This study was initiated to determine the interaction between two infectious bursal disease virus (IBDV) strains in the early stages of infection by detection and quantification of IBDV RNA in lymphoid and non-lymphoid tissues. SPF chickens were inoculated with single infection or dual infection by the mild strain B87 followed by the pathogenic strain BC6/85 at 0, 1, 2, and 3 days post-inoculation (dpi) with B87. Real-time RT-PCR assays were developed to examine the viral loads of the tissues collected at various time intervals. The results reveal that B87 could delay the time point of positive detection of the BC6/85 strain in the bursa of Fabricius from 1 dpi to 3 dpi, indicating that B87 interfered with the replication of BC6/85. The interference occurred when BC6/85 was inoculated at 2 dpi and 3 dpi with the B87 strain. Moreover, BC6/85 could affect the proliferation and duration of B87 in SPF chickens. The rates of positive detection for B87 decreased significantly during dual infection. The investigation of the interaction between the two strains is important for the implementation of appropriate control measures.
Keywords: B87 and BC6/85; IBDV; viral interference; virus quantification.