**1. Introduction**

The Indian economy is rural based and between 60% and 70% of Indian population depends on agriculture for their sustenance. The development of the Indian poultry industry over the most recent forty years from lawn side interest to the present coordinated scientific and vibrant industrial state is incredible. Subsequently, India has become one of the biggest manufacturers of eggs on the world and the development rate in the poultry industry is exceptional at 5–8% per annum. Besides the various issues that threaten the developments in poultry industry like feed cost, poor marketing and limited post harvest technology, incidence of infectious diseases like Newcastle disease (ND), avian infection bronchitis (IB), etc. also poses major hurdles. A large portion of the irresistible infection causes weighty mortality as well as leads to significant manufacturing misfortunes. The virus causing ND has been classified as the prototype of Avian Paramyxo virus (APMV). The eighth report of the International Committee on Taxonomy of viruses characterized Newcastle disease virus (NDV) under the order Mononegavirales in the family Paramyxoviridae, sub family Paramyxovirinae and the genus Avilavirus. Of the nine species in this genus (APMV 1 to APMV 9), APMV 1 APMV 1 with an intracerebral pathogenecity index (ICPI) value >0.7 has been reported to cause ND with respiratory distress and diarrhoea, with higher morbidity and death. The contamination has been accounted for to be far and wide, in those 240 types of birds addressing 27 of the 50 sets of birds that were so far impacted by ND.

The genome of APMV 1 has been reported to contain approximately 15,186 nucleotides comprising of genes namely HN, NP, P, M, F and L. The HN protein has been shown to be multifunctional, playing a role in cell attachment and release as well as playing an important role in the infection process, notably in the globular head and stem regions of the HN gene, then the fusion protein (F) has been shown to facilitate the fusion of the viral envelope with the cell membrane, and NP has been shown to be highly immunogenic. Thus, it has been confirmed that the virulence of NDV is multigenic. NDV strains are classified as velogenic (highly virulent), mesogenic (mid virulence), or lentogenic (nonvirulent). Velogenic strains induce severe neurological and respiratory symptoms, spread rapidly, and cause up to 90% fatality. Mesogenic strains cause coughing, affect egg quality and yield, and cause up to 10% mortality. Lentogenic strains cause minor symptoms with trivial mortality.

Clinical indications vary greatly depending on viral strain, bird species and age, concomitant sickness, and pre-existing immunity. There are four broad clinical syndromes recognized.
