Session #2003

Abstract

Reptiles have unique anatomy and physiology of their skin and dermis. This means our clinical approach to wound care has to be significantly modified compared to mammalian patients. Once you have an understanding of reptile wound healing then basic principles used in other species can easily be applied. This masterclass covers basic wound care through to surgical approaches taken to effectively close wounds.

Introduction

Reptile skin provides physical protection and is critical in the control of water, gas, and heat exchange. Skin injury or disease is commonly presented in clinical practice and the techniques used to facilitate healing can vary depending on the animal’s environment. Aquatic species such as freshwater Chelonia are particularly challenging to manage due to both their demeanour and the need to encourage healing in an aqueous environment. Healing and immunocompetence in reptiles are temperature dependent. It is critical that all reptiles are maintained at optimal temperatures to enable thermoregulation so wound healing can occur. Despite this, wound healing can be protracted in reptiles, with skin wounds typically taking six weeks to heal and shell deficits in chelonians taking considerably longer. Granulation, dermal bone formation, and filling in of defects in these species can take up to two years. Of concern are those species which hibernate over the winter where alternative strategies need to be in place to keep the reptile awake over the winter to enable wound healing to proceed. All of these factors can mean marked husbandry changes are needed to be in place before entering into protracted wound care in reptilian species.

Anatomy and Physiology

The major epidermal modification in reptiles are the scales. This is comprised of a heavily keratinised layer which is replaced at regular intervals through a process known as ecdysis. In chelonians, the epidermal layer over the shell are the scutes. Deeper to this layer is the dermis, which can also undergo marked species differences. Many lizard species have osteoderms which are radiographically evident and need to be avoided when cutting, debriding, or suturing wounds. Chelonians have the most extensive modifications, with the dermal layer becoming ossified to form the shell. There are also multiple glandular regions evident in the skin of reptiles with many species-specific adaptations.

In snakes and lizards, ecdysis occurs over a fourteen-day period. There are often behavioural changes noted at this time. Cells at the base of the epidermis regenerate and create a whole new layer of epidermis. Lymph then enters the space between the old and the new skin and can lead to a dulling of the reptile’s colouration. In snakes, this is clearly evident over their eyes, where a blue colouration change is found limiting normal vision. Snakes do not usually feed during this time. A lovely summary of the anatomy and physiology of reptile skin can be found in Skin Diseases of Exotic Pets.¹

Basic Wound Care

Wounds can present as a result of trauma from bite wounds from conspecifics, trauma from the environment (both in wildlife casualties and captive animals), or be a consequence of underlying deeper infection. Although there is often a focus on bacterial infections, caution is advised as mycotic diseases such as Nannizziopsis or Ophidiomyces in squamates or Emydomyces in aquatic chelonians are becoming increasingly recognized.^2-4 In addition, pathogens such as Mycobacteria can be present.⁵ Unresponsive chronic wounds require biopsy to identify underlying agents and disease processes to enable classification into fungal, bacterial, viral, parasitic, or neoplastic lesions. Cytology does allow for immediate results to guide suitable presumptive therapy. Culture is often recommended and a suitable representative sample should be taken. Aerobic, anaerobic, and fungal culture should be performed. Significant pathogens such as Ophidiomyces or Mycobacteria will not grow in routine cultures. For those organisms which cannot be cultured successfully, qualitative PCR may be done on fresh or stored frozen tissue.

Wounds should be flushed and cleaned, unless there are concerns for a coelomic breach or pulmonary damage. Knowledge of underlying organs is critical to enable a thorough assessment; imaging may also be required as deeper tissues can be involved leading to osteomyelitis or abscessation.

In general, wounds are cleaned with sterile saline. This acts to physically remove debris but also has minimal impact on the tissues. It is important to ensure that whatever topical agents are utilised, they stimulate granulation tissue formation and are not epitheliotoxic. Other local agents, such as manuka honey or hydrogels, can be used to facilitate granulation. If the skin is not broken, then agents such as silver sulfasalazine cream can be utilised and this is great for controlling infection and soothing burns for example.

