Management of Animal Bites and Envenomation

Benjamin N. Abo

INTRODUCTION TO NONVENOMOUS ANIMAL BITES

The world has been co-inhabited by a wide variety of animals since the dawn of time. As humans venture into the wilderness for both settlements and adventure-seeking, more and more animals and humans have negative encounters. Decades ago people would avoid certain areas because of dangerous wild animals, but more recently travel around the world specifically to see these same wild animals in person and often “up close.” There is no animal that prefers humans as its natural prey. Usually animal attacks are secondary to fear, real or perceived, territoriality, or accident. Despite living in the age of the Internet, incomplete information and frank myth has continued to spread, creating public misunderstandings of animal behavior. (As an aside, the Internet may very well be responsible for some myth propagation itself, with some arguing that it and other forces have moved us into a “post-truth era.”¹ See further discussion of this topic in our introductory chapter and Chapter 1.) However, some commonsensical publications have suggested ways to navigate between truth and falsehood on the Internet.² While this chapter could easily be a separate textbook of its own, it will discuss prevention and care of animal bites and envenomation. This chapter will focus discussion on general care of bites of particular species more medically prevalent or important than others, the venoms of a sampling of snakes and other reptiles, and the basics of antivenin; however, it is important to remember that it would be impossible to cover every single variant.

Definitions of Nonvenomous Bites

Bites of both wild and domestic animals are similar from other traumatic injuries that can damage skin, muscle, nerves, tendons, joints, blood vessels, and bones. This can be from the penetration into the human body, similar to being stabbed with a knife; however, it can also be a tearing or cutting mechanism as well as blunt trauma. Animal bites can lead to local infection as any wound can from various environmental sources or from inoculation of bacteria that live in the animal’s mouth.

Poisonous animals are not the same as venomous animals. Animals that have developed specific venom glands and venom delivery systems can be found in every class. The toxins and the apparatus to deliver them vary from class to class. For example, rattlesnakes have modified salivary glands and maxillary teeth, fangs that are mostly used for prey but also for defense. Bees on the other hand have a modified ovipositor that is used for defense only. It is important to discern that in this section venomous rather than poisonous animals are discussed. An animal with toxins distributed throughout its body like certain fish or toads that would cause death to humans after ingesting the animal is considered poisonous. More simply put, poisons must be ingested, inhaled, or absorbed. However, only animals with specific toxins and a means to deliver said toxin is considered venomous.

Scope of Discussion of Nonvenomous Bites

This chapter will cover a broad range of injuries and conditions related to wildlife, from bites to stings to envenomation and beyond. Prevention is the best tool. But when problems do occur, it is crucial for a good wilderness emergency medical services (WEMS) provider to be able to identify and understand the potential risks and outcomes of such emergencies and their treatment options in the wilderness environment.

EPIDEMIOLOGY OF NONVENOMOUS BITES

The incidence of animal bites and envenomation has been difficult to determine because many are simply not reported. Domestic animal bites are relatively common, whereas data for
wild animal attacks are significantly weaker. Furthermore, data pertaining to bites, infections, and envenomation is lacking in both quantity and quality. Perhaps the best epidemiologic data available come from the US Centers for Disease Control and Prevention (CDC), but the data sources are diverse and have varied over time, even among the most common types of animal-human encounters such as dogs and cats. Estimates of bites from other species are even more difficult to estimate in their data sources as reptilian and insect bites are also grouped into the same category as stings from plants, jellyfish, and coral.

Mammalian bites represent common presentations in WEMS and emergency departments. Most bites are from domesticated dogs and cats. Half of all Americans will be bitten by an animal or another human during their lifetime.³^,⁴ While, again, the true incidence is unknown, it is estimated that over 2 million bites result in medical treatment just within the United States.⁵ Another source quotes about 4.7 million dog bites annually in the United States, with almost 19% of them requiring medical attention. In this series, children are 3.2 times more commonly bitten than are adults.⁶^,⁷ Outside of the United States as well, dog bites constitute a majority of animal-related injuries. Data from 320 cases reported between 1998 and 2005 looked at animal-associated injuries among returning travelers. It found dogs involved in 51.3% of cases, followed by monkeys in 21.2%, cats in 8.2%, and bats tied with humans at 0.7%.⁸^,⁹ This study also showed, like others, that patients under the age of 15 years are more likely to have animal-associated injuries. Depending on where the person is living, visiting, or working, large reptiles without venom may be an important consideration, such as the crocodile or alligator.

