phylogenetic characterization of the fusion genes of the newcastle disease viruses isolated in fars province poultry farms during 2009-2011

despite routine vaccination programs against newcastle disease (nd), sporadic cases have occasionally occurred that remain a constant threat to commercial poultry. ten isolates of newcastle disease viruses (ndv) from infected broiler chicken cases were obtained from various locations in fars province during 2009-2011 and genetically analyzed using reverse transcription polymerase chain reaction (rt- pcr) with primers specific to the viral fusion (f) protein- gene. the viruses were confirmed as ndv by hemagglutination inhibition assay and rt- pcr. the isolates based on the sequence and phylogenetic analyses of partial f gene were genotypically analyzed by rt pcr. in the present investigation, the pathogenicity of ndv strains was determined by internationally recognized test mean death time (mdt). analysis based on f gene showed that characterized isolates possess three different types of protease cleavage site motifs and appear to show maximum identities with isolates in the region. the subsequent phylogenetic analysis was implemented using mega and the phylogenetic tree. the results of rt-pcr and mdt showed that 10 isolates were positive for ndv, (60% velogenic, 30% mesogenic and 10% lentogenic). the results of the phylogenetic analysis showed that 10 ndv isolates from iran belong to the class ii, genotype iii viruses. this information is fundamental to improve the efficacy of controlling strategies and vaccine development for ndv.