Calf Diphtheria

• Caused by Fusiformis.

Fibrinous/Diptheritic Inflammation

• Severe damage to epithelium produces exudation of fibrin - with formation of dry white fibrinous deposit - diptheritic membrane.
• Usually associated with organism Fusobacterium necrophorum found everywhere in environment (but strict anaerobe).
• Produces lesions that damage epithelium due to toxin that damages vessels.
• Often a secondary invader but can be a primary pathogen.

Clinical

• Seen in animals kept in cold, damp, muddy conditions.
• Usually associated with poor general health.

• Animals usually less than 6 months old, in groups and poorly kept.
• Lesions affect tongue, inside of mouth and larynx.
• Usually die fairly acutely as exudate blocks airway.

• May occur in young lambs secondary to orf (parapox) virus infection that can spread from lips to the inside of the mouth.

(These lesions then become secondarily infected with Fusiformis.)

• Involvement of the pharynx and larynx may result in dyspnoea and the development of pneumonia.
• May lead to death.

Macroscopically

• Grossly, there is a firm swelling visible on the outer aspect of the cheek
• On the mucosal surface there is a deep, irregular ulcer, covered by a thick diphtheritic membrane.

Microscopically

• There is complete loss of the surface epithelium:
  • a mass of necrotic debris
  • polymorphs and fibrin is found overlying severely inflamed subepithelial tissues in which bacterial colonies may be seen and around which there may be marked fibrosis in an attempt to “wall off” the lesion.

Necrotising laryngitis (Image sourced from Bristol Biomed Image Archive with permission)

Tracheitis in calf diphtheria (Image sourced from Bristol Biomed Image Archive with permission)

• Synonyms: laryngeal diphtheria, calf diphtheria
• Common disease in cattle, and can occur in swine
• Caused by infection with Fusobacterium necrophorum
• Lesions may also be found in other parts of the oropharynx
• The bacterium usually gains entry through damaged mucosal surfaces e.g. after viral infections or injury following (poor!) use of dosing guns, coarse poor quality roughage
• Results in severe acute neutrophilic laryngitis
• Extensive accumulation of fibrin and necrotic cellular debris on the ulcerated mucosal surface
• Lesions appear as dry plaques of fibrinonecrotic exudate and ulceration on the laryngeal mucosa
• Inhalation of exudate and bacterial organisms may cause bronchopneumonia
• Death may result from toxaemia or asphyxiation
• Also may occur in pigs