CLINICAL MANAGEMENT OF NONVENOMOUS ANIMAL BITES

Setting aside venomous bites and stings being for later in this chapter, management of nonvenomous animal bites is similar to any other traumatic injury. Bites are traumatic injuries that can damage skin, muscle, nerves, blood vessels, tendons, joints, and bones. Wounds themselves may be lacerations, contusions, scratches, tears, or deep punctures. Contamination from oral flora from the biting animal may be the principal treatment concern, but bleeding and other damage are also concerning as well as, to a far lesser degree, the prospect of rabies or tetanus.

Rabies is a viral illness transmitted when it is present in a rabid animal’s saliva and is introduced into bite wounds or onto mucous membranes. Once deposited into peripheral tissues, it travels to the central nervous system (CNS). Rabies causes tens of thousands of deaths annually on almost every continent, but mostly affects underserved communities with limited access to health care or incomplete rabies control programs. A huge majority of deaths occur in Africa and Asia, with dogs being the main source. Once in the CNS, rabies causes acute, progressive, incurable encephalitis. Where vaccination programs exist such as in the Americas, bats are the main cause of infection followed by foxes, raccoons, skunks, jackals, mongooses, and other carnivore host species. It should be known that less than 1% of human deaths occur after exposure to animals other than dogs or bats.¹⁰^,¹¹^,¹² Although rabies is almost always fatal once it becomes clinically evident, it is 100% preventable with vaccination. The CDC and the World Health Organization (WHO) has numerous resources for information for determining both preexposure prophylaxis (for those that are high risk) as well as postexposure prophylaxis (PEP). PEP is determined on the basis of the likelihood the implicated animal was rabid, the severity of exposure (activity and type of wound), the clinical features of the animal, and its vaccination status.¹¹^,¹²

Prevention of Nonvenomous Animal Bites

The old adage that “an ounce of prevention is worth a pound of cure” could not be more important to remember when it comes to animal bites and envenomation. It is important to have the basic knowledge of wildlife indigenous to whatever region one may be visiting or practicing in. Injuries caused by animals are considered “unintentional injuries” as opposed to “accidents” because research shows that they have the same type of predictability and identifiable risk factors.¹³ Unless provoked, domestic animals of any kind rarely attack. This is why it is important to have a basic understanding of animal behavior so as to not accidentally provoke an animal to feel that it needs to go to its last resort, which is a physical attack. This means humans must have an understanding of basic attacks of animals and understand what might be a warning sign. For instance, for the most part, if a human slowly and carefully backs away while acting confident and calm, an animal will usually not become aggressive. Wild animals that are captured, restrained, or kept as pets can be stressed and thus may be unpredictable and suddenly attack in self-defense. Most wild animals exhibit ample warning signs by use of visual, auditory, or olfactory senses before escalating to physical attack. People can often avoid injuries from attacks by successfully interpreting these signs.

Identification of Nonvenomous Animal Bites

Examination of the patient begins before even contacting him or her. When treating patients of animal attacks, whether domestic or wild, it is important to remain safe yourself. Auditory and visual senses need to be used to size up the scene for safety as well as to piece together the mechanism of injury and therefore potential injuries. Having an idea of the type of animal involved
and how it may act needs to be considered before approaching. One should take note of what type of animal was involved, how the animal was acting, what may have provoked the incident, and where the animal then went. The latter is particularly important for the rescuers’ safety. Once you have approached the patient, management is similar to the general trauma patient. If possible and not already done, identify the type of animal and general behavior of the animal. Remember, an animal put under duress can attack with more than impressive force. Attacks by larger animals can easily produce major blood loss, thoracic injury, spinal cord injury, or airway damage. As would be suspected, basic trauma care is needed and evacuation of the victim to a hospital as soon as possible may be paramount. The patient should be assessed for life-threatening hemorrhage, which often can be fairly obvious even at a distance while approaching the patient. This exsanguination should be managed immediately. If other providers or bystanders have begun care, it is important to confirm that this has been accomplished appropriately. The patient should then systematically be evaluated to avoid missing other life- or limb-threatening injuries. Chapter 21 contains more detailed information related to the further identification and treatment of traumatic injuries in the austere environment.

Treatment and Disposition of Nonvenomous Animal Bites

Beyond major life-threatening injuries from animal bites such as exsanguination, wound care is extremely important. When and to what extent a wound can be cleaned plays an important role in wound infection and healing. Therefore, local wound treatment should be initiated almost immediately if possible.⁹

First Aid

Basic first aid and trauma principles apply. Identify the problem overall. Be sure to identify all wounds and dress them with clean dressings. If major bleeding occurs, apply direct pressure with or without pressure points; this controls a majority of bleeding within 3 to 5 minutes. In cases of severe bleeding and shock, tourniquet application can be lifesaving.¹⁴ After this, the wound should be inspected, washed, and dressed with sterile dressing if possible.

