Molecular Characterization of Class II Newcastle Disease Virus from Field Outbreaks in Mizoram, India

Background: Newcastle disease (ND) is a highly contagious and economically important disease affecting poultry of all ages. The causative agent, class II NDV strains are frequently virulent and are classified into at least 21 distinct genotypes with several sub-genotypes. The circulating strains of NDV from mainland India are identified as genotype XIII, whereas emergence of a new genotype XXII has been reported recently from North East Region of India. Methods: A total of 25 poultry farms comprising a total population of 2165 birds were studied for field outbreaks of ND. Detailed post-mortem examination was conducted on a total of 121 dead birds and field outbreaks were confirmed by the detection of the F gene in tissue samples by reverse transcription PCR. Deduced amino acid sequence analysis of fusion proteins and phylogenetic analysis based on complete F gene were carried out to understand the molecular epidemiology of the circulating NDV strains. Result: This study has confirmed severe NDV outbreaks in the vaccinated flock, from Mizoram state of India. The three isolates from the outbreaks revealed the presence of the multi-basic amino acid residues at the fusion protein cleavage site (112RRQKRF117) identified as characteristic of velogenic strain. The phylogenetic analysis based on the complete F gene has characterized the isolates belonging to newly identified genotype XXII and subgroup XXII.2. The evolutionary evidence of this new genotype of NDV in the unique ecosystem of NER, India, warrants detailed studies for better understanding of the variant.