Animal and snake bites: Nursing

Bites can be caused by a wide variety of animals, including dogs, cats, and small rodents, like hamsters or squirrels; as well as wild animals, such as snakes. Perhaps more surprisingly, bites can also be caused by humans!

Let’s start by looking at the anatomy and physiology of the skin. The skin is made of the epidermis, which is an outer layer that acts as a protective barrier against the environment; the dermis, which primarily contains blood vessels and nerve endings; and the hypodermis, which is a layer of connective tissue that provides structural support to the skin.

The skin also contains several immune cells which are responsible for phagocytizing invading pathogens, such as those that may have broken through the epidermis via a cut, scrape, or bite wound. When activated, immune cells release inflammatory molecules, like cytokines and histamine, which attract more immune cells to the site of injury. In addition, the release of cytokines causes capillaries to get larger and become more permeable, allowing plasma proteins and fluid to leave the circulation. Ultimately, all of these factors contribute to the classic signs of inflammation: heat, pain, redness, and swelling.

Now, the most common animal bites are from dogs, followed by cats and small rodents, like squirrels or rats. In particular, dog bites account for up to 90% of all animal bites, and they typically affect children under the age of 10. On the other hand, cat bites are less common and tend to occur more frequently in adult clients.

Finally, snake bites are a major hazard in certain areas of the world, including Southeast Asia, sub-Saharan Africa, and Latin America, as well as certain parts of the United States, depending on the species. Most snake bites occur in forested areas, but also in regions of high density of snake population, typically farming regions where grain attracts rodents that, in turn, attract snakes. There are two main venomous snake families: the Elapids, like corals, cobras, and mambas; and the Vipers, like rattlesnakes and copperheads.

When it comes to animal bites, bites are considered provoked if done by a healthy animal when attempting to feed or handle it normally; or unprovoked, which usually occurs by an animal with rabies. Snakebites, on the other hand, can occur inadvertently when someone steps on or disturbs a snake in the field; they can present as a bite to the head or trunk in individuals sleeping outside on the ground.

All right, now the pathology of animal bites involves both the mechanical injury caused by the bite itself, as well as any complications, including bite wound infection, or envenomation, which is the exposure to a poison or toxin. In the case of snake bites, animal bites can range from mild lacerations or puncture wounds to severe destruction of the skin and underlying tissues, including blood vessels, muscles, and bones.

Since dogs have strong jaws, dog bites typically cause serious tissue injury, but the lesion rarely gets infected. It’s important to note that dog bites can transmit a bacteria called Capnocytophaga canimorsus, which may cause gangrene at the bite site and then disseminate and cause sepsis, especially in asplenic clients and those with liver disease. In contrast to dogs, cats have long, thin teeth that create deep puncture wounds, which very often get infected. Cat bites can even reach the underlying joint space or periosteum, leading to septic arthritis or osteomyelitis.

With snake bites, on the other hand, there are local changes at the bite site like erythema, swelling, and development of hemorrhagic bullae and tissue necrosis, as well as general symptoms depending on the type of snake venom. Besides envenomation, snakebites can also lead to allergic reactions, as well as lasting injuries such as loss of a finger or limb due to amputation.

Clinical manifestations of animal bites can range from a simple laceration or puncture wound, to severe tearing of multiple skin layers because of the animal's teeth, jaw, or fangs. In most cases, clients experience pain, swelling, redness, and possibly blistering, pus, or fluid oozing from the bite site. There can also be a loss of sensation around the bite.

With a systemic infection, manifestations can also include fatigue, fever or chills, and swollen lymph nodes. Regarding envenomation, some snakes’ venom, like that produced by cobras, can cause neurotoxicity. This causes rapidly developing descending paralysis, resulting in diplopia, difficulty swallowing or talking, as well as limb or even respiratory muscle paralysis.

Other venoms, like that of the Viper snakes, can cause direct cellular injury and hemotoxicity. Their venom alters the balance of the coagulation system, resulting in coagulopathy, which can result in gum bleeding, epistaxis, hematemesis, or hematochezia. In severe cases, hemorrhage secondary to coagulopathy can cause severe shock and cardiovascular collapse. Additionally, the venom may be myotoxic resulting in rhabdomyolysis. This leads to tender, weak muscles and dark red urine. Unfortunately, some snake bites can cause death if not treated promptly.

The diagnosis of animal and snake bites starts with the client’s history, including the animal species and the circumstances of the bite, and physical assessment. For mammal bites, follow-up testing may involve obtaining a CBC to look for leukocytosis, as well as ESR and CRP, which can be elevated in case of infection. If the bite appears infected, a gram stain and culture of the wound should be obtained before starting antibiotics. Additionally, if there are signs of systemic illness, like fever or fatigue, then blood cultures should also be taken. Finally, in a deep bite wound an X-ray should be taken to look for foreign bodies like teeth, bone or soft tissue injury, as well as subcutaneous gas.

As for snakebites, laboratory testing may reveal thrombocytopenia or an elevated PT and a decreased fibrinogen, all of which are indicative of coagulopathy. With rhabdomyolysis, laboratory testing shows an elevated CK level and an elevated urine myoglobin.