Etiology

• An infectious disease of the interdigital skin and subcutaneous tissues.
  • Caused by the bacteria Fusobacterium necrophorum Fusobacterium necrophorum.
    • This bacteria is ubiquitous in the environment, and is shed in feces from the gastrointestinal tract.
    • It is a gram negative anerobic bacillus, biotypes A, B and AB.
• Additional bacteria such as Porphyromonas levii and Prevotella intermedia may also be involved.
• While still unproven, Treponemes associated with digital dermatitis Digital dermatitis may be involved with the peracute form of the disease known as “super-foul”.

Predisposing factors

General

• Warm and moist environmental conditions in Spring and Autumn (Fall) provide ideal conditions, especially if there is a lot of slurry or pooling water.
• Mud.
• Mud balling between claws in drier weather.
• Pooled dirty water.
• Certain bedding materials such as sand or recycled wood chip. The latter can contain splinters, glass and occasionally sharp metal fragments.
• Uncontrolled digital dermatitis Digital dermatitis can result in a range of lesions from a milder “interdigital dermatitis” with a pungent odor through to the peracute and severe “super-foul”.
• Stubble fields, stalks from fodder crops or rough grazing pastures with thistles can predispose to interdigital foot injuries and entry of bacteria.

Specific

• Sand bedding.
• Incorrectly managed foot baths can predispose to epidemics.
• Muddy tracks, gateways, feeding trough, water troughs and pasture.
• Certain designs of automatic scrapers.
• Immunosuppression eg bovine viral diarrhea Bovine viral diarrhea.
• Skin trauma due to sharp ice has been reported.

Progression

• If left untreated, the infection can extend into the deeper structures of the foot, causing deep sepsis of the navicular bursa, osteomyelitis, septic arthritis and abscess formation in the retro-articular space
• The disease can be self-limiting in neglected cases

Pathophysiology

• Infection requires trauma or maceration of the interdigital skin (through prolonged exposure to moisture).
• Contamination of injured interdigital skin results in colonisation of F. necrophorum.
  • This bacteria has several virulence factors such as endotoxin, hemolysin, adhesins, proteases and leukotoxins.
  • The leukotoxins are cytotoxic for neutrophils, macrophages and epithelial cells, and can induce cell lysis to occur.
    • This leads to tissue necrosis.
• Granulation tissue can develop in the interdigital space, with secondary bacterial infections common.
  • Can predispose to development of chronic interdigital hyperplasia. Interdigital hyperplasia
• Cattle do not appear to develop protective immunity, so re-infection is common.

Timecourse

• The lesion develops over 1-5 days.