Background of the antigen
NDV is a contagious and fatal viral disease affecting most species of birds. Clinical signs are extremely variable depending on the strain of virus, species and age of bird, concurrent disease, and preexisting immunity. Four broad clinical syndromes are recognized by scientists. They are Viscerotropic velogenic, Neurotropic velogenic, Mesogenic, and Lentogenic. NDV is so virulent that many birds die without showing any clinical signs. A death rate of almost 100 percent can occur in unvaccinated poultry flocks. NDV can infect and cause death even in vaccinated poultry. Fortunately NDV has not infected domestic chicken flocks in the United States since the last outbreak was eradicated in 1974.
