NDV may be employed as an antigen in a wide range of serological tests, enabling neutralisation or enzymelinked
immunosorbent assays (ELISA) and HI to be used for assessing antibody levels in birds. At present, the HI
test is most widely used for detecting antibodies to APMV-1 in birds while the use of commercial ELISA kits to
assess post-vaccination antibody levels is common. In general, virus neutralisation or HI titres and ELISA-derived
titres correlate at the flock level rather than at the level of individual birds. Serological assays are also used in
diagnostic laboratories to assess antibody response following vaccination, but have limited value in surveillance
and diagnosis of ND because of the almost universal use of vaccines in domestic poultry