Burns in reptiles and amphibians (Proceedings)

Thermal burns in amphibians and especially reptiles are very common injuries seen by herp veterinarians. The exact reason why these animals seem so prone to burns is not understood, but, something about their behavior and their ability, or inability, to sense thermal injury makes them more susceptible to this type of trauma than any other captive animal. The goal of this paper is to discuss burns, specifically what causes burns, how to recognize them as early as possible and treat them as required.

Understanding Thermal Burns in Reptiles and Amphibians

Since reptiles & amphibians do everything slowly, it is not uncommon for an animal to get burned, but not actually show signs of the injury for several days. This is especially true for minor, or first degree burns. This is significant, since burns, even apparently mild injuries, can have severe consequences if not treated properly. In order to be able to treat burns properly, it is important to understand what causes burns, and how to recognize them in their early stages. Special thanks to Dr. Douglas Mader, MS, DVM, Diplomate ABVP (Ca). He has in previous lectures, articles, and chapters in books covered this topic extensively. Please refer to his and other previously published materials for more indepth coverage of the topic1.

Thermodynamics

The study of heat and its properties is called thermodynamics. As herptile veterinarians, we are all familiar with the importance of providing proper temperatures (i.e. P.O.T.Z) to the cage environment. Over the years we have seen the evolution of heating devices from the original "hot rocks" ("Death Rocks") to the more advanced, thermostatically controlled environmental chambers. We have learned that not only must captive reptiles & amphibians have supplemental heat, but, supplemental heat provided in the proper fashion. For instance, a ten foot long python would not fare well with a single, ten inch hot rock. Likewise, a nocturnal lizard would suffer if its cage were heated with a bright heat lamp.

In order for an object to get warm, or "heat up," there must be a transfer of heat from some outside source to the object that is being heated. Heat always moves from a warmer area to a cooler area. As the heat leaves the first object and enters the second object, the first object becomes cooler, and the second object becomes warmer. Eventually, the temperatures of the two objects will become equal. In other words, they will equilibrate. Heat will never continue to leave the first object such that it becomes cooler, resulting in the new object becoming the hotter of the two.

There are three ways that an object can gain heat, or become warmed. These are via conduction, convection and radiant heat.

Conduction is the transfer of heat within an object (such as down a long metal pole) or between two objects that are touching each other. A herpetological analogy here is the use of a "hot rock." Hot rocks, for those not familiar with these items, are a solid, block-like structure, usually made out of brick, concrete, plaster or heavy molded plastic. Imbedded within the rock is some sort of heating coil. When the heating coil is plugged in it generates heat. This heat, in turn, heats up the rock. If a reptile or amphibian crawls up on the rock, the heat from the hot rock will then transfer, via conduction, to the animal. The path of the heat transfers from the surface of the hot rock, through the feet, legs and abdomen of the animal, or whatever parts of the animal are in DIRECT contact with the rock's surface.

Convection, on the other hand, involves the motion of large-scale quantities of matter. In other words, convection usually involves the movement of either gasses (such as air) or liquids (such as water) – and heat is transferred via movement of this matter (e.g. air or water).

In reptiles & amphibians the heat transfer via convection is through exposure to drafts/movements of air or liquids.

Radiant heat transfer involves the flow of thermal energy by electromagnetic waves. In contrast to conductive heating, where objects must be touching, or convective heating, where the matter (gas or water) must touch the object to be heated, radiant heat does not have to have any matter involved (no touching/contact needed for heat transfer).

An example of radiant heat transfer is the reptile or amphibian basking in the sunlight. It is soaking up the electromagnetic radiation produced by the sun's rays. In captivity, this source of electromagnetic radiation is replaced by any number of artificial means - usually a heat lamp or a ceramic heating element .

In review, means by which reptiles & amphibians can become warmed is:

1. Radiant heat - The animal absorbs the electromagnetic radiation from the sun/heat element.

2. Convective heat - The warm air/water that blows/flows across the animal.

3. Conductive heat - from sitting on a basking spot that has been warmed by the sun/heating element shining on it, or from within in the case of a heating pad/rock. The basking spot/heating pad/rock then acts as a conductive heat source, passing the warmth back into the animal resting on it.

