FUSOBACTERIUM-NECROPHORUM INFECTIONS - VIRULENCE FACTORS, PATHOGENIC MECHANISM AND CONTROL MEASURES

Fusobacterium necrophorum, a Gram-negative, non-spore-forming anaerobe , is a normal inhabitant of the alimentary tract of animals and humans . Two types of F. necrophorum, subspecies necrophorum (biotype A) and funduliforme (biotype B), have been recognized, which differ morpholog ically, biochemically, and biologically. The organism is an opportunis tic pathogen that causes numerous necrotic conditions (necrobacillosis ) such as bovine hepatic abscesses, ruminant foot abscesses and human oral infections. The pathogenic mechanism of F. necrophorum is complex and not well defined. Several toxins, such as leukotoxin, endotoxin, haemolysin, haemagglutinin and adhesin, have been implicated as virule nce factors. Among these, leukotoxin and endotoxin are believed to be more important than other toxins in overcoming the host's defence mech anisms to establish the infection. F. necrophorum is encountered frequ ently in mixed infections and, therefore, synergisms between F. necrop horum and other pathogens may play an important role in infection. Sev eral investigators have attempted to induce protective immunity agains t F. necrophorum using bacterins, toxoids, and other cytoplasmic compo nents. Generally, none of the immunogens has afforded satisfactory pro tection against Fusobacterium infections. Because of the unavailabilit y of suitable immunoprophylaxis, the control of F. necrophorum infecti on has depended mainly on the use of antimicrobial compounds.