A snakebite is an injury caused by a bite from a snake, often resulting in puncture woundsinflicted by the animals fangs and sometimes resulting in envenomation. Although the majorityof snake species are non-venomous and typically kill their prey with constriction rather thanvenom, venomous snakes can be found on every continent except Antarctica. Snakes oftenbite their prey as a method of hunting, but also for defensive purposes against predators. Sincethe physical appearance of snakes may differ, there is often no practical way to identify a speciesand professional medical attention should be sought.The outcome of snake bites depends on numerous factors, including the species of snake, thearea 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 setof 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 thesnakes 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 inhabitingthe region, as effective treatments for bites inflicted by some species can be ineffective forothers.The number of fatalities attributed to snake bites varies greatly by geographical area. Althoughdeaths are relatively rare in Australia, Europe and North America, the morbidity andmortality associated with snake bites is a serious public health problem in many regions of theworld, particularly in rural areas lacking medical facilities. Further, while South Asia, SoutheastAsia, and sub-Saharan Africa report the highest number of bites, there is also a high incidence inthe Neotropics and other equatorial and subtropical regions. Each year tens of thousandsof people die from snake bites, yet the risk of being bitten can be lowered with preventivemeasures, such as wearing protective footwear and avoiding areas known to be inhabited bydangerous snakes.
The most common symptoms of all snakebites are overwhelming fear, panic, and emotional instability, which may cause symptoms such asnausea and vomiting, diarrhea, vertigo, fainting, tachycardia, and cold, clammy skin. Television, literature, and folklore are in part responsiblefor the hype surrounding snakebites, and a people may have unwarranted thoughts of imminent death.Dry snakebites, and those inflicted by a non-venomous species, can still cause severe injury. There are several reasons for this: a snakebite maybecome infected with the snakes saliva and fangs sometimes harboring pathogenic microbial organisms, including Clostridium tetani. Infection isoften reported with viper bites whose fangs are capable of deep puncture wounds. Bites may cause anaphylaxis in certain people.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 sometimesbecoming tender and severely swollen within 5 minutes. This area may also bleed and blister and can eventually lead to tissue necrosis. Othercommon initial symptoms of pitviper and viper bites include lethargy, bleeding, weakness, nausea, and vomiting. Symptoms may becomemore life-threatening over time, developing into hypotension, tachypnea, severe tachycardia, severe internal bleeding, altered sensorium, kidneyfailure, and respiratory failure.Interestingly, bites caused by the Mojave rattlesnake, kraits, coral snake, and the speckled rattlesnake reportedly cause little or no pain despitebeing serious injuries. Those bitten may also describe a "rubbery," "minty," or "metallic" taste if bitten by certain species of rattlesnake. Spitting cobras and rinkhalses can spit venom in a persons eyes. This results in immediate pain, ophthalmoparesis, and sometimesblindness.Some Australian elapids and most viper envenomations will cause coagulopathy, sometimes so severe that a person may bleed spontaneouslyfrom the mouth, nose, and even old, seemingly-healed wounds. Internal organs may bleed, including the brain and intestines and will causeecchymosis (bruising) of the skin.Venom emitted from elapids, including sea snakes, kraits, cobras, king cobra, mambas, and many Australian species, contain toxins which attackthe nervous system, causing neurotoxicity. The person may present with strange disturbances to their vision, including blurriness.Paresthesia throughout the body, as well as difficulty in speaking and breathing, may be reported.  Nervous system problems will cause a hugearray of symptoms, and those provided here are not exhaustive. If not treated immediately they may die from respiratory failure.Venom emitted from some types of cobras, almost all vipers, some Australian elapids and some sea snakes causes necrosis of muscle tissue.Muscle tissue will begin to die throughout the body, a condition known as rhabdomyolysis. Rhabdomyolysis can result in damage to the kidneysas a result of myoglobin accumulation in the renal tubules. This, coupled with hypotension, can lead to acute renal failure, and, if left untreated,eventually death.
Since envenomation is completely voluntary, all venomous snakes are capable of biting withoutinjecting venom into their victim. Snakes may deliver such a "dry bite" rather than waste theirvenom on a creature too large for them to eat. However, the percentage of dry bites variesbetween species: 80% of bites inflicted by sea snakes, which are normally timid, do not result inenvenomation, whereas only 25% of pitviper bites are dry. Furthermore, some snakegenera, such as rattlesnakes, significantly increase the amount of venom injected in defensivebites compared to predatory strikes.Some dry bites may also be the result of imprecise timing on the snakes part, as venom may beprematurely released before the fangs have penetrated the victims flesh. Even withoutvenom, some snakes, particularly large constrictors such as those belonging to the Boidae andPythonidae families, can deliver damaging bites; large specimens often cause severe lacerationsas the victim or the snake itself pull away, causing the flesh to be torn by the needle-sharprecurved teeth embedded in the victim. While not as life-threatening as a bite from a venomousspecies, the bite can be at least temporarily debilitating and could lead to dangerous infectionsif improperly dealt with.While most snakes must open their mouths before biting, African and Middle Eastern snakesbelonging to the family Atractaspididae are able to fold their fangs to the side of their headwithout opening their mouth and jab at victims.