The best type of heat source for a captive pet will depend on the type of animal being housed. As mentioned, a small heat rock would be inappropriate for a large reptile. These animals do better with convective or radiant heat. Likewise, a big heat lamp would not be proper for an arboreal animal which would normally get its heat from either conduction or convection.

There are several other variables that play important roles in heat transfer and warming. A big factor is humidity. Moist air, or high humidity, tends to hold heat much better than dry air. When figuring temperatures and thermal gradients careful attention should be paid to humidity. A hot, humid cage will be much more stifling than a hot dry cage.

Ventilation is very important in any cage design. A well designed cage will have good ventilation. Stagnant air, especially in hot humid cages, leads to build up of pathogens, or disease-causing bacteria and fungi. Proper ventilation will dilute out any potential problem before it reaches concentrations that may be dangerous.

However, for all the good that proper ventilation does, it does have its drawbacks. A well ventilated cage tends to lose heat and humidity (it gets exhausted outside). There is really nothing wrong with this, except that the heat and humidity needs to be replaced, and, in the overall scheme of design, it ends up costing more to maintain a steady state of temperature and humidity. Thus it can be seen that there is a very close relationship between temperature, humidity and proper ventilation. This relationship must be considered when trying to provide the proper husbandry for the various species of reptiles & amphibians being kept in captivity.

Thermal Tissue Injury due to Heat Transfer

Of the three types of heat transfer, the two that cause the most injuries are radiant heat and conductive heat. "Hot Rocks" have been the direct cause for a great number of thermal injuries. These crude heating devices have a variable heat output. The heat is often unevenly distributed over the surface of the rock, resulting in hotspots that can reach temperatures that can burn due to direct/prolonged contact through the scales and will sear the flesh off any animal that rests on it. Not to mention that these heating devices can "short out." And, in a worst case scenario can result in a fire. Heat lamps have also been the cause of many radiant thermal injuries. Either due to prolonged or to close (but not direct) contact with the heating element. Humans have a withdrawal reflex. When we touch something hot, without any cognizant thought, we automatically, immediately, withdraw our hand. Even young children and mammals display this reflex. I have touched some brand new hot rocks, and their surface has been so hot, that I have experienced the same withdrawal reflex. They are so hot, I could not physically keep my hand on their surface. Why then, when a reptile rests on such a hot "hot rock", do they not also immediately jump off? This question does not have an easy answer. It is not uncommon for a snake to wrap its coils around a bare light bulb because it is attracted to the warmth that the light emits. So, it must feel the warmth, why then, does it not feel the burning heat? One possible answer is that the nerve receptors that sense heat and the receptors that sense pain are different. It is possible that, since in the wild, such pain receptors have no evolutionary significance (reptiles & amphibians do not normally come into contact with intensely hot objects in the wild). Therefore, evolutionarily, there would be no reason that a reptile or amphibian should have a hot-pain withdrawal reflex. Other possible theories put forth suggest that since reptiles & amphibians do not "reason" in the same fashion that people or other mammals do, even though the herptiles may feel pain, they do not associate it with the object that they are touching. Hence, they do not realize that they need to move in order for the pain to subside. Bottom line is, at the present time nobody really knows. So, until we understand why these animals are so prone to burns, the best thing to do is make every effort to prevent the burns in the first place.

Classification of Burns

Burns are classified by the type of burn and by the severity of the injury or extent of the body surface area affected. There are three basic classifications of burns in mammals. These categories can also be used in reptiles & amphibians. Understanding the nature of the burn will help you assess the need for intervention, i.e. is it something the client can treat at home, or, should it be hospitalized for competent/complete medical care ?

The extent and severity of a burn is related to several factors. Obviously the temperature of the heat source plays a significant role. Touching a stove burner set on "warm" will result in a far less severe burn than touching the same burner set on "high."