Basic Life Support

Basic trauma principles apply. Identify the problems beginning with life-threatening problems. Remember that some injuries may be more distracting than others. Identify any major bleeding and apply direct pressure and pressure dressings as needed. In the case of severe, arterial, or life-threatening bleeding, do not delay applying a commercial tourniquet or appropriate improvised tourniquet high and tight on the affected extremity. Remember that properly placed tourniquets should completely stop the bleeding and stop pulses distal to the tourniquet. Although tourniquets can save life and limb, a tourniquet that is not tight enough can actually increase venous bleeding.¹⁵^,¹⁶^,¹⁷^,¹⁸^,¹⁹ Chapter 21 discusses tourniquet placement in more detail. After any major bleeding has been stopped, identify any other wounds and dress them with clean dressings. If time allows without delaying evacuation, begin irrigation and cleaning of the wound with clean water avoiding if possible products like hydrogen peroxide. Do not forget to reassess any wounds you have already treated. Hand and foot wounds may require immobilization. Other extremity injuries may also require immobilization.

Advanced Life Support

Same principles apply for the basic life support (BLS) provider as they do for the advanced life support (ALS) provider. General principles for ALS trauma care discussed in Chapter 21 apply to animal-related bites and take precedence. Remember the potential for blunt trauma and injury to deeper and vital structures from falling or from penetrating claws, teeth, or horns. Spinal cord protection (SCP) may be needed as well as airway management. See Chapters 21 and 24 for a more complete discussion of the indications and procedure for SCP. Furthermore, be careful to assess and reassess thoracic injuries for the potential sucking chest wound or pneumothorax that may require occlusive dressings or needle decompression. After assessing and treating life-threatening injuries, one should treat the wounds, especially bite wounds, as soon as possible. Should you have fluids such as normal saline, irrigate the wound with moderate to high pressure with copious amounts to try to decrease the likelihood of infection. Although guidelines have varied regarding to how much fluid is needed for the irrigation of traumatic wounds, the actual volume should vary depending on the size of the wound.²⁰^,²¹ The old dictum of “the solution to pollution is dilution” rings true. Given its virucidal effect, irrigation with a 1% diluted povidone-iodine solution may be beneficial in bites in which rabies is a concern. There are some systems where ALS starts antibiotic therapy. Refer to the recommendations for the clinician below and your local protocols if antibiotics are an option. Chapter 11 discusses antibiotics in the WEMS environment in more detail. Going beyond immediate patient care, it is important to try to ascertain information about the animal and the situation to help determine whether rabies prophylaxis is needed. This information beyond type of animal includes unusual behavior, for instance, complete absence of fear of humans or an unprovoked attack in broad daylight.

Clinician

Basic and advanced trauma principles also apply to the wilderness clinician. One needs to evaluate for any potential blunt trauma and injury to deeper vital structures from penetrating injuries or associated falls. The clinician should also evaluate for potential nerve or tendon involvement as well as the more obvious blood
vessel involvement. Tetanus immunization needs to be ensured as soon as possible. Irrigation of the wound with copious volume of clean normal saline (NS) or diluted 1% povidone-iodine is vital. Again, whenever possible even in austere settings, wounds should be cleansed and irrigated thoroughly as soon as possible without delaying major resuscitation efforts. Early wound care reduces the chance of infection and has also proven beneficial in decreasing the risk of rabies transmission. It does this so well and is considered so likely to be beneficial that a randomized controlled trial (RCT) is considered unethical.²²^,²³^,²⁴

Wounds should be covered with sterile dressings or a dry, clean cloth. Unlike some other traumatic wounds, animal bites are not ever considered clean lacerations and should be treated as contaminated wounds. They may also be combined with crush injuries with devitalized tissue. Furthermore, especially in children, animal bites can penetrate vital structures such as joints or the cranium. If the wounds are at high risk for infection and definitive treatment is hours away, it is appropriate to start antibiotic therapy if an appropriate antibiotic is available. Chapter 11 and Chapter 20 discuss antibiotics in more detail. Bite injuries that are more likely to be considered low or lower risk for infection are based on location and the type of wound. Skin with a more substantial blood supply, such as the scalp or face, usually can be considered lower risk, as can large clean lacerations that can thoroughly be cleansed, partial-thickness abrasions, or simple contusions that do not actually break the skin.

