A simple and inexpensive method of antigen preparation by ultrafiltration was investigated using the V4 strain of Newcastle disease virus. The antigen designated XM300 was used in an indirect enzyme-linked immunosorbent assay (ELISA) for the detection of antibodies to Newcastle disease virus in chicken serum. The assay was evaluated using both experimental and field sera, as well as reference control reactor and non-reactor sera. Antigen prepared by the ultrafiltration method was compared with antigen prepared by ultracentrifugation and the ultrafiltration antigen was found to react specifically with Newcastle disease virus antiserum in this ELISA system. This antigen preparation technique is also suitable for use in developing countries. The ELISA provides an excellent method for measuring antibodies in the early stages of infection in serum samples of experimentally infected chickens. More than 14.58% of the total serum samples which failed to be recognized as reactors by the conventional haemagglutination inhibition test were detected in the ELISA.
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