Duration of contact also affects the severity of the burn wound. Again, touching a stove burner set on "warm" only briefly may result in a minor burn. Whereas, holding one's hand on the same burner for several minutes may result in much more severe tissue damage. This is perhaps why we see such intense damage in reptiles & amphibians that have fallen asleep on what seems like only a mildly hot heating element like a "hot rock".

Finally, the heat conductance characteristics of the material touched also plays a role in the severity of the burn. For instance, touching a hot piece of metal would cause a more severe burn than touching a piece of wood at the same temperature. Also moisture seems to increase the conductance and therefore intensify the possible thermal trauma.

Types of burns include thermal, electrical, chemical and radiation. Thermal burns include all the categories discussed thus far, i.e. burns by hot rocks and heat lamps. An electrical burn, although not common in reptiles, can be seen where there is direct contact with an electrical current, such as when there is a short in a wire that has electrical arcing, or when an animal bites through an electrical cord that is plugged into a live socket. Chemical burns are caused by strong acids or alkalis, such as cleaning supplies like pure bleach (an alkali agent). These are also uncommon in reptile patients, but may occur, especially when chemicals are spilled or agents are not thoroughly rinsed after cleaning a cage. Radiation burns in reptiles are extremely uncommon. These are usually related to the use of radiation therapy when treating certain types of cancers. Since radiation therapy has been used in reptile patients, this type of burn is possible.

In older terminology, burns used to be classified as first, second or third degree, depending on the severity of the damage. In more recent classification, the terms partial thickness and full thickness burns, are more commonly used. "Thickness" refers to the outer layer of skin.

First degree burns are superficial, or partial thickness injuries that only involve the epidermis (outer skin). These burns are painful. In mammals there may be damage to the hair or fur (singing). The skin is reddened, and in severe first degree burns there may be blisters (such as in a severe sun burn). In reptiles & amphibians, one rarely see blisters, although they may occur, and occasionally, one may see singing of the scales, depending on the type of exposure. Usually, one will see reddening of the skin, and often what looks likes "bruises" under the scales, especially in white, pale or clear scales. In amphibians these can be serious injuries and should be treated appropriately. In reptiles, these burns usually heal well and rarely leave a scar. In an otherwise healthy reptile, healing takes about one month and a good shed for the burn to completely resolve.

Second degree burns are deeper partial thickness injuries with usually full destruction of the epidermis, and variable damage to the underlying dermis (inner, deep layer). In mammals, although there is more damage to the dermis, the fur or hair may not necessarily be damaged. The burns are very painful, and extensive subcutaneous swelling does occur. In amphibians these are even more serious injuries and unless treated immediately and completely, effected animals may not survive. In reptiles, blistering and oozing of serum from the burn site are seen. There is extensive bruising and discoloration of the tissue. These injuries lead to the formation of a scab-like covering over the burn. In both reptiles & amphibians healing occurs from the margins of the wound inward. In these wounds, especially in burns that cover a large surface area, healing may be prolonged and significant scarring may occur.

In third degree burns, the entire thickness of the skin is destroyed. The burn is actually painless (all the pain sensing nerves are destroyed), and the tissue takes on either a whitish or charcoal black appearance. In mammals the hair and fur fall out or are destroyed. Third degree burns are four times as serious as second degree burns of similar size. These wounds are usually fatal for amphinians. Healing of third degree or full thickness burns occurs by contraction of the wound (shrinking) and epithelialization (re-growth and migration of new skin from the margins of the wound toward the center). In some cases of third degree burns, skin grafting may be necessary. These burns may take many months (4 - 6) to heal completely. Severe scarring is a hallmark of third degree burns.

The classification of a fourth degree burn is occasionally used to describe a third degree burn that not only involves the full thickness of the skin, but also the underlying tissue such as muscle and bone. These injuries carry a grave prognosis.

Treatment Options for the Different Types of Burn

Reptiles are amazing animals. They have a penchant for healing far greater than any mammal. Some of the wounds that I have seen in reptiles would have spelled doom for most other animals. Incredibly, I have also seen scars on wild reptiles that bore the legacy of previous severe wounds. Wounds that healed without the benefit of veterinary intervention. That does not mean that we should ignore wounds in captivity, that they will heal without help, but, it does give us hope when we see a bad wound, knowing that with proper care and time, it may actually be able to heal.

