VENOMOUS SNAKES: THEIR VENOM, BITES AND ANTIVENINS

VENOMOUS SNAKES


There are 250 to 400 venomous snakes depending on how they are counted. They include true vipers, pit vipers, cobras, and sea snakes . Even snakes like garter snakes that are not regarded as venomous actually are. Garter snakes produce a small amounts of venom, just enough to slow down prey such as frogs so they can immobilize and swallow them. The development of venom was seen as key to snake evolution, allowing them to shed their muscles and become more mobile and quick by negating their reliance on constriction as a means of subduing their prey.

Venomous is the correct term for snakes with poison. If you call them poisonous technically that means they are poisonous to eat, like poisonous mushrooms. Primitive back-fanged snakes have poisonous glands above their teeth and inject poison via grooves in their teeth. These snakes often have very potent poison but the need to maintain a grip and chew for a while to inject enough to kill or immobilize their prey.More advanced snakes have fangs on the front of their upper jaws and enclose venom glands that connect to tubes in the fangs that enable them to inject poison. Cobras, mambas and sea snakes have short and immobile fangs.

The fangs of vipers, which includes rattlesnakes, are much longer. They are so long they have hinges and lie folded up on the roof of the mouth until they are needed: then they flip into position when the mouth opens wide and the bone to which they fangs are connected rotates. The fangs are ready immediately. When they strike their prey they inject their venom like hypodermic needles. The fangs are periodically changed. Rattlesnakes shed their fangs every 60 days.

Poisonous snakes need their venom to immobilize prey (they don't to kill it necessarily) and defend themselves. To avoid injury from the claws and bites of large prey, snakes aim to immobilize it as quickly as possible with venom.

Snake Venoms

There are many kinds of venom. The two main types are 1) neurotoxins, which paralyze parts of the nervous system, especially those governing breathing and heart activity, and 2) hemotoxins, which destroy blood and tissue. Some snakes have poison with both neurotoxins and hemotoxins. Others have coagulants, which cause clotting of the blood, or anticoagulants, which prevent clotting and cause extensive bleeding.

Venom is first and foremost a feeding adaption used to subdue prey. Victims of snake bites are paralyzed and can do nothing as they are swallowed head first. By using venom to immobilize its prey, a venomous snake has to rely even less on a strong bite to achieve the same objective.


extracting venom

Venomous snakes manufacture their poison internally unlike poison dart frogs and some sea creatures which acquire their toxins from the food they eat. Snakes have a dozen or so different glands in their head and many of these produce toxic secretions. Venom production can vary with the season and takes approximately a month to replenish itself after it has been used. Studies of the Persian and African Saw-scaled vipers indicate that production of venom increases in the summer and falls off in the autumn and winter, a cycle that parallels the natural feeding and fasting rhythm of snakes.

The tiger snake and taipan of Australia and certain species of sea snake possess the most toxic poisons. While toxicity is a concern some scientist believe that the viper family can be deadlier because even though their toxicity level is lower they inject a lot more venom.

How is the potency of snake venom measured. One method is to inject venom into a group of mice. the amount of venom that kills 50 percent of the mice in 24 hours is called the lethal dose, or LD50, and is measured in milligrams of venom per kilogram of mouse. The lower the LD50 number the more powerful the toxin is. The LD50 of a taipan from Australia is 0.25 milligrams. For the king cobra and western diamondback rattlesnake it is 1.7 milligrams and 18.5 milligrams respectively.

How Snake Venoms Work


snake bite

Snake venoms begin acting in seconds: with enzymes in the venom breaking down tissues; blood and other fluids beginning to leak into tissues; and blood losing its ability to clot. Snake venom strength varies depending on the age of the snake, when it last ate, the time of day the strike occurs, how deeply the fangs penetrate the skin and how much venom is injected.

