| Newcastle disease (ND) is primarily a pneumotropic virus but it also has viscerotropic and neurotropic forms. Primary clinical signs caused by the pneumotropic form of the virus include respiratory snicks and sneezes, sinus exudate, mild conjunctivitis, decreased rate of body weight gain, increased feed conversion ratio, and decreased egg production in mature birds. An experimental recombinant vaccine, Herpes Virus of Turkeys (rHVT) vector carrying genes to the hemagglutinin-neuraminidase (HN) and fusion (F) proteins of Newcastle disease virus (NDV) and genes to glycoproteins A and B (gps A and B) of Marek's disease virus (MDV), was tested in specific pathogen free (SPF) Leghorns, commercial broilers, Leghorns, and turkeys by vaccination either in ovo (broilers) or subcutaneously against Texas GB NDV challenge.; In Trial 1, SPF Leghorns, commercial broilers, Leghorns, and turkeys were not vaccinated, but infected with Texas GB, NDV at a final dose of 10 4--5 embryo lethal dose fifty (ELD50) at 6 weeks of age either by the eye-drop (ED) or intramuscular (IM) route. Nearly 100% mortality was observed in all chicken types infected regardless of route of challenge. However, statistically fewer turkeys infected by ED challenge died than IM challenged turkeys.; In Trial 2, commercial broilers were vaccinated with either the rHVT vaccine in ovo or subcutaneously or the commercial B1B1 NDV vaccine by ED vaccination and challenged with 104--5 ELD50 of Texas GB, NDV. Likewise turkeys were vaccinated with either the rHVT subcutaneously or eye-drop with commercial B1B1 vaccine. Results showed that the rHVT vaccine produced equal protection (∼100% protection) to the commercial B1B1 vaccine, without the vaccine reactions.; In Trial 3, commercial broilers were vaccinated with the rHVT alone or in combination with HVT/SB1 or CVI988 Marek's disease (MD) vaccines in ovo or subcutaneously, or eye-drop vaccinated with commercial B1B1. Results showed that combining rHVT with HVT/SB1 drastically reduced protection from 10 4--5 ELD50, Texas GB NDV challenge at 28 days of age compared to the commercial vaccine or the rHVT alone or in combination with CVI988.; The rHVT vaccine effectively immunizes and subsequently protects chickens and turkeys against NDV challenge when administered alone or in combination with CVI988. However, it is not an efficacious vaccine when combined with HVT/SB1 and administered in ovo or subcutaneously. |
