Snake Bites

A snakebite is an injury caused by a bite from a snake, often resulting in puncture wounds inflicted by the animal's fangs and sometimes resulting in envenomation. Although the majority of snake species are non-venomous and typically kill their prey with constriction rather than venom, venomous snakes can be found on every continent except Antarctica. Snakes often bite their prey as a method of hunting, but also for defensive purposes against predators. Since the physical appearance of snakes may differ, there is often no practical way to identify a species and professional medical attention should be sought.

The outcome of snake bites depends on numerous factors, including the species of snake, the area of the body bitten, the amount of venom injected, and the health conditions of the victim. Feelings of terror and panic are common after a snakebite and can produce a characteristic set of symptoms mediated by the autonomic nervous system, such as a racing heart and nausea. Bites from non-venomous snakes can also cause injury, often due to lacerations caused by the snake's teeth, or from a resulting infection. A bite may also trigger an anaphylactic reaction, which is potentially fatal. First aid recommendations for bites depend on the snakes inhabiting the region, as effective treatments for bites inflicted by some species can be ineffective for others.

The number of fatalities attributed to snake bites varies greatly by geographical area. Although deaths are relatively rare in Europe and North America, the morbidity and mortality associated with snake bites is a serious public health problem in many regions of the world, particularly in rural areas lacking medical facilities. Further, while South Asia, Southeast Asia, and sub-Saharan Africa report the highest number of bites, there is also a high incidence in the Neotropics and other equatorial and subtropical regions. Each year tens of thousands of people die from snake bites, yet the risk of being bitten can be lowered with preventive measures, such as wearing protective footwear and avoiding areas known to be inhabited by dangerous snakes.

Signs and symptoms

The most common symptoms of all snakebites are overwhelming fear, panic, and emotional instability, which may cause symptoms such as nausea and vomiting, diarrhea, vertigo, fainting, tachycardia, and cold, clammy skin. Television, literature, and folklore are in part responsible for the hype surrounding snakebites, and a victim may have unwarranted thoughts of imminent death.

Dry snakebites, and those inflicted by a non-venomous species, can still cause severe injury to the victim. There are several reasons for this: a snakebite which is not treated properly may become infected (as is often reported by the victims of viper bites whose fangs are capable of inflicting deep puncture wounds), the bite may cause anaphylaxis in certain people, and the snake's saliva and fangs may harbor many dangerous microbial contaminants, including Clostridium tetani. If neglected, an infection may spread and potentially kill the victim.

Most snakebites, whether by a venomous snake or not, will have some type of local effect. There is minor pain and redness in over 90% of cases, although this varies depending on the site. Bites by vipers and some cobras may be extremely painful, with the local tissue sometimes becoming tender and severely swollen within 5 minutes. This area may also bleed and blister. Other common initial symptoms of pitviper bites include lethargy, weakness, nausea, and vomiting. Symptoms may become more life-threatening over time, developing into hypotension, tachypnea, severe tachycardia, altered sensorium, and respiratory failure.

Interestingly, bites caused by the Mojave rattlesnake, coral snake, and the speckled rattlesnake reportedly cause little or no pain despite being serious injuries. Victims may also describe a "rubbery," "minty," or "metallic" taste if bitten by certain species of rattlesnake. Spitting cobras and rinkhalses can spit venom in their victims' eyes. This results in immediate pain, ophthalmoparesis, and sometimes blindness.

Some Australian elapids and most viper envenomations will cause coagulopathy, sometimes so severe that a person may bleed spontaneously from the mouth, nose, and even old, seemingly-healed wounds. Internal organs may bleed, including the brain and intestines and will cause ecchymosis (bruising) of the victim's skin.

Venom emitted from elapids, including cobras, kraits, mambas, sea snakes, and many Australian species, contain toxins which attack the nervous system, causing neurotoxicity. The victim may present with strange disturbances to their vision, including blurriness. Paresthesia throughout the body, as well as difficulty speaking and breathing may be reported. Nervous system problems will cause a huge array of symptoms, and those provided here are not exhaustive. If the victim is not treated immediately they may die from respiratory failure.

Venom emitted from some Australian elapids, almost all vipers, and all sea snakes causes necrosis of muscle tissue. Muscle tissue will begin to die throughout the body, a condition known as rhabdomyolysis. Dead muscle cells may even clog the kidney which filters out proteins. This, coupled with hypotension, can lead to acute renal failure, and, if left untreated, eventually death.

