Systematic Veterinary Virology

SEROLOGY

• A number of tests are performed to identify antibodies against NDV in chickens. The two common tests are
  • Haemagglutination inhibition (HI) test and
  • ELISA.
• HI test is preformed in most of the laboratories. The HI test is based on the principle that the haemagglutinin on the viral envelope can bring about the agglutination of chicken red blood cells and that this can be inhibited by specific antibodies. A titre of log2³ is indicative of protection and a titre of log2⁶ or more suggests a recent infection by the virus.
• The ELISA works on the principle of recognition of anti-NDV antibodies, attached to a plate coated with viral antigen, by antibodies produced in another species against chicken antibodies. This anti-chicken antibody is conjugated to an enzyme that catalyses a reaction, causing a change of colour which can then be read quantitatively on a photo spectrometer designed to read microtitration plates

Monoclonal antibody based HI

• Mouse monoclonal antibodies (MAbs) directed against strains of ND virus have been used in HI tests to allow rapid identification of ND virus without the possible cross-reactions with other APMV serotypes that may occur with polyclonal sera. MAbs have been produced that give reactions in HI tests that are specific for particular strains or variant ND virus isolates.