Comparative Evaluation of Conventional and Molecular Diagnostic Methods for Newcastle Disease During an Outbreak in Punjab, Pakistan

Field survey of broiler poultry farms suspected to be infected with Newcastle disease (ND) was carried out during an outbreak in district Faisalabad, Punjab in 2012. The validity of different diagnostic methods; like virus isolation, identification and two-step Reverse Transcriptase Polymerase Chain Reaction (RT-PCR), was assessed and compared for the effective and rapid diagnosis of ND virus (NDV). Moreover, suitability of different postmortem samples (pooled tissues) and clinical samples (tracheal swabs) was also evaluated for efficient diagnosis. A higher rate of NDV detection was found with pooled tissue samples than tracheal swabs with virus isolation, identification and RT-PCR tests. Coefficient of agreement (K value) was calculated and a perfect and substantial agreement was found between both antigen-detection assays with K value of 0.82 and 0.72 when applied on pooled tissues samples and tracheal swabs, respectively. After molecular detection of NDV, a significant relationship was observed between nervous signs and RT-PCR (P<1.00), while a non significant relationship of RT-PCR results was recorded with enteric and respiratory signs (P<0.08-0.48). Data obtained from the field study suggests that pooled tissue samples are more suitable for the detection of NDV than tracheal swabs with both of the diagnostic techniques. Moreover, NDV detection rate was higher with RT-PCR than the conventional virus isolation and identification method along with an additional advantage of being quick to perform which is a basic necessity in case of ND outbreaks.