Pathophysiology

Since envenomation is completely voluntary, all venomous snakes are capable of biting without injecting venom into their victim. Snakes may deliver such a "dry bite" rather than waste their venom on a creature too large for them to eat. However, the percentage of dry bites varies between species: 50% of bites from the normally timid coral snake do not result in envenomation, whereas only 25% of pitviper bites are dry. Furthermore, some snake genera, such as rattlesnakes, significantly increase the amount of venom injected in defensive bites compared to predatory strikes.

Some dry bites may also be the result of imprecise timing on the snake's part, as venom may be prematurely released before the fangs have penetrated the victim's flesh. Even without venom, some snakes, particularly large constrictors such as those belonging to the Boidae and Pythonidae families, can deliver damaging bites; large specimens often cause severe lacerations as the victim or the snake itself pull away, causing the flesh to be torn by the needle-sharp recurved teeth embedded in the victim. While not as life-threatening as a bite from a venomous species, the bite can be at least temporarily debilitating and could lead to dangerous infections if improperly dealt with.

While most snakes must open their mouths before biting, African and Middle Eastern snakes belonging to the family Atractaspididae are able to fold their fangs to the side of their head without opening their mouth and jab at victims.

Snake venom

It has been suggested that snakes evolved the mechanisms necessary for venom formation and delivery sometime during the Miocene epoch. During the mid-Tertiary, most snakes were large ambush predators belonging to the superfamily Henophidia, which use constriction to kill their prey. As open grasslands replaced forested areas in parts of the world, some snake families evolved to become smaller and thus more agile. However, subduing and killing prey became more difficult for the smaller snakes, leading to the evolution of snake venom. Other research on Toxicofera, a hypothetical clade thought to be ancestral to most living reptiles, suggests an earlier time frame for the evolution of snake venom, possibly to the order of tens of millions of years, during the Late Cretaceous.

Snake venom is produced in modified parotid glands normally responsible for secreting saliva. It is stored in structures called alveoli behind the animal's eyes, and ejected voluntarily through its hollow tubular fangs. Venom is composed of hundreds to thousands of different proteins and enzymes, all serving a variety of purposes, such as interfering with a prey's cardiac system or increasing tissue permeability so that venom is absorbed faster.

Venom in many snakes, such as pitvipers, affects virtually every organ system in the human body and can be a combination of many toxins, including cytotoxins, hemotoxins, neurotoxins, and myotoxins, allowing for an enormous variety of symptoms. Earlier, the venom of a particular snake was considered to be one kind only i.e. either hemotoxic or neurotoxic, and this erroneous belief may still persist wherever the updated literature is hard to access.

The strength of venom differs markedly between species and even more so between families, but Australian snakes are known to possess particularly potent venom: 10 of the world's most venomous snakes, as measured by LD50 in mice, inhabit the continent. Of these, the inland taipan possesses the most potent venom, but because the snake is timid and rarely encountered by humans, bites are extremely rare. The amount of venom produced also differs among species, with the Gaboon viper able to potentially deliver from 5–7 ml (450–600 mg) of venom in a single bite, the most of any snake.

Prevention

Snakes are most likely to bite when they feel threatened, are startled, are provoked, or have no means of escape when cornered. Encountering a snake is always considered dangerous and it is recommended to leave the vicinity. There is no practical way to safely identify any snake species as appearances may vary dramatically.

Snakes are likely to approach residential areas when attracted by prey, such as rodents. Practicing regular pest control can reduce the threat of snakes considerably. It is beneficial to know the species of snake that are common in local areas, or while traveling or hiking. Areas of the world such as Africa, Australia, the Neotropics, and southern Asia are inhabited by many highly dangerous species. Being wary of snake presence and ultimately avoiding it when known is strongly recommended.

When in the wilderness, treading heavily creates ground vibrations and noise, which will often cause snakes to flee from the area. However, this generally only applies to North America as some larger and more aggressive snakes in other parts of the world, such as king cobras and black mambas, will protect their territory. When dealing with direct encounters it is best to remain silent and motionless. If the snake has not yet fled it is important to step away slowly and cautiously.

The use of a flashlight when engaged in camping activities, such as gathering firewood at night, can be helpful. Snakes may also be unusually active during especially warm nights when ambient temperatures exceed 21 °C (70 °F). It is advised not to reach blindly into hollow logs, flip over large rocks, and enter old cabins or other potential snake hiding-places. When rock climbing, it is not safe to grab ledges or crevices without examining them first, as snakes are cold-blooded and often sunbathe atop rock ledges.

