Pathotyping of Newcastle disease virus by mean death time and real-time PCR assay: an empirical comparison

Newcastle disease (ND) remains the most significant disease of poultry sector and contributes to huge economic loss. Early detection and pathotyping of Newcastle disease virus associated with field infection are highly crucial. In vivo pathogenicity assaying is sensitive and specific pathotyping tool used for detection and identification of NDV used until the recent past. Genome based sequence analysis yields promising results in virulence determination. Keeping the above facts, the present study was designed to compare the efficacy of conventional and molecular assays in NDV virulence determination. In this study twelve NDV isolates (Isolate numbers 463, 464, 475, 476, 122-17C, 122-17D, 122-17E, 128-17A, 128-17D, 137, 139, 141) available in the Department of Veterinary Microbiology, Madras Veterinary College (MVC), Chennai was subjected for differentiation of virulent and avirulent strains using mean death time (MDT) in specific pathogen-free (SPF) embryonated eggs and TaqMan minor groove binding (MGB) probe real-time PCR assay. Pathotyping based on the MDT revealed two NDV isolates (isolate no. 476 and 128-17D) as velogenic strains and the remaining ten NDV isolates as lentogenic strains. Pathotyping based on TaqMan MGB probe real-time PCR assay revealed six NDV isolates (476, 128-17D, 463, 464, 475, 137) as velogenic/mesogenic strains and remaining six NDV isolates (122-17C, 122-17D, 122-17E 128-17A, 139, 141) as lentogenic strains. Using a TaqMan MGB probe real-time PCR assay, four NDV isolates (463, 464, 475, 137) which were MDT pathotyped as lentogenic strains were re-pathotyped as velogenic/mesogenic strains, which indicates the greater sensitivity of TaqMan MGB probe real-time PCR assay in pathotyping of NDV over conventional MDT.