Biological and biochemical characteristics of the leukotoxin of Fusobacterium necrophorum were determined. Culture supernatant of F necrophorum was toxic to polymorphonuclear neutrophilic leukocytes from cattle and sheep, but not to those from pigs and rabbits. Culture supernatant and sonicated bacterial cell fractions had low hemolytic activity and did not cause dermonecrosis in a guinea pig. Supernatant-derived leukotoxin was inactivated at 56 C for 5 minutes and became unstable at pH > 7.8 or < 6.6. Chemical treatment with 0.1% sodium dodecyl sulfate, 0.25% sodium deoxycholate, 5.2% sodium sulfide, or 0.25 mM titanium (III) citrate markedly decreased leukotoxicity. Enzymatic treatment with protease, trypsin, and chymotrypsin inactivated the toxin completely, whereas amylase had no effect. Use of protease inhibitors failed to prevent loss of leukotoxin activity. Using membrane partition chromatography and gel filtration, the estimated molecular weight of the toxin was > 300,000. On reduction and denaturation, the toxin dissociated into several components by use of sodium dodecyl sulfate-polyacrylamide gel electrophoresis.

Changes in serum alpha-1-acid glycoprotein (alpha-1 AG) concentration in cattle with hepatic abscesses were observed, and function of alpha-1 AG was evaluated, particularly its influence on cellular immune response. Test cattle (n = 4) were inoculated with Fusobacterium necrophorum, control cattle (n = 2) were inoculated with inactivated bacteria, and naturally affected cattle (n = 11) were found in a slaughterhouse. Determination of alpha-1 AG was made by use of a single radial immunodiffusion method. The action on lymphocyte blastogenesis was determined by [3H]thymidine incorporation. Cultured lymphocytes from healthy cattle were treated with variable concentrations of alpha-1 AG purified from serum obtained from cattle with hepatic abscesses and suppression of blastogenesis stimulated by each of 3 mitogens was measured. In cattle with experimentally induced abscesses, serum alpha-1 AG concentration increased for 7 to 10 days after F necrophorum inoculation, its change being parallel to that of sialic acid. High concentration of alpha-1 AG was found in naturally affected cattle and was highly correlated to sialic acid concentration. Suppression of lymphocyte blastogenesis in cattle with experimentally induced hepatic abscesses was highly correlated to serum alpha-1 AG concentration.

Hepatic abscesses were induced experimentally in 5 steers by inoculating Fusobacterium necrophorum via ultrasonography-guided, percutaneous catheterization of the portal vein. Hepatic ultrasonography was performed to determine the onset and progression of abscessation. Blood samples were collected before and after inoculation for performing leukocyte counts and hepatic function tests. Ultrasonographic evidence of liver abscesses was observed as early as 3 days after inoculation. Abscesses appeared as hyperechoic centers (cellular debris and pus) surrounded by hypoechoic or anechoic areas (fluid). Increases in rectal temperature, leukocyte counts, fibrinogen, globulin, bilirubin, gamma-glutamyltransferase, and sorbitol dehydrogenase concentrations were detected. Hepatic dysfunction was evidenced by decrease in serum albumin concentration and low sulfobromophthalein clearance. The ultrasonographic diagnosis of abscesses correlated well with necropsy findings.

At an abattoir, lesion specimens from 140 condemned sheep livers were collected for bacteriologic culture and for pathologic examination. Grossly, 23 lesions were abscesses; from 9 of which, Fusobacterium necrophorum biovar A (3 in pure culture and 6 in mixed culture) was isolated and from 14 of which, biovar B (6 in pure culture and 8 in mixed culture) was isolated. Escherichia coli was the predominant facultative anaerobic bacterium and Clostridium perfringens was the predominant obligate anaerobic bacterium isolated from the 14 lesions with mixed bacterial infection. Histologically, these lesions had a core of coagulation necrosis, encircled by a zone of necrotic phagocytic cells and bacteria with cellular characteristics of F necrophorum biovars A or B, and a connective tissue capsule. Of the 117 lesions without F necrophorum, 49 were culture-positive (for other organisms) and 69 were culture-negative. These 117 lesions were fibrous and were smaller than the 23 abscesses. A variety of gram-positive and gram-negative facultative anaerobic and obligate anaerobic bacteria was isolated from the culture-positive lesions, but always in low numbers. Eleven culture-negative and 18 culture-positive lesions were examined and had histologic characteristics of parasite-induced granulomas, with numerous eosinophils and epithelioid giant cells. Results of the study indicated that the histologic appearance of ovine hepatic lesions with F necrophorum was similar to bovine liver abscesses caused by F necrophorum, but unlike bovine liver abscesses, F necrophorum biovar B was isolated more frequently than was biovar A and often in pure culture. Most of the lesions in the condemned livers were parasite-induced granulomas.