Vaccination against Newcastle disease in chickens.

Vaccination against Newcastle disease in chickens. Newcastle Disease (ND), also termed fowl pest, is a highly contagious and devastating disease in poultry. It is induced by an avian paramyxoviruses serotype 1, named ND virus (NDV). NDV has been shown to be able to infect over 200 different species of birds but the virulence of this virus and clinical signs of ND vary largely with both host and strain of virus. Virulent strains require to be reported to the World Organisation for Animal Health (OIE) and outbreaks result in strict embargoes for the trade of avian products among countries. Control of ND primarily consists of vaccination of flocks and culling of infected or likely infected birds. At the present time, vaccination programs for NDV include the use of either inactivated (killed) or attenuated (live) vaccines to induce protective immunity while producing minimal adverse reactions in birds. Live viruses of low virulence (apathogenic, lentogenic) or of moderate virulence (mesogenic) are used depending on the disease situation and the regulations. Nevertheless, vaccination schedules might vary among poultry breeds. Generally, post-vaccination serology is used to confirm successful application of vaccine and an adequate immune response by the bird. However, it is well recognized that many chickens with low or no antibody titer are protected in challenge experiments and that present vaccination schedules do not protect well against viral re-excretion. One of the most important considerations affecting vaccination programs is the level of maternal immunity in young chickens, which may vary considerably from farm to farm and among individual chickens. Additionally, vaccine strains are phylogenetically different from circulating virulent strains. Then, new vaccines candidates are investigated in laboratory to improve the efficacy of conventional commercial vaccines while new tools of immunity measure are developed to increase the understanding of the protective immune response against NDV.