Submitted to: Avian Diseases
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/17/2001
Publication Date: N/A
Interpretive Summary: Infectious bursal disease is a highly contagious disease of young chickens. It is of economic importance to the poultry industry due to the severe immunosuppression that it causes. The etiological agent, infectious bursal disease virus (IBDV), destroys actively dividing lymphocytes, especially in the bursa of Fabricius. The ability to detect IBDV in tissues is important, ,as other agents can cause lymphoid depletion and necrosis in the bursa. Using in situ hybridization (ISH) to determine the pathogenesis of different pathotypes of IBDV, the sites of virus replication were identified in various tissues. Results of this study indicate specific detection of IBDV viral mRNA in bursal and non-bursal lymphoid tissues as rapidly as 24 hours post-inoculation. Thus, the use of ISH for early detection of IBDV can be useful to the industry for monitoring flock infection, as well as in pathogenesis of field isolates of IBDV.
Technical Abstract: In situ hybridization (ISH) was utilized in a pathogenesis study of three vaccine pathotypes (Delaware variant A, D78, and BursaVac) of infectious bursal disease virus (IBDV). Tissues were taken (bursa, thymus, spleen, proventriculus, and cecal tonsils), fixed in formalin and paraffin-embedded at 12, 24, 48, 72, and 120 hours post-inoculation (h.p.i.). Using an antisense VP2 gene probe, viral nucleic acid was detected in bursas from both D78 and BursaVac infected chickens at 24, 48, 72, and 120 h.p.i. However, viral RNA was only detected in the Delaware variant A infected birds at 72 h.p.i. Thymus and spleen were positive in the D78 infected birds at 48 h.p.i. and in the BursaVac inoculated group at 72 h.p.i. Viral nucleic acid was not present in detectable levels among any of the tissues tested at 12 h.p.i. However, by 24 hours, scattered positive lymphoid cells were visualized in the bursal follicles of chickens infected with D78 8and BursaVac. In addition, low levels of virus were detected in the thymu and spleen among the D78 and BursaVac infected birds. The sites of viral replication were consistent between the two vaccine infected groups (D78 and BursaVac), whereas the chickens infected with Delaware variant A had limited IBDV replication in the bursa.