Wednesday, June 24, 2009

Tuesday, June 23, 2009



Classification and external resources
Cobra Naja naja
ICD-10 T63.0
ICD-9 989.5
DiseasesDB 29733
MedlinePlus 000031
eMedicine med/2143
MeSH D012909

Snakes often bite their prey when feeding, but occasionally they also bite humans. People can avoid and treat snakebites by knowing their etiology, along with prevention tips, and first aid and hospital treatment.


Most snakebites are caused by non-venomous snakes. Of the roughly 3,000 known species of snake found worldwide, only 15 percent are considered dangerous to humans.[1] Snakes are found on every continent except Antarctica. The most diverse and widely distributed snake family, the Colubrids, has only a few members which are harmful to humans. Of the 120 known indigenous snake species in North America, only 20 are venomous to human beings, all belonging to the families Viperidae and Elapidae.[2] However, in the United States, every state except Maine, Alaska, and Hawaii is home to at least one of 20 venomous snake species.[2]

Since the act of delivering venom is completely voluntary, all venomous snakes are capable of biting without injecting venom into their victim. Such snakes will often deliver such a "dry bite" (about 50% of the time)[citation needed] rather than waste their venom on a creature too large for them to eat. 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 causing severe lacerations as the victim or the snake itself pulls away, causing the flesh to be torn by the needle-sharp recurved teeth embedded in the victim. While not normally as life-threatening as a bite from a venomous species, the bite can be at least temporarily debilitating and as mentioned below, could lead to dangerous infections if improperly dealt with.

While most snakes must open their mouths wide before biting the victim, one type of African snake, the stiletto snake, can stab its victim from the side with its mouth closed.

Frequency and statistics

Map showing global distribution of snakebite morbidity.

Reporting is not mandatory, many snakebites go unreported. Consequently, no accurate study has ever been conducted to determine the frequency of snakebites on the international level. However, some estimates put the number at 2.5 million bites per year, resulting in perhaps 125,000 deaths.[3] Worldwide, snakebites occur most frequently in the summer season when snakes are active and humans are outdoors.[4] Agricultural and tropical regions report more snakebites than anywhere else.[1] Victims are typically male and between 17 and 27 years of age.[4] [5]. The majority of bites in the United States occur in the southwestern part of the country, in part because rattlesnake populations in the eastern states are much lower.[6]p.163

Sri lanka has world's highest death rates from snake bites. Almost all deaths from snake bites are caused by four out of five species of highly venomous land snakes.Those are Russels Viper, Cobra, Sri Lankan Krait and common Krait. Most snakebite related deaths in the United States are attributed to eastern and western diamondback rattlesnake bites. Children and the elderly are most likely to die.[7] The state of North Carolina has the highest frequency of reported snakebites, averaging approximately 19 bites per 100,000 persons. The national average is roughly 4 bites per 100,000 persons.[8]


Sign at Sylvan Rodriguez Park in Houston warning of the presence of snakes

Snakes are most likely to bite when they feel threatened, are startled, provoked, and/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 vary dramatically, see below.

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 home areas, while traveling, or hiking. Areas of the world such as Africa, Australia, Neotropics, and southern Asia are inhabited by many particularly dangerous snakes species. Being wary of snake presence and ultimately avoiding it when known is strongly recommended.

Responsible behavior offers effective protection from snakebites when in the wilderness. It is important to tread heavily and cause loud ground noises. The rationale behind this is that the snake will feel the vibrations and 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 actually 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.

When doing camping activities such as gathering firewood at night, it is important to make use of a flashlight. Approximately 85% of the natural snakebites occur below the victims' knees.[citation needed] Snakes may be unusually active during especially warm nights with ambient temperatures exceeding 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 thoroughly and extensively examining them first, as snakes are coldblooded creatures and often sunbathe atop rock ledges.

Pet owners of domestic animals and/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 harms 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.[9]

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 bite can induce just as bad an effect as a live snake bite.[10] 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.


The most common symptoms of all snakebites are panic, fear and emotional instability, which may cause symptoms such as nausea and vomiting, diarrhea, vertigo, fainting, tachycardia, and cold, clammy skin.[11] 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, are still able to 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 saliva and fangs of the snake may harbor many dangerous microbial contaminants, including Clostridium tetani. If neglected, an infection may spread and potentially even kill the victim.

Most snakebites, whether by a venomous snake or not, will have some type of local effect. Usually there is minor pain and redness, but 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.

Interestingly, bites caused by the Mojave rattlesnake 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, vision problems, 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. If the bleeding is left unchecked the victim may die of blood loss.