Pet owners of domestic animals or snakes should be wary that a snake is capable of causing injury and that is necessary to always act with caution. When handling snakes it is never wise to consume alcoholic beverages. In the United States more than 40% of snakebite victims intentionally put themselves in harm's way by attempting to capture wild snakes or by carelessly handling their dangerous pets—40% of that number had a blood alcohol level of 0.1 percent or more.

It is also important to avoid snakes that appear to be dead, as some species will actually roll over on their backs and stick out their tongue to fool potential threats. A snake's detached head can immediately act by reflex and potentially bite. The induced bite can be just as severe as that of a live snake. Dead snakes are also incapable of regulating the venom they inject, so a bite from a dead snake can often contain large amounts of venom.

Treatment

It is not an easy task determining whether or not a bite by any species of snake is life-threatening. A bite by a North American copperhead on the ankle is usually a moderate injury to a healthy adult, but a bite to a child's abdomen or face by the same snake may be fatal. The outcome of all snakebites depends on a multitude of factors: the size, physical condition, and temperature of the snake, the age and physical condition of the victim, the area and tissue bitten (e.g., foot, torso, vein or muscle), the amount of venom injected, the time it takes for the patient to find treatment, and finally the quality of that treatment. Promptly securing qualified medical treatment is the best course of action, and conservative management in the meantime is recommended.

Snake identification

Identification of the snake is important in planning treatment in certain areas of the world, but is not always possible. Ideally the dead snake would be brought in with the patient, but in areas where snake bite is more common, local knowledge may be sufficient to recognize the snake. However, in countries where polyvalent antivenoms are available, such as North America, identification of snake is not a high priority item.

The three types of venomous snakes that cause the majority of major clinical problems are vipers, kraits, and cobras. Knowledge of what species are present locally can be crucial, as is knowledge of typical signs and symptoms of envenomation by each type of snake. A scoring systems can be used to try and determine the biting snake based on clinical features, but these scoring systems are extremely specific to particular geographical areas.

First aid

Snakebite first aid recommendations vary, in part because different snakes have different types of venom. Some have little local effect, but life-threatening systemic effects, in which case containing the venom in the region of the bite by pressure immobilization is highly desirable. Other venoms instigate localized tissue damage around the bitten area, and immobilization may increase the severity of the damage in this area, but also reduce the total area affected; whether this trade-off is desirable remains a point of controversy.

Because snakes vary from one country to another, first aid methods also vary. As always, this article is not a legitimate substitute for professional medical advice. Readers are strongly advised to obtain guidelines from a reputable first aid organization in their own region, and to be wary of homegrown or anecdotal remedies.

However, most first aid guidelines agree on the following:

1. Protect the patient (and others, including yourself) from further bites. While identifying the species is desirable in certain regions, do not risk further bites or delay proper medical treatment by attempting to capture or kill the snake. If the snake has not already fled, carefully remove the victim from the immediate area.
2. Keep the victim calm. Acute stress reaction increases blood flow and endangers the patient. Keep people near the patient calm. Panic is infectious and compromises judgment.
3. Call for help to arrange for transport to the nearest hospital emergency room, where antivenom for snakes common to the area will often be available.
4. Make sure to keep the bitten limb in a functional position and below the victim's heart level so as to minimize blood returning to the heart and other organs of the body.
5. Do not give the patient anything to eat or drink. This is especially important with consumable alcohol, a known vasodilator which will speed up the absorption of venom. Do not administer stimulants or pain medications to the victim, unless specifically directed to do so by a physician.
6. Remove any items or clothing which may constrict the bitten limb if it swells (rings, bracelets, watches, footwear, etc.)
7. Keep the victim as still as possible.
8. Do not incise the bitten site.

Many organizations, including the American Medical Association and American Red Cross, recommend washing the bite with soap and water. However, do not attempt to clean the area with any type of chemical. Australian recommendations for snake bite treatment strongly recommend against cleaning the wound. Traces of venom left on the skin/bandages from the strike can be used in combination with a snake bite identification kit to identify the species of snake. This speeds determination of which antivenom to administer in the emergency room.

Pressure immobilization

In 1979, Australia's National Health and Medical Research Council formally adopted pressure immobilization as the preferred method of first aid treatment for snakebites in Australia. As of 2009, clinical evidence for pressure immobilization remains limited, with current evidence based almost entirely on anecdotal case reports. This has led most international authorities to question its efficacy. Despite this, all reputable first aid organizations in Australia recommend pressure immobilization treatment; however, it is not widely adhered to, with one study showing that only a third of snakebite patients attempt pressure immobilization.

