F.necrophorum is a pathogenic, anaerobic, non-spore-forming Gram-negative bacteria; it is a normal inhabitant of the mammalian gut and cannot invade normal tissue.
F.necrophorum is pleimorphic and is either long and filamentous or a short cocci. It is fermentative and haemolytic on blood agar. It produces grey, round and shiny colonies. There are three biotypes, biotype A has the greatest haemolytic activity and virulence.
Pathogenesis and pathogenicity
F.necrophorum is a primary pathogen in various diseases of farm animals. It forms mixed bacterial infections and can be secondary to IBR. Extracellular haemolysin contributes to infection and heat-stable leucocidin is correlated with biotype and virulence. Cytoplasmic toxin is haemolytic and LPS endotoxin causes host damage. Antibody levels to F.necrophorum rise with age, suggesting that these are not protective.
F.necrophorum is associated with bucket feeding, where buckets are contaminated with faeces. Bacteria enter through abrasions in the mucosa of the pharynx and larynx and cause fever, depression, anorexia, salivation, respiratory distress and halitosis. Aspiration of necrotic material into lungs may cause fatal bronchopneumonia.
F.necrophorum causes a number of necrotic wound infections often in association with facultative anaerobes. It causes;
Cows: calf diphtheria or necrotic laryngitis in cattle and necrobacillosis of the mouth and pharynx of young calves. Also, bovine liver abscesses and localised necrosis and scab formation of the teat orifice and sphincter of dairy cows.
Pigs: necrotic rhinitis in pigs.
Sheep: interdigital dermatitis, (pododermatitis) in sheep in association with D. nodosus and Arcanobacter pyogenes, predisposing to footrot. It also causes laryngeal chondritis in sheep and mixed infections in heel abscesses.
F.necrophorum is also involved in; hoof thrush; Mixed infections in pyothorax; mixed infections in aspiration pneumonia and in bovine traumatic reticuloperitonitis and pericarditis; subcutaneous abscesses due to cat bites; chronic fibronecrotic rhinitis; osteitis; contagious footrot; necrobacillosis and laryngeal chondritis.
Treatment against F.necrophorum includes potentiated sulphonamides or tetracyclines.
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