Many animals possess venoms that can be injected into the unfortunate traveler by a variety of mechanisms. The normal purpose of envenoming is to discourage enemies or to immobilize prey.
Some people become sensitized to venoms if they are stung or bitten repeatedly. In this case, the allergic reaction to the venom may prove far more dangerous than its toxic effects, and in some parts of the world, such as Europe and North America, there are more deaths from allergic (anaphylactic) reactions to bee and wasp stings than from lethal snake, scorpion, and spider venoms.
Tropical regions have the richest venomous fauna, and travelers to such regions often regard snake bite and scorpion sting as the two greatest medical hazards of their journey. However, it is nearly always the indigenous population, rather than the travel, that falls victim to venomous animals.
Snakebite is a major cause of death among South American Indians who hunt barefooted in the jungle, and among rice farmers in South-East Asia who work barefooted and barehanded in the paddy fields. Travelers are usually less exposed and better protected, and there has been no report of a European traveler dying from a venomous bite or sting in recent years. However, a German tourist came close to death after being bitten by a cobra in central Bangkok, and several other Europeans have been severely envenomed in the jungles of South America and South-East Asia.
Anyone planning to travel off the beaten track in a tropical country should find out about the venomous fauna well before leaving home. An expedition to a particularly remote and snake- infested area may want to take its own supply of antivenin. Usually, this can be supplied only by a national center of antivenom production; contact will have to be made with the center well in advance. Many antivenins available in Europe and in tropical countries are of dubious potency. Information supplied with commercial antivenoms (the ‘package insert’) may be misleading or even dangerous! It is also important to find out something about the quality of local medical services or referral centers in the larger cities.
Information and advice about venomous fauna and availability of antivenins can be obtained from the centers listed at the end of this chapter.
Venomous snakes have one or more pairs of enlarged teeth, the fangs, in the upper jaw. Venom is conducted from the venom gland just behind the eye, through a duct to the base of the fang, and then through a channel to its tip.
Important venomous snakes belong to four families:
The Colubridae, of which some members have small fangs at the back of their mouth. Effective bites in humans are very uncommon but a few species, notably the African boomslang has caused some fatalities.
The Elapidae, which include cobras, kraits, mambas and coral snakes, the South African ringtails and African and Asian spitting cobras can eject venom from the tips of their fangs as a defensive strategy.
The Hydrophiidae, which include sea-snakes and the Austra¬lian terrestrial venomous snakes.
The Viperidae, which are the largest and best-known family of venomous snakes and include the subfamilies Viperinae, the Old World vipers and adders; and Crotalinae, the New World rattlesnakes, moccasins and lance-headed vipers and Asian pit vipers.
Venomous snakes do not occur at high altitudes (more than 4000 meters or about 13 000 ft), in the Antarctic, nor in a number of islands such as Ireland, Iceland, Crete, New Zealand, Madagascar, and most Caribbean and Pacific islands.The incidence and medical significance of snake bite have been underestimated because it is a problem of the rural tropics, often little known to academic centers in the capital cities even of countries where it is particularly common. As mentioned above, the incidence of snake bite is highest among native populations who are forced to live and work, relatively unprotected, within the snake’s chosen environment.
Effects of snake venom
Snake venoms are complicated substances which contain a large number of harmful components. The main clinical effects of snake venoms are summarized below:
- Local swelling, blistering, and necrosis (gangrene) of the bitten limb are seen particularly with Viperidae and some cobras. Fluid and blood leaks into the tissues of the bitten limb. Swelling starts soon after the bite and may spread to involve the whole limb and adjoining area of the trunk.
- Bleeding and blood-clotting disorders occur mainly in patients bitten by Viperidae, Colubridae, and Australian venomous snakes. The commonest sites of bleeding are the gums, nose, and stomach.
- Shock (fall in blood pressure) may occur in patients bitten by Viperidae.
- Paralysis (‘neurotoxicity’) is first manifest by an inability to open the eyes (ptosis) but later spreads to other muscles, particularly those responsible for swallowing and breathing. The Elapidae, Hydrophiidae and a few of the Viperidae have neurotoxic venoms. Venoms of Hydrophiidae, especially the true sea- snakes, and of several species of the Viperidae may cause extensive direct muscle damage, with painful stiff muscles and paralysis.
- Kidney failure resulting from clotting of blood in the small blood vessels or prolonged shock is a major feature of bites by Russell’s viper, and some of the Crotalinae in the Americas.