It has been suggested that snakes evolved the mechanisms necessary for venom formation and deliverysometime during the Miocene epoch. During the mid-Tertiary, most snakes were large ambush predatorsbelonging to the superfamily Henophidia, which use constriction to kill their prey. As open grasslandsreplaced forested areas in parts of the world, some snake families evolved to become smaller and thus moreagile. However, subduing and killing prey became more difficult for the smaller snakes, leading to theevolution of snake venom. Other research on Toxicofera, a hypothetical clade thought to be ancestral tomost living reptiles, suggests an earlier time frame for the evolution of snake venom, possibly to the order oftens of millions of years, during the Late Cretaceous.Snake venom is produced in modified parotid glands normally responsible for secreting saliva. It is stored instructures called alveoli behind the animals 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 ofpurposes, such as interfering with a preys cardiac system or increasing tissue permeability so that venom isabsorbed faster.Venom in many snakes, such as pitvipers, affects virtually every organ system in the human body and can bea combination of many toxins, including cytotoxins, hemotoxins, neurotoxins, and myotoxins, allowing for anenormous variety of symptoms. Earlier, the venom of a particular snake was considered to be one kindonly i.e. either hemotoxic or neurotoxic, and this erroneous belief may still persist wherever the updatedliterature is hard to access. Although there is much known about the protein compositions of venoms fromAsian and American snakes, comparatively little is known of Australian snakes.The strength of venom differs markedly between species and even more so between families, as measuredby median lethal dose (LD50) in mice. Subcutaneous LD50 varies by over 140-fold within elapids and by morethan 100-fold in vipers. The amount of venom produced also differs among species, with the Gaboon viperable to potentially deliver from 450–600 milligrams of venom in a single bite, the most of any snake.Opisthoglyphous colubrids have venom ranging from life-threatening (in the case of the boomslang) tobarely noticeable (as in Tantilla).
Snakes 26] 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 anysnake species as appearances may vary dramatically.Snakes are likely to approach residential areas when attracted by prey, such as rodents. Practising regular pest control can reduce the threat ofsnakes considerably. It is beneficial to know the species of snake that are common in local areas, or while travelling or hiking. Areas of the worldsuch as Africa, Australia, the Neotropics, and southern Asia are inhabited by many highly dangerous species. Being wary of snake presence andultimately 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, thisgenerally only applies to North America as some larger and more aggressive snakes in other parts of the world, such as king cobras and blackmambas, will protect their territories. When dealing with direct encounters it is best to remain silent and motionless. If the snake has not yetfled 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 unusuallyactive during especially warm nights when ambient temperatures exceed 21 °C (70 °F). It is advised not to reach blindly into hollow logs, flip overlarge rocks, and enter old cabins or other potential snake hiding-places. When rock climbing, it is not safe to grab ledges or crevices withoutexamining them first, as snakes are cold-blooded and often sunbathe atop rock ledges.Pet owners of domestic animals or snakes should be aware that a snake is capable of causing injury and that it is necessary to always act withcaution. When handling snakes it is never wise to consume alcoholic beverages. In the United States more than 40% of snakebitevictims intentionally put themselves in harms way by attempting to capture wild snakes or by carelessly handling their dangerous pets—40% ofthat number had a blood alcohol level of 0.1% 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 foolpotential threats. A snakes detached head can immediately act by reflex and potentially bite. The induced bite can be just as severe as that of alive snake. Dead snakes are also incapable of regulating the venom they inject, so a bite from a dead snake can often contain large amountsof venom.[
It is not an easy task determining whether ornot a bite by any species of snake is life-threatening. A bite by a North Americancopperhead on the ankle is usually a moderateinjury to a healthy adult, but a bite to a childsabdomen or face by the same snake may befatal. The outcome of all snakebites dependson a multitude of factors: the size, physicalcondition, and temperature of the snake, theage and physical condition of the victim, thearea and tissue bitten (e.g., foot, torso, vein ormuscle), the amount of venom injected, thetime it takes for the person to find treatment,and finally the quality of that treatment
Identification of the snake is important inplanning treatment in certain areas of theworld, but is not always possible. Ideally thedead snake would be brought in with theperson, but in areas where snake bite is morecommon, local knowledge may be sufficient torecognize the snake. However, in regionswhere polyvalent antivenoms are available,such as North America, identification of snakeis not a high priority item. Attempting to catchor kill the offending snake also puts one at riskfor re-envenomation or creating a secondvictim, and generally is not recommended.The three types of venomous snakes thatcause the majority of major clinical problemsare vipers, kraits, and cobras. Knowledge ofwhat species are present locally can be crucial,as is knowledge of typical signs and symptomsof envenomation by each type of snake. Ascoring system can be used to try to determinethe biting snake based on clinical features,but these scoring systems are extremelyspecific to particular geographical areas.
