There are a variety of commercial ELISA kits available and these are based on several different strategies
for the detection of NDV antibodies, including indirect, sandwich and blocking or competitive ELISAs using
MAbs. At least one kit uses a subunit antigen. Usually such tests have been evaluated and validated by the
manufacturer, and it is therefore important that the instructions specified for their use be followed carefully.
The HI test and ELISA may measure antibodies to different antigens; depending on the system used ELISAs
may detect antibodies to more than one antigen while the HI test is probably restricted to those directed
against the HN protein. However, comparative studies have demonstrated that the ELISAs are reproducible
and have high sensitivity and specificity; they have been found to correlate well with the HI test (Brown et al.,
1990). Conventional ELISAs have the disadvantage that it is necessary to validate the test for each species
of bird for which they are used. Competitive ELISAs may not recognise all strains of APMV-1 if they use
MAb known for their specificity for single epitopes