Minor burns will often do well with first aid. However, severe burns will require medical attention and possible hospitalization in order to provide pain relief, infection control and treatment for shock.

In general, first degree burns, unless affecting extensive portions of the body, can be treated at home. If the burn is recent, apply cold water rinses/soaks or cold compresses (not ice!) for no more than twenty minutes. This helps reduce swelling and pain to the affected area. Applying ice to the tissue can cause frost bite, actually causing freeze damage to the tissue.

If blisters are present, they should NOT be broken. Doing so damages down the body's natural barrier against infection. Let the blisters either resolve or break on their own.

Infection is a common, and potentially serious complication of burns. When the skin is compromised, as with broken blisters, always pay careful attention to contamination, keeping the affected area as clean as possible. A non-irritating antibacterial soap, such as Nolvasan, or even a gentle hand soap, such as Ivory or Dove, will work well.

If there is damaged skin, then application of a topical burn dressing, after gentle wound cleansing, is appropriate. The burn should then be dressed, or covered, with a sterile non-stick bandage. This can be tricky, especially when the burn is on the underside of a snake.

In animals where there are extensive burns, I recommend keeping them in a glass or Plexiglas enclosure without substrate. Even though this is not a natural way to house a reptile, these cages are easy to clean and disinfect, thus minimizing the risk of infection. Their benefits outweigh the disadvantages of the temporary housing.

Second degree burns, because of the extensive tissue damage, need veterinary attention. If for no other reason, pain is a hallmark of second degree burns, and the veterinarian can provide medications for pain relief.

If the animal is in shock, therapy must be initiated to counter the effects. Wounds must be cleaned and debrided. Topical burn creams, such as Silvadene, are applied, and the patient is started on antibiotics to prevent infection at the burn site. Injectable cephazolin or oral cephalexin (20 mg/kg/day) are my first drugs of choice.

Fluids, either intravenous, oral or otherwise, must be administered to counter the effects of shock and fluid loss from the burn. Daily cleansing of the wound and sterile bandage changes are needed to effect rapid healing. These may take several weeks to months to fully heal.

Third degree, or full thickness burns may require intensive care at the outset. For human patients, there are entire burn centers dedicated to the care of burn victims.

Depending on the extent of the burn, the owner of the reptile should be appraised of the potentially grave prognosis. Treatment involves all the care involved for the second degree burn, plus more. As the tissue starts to heal, the pain can be intense. The pain from the daily cleanings and debridements can also intensify as the patient recovers feeling to the burn area.

Antibiotic therapy may be protracted, often lasting for several months. Wound care can get expensive, considering that the bandages may need to be changed daily for many months. As a veterinarian, it is important to consider all the costs of return visits, bandage materials, follow-up laboratory sampling and other miscellaneous costs when quoting estimates to the clients. Even in the face of such odds, many people do elect to treat their pets that are suffering from burns.

Even some of the fourth degree burns, where not only the skin is destroyed, but also the underlying tissue, have the potential to heal if cared for properly.

Although not discussed, many patients exposed to heat may not actually be burned, but, may suffer from smoke or other toxic fume inhalation. Many melted glues and plastics produce noxious fumes, as well as smoke that can damage delicate lung tissue. Although initially these patients may appear to be uninjured, they may develop a fatal fluid build-up within their lungs, and could potentially die if not treated properly in a timely fashion.

In conclusion, understanding the reason why reptiles are so prone to burn injury remains somewhat of a mystery. But, understanding the causes of burns and the mechanics of tissue injury will help us to prevent such occurrences, and in the unfortunate event that they do happen, to better manage their care. The most important point is when dealing with burns in reptile patients, be diligent, be clean and, above all, be patient!

Reference

Mader, D.R. (1998). Understanding Thermal Burns in Reptile Patients. Proc. 5th ARAV Conference, Kansas City, Mo. p. 143 – 149.