Infectious bursal disease virus and chicken anemia virus testing update
Davor Ojkic, Andrew Brooks
Animal Health Laboratory, University of Guelph, Guelph, ON.
AHL Newsletter 2022;26(1):16.
Immunosuppression associated with viral infection is frequently suspected as an underlying cause or contributor in various aspects related to management of poultry health issues. Infection with many viruses can cause, or be involved in, immunosuppression, e.g., infection with Marek's disease virus (MDV), reticuloendotheliosis virus (REV), avian leukosis virus (ALV), chicken anemia virus (CAV), infectious bursal disease virus (IBDV), avian reovirus (ARV) and fowl adenovirus (FAdV). Viruses such as CAV and IBDV produce significant lesions in the primary lymphoid tissues (Fig. 1). The impact of some of these agents in modern poultry production systems has been minimized through vaccination (MDV) and/or eradication (REV, ALV). Despite intensive vaccination programs in both breeder and broiler flocks, IBDV infection has continued to evade control attempts. On the other hand, the impact of CAV infection appears to be less significant, and is better controlled by breeder vaccination and subsequent maternal antibody transfer to broiler birds. Still, synergism of IBDV and CAV co-infection has been reported, and can exacerbate the negative effects of these immunosuppressive viruses.
AHL previously had two separate PCR tests for the detection of IBDV and CAV. Recently, we investigated the frequency of IBDV and CAV co-infection by testing forty-eight samples (bursa of Fabricius) that were positive for IBDV by CAV PCR. Fourteen samples (29%) were also positive for CAV, and based on PCR Ct values, 79% (11 of 14) of these CAV-positive samples had a higher load of CAV than IBDV (Table 1).
As a consequence, AHL has combined IBDV and CAV PCR tests into a duplex PCR test to allow continuous detection/monitoring of IBDV/CAV co-infection. The duplex test is now routinely available and is offered for the same fee as a single PCR test (currently $36). Genotyping of samples positive for IBDV and/or CAV is available at an additional cost. AHL
Table 1. IBDV and CAV co-infection and viral load (Ct value) in the bursa of Fabricius
Figure 1. Histologic lesions caused by immunosuppressive viruses. A. Thymic atrophy in a 10-week-old broiler-breeder chicken associated with CAV infection (the flock was not vaccinated for CAV). B. Severe depletion of lymphocytes from the bursa of Fabricius of a 6-week-old layer chicken associated with IBDV infection. Vp2 gene sequencing indicated a field strain of IBDV. (H&E stain).