Haemophilus parasuis is one of the most important bacterial diseases of pigs worldwide. Haemophilus parasuis (H. parasuis) is a Gram-negative, nonhemolytic, NAD-dependent bacterium. To date, 15 serovars of H. parasuis have been described, but c. 15% to 41% of the field isolates are untypeable. In recent years, H. parasuis infection has been considered as a major cause of nursery mortality in swine herd.