Venom emitted from cobras, kraits, most sea snakes, mambas, and other elapids contain toxins which attack the nervous system. The victim may present with strange disturbances to their vision, including blurriness. This is commonly due to the venom paralyzing the ciliary muscle, which is responsible for focusing the lens of the eye, but can be the result of eyelid paralysis as well. Victims will also report paresthesia throughout their body, as well as difficulty speaking and breathing. Nervous system problems will cause a huge array of symptoms, and those provided here are not exhaustive. In any case, 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 may 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 kidney failure, and, if left untreated, eventually death.


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, etc.), the amount of venom injected, the time it takes for the patient to find treatment, and finally the quality of that treatment. The ancient rule of medicine applies here, "First, do no harm." 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.

In countries where polyvalent antivenins 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 the viper, krait, and cobra. Knowledge of what species are present locally can be crucially important, 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,[12] but these scoring systems are extremely specific to a particular geographical area.

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 (e.g., 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; treatment methods suited for rattlesnake bite in the United States might well be fatal if applied to a tiger snake bite in Australia. 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 beware 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 patient from the immediate area.
  2. Keep the patient calm. 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 antivenin 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 patient 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.[13]

Pressure immobilization

Pressure immobilization is not appropriate for cytotoxic bites such as those of most vipers,[14][15][16] but is highly effective against neurotoxic venoms such as those of most elapids.[17][18][19] Developed by Struan Sutherland in 1978,[20] 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 in the body core. 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 can contain venom so effectively that no symptoms are visible for more than twenty-four 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.

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.

Old style snake bite kit that should not be used.
  • Application of a tourniquet to the bitten limb is not generally recommended. There is no generally convincing evidence that it is an effective first-aid tool as generally applied[21]. Tourniquets have been found to be completely ineffective in the treatment of Crotalus durissus[22], but some positive results have been seen with properly applied tourniquets for cobra venom in the Phillipines[23]. Uninformed tourniquet use is dangerous, since reducing or cutting off circulation can lead to gangrene, which can be fatal.[21]. 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 (see also below) since it causes 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.[24] Suction started after 3 minutes removes a clinically insignificant quantity - less than one thousandth of the venom injected - as shown in a human study.[25] In a study with pigs, suction not only caused no improvement but led to necrosis in the suctioned area.[26] Suctioning by mouth presents a risk of further poisoning through the mouth's mucous tissues.[27] 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 Black Stones or 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.[28][29][30][31]

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, thus completely shutting off blood flow to the area. By the time the victims finally reached appropriate medical facilities their limbs had to be amputated.

