Protection by recombinant viral proteins against a respiratory challenge with virulent avian metapneumovirus

Protection by recombinant avian metapneumovirus (aMPV) N or M proteins against a respiratory challenge with virulent aMPV was examined. N, M or N + M proteins were administered intramuscularly (IM) with incomplete Freundʹs adjuvant (IFA) or by the oculonasal (ON) route with cholera toxin-B (CTB). Each turkey received 40 or 80 μg of each recombinant protein. Birds were considered protected against challenge if the challenge virus was not detectable in the choanal swabs by RT-PCR. At a dose of 40 μg/bird, N protein given with IFA by the IM route protected eight out of nine birds. M protein at the same dose protected three out of seven birds, while a combination of N + M proteins (40 μg each) protected three out of four birds. At a dose of 80 μg of each of N and M proteins per bird given with IFA by the IM route, 100% protection was achieved. ON immunization with a mixture of N and M proteins induced partial protection when the proteins were given with CTB; no detectable protection was noted without CTB. N and M proteins induced anti-aMPV antibodies, although protection against virulent virus challenge did not appear to be associated with the level or presence of antibodies.