A novel experimental intraperitoneal infection model for Haemophilus parasuis in neutropenic guinea pigs

Abstract Introduction Haemophilus parasuis , one of the major swine pathogens, has at least fifteen different types, all of which have significant economic effects on the global swine industry. The aim of this study was to establish an experimental intraperitoneal infection model for H. parasuis in neutropenic guinea pigs. Methods Intraperitoneal administration of cyclophosphamide and Haemophilus parasuis was conducted in guinea pigs. Clinical signs, gross pathology, and histopathology were observed in neutropenic guinea pigs infected with H. parasuis. Results Intraperitoneal administration of 100 mg/kg cyclophosphamide led to immunosuppression with white blood cells, lymphocytes, and neutrophils all 3 , while no histological tissue damage was observed. Intraperitoneal administration of 10 9 colony-forming units (CFU) of H. parasuis led to typical respiratory symptoms, 90% morbidity, and 20% mortality in a 72 h-period. Bacteriological screening revealed that multiple organs, including the heart, liver, spleen, lungs, kidneys, and blood, were infected with H. parasuis. The threshold loads of bacteria in blood and the lungs were (7.04 ± 0.53)log 10 CFU/mL and (6.24 ± 0.62)log 10 CFU/g, respectively, at 3 d after infection. Gross pathology examination showed celiac effusion, intestinal mucosal hemorrhage, and liver, spleen, or lung swelling, necrosis, and hemorrhage. Congestion, mild interstitial pneumonia, inflammatory exudation, and endothelial cell proliferation were observed in the histological examination. Discussion All the results suggest that we have established an experimental intraperitoneal infection model for H. parasuis in neutropenic guinea pigs. It is especially useful as a tool for pharmacokinetics, pharmacodynamics, or a pharmacokinetics/pharmacodynamics (PK/PD) model of antimicrobial agents against respiratory disease.