Newcastle disease outbreaks in Kazakhstan and Kyrgyzstan during 1998, 2000, 2001, 2003, 2004, and 2005 were caused by viruses of the genotypes VIIb and VIId

Newcastle disease virus (NDV) infects domesticated and wild birds throughout the world, and infections with virulent NDV strains continue to cause disease outbreaks in poultry and wild birds. To assess the evolutionary characteristics of 28 NDV strains isolated from chickens in Kazakhstan and Kyrgyzstan during 1998, 2000, 2001, 2003, 2004, and 2005, we investigated the phylogenetic relationships among these viruses and viruses described previously. For genotyping, fusion (F) gene phylogenetic analysis (nucleotide number 47–421) was performed using sequences of Kazakhstanian and Kyrgyzstanian isolates as compared to sequences of selected NDV strains from GenBank. Phylogenetic analysis demonstrated that the 14 newly characterized strains from years 1998 to 2001 belong to the NDV genotype VIIb, whereas the 14 strains isolated during 2003–2005 were of genotype VIId. All strains possessed a virulent fusion protein cleavage site (R-R-Q-R/K-R-F) and had intracerebral pathogenicity indexes in day-old chickens that ranged from 1.05 to 1.87, both properties typical of NDV strains classified in the mesogenic or velogenic pathotype.