ISOLATION AND DETECTION OF NEWCASTLE DISEASE VIRUS FROM FIELD OUTBREAKS IN BROILER AND LAYER CHICKENS BY REVERSE TRANSCRIPTION–POLYMERASE CHAIN REACTION

The present research work was carried out to isolate and identify Newcastle disease virus (NDV) by using haemagglutination inhibition (HI) test and reverse transcription-polymerase chain reaction (RT-PCR) assay. A total of 160 clinical (blood, tracheal and cloacal swabs) and post-mortem (brain, lung, colon and spleen) samples were collected from chickens of two field outbreaks of Newcastle disease (ND) in 2006, one in a broiler (Cobb-500) farm of Mymensingh district and other one in a layer (Sonali) farm of Gazipur district. All the samples were inoculated onto 10-day-old embryonated chicken eggs through allantoic sac route and in the chicken embryo fibroblasts (CEFs) cell culture. The allantoic fluid (AF) of the dead embryos and the infected culture fluid (ICF) of the CEF were harvested at 48 and 96 hours of post-infection, respectively. The HI and RT-PCR were employed to detect NDV in tissue homogenates of all the clinical and post-mortem samples as well as laboratory samples (AF and ICF). Among the clinical samples, virus isolation rate was found higher from tracheal swab (90%) compared to those of cloacal swab (85%) and serum (65%). On the other hand, among the four different types of post-mortem samples, virus isolation rate was found higher in spleen (100%) compared to those of lungs (80%), colon (60%), and brain (80%) samples. In CEF cell culture system, the rate of virus isolation from all the aforesaid samples was found 100 % with the exception of serum samples. The isolation rate of NDV was higher in CEF culture system (93.8%) compared to that of avian embryos (80%). Among the clinical and post-mortem samples, inoculum of only cloacal swab an