.1 ml). In contrast, although CAV was recovered from Bcs in most of the chickens inoculated with CAV alone, the titers were lower (10(1.0) to 10(2.5) TCID50/0.1 ml). No CAV was detected from the rectal swabs of these chickens. The results of virus recovery were confirmed by polymerase chain reaction. This study first examined the persistency of CAV in BCS and the effective enhancement of primary CAV infection as a result of immunosuppression caused by hvIBDV infection. (C) 1999 Harcourt Publishers Limited.