Despite this formidable repertoire of toxic effects, the majority of people bitten by venomous snakes suffer negligible or no envenoming. It may be that the snake’s strike is not well adapted to human anatomy and that a large number of bites are therefore mechanically ineffective and fail to inject significant amounts of venom.
Management of snake bite
First aid for snake bite, either by the victim or a person on the spot, is summarized in the Box on p. 206. It is important to keep calm, immobilize the bitten limb as far as is practicable, avoid harmful first-aid measures and get to hospital or dispensary as soon as possible.
Most of the traditional first-aid remedies for snake bite, such as suction, local incisions, application of potassium permanganate crystals, cold packs, electric shocks, and tourniquets, do more harm than good and should not be used. All commercially produced snake-bite kits that I have seen are both useless and potentially dangerous.
Tourniquets and bandaging To prevent the spread of venom from the bite site a tourniquet must be applied very tightly, but the tighter the tourniquet the greater the risk of complications caused by local pressure and restriction of blood flow to the limb. The only circumstance where a tight tourniquet should be used is a definite bite by a dangerously neurotoxin elapid or hydrophilic such as some cobras, mambas, and Australian venomous snakes.
In such cases, crepe (ace) bandaging and splinting of the whole bitten limb is more comfortable and possibly a more effective method than applying a pressure pad over the wound or a conventional tight (arterial) tourniquet around the upper arm or thigh. No tourniquet should be left in place for more than two hours. Ideally, a tight tourniquet used in these circumstances should not be released until medical help is available and antivenom treatment has been started.
Reassurance is a most important part of treatment. Most snakebite victims are terrified, but only a minority of bites, even by dangerously venomous species, produce serious envenoming.
The speed of the lethal effects of snake venoms has been greatly exaggerated. To kill a man, lethal doses of venom usually take hours in the case of neurotoxic species such as cobras, mambas, and sea-snakes, or days in the case of vipers and rattlesnakes, not seconds or minutes as is commonly believed. This interval between bite and death is usually sufficiently long to allow effective treatment.
Pain If the pain is a problem, a safe pain-killing drug for snake-bite victims is paracetamol (Panadol, Tylenol), the dose is one or two 500 mg tablets for adults. Aspirin should never be used in snake-bite victims as it may cause stomach bleeding.
Medical treatment at the hospital or dispensary, medically trained staff should examine the patient and dead snake if brought, and decide about further treatment. The only specific remedy for the snake bite is antivenin (also known as antivenin, antivenin, or anti-snakebite serum) which is made in animals, usually horses, by immunizing them with increasing doses of snake venom. Although most modern ant venoms are refined and purified, injection of ‘foreign’ protein (i.e. from another species of animal) always carries the risk of potentially serious reactions. To be optimally effective, antivenom must be given by a slow intravenous injection or infusion.
Not all people bitten by snakes require antivenin. Since the decision about antivenin treatment, the administration of anti
Snakebite: First aid
1 Reassure the patient.
2 Immobilize the bitten limb with a splint or sling.
3 Move the patient to a hospital or a dispensary as quickly as possible.
4 Avoid harmful measures such as incisions, suction, potassium permanganate crystals, electric shocks, and tourniquets.
5 If the patient has definitely been bitten by a dangerous neurotoxin species (e.g. cobra, mamba, krait, coral snake, Australian snake, sea-snake) apply a tight tourniquet around upper arm or thigh or apply a pressure pad over the wound or firmly crepe-bandage and splint the bitten limb.
6 Use paracetamol not an aspirin to treat pain.
7 If you have your own supply of antivenom, take it with you to hospital or dispensary.
8 If the snake has been killed take it along with you to hospital or dispensary, but do not handle it with your bare hands, even if it appears dead.
venom by the intravenous route and the treatment of antivenom reactions all require clinical skill, lay people should not undertake the medical treatment of snake bite except under most unusual conditions (for example a serious bite in a member of an expedition in a very remote area).
As a life-saving measure, antivenom may be given by intramuscular injection (the dose divided between the upper outer quadrants of both buttocks) followed by the message to promote absorption of the antivenom into the bloodstream. However, this is certainly not recommended as a general rule!
