Which Fusobacterium species is described as much more virulent and commonly implicated in severe infections?

• A. Fusobacterium necrophorum
• B. Fusobacterium varium
• C. Fusobacterium nucleatum
• D. Fusobacterium mortiferum

Answer: (A)

Fusobacterium necrophorum stands out for its high virulence and its frequent association with severe infections. It can start from a seemingly routine oropharyngeal infection and progress rapidly to serious systemic disease, such as septic thrombophlebitis of the internal jugular vein (Lemierre’s syndrome), with potential spread to liver and other sites. This aggressive behavior is linked to potent virulence factors like leukotoxins and endotoxin activity that promote tissue invasion and systemic spread. In contrast, Fusobacterium nucleatum is a common oral commensal and is more often involved in localized dental or periodontal infections, not the severe, invasive disease patterns seen with necrophorum. The other listed species are less frequently implicated in severe infections. Thus, the much higher virulence and its frequent involvement in severe infections point to Fusobacterium necrophorum.