Abstract:

To study the virulence characteristics of H. parasuis, we determined the 50% lethal doses (LD50) of H. parasuis serotype 5 strain in guinea pigs with the improved the Karber method. The LD50 was 1.33×109CFU, the 95% confidence range of the LD50 was 1.35×109-1.30×109CFU. Then guinea pigs were infected with 1 LD50 doses of H. parasuis by the nasal cavity, trachea, lungs, muscles, the abdominal cavity and subcutaneous inoculation respectively to explore pathogenic differences among different inoculation route. Guinea pigs have been 4/8, 2/8 and 5/8 deaths in 3 experimental groups by the trachea, lungs and the abdominal cavity inoculation, respectively. The tissue distribution of H. parasuis in infected guinea pig was tested by using paraffin sections and immunohistochemical techniques. After trachea infection with 1 ×LD50dose of H. parasuis, brain, heart, liver, lung, spleen and kidney tissues of guinea pigs were collected. Lung tissue showed positive result by immunohistochemistry staining from 6 h post trachea inoculation, then after 8 h, the abovementioned tissues presented positive. The results showed that H. parasuis can induce disease in guinea pig through 4 inoculation routes, such as the trachea, lungs, muscles and the abdominal cavity inoculation, and the H. parasuis can infect lungs, heart, liver, spleen and kidney tissues, and can lead to brain infection by breaking through bloodbrain barrier.

Key words: Haemophilus parasuis, infection, medial lethal dose, immunohistochemistry