Patients who need antivenom are those in whom there is evidence that venom has been absorbed and is circulating throughout the body to produce severe general effects (‘systemic envenoming’). The important signs are the loss of consciousness, low Venomous bites end stings, Blood pressure, failure of the blood to clot, bleeding from the nose or gums or vomiting blood, generalized pain and stiffness in the muscles, and paralysis.
The earliest sign of neurotoxin poisoning is an inability of the upper eyelids to retract when the bitten person tries to look up (‘ptosis’). Slight bleeding from the site of the bite and mild local swelling and bruising are not normally regarded as justification for antivenin treatment, but massive local swelling involving more than half the bitten limb (for example above the knee and above the elbow in bites of the foot and hand respectively) indicate that significant amounts of venom have been injected and that antivenin is probably required, especially if the snake is known to have a venom that causes necrosis (gangrene).
Administration of antivenin by a medically-qualified person For intravenous injection, freeze-dried antivenin is reconstituted with sterile water for injection (usually 10 ml per ampoule) and liquid antivenin is given neat. The injection should be given slowly, at a rate not more than 2 ml per minute. A method that is easier to control, but requires more equipment, is to reconstitute or dilute antivenin with ‘normal isotonic saline or 5 percent dextrose solution, making up the volume to 200 ml. This is given through an intravenous giving set and is infused over about thirty minutes, starting slowly (30 drops per minute), then speeding up after about ten minutes if there is no reaction. The dose of antivenin varies with the manufacturer and the severity of envenoming. It is usually not less than five ampoules. The same dose should be given to children as to adults.
Antivenin should never be given, even by medically qualified staff, unless adrenaline (05 ml of a 1 mg/ml or 1 in 1000 solution by subcutaneous injection) is available to treat antivenin reactions.
The commonest symptoms of an antivenin reaction are itching, the appearance of a raised reddened rash (urticaria) and a throbbing headache. More serious symptoms include coughing, vomiting, wheezing, and fall in blood pressure leading to unconsciousness. At the first sign of a reaction, adrenaline should be given by subcutaneous injection.
Adrenaline is dangerous if given by other routes. An antihistamine drug should also be given, preferably chlorpheniramine maleate (Piriton) 10 mg by intravenous injection. Allergic patients (those suffering from asthma, hay fever, and eczema) I am more likely to develop severe antivenin reactions than other people. Unfortunately, there is no reliable way of predicting, by the use of a skin test, whether or not someone will develop a reaction.
Although 1 would strongly discourage lay people from giving antivenin themselves, it may be worth some expeditions taking a small supply (5-10 ampoules) of antivenin to be given by a local doctor or dispensary if the need arises. Unfortunately, the supply of antivenin to rural hospitals and health centers in the tropics is often very unreliable.
Infection There is a small but definite risk of tetanus and secondary bacterial infection following snake-bite. A booster dose of tetanus toxin and a course of penicillin should, therefore, be given.
Prevention of snake bite
Fortunately, travelers can virtually exclude the risk of being bitten by a snake if they heed the following advice.
Snakes and snake-charmers should be avoided as far as possible. If you happen to see a snake, do not disturb, corner, or attack it, and never attempt to handle a snake even if it is said to be a harmless species or appears to be dead. Even a severed head can bite!
If you should happen to And yourself confronted with a snake at close quarters, try to keep absolutely still until it has slithered away: snakes strike only at moving objects.
Never walk in undergrowth or deep sand without boots, socks, and long trousers; and at night always carry a light. Unlit paths are particularly dangerous after rainstorms. Never collect firewood or move logs and boulders with your bare hands, and never push your hands or sticks, into burrows, holes, or Services. Avoid climbing trees and rocks that are covered with thick foliage and never swim in overgrown rivers or lakes (there are a good many other reasons for not swimming in lakes and rivers in the tropics!).
If you are forced to sleep in the open or under canvas, try to raise your bed at least one foot off the ground or else use a sewn- in ground-sheet or mosquito net that can be zipped up or well tucked in. Snakes never attackman without provocation but will if grabbed* trodden on or even if someone roll* on to them in their sleep Snake* are sometimes attracted to human dwelling in pursuit of their prey (domestic chicks, rats, mice, toads, and lizards). Sea-snakes bite only when they are picked out of aching nets.
It has not proved possible, nor would it be desirable, to exterminate venomous snakes. The Burmese rice farmer may regard Russell’s viper as his enemy, but in fact, the snake protects his livelihood, the rice crop, by controlling the rodent population.
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