CHARACTERIZATION AND DEVELOPMENT OF REVERSE GENETICS SYSTEM FOR AVIAN PARAMYXOVIRUS TYPE-3 AND ITS EVALUATION AS A LIVE VIRAL VECTOR
Samal, Siba K
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Avian Paramyxovirus (APMV) serotype 3 is one of the nine serotypes of APMV that infect a variety of avian species around the world. In chickens and turkeys, APMV-3 causes respiratory illness and drop in egg production. To understand the molecular characteristics of APMV-3, the complete genome sequences of prototype strain Netherlands and strain Wisconsin were determined. The genome length of APMV-3 strain Netherlands is 16,272 and for strain Wisconsin is 16,181 nucleotides (nt). Each genome consists of six non-overlapping genes in the order 3'N-P/V/W-M-F-HN-L5' similar to most of APMVs. Comparison of the APMV-3 strain Wisconsin nt and the aggregate predicted amino acid (aa) sequences with those of APMV-3 strain Netherlands revealed 67 and 78%, identity, respectively. The phylogenetic and serological analyses of APMV-3 strains Netherlands and Wisconsin indicated the existence of two subgroups within the same serotype. Both the strains were found to be avirulent for chickens by mean death time and intracerebral pathogenicity test. To further study the molecular biology and pathogenesis of APMV-3, a reverse genetics system for strain Netherlands was established in which infectious recombinant APMV-3 was recovered from a cloned APMV-3 antigenomic cDNA. The recovered recombinant virus showed in vitro growth characteristics and in vivo pathogenicity similar to parental virus. A recombinant APMV-3 expressing enhanced green fluorescent protein was also recovered, suggesting its potential use as a vaccine vector. Furthermore, generation and characterization of recombinant APMV-3 expressing Newcastle disease virus (NDV) F and HN proteins demonstrated that the F protein plays a major role in protection against virulent NDV challenge. Overall, the study conducted here has several downstream applications. The complete genome sequence of APMV-3 is useful in designing diagnostic reagents and in epidemiological studies. The reverse genetics system for APMV-3 would be of considerable utility for introducing defined mutations into the genome of this virus and developing a vaccine vector for animal and human pathogens.