Although there is an urge to provide the best veterinary care, overtreatment can actually be detrimental. In the correct environment, the regenerative potential of reptile skin is massive. The clinician is advised to be optimistic. Significant wounds that may lead the clinician to consider euthanasia or complex reconstruction (in a mammalian patient for example) may actually heal best without complex procedures being undertaken. A recent study in sea turtles demonstrated longer rehabilitation times in patients undergoing procedures versus simple management of comparable wounds.⁶

The lack of elasticity in reptile skin means that often primary closure of wounds is not achievable. Self trauma to wounds is unusual in reptilian patients. However, keeping topical therapy in place or bandaging of wounds can be problematic due to their varying anatomy. One solution to this is to suture hydrocolloid dressings in place to act both as a stent to prevent would breakdown, cover a wound to stop increased contamination, and also to stimulate healing. These are tolerated well by lizard patients. In chelonians with shell damage, traditional bandaging techniques work well provided the bandage is outwith the reach of the limbs. Adhesive dressings can be used, or alternatively, dressings stuck in place using surgical tape.

Vacuum-assisted therapy (VAC) has been used to speed the formation of granulation beds in open chelonian wounds, significantly reducing healing time.⁷

Primary Closure

Reptile skin has a tendency to curl inwards and this can impair wound healing, and primary closure using horizontal mattress sutures may be indicated once the extent of the wound is known. As soft tissue injuries can take six weeks to heal, monofilament suture materials which retain strength for longer are preferred. Reptiles can lack some of the proteolytic enzymes to break down some suture materials, so selection of the right material is paramount, with poliglecaprone 25 being a commonly utilised option.⁸ It is important to place these sutures carefully in between scales wherever possible. The skin is the holding layer in reptilian patients. For minor wounds, tissue glue has been advocated.⁸

For chelonian shell fractures, primary closure is an option, but it is important to ensure the entire wound can be visualised long term. Shell fractures heal first by granulation followed by de novo ossification of the granulation bed, so there is no need to oppose fracture sites perfectly. Any dead tissue is progressively sloughed as the granulation bed forms and so ongoing assessment to evaluate the wound is required, and ongoing debridement of the necrotic bone may be indicated to facilitate granulation.

In these cases, many novel repair approaches are considered, such as the use of pins, zip ties, sticky hooks, or plates to reconstruct tissue and hold depressed fractures in place. These are preferred over chemical acrylics such as polymethylmethacrylate.

Acknowledgements

Thank you to the staff at DVREP for providing images for the presentation.

References

1.  Goodman G. Structure and function of reptile skin. In: Paterson S, ed. Skin Disease of Exotic Pets. Blackwell Science; 2006:75–80.

2.  Gentry SL, Lorch JM, Lankton JS, et al. Koch’s postulates: confirming Nannizzipsis guarroi as the cause of yellow fungal disease in Pogona vitticeps. Mycologia. 2021;113(6):1253–1263.

3.  Franklinos LHV, Lorch JM, Bohuski E, et al. Emerging fungal pathogen Ophidiomyces ophiodiicola in wild European snakes. Sci Rep. 2017;7:3844. https://doi.org/10.1038/s41598-017-03352-1.

4.  Wodburn DB, Kinsel MJ, Poll CP, et al. Shell lesions associated with Emydomyces testavorans infection in freshwater aquatic turtles. Vet Pathol. 2021;58(3):578–586. doi: 10.1177/0300985820985217.

5.  Mitchell MA. Mycobacterial infections in reptiles. Vet Clin North Am Exot Anim Pract. 2012;15(1):101–111, vii. doi: 10.1016/j.cvex.2011.10.002.

6.  DJ L. Comparing various methods of shell fracture stabilization techniques on chelonian carapace fracture cases and whether they impact the total length of hospitalization time. 2022. Unpublished data Student Research Component R(D)SVS.

7.  Hedley J, Woods S, Eatwell K. The use of negative pressure wound therapy following subcarapacial abscess excision in a tortoise. J Small Anim Pract. 2013;54(11):610–613. doi: 10.1111/jsap.12118.

8.  McFadden MS, Bennet RA, Kinsel MJ, Mitchell MA. Evaluation of the histological reactions to commonly used suture materials in the skin and musculature of ball pythons (Python regius). Am J Vet Res. 2011:72(10):1397–1406.