Attempts at the detection of antibodies to Newcastle disease virus by haemofusion-inhibition test.

Two modifications of a haemofusion-inhibition test (HFI-1 and HFI-2) were applied for the titration of antibodies to Newcastle disease virus (NDV) in chicken sera. Statistical analysis revealed a positive correlation of the HFI-1 antibody titres with those measured by the standard haemagglutination-inhibition (HI), virus neutralization (VN) and haemolysis-inhibition (HLI) tests. The same appeared true when the HFI-2 antibody titres were compared with the HI, VN, and HLI tests. Except for the several sera collected from birds immunized with formalin-inactivated vaccine, the HFI-2 antibody titres of individual serum samples were usually lower than those determined by HFI-1. The interpretation of these differences as well as some advantages and disadvantages of the proposed test are discussed.