Necrobacillosis in Lagomorphs 

Disease Summary

• An uncommon, sporadic, severe bacterial infection of the skin and subcutaneous tissues of rabbits that is characterised by necrosis, ulceration, and abscessation. Skin infection is most commonly seen around the lips and head of the rabbit but fatal septicaemia with widespread necrosis of visceral organs has also been reported.

(B336.42.w42, B601.13.w13, B602.19.w19, B606.4.w4, B608.21.w21, B610.23.w23)

Alternative Names (Synonyms)

• Schmorl's disease
• Synonyms for Fusobacterium necrophorum include:
  • Streptothrix cuniculi
  • Sphaerophorus necrophorus
  • Fusiformis necrophorus
  • Bacillus necrophorus
• Lemierre's Syndrome

See also: 

• Abscessation in Rabbits
• Moist Dermatitis in Lagomorphs

(B614.8.w8)

Disease Type

Infectious/Non-Infectious Agent associated with the Disease

• Necrobacillosis in rabbits was first described in 1891 by Schmorl. (B611.9.w9)
• This disease is usually caused by Fusobacterium necrophorum; however there has been one reported case of Fusobacterium nucleatum causing a clinically and pathologically identical disease. (B614.8.w8)
• Fusobacterium necrophorum is an anaerobic, non-motile, non-spore-forming, gram-negative bacterium that is normally found in the gastrointestinal tract and rabbit faeces. (B602.19.w19, B614.8.w8, J213.4.w4)
  • The morphology of this organism ranges from coccobacillary to filamentous with the latter form being most commonly seen. (B614.8.w8)
• This organism is thought to be a secondary invader rather than a primary cause of disease. (B611.9.w9)

Pathogenesis

• Acute inflammation of the subcutaneous tissue is the first sign of necrobacillosis. This then rapidly develops into necrosis and ulceration of the overlying skin; sometimes there may also be invasion of deeper tissue including bone. Necrotising lesions may also occur in visceral organs if there is haematogenous spread of the bacteria. (B614.8.w8)

Risk factors for development of disease

• Poor husbandry: necrobacillosis is usually seen in rabbits that are kept in an environment with poor sanitation. (B611.9.w9)
• Skin wounds (B614.8.w8)
• Dental problems:  in one case, a retained premolar root was reported to act as a nidus for infection. (B614.8.w8)

Infective "Taxa"

• Fusobacterium necrophorum (Gracilicutes (Gram negative staining cell-walls))
• Fusobacterium nucleatum (Gracilicutes (Gram negative staining cell-walls))

Non-infective agents

Physical agents

References

Disease Author

Referees

Major References / Reviews

Code and Title List

Other References

Code and Title List

Detailed Clinical and Pathological Characteristics

Clinical Characteristics

• Inflammation      
• Swelling            
• Necrotic lesions, ulceration, abscessation.
• Distribution of lesions: 
  • Face, in particular the lips                
  • Head and neck       
  • Feet - occasionally the plantar surface of the feet may be affected.

Systemic infection:

• General malaise (including anorexia and cachexia) may develop and in some cases there may be pneumonia. 
  • Acute onset lethargy, anorexia and depression in a six-month-old New Zealand white rabbit. (J501.38.w1)
• The underlying bone is sometimes involved resulting in osteomyelitis. 

(B600.9.w9, B601.13.w13, B602.19.w19, B606.4.w4, B608.21.w21,B610.23.w23, B611.9.w9, B614.8.w8, J213.4.w4)

Incubation

Mortality / Morbidity

Mortality

• Necrobacillosis can occasionally lead to fatal septicaemia with widespread necrosis of visceral organs. (B614.8.w8)
• A six-month-old New Zealand white rabbit died within three hours of the onset of clinical signs. (J501.38.w1)

Prognosis

• Prognosis is poor unless the disease is recognised and treated in the early stages. (B606.4.w4)

Pathology

• Skin and subcutaneous tissue:
  • Caseous necrosis and ulceration of the skin and subcutaneous tissue. 
  • The caseous lesions are composed of necrotic cellular debris that is surrounded by an area of suppurative inflammation. In more chronic cases, the lesions may be partially encapsulated by a layer of fibrous tissue.
• Bone: 
  • Occasionally, there may also be inflammation and necrosis of the underlying bone.
• General: 
  • If there is haematogenous spread of infection, then similar necrotic lesions may be found in visceral organs.

(B614.8.w8)

In a six-month-old New Zealand white rabbit which died within three hours of the onset of clinical signs. (J501.38.w1)

• Facial: 
  • Soft, friable 3.5 x 4.5 x 3 cm swelling around the caudal left mandibular ramus, temporal bone and basisphenoid bone, containing multiple focal to coalescing necrotic foci of yellow, greenish or grey caseous material, surrounded by a zone of dark red. (J501.38.w1)
  • In the subcutis of the lower jaw and around the nasal orifice, focal accumulation of white to yellowish gelatinous fluid. (J501.38.w1)
• Oropharyngeal: Yellow necrotic material, necrosis, mucosal swelling and ulceration of the hard palate and larynx around the caudal two to three upper cheek teeth, and in the adjacent laryngeal ventricle. (J501.38.w1)
• Jugular veins and veins near and within swollen tissues: friable, dark red, rigid, containing intraluminal emboli/thrombi and necrotic debris. (J501.38.w1)
• Lung: particularly in the middle and caudal lobes, multifocal to coalescing dark red foci, some with pale centres. (J501.38.w1)
• Liver: multifocal necrosis and haemorrhage. (J501.38.w1)
• CNS: 
  • In the cerebrum, cerebellum and midbrain, multifocal necrosis and haemorrhage. (J501.38.w1)
  • Meninges above the area of the facial lesion cloudy and thick, with petechiae. (J501.38.w1)

