The differentation of infected from vaccinated depend on animal health satus infected with clinical signs ,carrier vaccinated ,kind of vaccine used .then serological (titer) of antibodies then isolations of virus and mapping to compare with vaccine strain and wild one.
Many thanks for your answer very clean. Could you tell me about the method of the differencing diagnostic low virulent and High virulence of Newcastle disease? Eg PCR/Realtime rt PCR technique or Sequencing,.....?