After adequate irrigation has been assured and evacuation to definitive care is not possible for many hours, primary closure of some wounds may be considered if they are simple bite wounds of the trunk or extremities (excluding hands and feet) less than 6 hours old or simple bite wounds of the head or neck less than 12 hours old. Primary closure is not recommended for clenched fist injuries, puncture wounds, hand and foot bites, bites with extensive crush injury, bite wounds clinically infected, or bite wounds where antibiotic prophylaxis will be significantly delayed. Certain species, including wild cats, primates, and pigs, tend to have bites that are more prone to infection. In contrast, select mammalian bites such as dogs may be able to be closed after adequate wound irrigation and preparation.²⁵^,²⁶^,²⁷^,²⁸^,²⁹^,³⁰^,³¹ Ideally, antibiotics should be given within a few hours of the bite or injury.

Beyond physically treating the bite victim, the consideration of rabies is an important aspect for the clinician. Information such as the species of animal, the behavior of the animal, the vaccination status of the animal (if domesticated), and what actions brought on the encounter with the animal is important in considering whether or not postexposure prophylaxis (PEP) for rabies is needed. In the United States, most rabies transmission is from bats, raccoons, skunks, and foxes. Given the frequency of bats in their environments, mountain and cave rescue teams in particular should be versed in bat exposures and indications for rabies PEP to adequately counsel patients and determine evacuation needs, as well as protect team safety given possible team member exposure.³² Accidents in North American Climbing (formerly known as Accidents in North American Mountaineering) describes multiple recent climber exposures to bats requiring rabies PEP and immunoglobulin treatment.³³^,³⁴ Also note that currently, in the case of bats, the CDC recommends PEP if a patient is simply in proximity to a bat and cannot prove absence of exposure, for example, waking up with the bat.³⁵ For most teams, rabies PEP and immunoglobulin needs will direct evacuation and destination facility but not field treatment. The Wilderness Medical Society and climbing authorities recommend that a wound with possible rabies be cleaned immediately and copiously with soap, water, and, if available, a virucidal agent such as povidone-iodine or chlorine dioxide-treated water.³²^,³⁶ Contacting receiving facilities to ensure they have PEP series available may be helpful—some smaller hospitals will not stock this, and although its urgency is measured in days rather than hours, for an extended WEMS extrication this may become a time-sensitive consideration. Note that bats also provide an important lesson that geography matters in logistical consideration, as, for example, the bats of Hawai’i have been proven to be rabies-free.³⁵ Understanding local epidemiologic parameters like this help ensure appropriate care and disposition decisions.

Another concern that needs to be remembered beyond rabies is tetanus. If there is any doubt regarding a victim’s immunization status including a full series plus a booster within the last 5 years, 0.5 mL of diphtheria-tetanus booster vaccine should be administered at some point in the patient’s care, although this is unlikely to be available to WEMS teams. Remember this is a vaccination, not a treatment, and so may be more effective in preventing the next exposure than the current one. If there is a concern for imminent tetanus exposure from the current wound, such as a high-risk dirty wound, the patient should receive 250 to 500 units of tetanus human immune globulin intramuscularly (IM), which is a more immediate treatment rather than preventive vaccination.

Select Animal Habits

Alligators and crocodiles are large reptiles in the order Crocodilia that are without venom and that have a well-known appearance among the few animal species that will attack and kill humans without being provoked.³⁷^,³⁸ Like other reptiles, these animals are ectothermic (cold-blooded) and thus their activities vary depending on weather and the time of day as they rely on the environment for body temperature. In cool environments, they can be found bathing in sunlight out of the water and commonly on roadways. In warmer environments, they will spend more time in the water to keep cool. Their long snouts have a keen sense of smell even when mostly submerged and have extremely strong jaws refined for grabbing and tearing. These reptiles are more commonly active during evening times, and most attacks have been seen during summer months and afternoon to twilight hours.
Because of their methods of crushing, tearing, and drowning, crocodilian bites can produce severe crush injuries, punctures, lacerations, avulsions, and drownings. Data have been sparse on the microbiology of human wounds inflicted by crocodilians, but a few case reports indicate significant polymicrobial infections.³⁹^,⁴⁰ Some recommendations to prevent crocodilian attacks include being cautious with small pets or children (even in relatively developed areas such as hotels),⁴¹ being cautious around still or slow-moving brackish water or freshwater, avoiding swimming at night, being diligent to dispose of food scraps, not feeding them or trying to handle them, and observing or photographing crocodiles and alligators only from a safe distance. If an attack should occur, it is advised to be aggressive and fight back while attempting to escape when they open their jaws for a better purchase on their prey or to further crush their prey. Crocodilians usually persist in their attacks until death or complete escape.

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