clone purification, characterization and standardization of lasota strain for developing a live vaccine against newcastle disease virus

newcastle disease (nd) is one of the most serious illnesses of chickens. live vaccines are widely used to prevent chicken from the disease all over the world. to access the effective and potentiate nd vaccine, a homogenous subpopulation from lasota strain was selected following cultivation of the virus on primary chicken embryofibroblast (cef) cells. pathogenicity indices and molecular characterization of a several plaques at 3rd passage were analyzed and then the selected clone was candidate for vaccine development. nd vaccine was prepared according to the standard protocols. the immunogenicity of the live vaccine was examined in specific pathogen free (spf) and commercial chickens. the geometric mean hemagglutination-inhibition (hi) titers induced in chickens vaccinated with the cloned vaccine were not significantly differ than those induced in chickens vaccinated with the similar nd clone vaccine. efficacy of the nd vaccine was estimated against the virus challenge. the result indicates the ability of the cloned vaccine to confer a complete protection against ndv.