Schmorl’s disease or skin necrosis due to

Fusobacterium necrophorum

Esther van Praag, Ph.D.

In 1891, the German pathologist C.G. Schmorl first described the disease caused by the bacterium Streptothrix cuniculi. It has been later renamed Fusobacterium necrophorum. Schmorl’s disease affects animals, as well as man.

Fusobacterium spp. is a non-motile, non-spore forming, anaerobic, Gram-negative bacterium that belongs to the normal intestinal bacterial flora of the rabbit. It is suspected that the disease is spread by cecotropes. The lesions are indeed found mainly around the head, the neck and the feet. This bacterium is also responsible for dental disorders, like tooth root infections.

The disease is associated to poor hygiene, and husbandry, and is independent from the sex, the age or the breed of a rabbit. Further sporadic causes for the disease are:

• Ptyalism due to dental problems, like malocclusion or tooth root problems;

• Panting, related to a environment with high temperatures or respiratory distress (dyspnea);

• Inappropriate drinking tools, like a leaking water bottles, or an oversized dewlap getting wet while drinking;

• Cages with rusted and/or sharp edges.

afip.org/vetpath/WSC/WSC96/96wsc01.htm

High magnification showing mats and short chains of filamentous bacilli consistent with F. necrophorum.

Clinical signs and diagnosis

The first signs are an acute inflammation of the subcutaneous tissues. As the disease progresses, there is ulceration of the superficial skin layer, suppuration of the subcutaneous tissue and necrosis.

In rare cases, the disease is caused by Fusobacterium nucleatum in rabbits.

The disease is characterized by the formation of skin ulcers and subcutaneous abscesses on the head, neck and feet. In rare cases, encapsulation of the abscesses by fibrous tissue is observed. If the wounds remain untreated, the infection spread to the skin, leading to necrosis of the tissue. The wounds can spread into deeper tissue layer and cause osteomyelitis or septicemia, leading to infection of vital organs and general toxemia. The rabbit is feverish and its lesions spread a foul smell.

In some cases, the rabbits suffer a chronic attack of Fusobacterium sp. They show mainly a decreased appetite (anorexia) and chronic weakness (cachexia).

To confirm the diagnosis, a sample should be collected from the affected area and cultured. Similar lesions are indeed caused by various other bacteria, including Pasteurella multocida, Staphylococcus aureus or Pseudomonas aeruginosa.

Treatment

The fur around the lesions is carefully clipped and wounds are cleaned with an antiseptic solution. The treatment must be accompanied by parenteral administration of antibiotics like penicillin, cephalosporin, chloramphenicol, tetracycline or metronidazole. Due to its good penetration of the bone, cephalosporin’s is the antibiotic of choice when the bone is affected.

The abscesses and necrotic tissue must be excised surgically.

If surgery is not possible, the abscess cavity can be incised, drained and packed with an antibiotic impregnated dressing. Various methods are available:

• Permanent placement of antibiotic impregnated PMMA beads;

• Temporary filling with antibiotic impregnated haemostatic and bactericidal sterile compressed sponge. The dressing must be changed daily or every 2nd day, to avoid necrosis of surrounding tissues;

• Temporary filling with wet-to-dry hygroscopic and bactericidal sugar dressing (e.g. 50% dextrose, manuka or clear sterilized (g-rayed) honey). The dressing must be changed daily, to avoid necrosis of surrounding tissues.

The later filling presents the advantage to remove the malodorous smell of ammonium and sulfur compounds due to bacterial breakdown of serum or cell proteins.

Infection by Fusobacterium sp. is generally difficult to treat and tends to return as soon as the antibiotic treatment is stopped. To minimize recurrence the causes should be looked for and corrected.

More detailed information on Fusobacterium infections in rabbits can be found in: “Skin Diseases of Rabbits” by E. van Praag, A. Maurer and T. Saarony, MediRabbit.com, 2010. Paperback, 408 pages.

Further information

Crociani F, Biavati B, Castagnoli P, Matteuzzi D. Anaerobic ureolytic bacteria from caecal content and soft faeces of rabbit. J Appl Bacteriol. 1984; 57(1):83-88.

Garibaldi BA, Moyer C, Fox JG. Diagnostic exercise: mandibular swelling in a rabbit. Lab Anim Sci. 1990; 40(1):77-78.

Hofstad T, Sveen K. Endotoxins of anaerobic gram-negative rods. Scand J Infect Dis Suppl. 1979; (19):42-45.

Kanoe M, Toyoda Y, Shibata H, Nasu T. Fusobacterium necrophorum haemolysin stimulates motility of ileal longitudinal smooth muscle of the guinea-pig. Fundam Clin Pharmacol. 1999; 13(5):547-554.

Licois D. Tyzzer's disease. Ann Rech Vet. 1986;17(4):363-386.

Nakajima Y, Ueda H, Takeuchi S, Fujimoto Y. The effects of Escherichia coli endotoxin as a trigger for hepatic infection of rabbits with Fusobacterium necrophorum. J Comp Pathol. 1987; 97(2):207-215.

Ormerod D, Koh K, Juarez RS, Edelstein MA, Rife LL, Finegold SM, Smith RE. Anaerobic bacterial endophthalmitis in the rabbit. Invest Ophthalmol Vis Sci. 1986; 27(1):115-118.

Seps SL, Battles AH, Nguyen L, Wardrip CL, Li X. Oropharyngeal Necrobacillosis with Septic Thrombophlebitis and Pulmonary Embolic Abscesses: Lemierre's Syndrome in a New Zealand White Rabbit. Contemp Top Lab Anim Sci. 1999; 38(5):44-46.

Tyrrell KL, Citron DM, Jenkins JR, Goldstein EJ. Periodontal bacteria in rabbit mandibular and maxillary abscesses. J Clin Microbiol. 2002; 40(3):1044-1047.

Ward GS, Crumrine MH, Mattloch JR. Inflammatory exostosis and abscessation associated with Fusobacterium nucleatum in a rabbit. Lab Anim Sci. 1981; 31(3):280-281.

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