Distribution of virulence-associated genes and their associations with serotypes of Glaesserella parasuis isolates in Viet Nam and China

Abstract

Glaesserella parasuis resently still known as Haemophilus parasuis is a common opportunistic
pathogen known for its ability to colonize in the healthy pigs and causes Glasser’s disease with the
characteritics of fibrinous polyserositis, arthritis and meningitis. Glasser’s disease is one of the major
causes of high mortality rates in piglets, resulting in significant economic losses to the swine production
in the worldwide. In this study, the serotypes and 9 known virulence-associated genes (VGs) of
400 G. parasuis field strains were identified by one-step multiplex PCR (mPCR), and PCR method,
respectively. The correlations between serotypes and VGs were analysed. The studied results showed
that the most prevalent serotypes were 5/12, 4, 1, and 6 for all the strains. However, difference was
observed between Chinese isolates and Vietnamese isolates in which the dominant serotypes were
5/12, 4, and 1 for the Chinese strains and 5/12, 2 and 4 for the Vietnamese ones. The prevalence of
serotypes 1, 2, 10, and non-typeable were significantly different between the Chinese and Vietnamese
strains (p<0.05). Most of strains carried at least one of the nine tested VGs, while only 16 strains did
not carry any VG. The vta1 (91.3%) was the most frequently detected, followed by vta3 (86.5%), vta2
(82.5%), and wza (68.0%). Several positive associations between serotypes and VGs were observed which were between serotype 1 and wza, HPM-1373, vta2, and vta3; serotype 5 and lgsB, capD,
HPM-1371, and HPM-1372; serotype 6 and vta2; and serotype 7 and wza, HPM-1371, and HPM-1372.
The prevalence of VGs was significantly higher among strains belonging to the highly virulent group
than those belonging to the moderate and non-virulent groups. The results in this study confirmed
the diversity and prevalence of serotypes and VGs in G. parasuis field strains. This is important for
developing vaccine candidates allowing for the control of Glasser’s disease in China and Viet Nam.