Histopathology

• In facial and oropharyngeal tissues, periodontal tissues, alveolar bone, lung, liver, myocardium, brain, meninges, small intestines: necrotic foci and/or embolic abscesses, "orientated around vessels, containing amorphous debris, degenerating cells, and long filamentous bacteria, and were surrounded by a zone of purulent inflammation, congestion and hemorrhage." (J501.38.w1)
• In blood vessels of affected tissues: cellular and bacterial thrombi/emboli, with transmural necrosis. (J501.38.w1)
• Affected molar teeth and adjacent bones: osteolysis and periosteal osteoid proliferation. (J501.38.w1)
• Culture: pure growth of Fusobacterium necrophorum from the mandibular abscess and from heart blood. (J501.38.w1)

Human Health Considerations

Disease has been reported in either the wild or in captivity in:

• Necrobacillosis is a sporadic disease of rabbits. (B614.8.w8)
• A six-month-old New Zealand white rabbit, with a facial abscess and rapid death. (J501.38.w1)

Further information on Host species has only been incorporated for species groups for which a full Wildpro "Health and Management" module has been completed (i.e. for which a comprehensive literature review has been undertaken). Host species with further information available are listed below:

Host Species List

• Oryctolagus cuniculus domesticus - Domestic European rabbit

(List does not contain all other species groups affected by this disease)

Disease has been specifically reported in Free-ranging populations of:

• --

Further information on Host species has only been incorporated for species groups for which a full Wildpro "Health and Management" module has been completed (i.e. for which a comprehensive literature review has been undertaken). Host species with further information available are listed below:

Host Species List

• --

(List does not contain all other species groups affected by this disease)

General Information on Environmental Factors/Events and Seasonality

• This organism will not live long if exposed openly to the air as it is quite sensitive to aerobic conditions. (B611.9.w9)

Regions / Countries where the Infectious Agent or Disease has been recorded

• Necrobacillosis is known to have a wide geographical distribution. (B611.9.w9)

Regions / Countries where the Infectious Agent or Disease has been recorded in Free-ranging populations

• --

General Information on Investigation / Diagnosis

• Bacterial culture of affected tissue. (B601.13.w13, B602.19.w19, B608.21.w21, B610.23.w23)
• Culture on blood agar at 37 °C for two days. (B614.8.w8)

• Environmental Assessment
• History & Documentation
• Physical Examination of Mammals
• Necropsy of Mammals
• Imaging in Lagomorph Diagnosis and Treatment
• Clinical Pathology of Lagomorphs
• Chapter 2 - B36 Field Manual of Wildlife Diseases - Specimen Collection and Preservation
• Chapter 3 - B36 Field Manual of Wildlife Diseases - Specimen shipment
• Appendix A - B36 Field Manual of Wildlife Diseases - Sample specimen history form

Similar Diseases (Differential Diagnosis)

• Abscessation in Rabbits
• Moist Dermatitis in Lagomorphs

Similar lesions may be seen with the following bacterial infections:

• Pasteurella multocida (Pasteurellosis in Lagomorphs)
• Staphylococcus aureus (Staphylococcosis (with special reference to Waterfowl, Hedgehogs, Bears and Lagomorphs))
• Pseudomonas aeruginosa (Pseudomonas Infection in Waterfowl (with notes on Hedgehogs))

(B614.8.w8)

Specific Medical Treatment

Systemic Antibiotics

• Use antibiotics that are effective against anaerobic bacteria. (B602.19.w19):
• Penicillin G procaine (B602.19.w19, B608.21.w21)
  • 40000 IU/kg once daily by subcutaneous injections for ten to thirty days. (B601.13.w13, B610.23.w23, J213.4.w4)
  • Penicillin is usually the antibiotic of choice. (B614.8.w8)
• Tetracycline  (B601.13.w13, B608.21.w21, B610.23.w23, B614.8.w8)
• Cephalosporins are useful in cases of osteomyelitis because they have good distribution in bone. (B614.8.w8)
• Long-term high-dose wide-spectrum antibiotic therapy is recommended, e.g. Metronidazole, Penicillin G, cephalosporin, Chloramphenicol, Tetracycline, since this organism may occur as part of a mixed anaerobe infection as well as alone. (J501.38.w1)

Topical Antibiotics 

• Antibiotic PMMA beads have been used successfully. (B601.13.w13, B610.23.w23, J213.4.w4)
  • See: Production of Antibiotic-Impregnated Beads
• For more information on their use, see: Abscessation

• Production of Antibiotic-Impregnated Beads
• Treatment and Care

General Nursing and Surgical Techniques

Surgical debridement

• Drainage and debridement of wounds is important.

(B601.13.w13, B606.4.w4, B608.21.w21, B610.23.w23, B614.8.w8, J213.4.w4, J501.38.w1)

• For further information on treatment of rabbit abscesses see: 
  • Abscessation in Lagomorphs
  • Facial Abscesses in Rabbits

• --

Preventative Measures

--

• Preventative Medicine for Mammals

Environmental and Population Control Measures

Lagomorphs

• Environmental and Population Management