Molecular and biological properties of pathogenic Newcastle disease viruses isolated in Kazakhstan

Currently, Newcastle disease (ND) is highly contagious viral infection of birds, characterized by pneumonia, encephalitis, multiple pointed hemorrhages and defeat of internals is spread in various regions of the world. All isolated to the present ND viruses ( Paramyxoviridae, Paramyxovirus ) are divided into two classes, representing the diverse and constantly developing group of viruses. Despite the conducting universal vaccination, the disease is difficult to control, in connection with what it is listed in the most important pathogens. In recent years, studies on the genetic variability of the ND strains in Kazakhstan were not conducted, although exactly here many transcontinental migratory routes of wild birds, the main carriers of the pathogens, are crossed. The present study was conducted to examine the characteristics of the circulation, as well as the isolation and characterization of isolates of Newcastle disease virus that caused the disease of birds in different regions of Kazakhstan in 2010, 2012 and 2013. Using 10-day-old developing chicken embryos (DCE), we studied virus isolates from dead hens at ND outbreaks in poultry farms and private yards in Almatinskaya, North Kazakhstan and Zhambylskaya provinces of Kazakhstan. The mean death time of embryos (MDT) and intracerebral pathogenicity index (ICPI) were estimated. Viral RNA was isolated and used for PCR. Amplified products were further detected, purified and sequenced. The obtained nucleotide sequences were analyzed using Sequencher v. 4.5 (Gene Codes Corporation, USA). A set of nucleotide sequences from an international database GenBank was used to construct the dendrogram and determine the genotype. Phylogenetic analysis of the sequences was performed using Mega 6.06 and the following parameters: Statistical Method - Neighbor-joining; Test of Phylogeny - Bootstrap method; No. of Bootstrap Replications - 500; Model/Method - Kimura 2-parameter model. Studies have shown that the ND causes outbreaks both among vaccinated and non-vaccinated poultry. The ND isolates belong to velogenic strains. All of them had a proteolytic cleavage site 110GGRRQKRF117 of fusion protein, which is characteristic of the V-pathotype. The sequencing and phylogenetic analysis of the F -gene showed that the virus from dead birds of those vaccinated at the poultry farm in Almatinskaya Province belongs to VIId genotype, while the isolates from non-vaccinated birds of the private farms in Almatinskaya, Zhambylskaya and North Kazakhstan provinces belong to VIIb genotype. According to the obtained information, despite the geographical distance of outbreaks, the same ND genotypes are circulating in the territory of Northern Kazakhstan and in the southern regions of the country. Wide spread of the virus in Kazakhstan requires from veterinary services to develop effective control measures with regard to ND molecular epidemiology.