Shell rot: a clinical approach and treatment

The chelonian shell consists of an upper carapace and lower plastron, connected by lateral bridges.

The shell is composed of plates of dermal bone covered by horny epidermal keratin scutes. The keratin scutes are not shed regularly, but if this does happen, it could indicate a pathological condition.

The most common conditions affecting a tortoise’s shell are:

• deep shell abscesses
• shell fractures
• shell softening
• shell discolouration
• shell deformity
• shell rot

Recently, the author has encountered several cases of shell rot; it can affect any breed of tortoise, but burrowing species or individuals that dig tend to be more vulnerable.

The condition may arise following a minor crack or injury that penetrates the outer keratin layer of the shell. Poor husbandry, a moist environment and nutritional deficiencies may also be responsible.

Shell rot can involve either bacterial or fungal agents, but both can be reported simultaneously. The prognosis is generally good if treatment is fast and effective.

This article will consider an approach to the clinical examination, investigation (bloods), diagnosis, treatment, follow-up, outcome, discussion and prevention.

Clinical examination

A healthy shell should appear shiny, smooth, without irregularities or areas with discharge, and entire. It is recommended that patients with suspected shell rot follow a structured clinical examination using a sequential approach.

The overall condition of the patient must be assessed and recorded, and this should include bodyweight, appetite, hydration status and activity levels, since these may be decreased in affected patients that may become lethargic and inappetent.

The upper carapace is composed of marginal, pleural and vertebral scutes; every individual scute must be closely examined and any sign of pitted, denuded, flaky or loose scutes must be identified, while bearing in mind that deeper structures may also be involved.

Investigation

The author generally collects a blood sample for routine haematology and biochemistry, since affected individuals generally show a reduced white cell count; anaemia and liver involvement can also be reported, due to anorexia. It may also be beneficial to collect a swab from the deeper structures of the shell for culture and sensitivity analysis.

When severe cases of shell rot are suspected, a dorsoventral radiograph should be carried out to rule out severe bone osteomyelitis. Histology carried out in the samples from cases where fungal involvement is also suspected can demonstrate small fragments of fungal hyphae and occasional spores in the necrotic areas (Table 1).

Table 1. Improvement of white cell count after a month of antibiotics
Haematology	Units	Reference ranges as per Pinmoore Animal Laboratory Services		Elliot results
				Feb 09	Mar 09
Haemoglobin	g/dl	6.4 to 15.7		10.2	7.5
PCV	%	17 to 42		32	26
Red blood cells
Mean corpuscular volume
Mean corpuscular haemoglobin concentration	g/dl			31.9	28.8
Mean corpuscular haemoglobin
White cell count	109/L	1 to 4.5		*0.5	1.7
Heterophils	109/L	0.5 to 5	72%		0.46
Lymphocytes	109/L	0.27 to 2.5	27%		0.46
Eosinophils	109/L
Monocytes	109/L	0 to 0.5	1%		0
Azurophils	109/L
Basophils	109/L
Thrombocytes	109/L

Diagnosis

Diagnosis is normally achieved after all the aforementioned tests have been carried out. An experienced exotic animal vet can also diagnose it, depending on experience.

Treatment

Every shell rot case presented to the author has required aggressive surgical debridement under general anaesthesia. Anaesthesia is generally achieved by premedicating with 0.2mg/kg meloxicam and 0.01mg/kg buprenorphine administered intramuscularly one hour prior to induction.

General anaesthesia is induced with 2mg/kg propofol via the subcarapacial vein, intubating the trachea to maintain 5 per cent isoflurane and oxygen, which should then be reduced to 2.5 per cent once the patient is anaesthetised and stable. It is important to make sure the body temperature is well maintained during surgery.

The only way to know the extent of the infection is by removing all the scutes that appear raised or flaky, as well as all the scutes of the surrounding areas until healthy bone can be seen; this is normally done using an orthopaedic mallet and chisel.

On several occasions when the infection has been severe, the author has had to remove all the carapacial scutes. The exposed bony plate is debrided (she normally uses a Dremel at low speed) and thoroughly flushed with saline. The resultant wound is managed as an open wound.

Any tortoise that is too weakened, due to infection, or anorexic should be fitted with an oesophagostomy tube to assist feeding while the infection is being dealt with.

Over the years, the author has used various creams and bandage materials to manage the wound, depending on whether it is a wet or dry infection, as follows.

Wet infection

Wet-to-dry bandages applied twice daily for 10 days initially. A mixture of silver sulfadiazine and hydrogel is used to cover the affected area. Sterile swabs are then applied on top and the shell is wrapped in cling film to keep the bandage in place.

After the initial 10 days, the bandages should be changed every 2 or 3 days, depending on progress, until the lesions begin to epithelialise when the wound can be left uncovered (Figures 1 to 4).

• A thin layer of manuka honey applied once daily for seven days and covered with thin adhesive bandage. Depending on progress, reduce the bandage changes to every 3 days for a further 10 days. After this, just clean the affected area with undiluted iodine, allow it to dry and cover with thin adhesive foam wound dressing until the wound can be left uncovered.