Pressure immobilization is not appropriate for cytotoxic bites such as those inflicted by most vipers, but may be effective against neurotoxic venoms such as those of most elapids. Developed by medical researcher Struan Sutherland in 1978, the object of pressure immobilization is to contain venom within a bitten limb and prevent it from moving through the lymphatic system to the vital organs. This therapy has two components: pressure to prevent lymphatic drainage, and immobilization of the bitten limb to prevent the pumping action of the skeletal muscles.

Pressure is preferably applied with an elastic bandage, but any cloth will do in an emergency. Bandaging begins two to four inches above the bite (i.e. between the bite and the heart), winding around in overlapping turns and moving up towards the heart, then back down over the bite and past it towards the hand or foot. Then the limb must be held immobile: not used, and if possible held with a splint or sling. The bandage should be about as tight as when strapping a sprained ankle. It must not cut off blood flow, or even be uncomfortable; if it is uncomfortable, the patient will unconsciously flex the limb, defeating the immobilization portion of the therapy. The location of the bite should be clearly marked on the outside of the bandages. Some peripheral edema is an expected consequence of this process.

Apply pressure immobilization as quickly as possible; if you wait until symptoms become noticeable you will have missed the best time for treatment. Once a pressure bandage has been applied, it should not be removed until the patient has reached a medical professional. The combination of pressure and immobilization may contain venom so effectively that no symptoms are visible for more than 24 hours, giving the illusion of a dry bite. But this is only a delay; removing the bandage releases that venom into the patient's system with rapid and possibly fatal consequences.

Antivenom

Until the advent of antivenom, bites from some species of snake were almost universally fatal. Despite huge advances in emergency therapy, antivenom is often still the only effective treatment for envenomation. The first antivenom was developed in 1895 by French physician Albert Calmette for the treatment of Indian cobra bites. Antivenom is made by injecting a small amount of venom into an animal (usually a horse or sheep) to initiate an immune system response. The resulting antibodies are then harvested from the animal's blood.

Antivenom is injected into the patient intravenously, and works by binding to and neutralizing venom enzymes. It cannot undo damage already caused by venom, so antivenom treatment should be sought as soon as possible. Modern antivenoms are usually polyvalent, making them effective against the venom of numerous snake species. Pharmaceutical companies which produce antivenom target their products against the species native to a particular area. Although some people may develop serious adverse reactions to antivenom, such as anaphylaxis, in emergency situations this is usually treatable and hence the benefit outweighs the potential consequences of not using antivenom.

Outmoded treatments

The following treatments have all been recommended at one time or another, but are now considered to be ineffective or outright dangerous. Many cases in which such treatments appear to work are in fact the result of dry bites.

• Application of a tourniquet to the bitten limb is generally not recommended. There is no convincing evidence that it is an effective first aid tool as ordinarily applied. Tourniquets have been found to be completely ineffective in the treatment of Crotalus durissus bites, but some positive results have been seen with properly applied tourniquets for cobra venom in the Philippines. Uninformed tourniquet use is dangerous, since reducing or cutting off circulation can lead to gangrene, which can be fatal. The use of a compression bandage is generally as effective, and much safer.
• Cutting open the bitten area, an action often taken prior to suction, is not recommended since it causes further damage and increases the risk of infection.
• Sucking out venom, either by mouth or with a pump, does not work and may harm the affected area directly. Suction started after 3 minutes removes a clinically insignificant quantity—less than one thousandth of the venom injected—as shown in a human study. In a study with pigs, suction not only caused no improvement but led to necrosis in the suctioned area. Suctioning by mouth presents a risk of further poisoning through the mouth's mucous tissues. The well-meaning family member or friend may also release bacteria into the victim's wound, leading to infection.
• Immersion in warm water or sour milk, followed by the application of snake-stones (also known as la Pierre Noire), which are believed to draw off the poison in much the way a sponge soaks up water.
• Application of potassium permanganate.
• Use of electroshock therapy. Although still advocated by some, animal testing has shown this treatment to be useless and potentially dangerous.
• In extreme cases, where the victims were in remote areas, all of these misguided attempts at treatment have resulted in injuries far worse than an otherwise mild to moderate snakebite. In worst case scenarios, thoroughly constricting tourniquets have been applied to bitten limbs, completely shutting off blood flow to the area. By the time the victims finally reached appropriate medical facilities their limbs had to be amputated.