Development of a clinical syndrome resembling haemorrhagic septicaemia in the buffalo following intravenous inoculation of Pasteurella multocida serotype B:2 endotoxin and the role of tumour necrosis factor-α

Abstract Clinical changes and acute phase responses, including tumour necrosis factor-α ( tnf α), in six buffalo calves were examined following intravenous inoculation of a bolus of endotoxin (1 μg kg −1 bodyweight in 10 ml of phosphate-buffered saline [ pbs ]) extracted from Pasteurella multocida serotype B:2, the bacterium responsible for haemorrhagic septicaemia ( hs ) in Asia. Endotoxin injection caused a rapid onset of clinical signs characterised by dullness, sternal recumbency, elevated rectal temperatures, excessive salivation and dyspnoea that lasted for up to 12 hours post-inoculation (p.i.). Serum concentrations of tnf α rose within 1 hour p.i. to reach peak values ranging between 8 and 140 ng ml −1 at 1–2 hours p.i. and then declined rapidly to baseline levels 3–5 hours p.i. Endotoxin injection induced other acute phase changes, including a rapid leucopenia and reductions in the serum concentrations of iron and zinc and a delayed but prolonged increase in haptoglobin from 12 hours p.i. that reached a plateau from about 60 hours p.i. Three control calves injected with 10 ml pbs showed no clinical or blood compositional changes. By reproducing key signs of hs the work confirms a pivotal role of endotoxin in the pathogenesis of hs and emphasises the exquisite sensitivity of the buffalo to P multocida endotoxin.