Efficacy of combined killed-in-oil emulsion and live Newcastle disease vaccines in chickens.

Following the introduction of routine vaccination regimes with different types of Newcastle disease (ND) vaccines, the incidence of velogenic viscerotropic Newcastle disease (VVND) in commercial poultry worldwide has declined dramatically. Unfortunately, these vaccination regimes are not feasible in free-range and backyard systems of poultry production practiced in many developing countries. In this study, we sought to develop a single vaccination regime in chickens with ND vaccines to elicit a long-lasting high level of ND virus (NDV) antibodies adequate to protect chickens against ND. The level of antibody response, as measured by the hemagglutination-inhibition (HI) test, and the degree of protection against the virulent strain of NDV were studied in chickens immunized with different vaccines. The vaccines used were: killed-in-oil emulsion (subcutaneous; s.c.) plus live virus (oculanasal; o.n.), given concurrently; experimental vaccine (s.c.) plus live virus (o.n.), given concurrently; killed-in-oil (s.c.); experimental vaccine prepared by homogenizing commercial live vaccine and oil emulsion (s.c.); and live virus (o.n.). The results obtained in this study indicate that concurrent administration of oil emulsion and live NDV vaccines induced the best antibody response, but there was no significant difference in protection among the vaccinated groups.