Study On Real-time RT-PCR Assay And RNA Interference For Newcastle Disease Virus

Newcastle disease virus (NDV)is the etiological agent of Newcastle disease, an affliction which can cause severe losses in domestic poultry production. The highly virulent types are list A agents that require reporting to the Office of International Epizootes, and their occurrence results in quarantine and trade embargoes。 The virus is enveloped and has a negative-sense, single-stranded RNA genome of approximately 15 kb which codes for six proteins, including an RNA-directed RNA polymerase (L), hemagglutinin-neuraminidase protein (HN), fusion protein (F), matrix protein (M), phosphoprotein (P), and nucleoprotein (N). Newcastle disease virus isolates are characterized by virulence in chickens and may be categorized into three main pathotypes depending on severity of disease., i.e. Lentogeni, cmesogenic and velogenic isolates. The virulence of new NDV isolates is assessed primarily on the basis of in vivo tests, including the intracerebral pathogenicity index in 1-day-old chickens, the inoculation of embryonated eggs to determine mean death time of the embryo, and the intravenous pathogenicity index in 6-week-old chickens. It cost 1 weak or more for a routine test. Additionally, the virulence of NDV isolates is known to be related to the amino acid sequence at the F protein cleavage site and the ability of specific cellular proteases to cleave the protein of different pathotypes. Lentogenic NDV isolates have cleavage site sequences as RR (K) QR(E) RL, wile the mesogenic and velogenic NDV isolates have similar cleavage site sequences as RRQ K(R) RF. The OIE now accepts reporting of the F cleavage sequence as a primary virulence determinant. Real-time PCR...