Characterization of serotypes and virulence genes of Haemophilus parasuis isolates from Central Vietnam.

Haemophilus parasuis is a commensal Gram-negative bacterial pathogen in the upper respiratory tract of pigs, which causes Glässer's disease. More than 15 serotypes of H. parasuis have been identified with apparent differences in virulence. In this research, we surveyed the prevalence and distribution of serotypes and known virulence genes of the H. parasuis isolates collected from sick and healthy pigs in Quang Binh and Thua Thien Hue provinces in Central Vietnam. By using bacterial isolation and polymerase chain reaction (PCR), 56 out of 814 (6.9%) samples were positive for H. parasuis. The most prevalent serotypes were serotype 5 (15/56, 26.8%), followed by serotype 2 (13/56, 23.2%) and serotype 4 (10/56, 17.9%). The vta1 was the most frequently detected virulence gene which was present in 62.5% of the strains, followed by vta3 (42.9%), vta2 (39.3%), HPM-1371 (35.7%), capD (30.4%), HPM-1372 (12.5%), lsgB and HPM-1373 (both shared 8.9%). Strong correlations between some serotypes and known virulence genes were observed, in which virulence genes HPM-1371, HPM-1372, vta3, vta2 and capD were mainly clustered in serotypes 5/12, and vta2 clustered in serotype 2. This study presents the first baseline information on the epidemiological characteristics of H. parasuis isolates from Central Vietnam.