Detection and differentiation of Newcastle disease virus (avian paramyxovirus type 1)

Substantial variation in the virulence of Newcastle disease virus (NDV) iso lates means that the detection of NDV or evidence of infection is insuffici ent for an adequate diagnosis, as control measures for avirulent viruses ar e very different to those for virulent viruses. Diagnosis therefore require s further characterization, at least as to whether an isolate is virulent o r avirulent. Conventional detection and differentiation of ND viruses is pe rceived as slow, laborious and requiring an undesirable use of in vivo tech niques. In addition, further characterization is needed to give greater inf ormation on origin and spread. This review concentrates on the application of monoclonal antibody and molecular biological approaches. Panels of monoc lonal antibodies were a major advance for the characterization of NDV isola tes, although confirmation of virulence for poultry still required in vivo testing. As molecular-based techniques become easier and more reliable, the y are likely to supersede the use of monoclonal antibodies, especially for characterizing viruses for epidemiological purposes. The attraction of mole cular-based techniques is that they may be able to cover all three aspects of Newcastle disease diagnosis (detection of virus, characterization, inclu ding inference of virulence, and epidemiology) quickly, accurately and defi nitively in a single test. A number of approaches based on the reverse tran scriptase polymerase chain reaction have been developed, with subsequent an alysis of the product by restriction enzyme analysis, probe hybridization a nd nucleotide sequencing. Although extensive variation among NDVs still pos es technical problems, the real and potential advantages of a molecular bio logical approach to Newcastle disease diagnosis appear to be overwhelming.