Supported by Ministry of Agriculture of the Russian Federation Received March 29, 2016 doi: 10.15389/agrobiology.2016.4.491eng A b s t r a c t Glasser’s disease is a bacterial infection typically characterized by fibrinous polyserositis, polyarthritis, meningitis, and occasionally acute pneumonia and septicemia. <...> Haemophilus parasuis is the etiologic agent of Glasser’s disease, leading to significant economic losses in swine industry. <...> H. parasuis normally colonizes the upper respiratory tract of healthy pigs. <...> However, stress, concomitant viral infections, or poor immune status allow H. parasuis to cause disease. <...> The current literature contains a few studies that clarify differences in the genome between highly virulent and avirulent strains in the context of putative virulence factors. <...> The objective of this study was to examine H. parasuis strains isolated on Russian pig farms during the 11-year study period (20002011) for the presence of putative virulence loci. <...> We screened 6 strains and 23 field isolates for the presence of 10 virulence factors. <...> Identification of NAD-dependent isolates was performed by biochemical analysis and species-specific real-time PCR. <...> Putative virulence genes were amplified by PCR using different primer pairs. <...> Genetic analysis confirmed that the virulence factors (vtaA, fhuA, hhdA, hhdB, nhaC, HAPS_0254, sclB7, sclB11 and phage_related) exist in different combinations. <...> Out of 28 strains studied, the vtaA gene was found in all strains, sclB7 and sclB11 genes were present in 24 and 25 strains respectively, the cirA gene in 18 out of 28, the fhuA gene in HAPS_0254, the hhdA gеne in 15, the hhdB gene in 14, the nhaC gene in 12, the phage_related target in only 3 strains. <...> The strains IL-1-DEP, KOMI DEP and isolate Nadeevo-2 carried all the loci, except for phage_related, which has only been reported for the virulent strains IA-84-17975, IA-84-22113 and SD-84-15995. <...> In contrast to the paper by A.V. Potehin et al. (2007), IL-1-DEP turned out to be highly virulent, KOMI DEP exhibited moderately virulence, and Nadeevo-2 showed no virulence at all. <...> Interestingly, the vtaA group 1 gene, the main determinant of virulence, was identified in SK-1-DEP avirulent strain and Botovo-2 and Nadeevo-2 avirulent isolates <...>