Development of a highly sensitive and specific enzyme-linked immunosorbentassay based on recombinant matrix protein for detection of avian pneumovirus antibodies

The matrix (M) protein of avian pneumovirus (APV) was evaluated for its ant igenicity and reliability in an enzyme-linked immunosorbent assay (ELISA) f or diagnosis of APV infection, a newly emergent disease of turkeys in Unite d States. Sera from APV-infected turkeys consistently contained antibodies to a 30-kDa protein (M protein), An ELISA based on recombinant M protein ge nerated in Escherichia coli was compared with the routine APV ELISA that ut ilizes inactivated virus as antigen, Of 34 experimentally infected turkeys, 33 (97.1%) were positive by M protein ELISA whereas only 18 (52.9%) were p ositive by routine APV ELISA 28 days after infection. None of the serum sam ples from 41 uninfected experimental turkeys were positive by M protein ELI SA. Of 184 field sera from turkey flocks suspected of having APV infection, 133 (72.3%) were positive by M protein ELISA whereas only 99 (53.8%) were positive by routine APV ELISA. Twelve serum samples, which were negative by M protein ELISA but positive by routine APV ELISA, were not reactive with either recombinant M protein or denatured purified APV proteins by Western analysis. This indicates that the samples had given false-positive results by routine APV ELISA. The M protein ELISA was over six times more sensitive than virus isolation (11.5%) in detecting infections from samples obtained from birds showing clinical signs of APV infection. Taken together, these results show that ELISA based on recombinant M protein is a highly sensitiv e and specific test for detecting antibodies to APV.