The author has only started using manuka honey on shell infections recently, but she has found that the results are outstanding (Figures 5 to 9).

Manuka honey is a type of honey native to New Zealand. It is produced by bees that pollinate the flower Leptospermum scoparium, commonly known as the manuka bush. Manuka honey’s antibacterial properties are what set it apart from traditional honey. Methylglyoxal is its active ingredient and likely responsible for these antibacterial effects.

Additionally, manuka honey has antiviral, anti-inflammatory and antioxidant benefits. In fact, it has traditionally been used for wound healing, soothing sore throats, preventing tooth decay and improving digestive issues.

Note vacuum-assisted closure, incorporating silver-impregnated bandaging materials, has been reported to reduce the wound healing period compared to traditional methods; however, the author has not tried this to date as she has obtained excellent results with the traditional methods.

Dry infection

A thin layer of hydrogel gel once a week – covered with thin adhesive foam wound dressing or breathable transparent adhesive dressing – is sufficient in these cases until the lesions begin to epithelialise when the wound can be left uncovered (at around three to four weeks; Figures 10 to 14).

In all cases, pain relief and a broad-spectrum cover must be administered at 0.2mg/kg meloxicam IM and 20mg/kg ceftazidime IM, which should be continued for 2 and 12 weeks respectively. Multivitamin injections at 0.15ml/kg IM may also be administered twice, three weeks apart, to help with the healing process.

The most severely immunocompromised individuals require monthly blood tests, usually for three months, while they are receiving antibiotics to assess the immune system’s response to the therapy. An increment in the white cell count is normally observed on the second blood test.

Granulation tissue starts to cover the superficial wound normally between three to four weeks after debridement.

Follow-up

The author normally schedules follow-up appointments once a week for the first month, then once every two weeks the month after and then once a month for three more months.

Outcome

The shell tends to heal fully within five months.

Discussion

Shell rot (osteomyelitis) is a chronic disease that can affect the shell of tortoises, turtles and terrapins as a result of wounds that penetrate the outer keratin layer of the shell, trauma, poor husbandry conditions (moist environment and nutritional deficiencies) and renal disease.

To aid the identification of the underlying cause and treatment of shell rot, laboratory tests – especially bacteriology and histopathology – are advisable. Radiography is also useful when bone damage is suspected.

In several individuals the author has treated, Stenotrophomonas maltophilia has been isolated from a swab of the shell – this is an aerobic, non-fermentative, Gram-negative bacterium, ubiquitous in aqueous environments, soil and plants.

In another patient in which histology was carried out, an opportunistic fungal organism was reported in the necrotic areas.

Haematology and biochemistry generally provide an indication of the patient’s immune system and renal function; lymphopenia is normally observed and can be secondary to an underlying disease. The scute is normally associated with the infection, but it has also been reported in patients suffering from chronic renal disease.

Shell rot lesions commence at the seams and spread towards the middle of the scutes. Lesions tend to be grey-white, sometimes orange and can have a roughened appearance. In certain cases, the spread of the lesions is difficult to determine by changes in the colouration of the shell, so all the loose scutes and those behind them should be removed to prevent recurrence and further complications.

The prognosis in severely affected immunosuppressed individuals showing renal impairment is generally poor. In all of the patients the author has treated, the renal function was normal; however, all were severely leukopenic. Nevertheless, follow-up blood tests revealed the immune system was satisfactorily responding to the antibiotic treatment.

Aggressive debridement of the lesions down to healthy tissue – combined with topical and systemic antibiotics, and correction of underlying husbandry problems – are indicated. The affected areas of keratolysis soon regenerate without further intervention. If pitting is deep, lesions may be covered with antibiotic dressings, which should be changed daily until keratin regeneration and epithelialisation are well under way.

It generally takes several months for the shell to heal fully. Vacuum-assisted closure incorporating silver-impregnated bandaging materials has been reported to reduce the wound healing period, compared to traditional methods.

In case of delayed epithelialisation caused by opportunistic fungal involvement, systemic ketoconazole at a dose of 15mg/kg to 30mg/kg by mouth once daily for two to four weeks is indicated. Also, F10 at a dilution of 1:250 has been indicated topically to treat any fungal agents involved.

Prevention

Tortoises should have a health check every six months, during which the overall condition of the individual can be assessed – including bodyweight, skin, shell and plastron condition, parasitology test and hydration status – so that any abnormalities can be dealt with promptly.

No tortoise that has been subject to any health-related issues should be hibernated in the same year, since hibernation can put the health of the individual at risk, and the tortoise may struggle to come out of this and may potentially die.

In the author’s experience, shell rot is usually confined to one individual, but on one occasion, several individuals from the same household required treatment for shell rot simultaneously.

Adequate management and husbandry practices when keeping reptiles can prevent shell rot, so owners must ensure the environment where their reptiles are kept is regularly monitored by the vet.

Acknowledgements

The author acknowledges Ross Brown – professional proofreader, business writer and editor – for kindly proofreading this article. The author also acknowledges Joanne Ankers of Pinmoore Animal Laboratory Services for retrieving all lab data from past years for her.

• Drugs mentioned in this article are used under the cascade.