Immunogenicity of Newcastle disease vaccine in southern ground-hornbill (Bucorvus leadbeateri)

Abstract

The southern ground-hornbill (Bucorvus leadbeateri; hereafter SGH) is endangered in South Africa, Namibia, and Swaziland. Through a conservation program established in South Africa by the Mabula Ground Hornbill Project, wild populations are being re-established by the reintroduction of captive-reared birds. The SGH is susceptible to infection with avian avulavirus 1, which causes Newcastle disease (ND). Four different vaccines to protect against ND were administered through various vaccination schedules and evaluated by serologic monitoring to assess the efficiency and safety of various combinations of vaccines (live versus inactivated/killed), vaccine strains (Ulster strain, live; Avivac Cellimune, live; VG/GA strain, live; and Avivac Struvac, killed), and administration routes (intraocular versus subcutaneous versus intramuscular injection versus oral). We vaccinated 75 individuals and evaluated antibody titers in 53 individuals (24 juveniles, 13 subadults, and 16 adult SGH; 26 males and 27 females) over a period of 9 years. Antibody titers to avian avulavirus 1 in sera were monitored by a hemagglutination inhibition test. Protective titers were generated with 3/6 vaccine regimes tested in the SGH. The highest vaccine titers were established in birds vaccinated with the Ulster strain in the conjunctiva and followed with an intramuscular Struvac injection (mean log2 titer 8.6 ± 2.6) booster. Our aim was 1) to assess whether optimal vaccination protocols could be developed and 2) to then be able, by oral administration, to remove the need to recapture free-roaming, reintroduced birds to administer the initial vaccine or booster, thus remove the threat or mortality associated with ND to this endangered avian species in both captive birds and birds released back into the wild.