Effects on Endotoxin Pathogenicity in Pigs with Acute Septicemia of Haemophilus parasuis Infection

Abstract

Changes of endotoxin in plasma, and the response of the coagulation system and blood cells in septicemia of Haemophilus parasuis infection were examined by inoculation with H. parasuis in specific pathogen-free (SPF) pigs. Eight pigs were inoculated intratracheally with 105, 106 and 107 colony formation units (CFU) of the strain Nagasaki (serovar 5). All pigs died 28 to 42 hr after inoculation. Haematologically, severe leukopenia occurred 24 hr post inoculation (hpi) until death. Glucose concentration decreased from 24 hpi to death. In the coagulation system, decrease of platelet counts, prolongation of prothrombin time, activated partial thromboplastin time, and increase of fibrinogen-fibrin degradation products were observed in all inoculated pigs. Endotoxin was detected in the plasma of all the inoculated pigs from 16 hpi to death, and its concentration rose dramatically just before death. H. parasuis was re-isolated from the blood of all inoculated pigs from 16 hpi to death, and also from almost all organs and body fluids of the pigs. The pigs had microthrombi in the kidney, liver and lungs, and many also had pneumonia, meningitis and serositis. H. parasuis antigen was detected in the lesions by the immunoperoxidase technique. The results indicated that disseminated intravascular coagulation (DIC) and endotoxin shock involved aggravation of clinical signs and death on the pigs induced to septicemia of H. parasuis.