Snakebite first aid recommendations vary, in part because different snakes have different types of venom. Some have littlelocal effect, but life-threatening systemic effects, in which case containing the venom in the region of the bite by pressureimmobilization is desirable. Other venoms instigate localized tissue damage around the bitten area, and immobilization mayincrease the severity of the damage in this area, but also reduce the total area affected; whether this trade-off is desirableremains a point of controversy. Because snakes vary from one country to another, first aid methods also vary.However, most first aid guidelines agree on the following:Protect the person and others from further bites. While identifying the species is desirable in certain regions, risking furtherbites or delaying proper medical treatment by attempting to capture or kill the snake is not recommended.Keep the person calm. Acute stress reaction increases blood flow and endangers the person. Panic is infectious andcompromises judgment.Call for help to arrange for transport to the nearest hospital emergency room, where antivenom for snakes common to thearea will often be available.Make sure to keep the bitten limb in a functional position and below the victims heart level so as to minimize bloodreturning to the heart and other organs of the body.Do not give the person anything to eat or drink. This is especially important with consumable alcohol, a known vasodilatorwhich will speed up the absorption of venom. Do not administer stimulants or pain medications to the victim, unlessspecifically directed to do so by a physician.Remove any items or clothing which may constrict the bitten limb if it swells (rings, bracelets, watches, footwear, etc.)Keep the person as still as possible.Do not incise the bitten site.Many organizations, including the American Medical Association and American Red Cross, recommend washing the bitewith soap and water. Australian recommendations for snake bite treatment recommend against cleaning the wound. Tracesof venom left on the skin/bandages from the strike can be used in combination with a snake bite identification kit toidentify the species of snake. This speeds determination of which antivenom to administer in the emergency room.India developed a national snake-bite protocol in 2007 which includes advice to:Reassure the patient. 70% of all snakebites are from non- venomous species. Only 50% of bites by venomous speciesactually envenomate the patientImmobilise in the same way as a fractured limb. Use bandages or cloth to hold the splints, not to block the blood supply orapply pressure. Do not apply any compression in the form of tight ligatures, they don’t work and can be dangerous!Get to Hospital Immediately. Traditional remedies have no proven benefit in treating snakebite.Tell the doctor of any systemic symptoms, such as droopiness of a body part, that manifest on the way to hospital.
In 1979, Australias National Health and Medical Research Council formally adopted pressureimmobilization 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 entirelyon anecdotal case reports. This has led most international authorities to question its efficacy.  Despitethis, 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 people attemptpressure 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 bymedical researcher Struan Sutherland in 1978, the object of pressure immobilization is to contain venomwithin a bitten limb and prevent it from moving through the lymphatic system to the vital organs. Thistherapy has two components: pressure to prevent lymphatic drainage, and immobilization of the bitten limbto prevent the pumping action of the skeletal muscles.Pressure is preferably applied with an elastic bandage, but any cloth will do in an emergency. Bandagingbegins two to four inches above the bite (i.e. between the bite and the heart), winding around inoverlapping turns and moving up towards the heart, then back down over the bite and past it towards thehand or foot. Then the limb must be held immobile: not used, and if possible held with a splint or sling. Thebandage should be about as tight as when strapping a sprained ankle. It must not cut off blood flow, or evenbe uncomfortable; if it is uncomfortable, the person will unconsciously flex the limb, defeating theimmobilization portion of the therapy. The location of the bite should be clearly marked on the outside ofthe 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 willhave missed the best time for treatment. Once a pressure bandage has been applied, it should not beremoved until the person has reached a medical professional.
Until the advent of antivenom, bites from some species of snake were almost universallyfatal. Despite huge advances in emergency therapy, antivenom is often still the only effectivetreatment for envenomation. The first antivenom was developed in 1895 by French physicianAlbert Calmette for the treatment of Indian cobra bites. Antivenom is made by injecting a smallamount of venom into an animal (usually a horse or sheep) to initiate an immune systemresponse. The resulting antibodies are then harvested from the animals blood.Antivenom is injected into the person intravenously, and works by binding to and neutralizingvenom enzymes. It cannot undo damage already caused by venom, so antivenom treatmentshould be sought as soon as possible. Modern antivenoms are usually polyvalent, making themeffective against the venom of numerous snake species. Pharmaceutical companies whichproduce antivenom target their products against the species native to a particular area.Although some people may develop serious adverse reactions to antivenom, such asanaphylaxis, in emergency situations this is usually treatable and hence the benefit outweighsthe potential consequences of not using antivenom.