See also


  1. ^ Russell F (1990). "When a snake strikes". Emerg Med 22 (12): 33–4, 37–40, 43.
  2. ^ a b "For Goodness Snakes! Treating and Preventing Venomous Bites". FDA Consumer magazine. 1995.
  3. ^ "Animal sera". WHO: Blood products and related biologicals.
  4. ^ a b Wingert W, Chan L (01 Jan 1988). "Rattlesnake bites in southern California and rationale for recommended treatment". West J Med 148 (1): 37–44. PMID 3277335. Retrieved on 2006-05-26.
  5. ^ Parrish H (1966). "Incidence of treated snakebites in the United States". Public Health Rep 81 (3): 269–76. PMID 4956000.
  6. ^ Russell, Findlay E. (1983). Snake venom poisoning: repr. with corr. Great Neck, N.Y: Scholium International. ISBN 0-87936-015-1.
  7. ^ Gold BS, Wingert WA (June 1994). "Snake venom poisoning in the United States: a review of therapeutic practice". South. Med. J. 87 (6): 579–89. PMID 8202764.
  8. ^ Russell F (1980). "Snake venom poisoning in the United States". Annu Rev Med 31: 247–59. doi:10.1146/ PMID 6994610.
  9. ^ Kurecki B, Brownlee H (1987). "Venomous snakebites in the United States". J Fam Pract 25 (4): 386–92. PMID 3655676.
  10. ^ Gold B, Barish R (1992). "Venomous snakebites. Current concepts in diagnosis, treatment, and management". Emerg Med Clin North Am 10 (2): 249–67. PMID 1559468.
  11. ^ Kitchens C, Van Mierop L (1987). "Envenomation by the Eastern coral snake (Micrurus fulvius fulvius). A study of 39 victims". JAMA 258 (12): 1615–8. doi:10.1001/jama.258.12.1615. PMID 3625968.
  12. ^ Pathmeswaran A, Kasturiratne A, Fonseka M, Nandasena S, Lalloo D, de Silva H (2006). "Identifying the biting species in snakebite by clinical features: an epidemiological tool for community surveys". Trans R Soc Trop Med Hyg 100 (9): 874–8. doi:10.1016/j.trstmh.2005.10.003. PMID 16412486.
  13. ^ Chris Thompson. "Treatment of Australian Snake Bites". Australian anaesthetists' website.
  14. ^ Rogers I, Celenza T (2002). "Simulated field experience in the use of the Sam splint for pressure immobilization of snakebite". Wilderness Environ Med 13 (2): 184–5. PMID 12092977.
  15. ^ Bush S, Green S, Laack T, Hayes W, Cardwell M, Tanen D (2004). "Pressure immobilization delays mortality and increases intracompartmental pressure after artificial intramuscular rattlesnake envenomation in a porcine model" (PDF). Ann Emerg Med 44 (6): 599–604. doi:10.1016/j.annemergmed.2004.06.007. PMID 15573035. Retrieved on 2006-06-25.
  16. ^ Sutherland S, Coulter A (1981). "Early management of bites by the eastern diamondback rattlesnake (Crotalus adamanteus): studies in monkeys (Macaca fascicularis)". Am J Trop Med Hyg 30 (2): 497–500. PMID 7235137. Retrieved on 2005-06-25.
  17. ^ Rogers I, Winkel K (2005). "Struan Sutherland's "Rationalisation of first-aid measures for elapid snakebite"--a commentary". Wilderness Environ Med 16 (3): 160–3. PMID 16209471. Retrieved on 2006-06-25.
  18. ^ Sutherland S. "Deaths from snake bite in Australia, 1981-1991". Med J Aust 157 (11-12): 740–6. PMID 1453996.
  19. ^ Sutherland S, Leonard R. "Snakebite deaths in Australia 1992-1994 and a management update". Med J Aust 163 (11-12): 616–8. PMID 8538559.
  20. ^ Sutherland S, Coulter A, Harris R (1979). "Rationalisation of first-aid measures for elapid snakebite". Lancet 1 (8109): 183–5. doi:10.1016/S0140-6736(79)90580-4. PMID 84206.
  21. ^ a b Theakston RD (October 1997). "An objective approach to antivenom therapy and assessment of first-aid measures in snake bite" (PDF). Ann. Trop. Med. Parasitol. 91 (7): 857–65. doi:10.1080/00034989760626. PMID 9625943.
  22. ^ Amaral CF, Campolina D, Dias MB, Bueno CM, Rezende NA (May 1998). "Tourniquet ineffectiveness to reduce the severity of envenoming after Crotalus durissus snake bite in Belo Horizonte, Minas Gerais, Brazil". Toxicon 36 (5): 805–8. doi:10.1016/S0041-0101(97)00132-3. PMID 9655642.
  23. ^ Watt G, Padre L, Tuazon ML, Theakston RD, Laughlin LW (May 1988). "Tourniquet application after cobra bite: delay in the onset of neurotoxicity and the dangers of sudden release". Am. J. Trop. Med. Hyg. 38 (3): 618–22. PMID 3275141.
  24. ^ Holstege CP, Singletary EM (2006). "Images in emergency medicine. Skin damage following application of suction device for snakebite". Annals of emergency medicine 48 (1): 105, 113. doi:10.1016/j.annemergmed.2005.12.019. PMID 16781926.
  25. ^ Alberts M, Shalit M, LoGalbo F (2004). "Suction for venomous snakebite: a study of "mock venom" extraction in a human model". Ann Emerg Med 43 (2): 181–6. doi:10.1016/S0196-0644(03)00813-8. PMID 14747805.
  26. ^ Bush SP, Hegewald KG, Green SM, Cardwell MD, Hayes WK (2000). "Effects of a negative pressure venom extraction device (Extractor) on local tissue injury after artificial rattlesnake envenomation in a porcine model". Wilderness & environmental medicine 11 (3): 180–8. PMID 11055564.
  27. ^ Riggs BS, Smilkstein MJ, Kulig KW, et al. Rattlesnake envenomation with massive oropharyngeal edema following incision and suction (Abstract). Presented at the AACT/AAPCC/ABMT/CAPCC Annual Scientific Meeting, Vancouver, Canada, September 27-October 2, 1987.
  28. ^ Russell F (1987). "Another warning about electric shock for snakebite". Postgrad Med 82 (5): 32. PMID 3671201.
  29. ^ Ryan A (1987). "Don't use electric shock for snakebite". Postgrad Med 82 (2): 42. PMID 3497394.
  30. ^ Howe N, Meisenheimer J (1988). "Electric shock does not save snakebitten rats". Ann Emerg Med 17 (3): 254–6. doi:10.1016/S0196-0644(88)80118-5. PMID 3257850.
  31. ^ Johnson E, Kardong K, Mackessy S (1987). "Electric shocks are ineffective in treatment of lethal effects of rattlesnake envenomation in mice". Toxicon 25 (12): 1347–9. doi:10.1016/0041-0101(87)90013-4. PMID 3438923.


Saturday, June 20, 2009

Rural Medics - a newspaper for the health education of Rural people

Rural Medics is a newspaper for the health education of Rural people