A 5-month-old, 22-kg intact female Rhodesian Ridgeback was examined at the Tufts Cummings School of Veterinary Medicine Foster Hospital for Small Animals for progressive hind limb pain, fever, lethargy, and anorexia of 3-days duration. The dog had been examined for pain and prescribed meloxicam at an unknown dose on initial visit to the referring veterinarian, but the clinical signs and fever worsened. The local emergency clinic performed 2 examinations over the following days as the condition progressed. The dog had been previously healthy with no significant medical history before the acute onset of clinical signs.The dog was referred for further evaluation, and on presentation was quiet but responsive, febrile (103.5uF), with a heart rate at 120 beats per minute and high respiratory rate at 36 breaths per minute. A loud S3 gallop was auscultated, but no audible murmurs or arrhythmias were present. The jugular vein observation was normal. Femoral arterial pulses were judged to be weak. Multiple joint effusions were present, with distension and edema observed particularly over the left stifle and tarsus and marked edema to the entire left distal pelvic limb. The right and left carpi and the right stifle and tarsus were also slightly swollen. The neurologic examination findings were normal, although the dog was unwilling to walk. Oral examination documented pale mucous membrane color and evidence of lost deciduous and newly erupting permanent teeth. The joint fluid was purulent, and numerous degenerative neutrophils with intracellular bacteria were visualized on cytologic examination.There was a white blood count of 14,600/mL (reference range, 4,900-16,900/ ml) with 9,336 mature neutrophils/mL, a left shift (band neutrophils, 584 mL; reference range, 0-300/uL) and a monocytosis (3,358 mL; reference range, 100-1,500mL). The neutrophils were moderately to markedly toxic. Platelet count was low at 56,000/mL (reference range, 181-525,000/mL). Hyponatremia (141 mEq/L; reference range, 142-158 mEq/L), hypochloremia (105 mEq/L; reference range, 106-126 mEq/L), increase in total bilirubin (2.40 mg/dL; reference range, 0.1-0.3 mg/dL), increase in alkaline phosphatase (1,691 U/L; reference range, 12-121 U/L), increase in alanine aminotransferase activity (1,344 U/L; reference range, 18-86 U/L), and increase in aspartate aminotransferase activity (928 U/L; reference range, 16-54 U/L) were present. The serum was icteric. Urinalysis results indicated concentrated urine (specific gravity, 1.050) with the presence of heme, bilirubin, and protein (100 mg/dL). Bilirubin crystals were visible in the sediment.Culture of the tarsal joint fluid yielded Pasteurella multocida (4+ growth), whereas the aerobic and anaerobic blood cultures obtained on the day of admission were positive for P multocida and Peptostreptococcus spp., respectively. There are no National Committee of Clinical Laboratory Standards for susceptibility testing for P multocida, but rather ampicillin/penicillin, potentiated amoxicillin, tetracycline, trimethoprim/su...