DETECTION AND DISCRIMINATION OF VIRULENT AND AVIRULENT NEWCASTLE DISEASE VIRUS STRAINS IN CHICKENS IN BANGLADESH USING F-GENE-BASED RRT-PCR

Abstract

Newcastle disease (ND) is endemic to Bangladesh and causes significant morbidity and mortality in chickens. Virulent strains of Newcastle disease virus (NDV) are mainly responsible for frequent outbreaks in chickens. Real-time reverse-transcription PCR (rRT-PCR) is the most reliable confirmatory test for primary screening of NDV, which detects the matrix gene of NDV. However, the matrix gene-based rRT-PCR assay is not capable of distinguishing between virulent and avirulent NDV strains.

This study evaluated the performance of F-gene-based rRT-PCR assay to discriminate virulent NDV from an avirulent virus in a single test.

To detect NDV strains, tracheal swabs were collected from clinically sick poultry and dead chickens respectively. We used a F-gene based real-time quantitative reverse transcription polymerase chain reaction (rRT-PCR) to discriminate between virulent and avirulent NDV strains. Further partial sequencing of the fusion (F) gene was performed for phylogenetic analysis of the selected virulent NDV strains.

A total of 262 commercial chickens and 94 hilly chickens were sampled. Out of the samples tested, 56 (15.7%, 95% CI: 12.1-19.9) were confirmed to have NDV. Among the NDV positive chicken samples, 38 samples (67.9%, 95% CI: 54.0 – 79.7) tested positive for virulent NDV strains and 18 samples (32.1%, 95% CI: 20.3 – 46.0) for avirulent NDV strains. The phylogenetic analysis of the F-gene based sequences showed that the isolated virulent NDV strains were closely related to the previously identified NDV strains isolated from Bangladesh and India in the recent past.

The F-genes based rRT-PCR in a single test using two probes was found to be efficient to discriminate virulent and avirulent NDV. Rapid detection and differentiation of virulent NDV can importantly contribute to local public health through an improved disease surveillance outbreak response, and reporting to WOAH. This approach may also support the development of more effective vaccination strategies in Bangladesh, helping to reduce the impact of Newcastle disease in both commercial and native hilly chicken populations.