Amputation of a Mycobacterium marinum-infected hindlimb in an African bullfrog (Pyxicephalus adspersus)

THE African bullfrog (Pyxicephalus adspersus) is a long-lived southern African species, and is one of the largest anurans kept in captivity. It can spend up to 10 months per year below ground during dry periods (O’Shea and Halliday 2001), and its health may be difficult to monitor in captivity. This short communication describes the amputation of a Mycobacterium marinum-infected hindlimb of an African bullfrog. A captive adult male African bullfrog was presented with swelling and ulcerations of the right hindlimb (Fig 1). The referring veterinarian had attempted treatment with topical fusidic acid ointment (Fucithalmic; Vetxx) and bandaging; bacterial and fungal culture had yielded no growth. The animal’s condition deteriorated and the case was referred. Besides swelling and skin ulceration, crepitus was present in the tibiofibular region. Radiographs demonstrated a midshaft tibiofibular fracture at the nutrient foramen, with osteomyelitis and surrounding cellulitis, and it was decided to amputate the leg. Subcutaneous enrofloxacin (Baytril 2·5 per cent injectable; Bayer) injections at 5 mg/kg once daily (Stein 1996, Carpenter and others 2001) were administered for five days preoperatively. Anaesthesia was induced in a shallow bath of 2 g/l tricaine methane sulphonate (MS222; Thompson and Joseph) and was deemed to be deep enough for surgery when there was no corneal reflex, no righting reflex, slow, regular respiration and no response or change in respiration with painful stimuli (Downes 1995, Williams 2002). The bullfrog was positioned in dorsal recumbency on a wet, soft towel in a tray. Surgicaldepth anaesthesia was maintained by syringing the tricaine solution over the skin when needed. Healthy musculature was sectioned at least 2 cm from the nearest lesions. The ishiadic and cutaneous femoral arteries and veins, the major vessels of the anuran hindlimb (Duellman and Trued 1986), were ligated with 4/0 polydioxanone (PDS II; Ethicon). The femur was transected at the proximal quarter and the remaining musculature was sutured with 4/0 polydioxanone to form a protective cushion. Closure was with simple interrupted 2/0 polydioxanone sutures, and the wound was protected with a protective paste composed of gelatin, pectin and sodium carboxymethylcellulose in a plasticised hydrocarbon gel (Orabase; ConvaTec). The bullfrog was rinsed, and recovered from anaesthesia over the following 30 minutes. The enrofloxacin injections were continued. Skin discoloration appeared dorsally over the suprascapula, vertebrae and urostyle five days after surgery, developing into full-thickness skin ulcerations. These were judged to be due to the dorsal recumbency during surgery. Enrofloxacin administration continued until healing had occurred, four weeks after surgery, and the ulcers were protected with Orabase. The skin sutures were removed eight weeks after surgery. Histological examination of the leg showed necrotic bone fragments and debris containing acid-fast bacteria. Surrounding the fracture was a small quantity of new bone and cartilage, with granulation tissue and an inflammatory exudate, again with large numbers of acid-fast bacteria. The owner was advised about the zoonotic potential at this stage but declined euthanasia or any further diagnostics. The bullfrog presented four months after surgery with two 4 to 7 mm diameter cutaneous ulcerations over the urostyle and haemorrhage from the cloaca. The animal was euthanased by administration of intracardiac pentobarbitone sodium (Euthatal; Merial Animal Health) and a postmortem examination was performed. Cellulitis and early granuloma formation were present in the remaining femoral musculature. Numerous large hepatic granulomas with necrotic centres, and adhesions between the liver and adipose bodies, were the most noticeable macroscopic lesions (Fig 2). Granulomas were also present in the lungs, adipose bodies and kidneys, with numerous adhesions between the organs. Multifocal granulomatous and pyogranulomatous inflammation in the liver, lung, kidney and spleen, all containing large numbers of acid-fast bacteria, was evident on histology. Microbiological culture from a hepatic granuloma isolated Mycobacterium marinum. The amputation described in the present case differs from those described previously in anurans in which coxofemoral dislocation was performed (Brown 1995, Frye and Williams 1995). Abrasion was adequately prevented by suturing the well-developed femoral muscles over the transected bone, due to the sedentary nature of the species. This also allowed for a shorter period of anaesthesia. Non-absorbable skin sutures have been recommended in amphibians (Wright 1994, Brown 1995); however, in the present case interrupted polydioxanone absorbable sutures were used as this species is not aquatic. The surgical site healed normally. Short Communications