Rapid Differentiation of Infectious Bursal Disease Virus Serotypes by Polymerase Chain Reaction

Abstract

Infectious bursal disease (IBD) remains one of the most important contributors to economic loss in the poultry industry. The disease primarily affects the bursa of Fabricius of young chickens, resulting in reduced feed efficiency, reduced weight gain, increased mortality, and immunosuppression. Immunosuppression may increase susceptibility to other infectious disease agents. Infectious bursal disease virus (IBDV) is highly contagious and very resistant to disinfectants. Once the virus becomes established on the premises, it tends to persist for a long time. Infectious bursal disease virus, a member of the Bimaviridae, is a double-stranded RNA virus and contains 2 segments designated A and B. 3,5 Genome segment A encodes the structural proteins, VP-2, VP-3, and VP-4. Genome segment B encodes VP-l, a viral polymerase. There are at least two distinct serotypes of IBDV, serotypes 1 and 2. Only serotype 1 viruses cause disease, whereas all known serotype 2 viruses are not pathogenic to chickens. However, both serotypes are widespread in chickens. Polyclonal and monoclonal antibodies have been developed and used in differentiating IBDV serotypes by the virus neutralization (VN) test. Most IBD field samples cannot be directly used in the VN test. The viruses for the VN test are usually obtained by inoculating field samples into chicken embryos or are adapted to grow in primary cell cultures or mammalian cell lines. The essential element of the VN test requires that the amounts of IBDV or its replication products should be high enough for antigen-antibody reaction and serotype differentiation. Furthermore, the VN test is time consuming and inconvenient. Early diagnosis of IBD is necessary for the control of the disease, and rapid detection of IBDV and differentiation of IBDV serotypes is warranted. Recently, the polymerase chain reaction (PCR) was applied to the detection of IBDV and resulted in a very specific and sensitive assay. Although both IBDV serotypes were recognized by the PCR technique in that study, the PCR does offer several advantages. First, there is no need to grow or isolate virus from clinical specimens before PCR amplification, which significantly reduces the time and labor. Second, the PCR results in exponential amplification of a specific IBDV cDNA sequence flanked by a pair of primers selected from a known cDNA sequence of IBDV genome. By carefully analyzing the published genomic