Some venoms contain 130 ingredients and scientist still don’t understand how they interact and cause the reactions they do. "There are blood clotting agents," Adrian Forsyth wrote in Smithsonian magazine, "substances that reduce blood clotting; others that specifically destroy red blood cells, white blood cells and the cells of other tissues; bacterial agents; and compounds that stimulate digestion. Cobras, kraits and coral snakes have a toxin that can stop a prey's heartbeat."

Carl Zimmer wrote in the New York Times: “The intricate shape of snake venom molecules allow them to lock onto particular receptors on the surface of the cells or onto specific proteins floating in the blood stream. Some venom molecule can plug the channels that muscle cells use to receive signals from neurons to contact. Without the signals the muscles go flaccid, leading to asphyxiation. Other venoms send the immune system into a tailspin, making it attack the prey’s organs. Still others loosen blood vessel walls, leading to shock and bleeding. Rather than rely on one of these attacks most venomous snakes produce a cocktail of molecules.”

Advances in DNA analysis have greatly aided the study of snake venom. Sequencing the proteins found in venom used to be done at a rate of three a month but new technologies have enabled scientists to do them at about 2,000 a month. Scientists have been able to identify all the genes that are active in venom glands cells; realize that snake venoms originated in one ancient species and was passed on to ancestor species rather than evolving independently in different species; and that many of the toxins developed in other part of the body such as brain, liver and blood not the venom glands.

Many snakes venoms contain coagulants and anticoagulants. Compounds similar to snake venom are now being used to treat anti-blood clotting disorders in humans. Venom from the saw-scaled viper has been used to design drugs that treat blood clots by prevented the blood from coagulating by keeping the blood platelets from sticking together.

Vipers


pit organ of a viper

There are about 40 species of true vipers. Among them are the common adder of Europe, the puff adder and horned viper of northern Africa, the sand viper, and rattlesnakes of the Americas. With the exception of one African species all true vipers give birth to live young.

Vipers are regarded as the most highly evolved of all snakes. Other snakes have more potent toxins than vipers but vipers have longer fangs and a better system for delivering poisons deep into the victims flesh plus a spade-shaped head able to accommodate the large venom glands.

Vipers have enlarged fangs that spring up when the viper opens its mouth and point forward, ideal for inflicting a bite. They can also make their upper jaws which holds the fangs stand up. This springs the fangs close to the victims. This allows them to strike prey and recoil and track down the prey later and avoid being injured by claws or teeth in a fight.

The largest and most dangerous viper is the Russell's viper, or daboia of India and South Asia. A man in Sri Lanka that nearly died from a bite from this snake told Reuters, “I was seeing everything double, so I knew the venom had broken into my body. After that I threw up foul green stuff from by body.” He suffered from severe bleeding, neurological problems and kidney failure. It took a whopping 110 vials of antivenin to save him.

Pit Vipers

There are about 60 species of pit vipers. They live mostly in Latin America. Pit vipers look like rattlesnakes. They have: 1) huge poison glands that puff out their cheek and give their head a triangular shape; 2) long hollow fangs in the front of the mouth that are folded down when the mouth is closes but automatically open when the mouth opens. 3) hunts in day and at night. They have heat sensitive glands that allow them to locate birds and mammals in the dark.

Pit vipers hunt frogs and small mammals. Despite their fearsome appearance they are shy creatures that avoid human contact. Rattlesnakes give birth to live young.

Rattlesnakes and pit vipers are adept at detecting heat. They have infrared sensors near their nostrils that allow to locate prey by sensing their heat. Pit vipers can strikes a mouse using these sensors even when they are blindfolded.

Snakes and Animals

Many animals either have an innate fear os snakes or develop a fear at an early age. Even newborn monkeys jump back when they are shown an image of a snake.

Many animals such as hawks, eagles, other birds, mongooses and predatory cats feed on snakes, especially young snakes. For defense snakes try to avoid detection by being inconspicuous, quiet and hidden or positioned someplace they can quickly seek cover When under attack snakes use the same methods as defense that use when attacking.

Other techniques that snakes used to fend off attackers include: 1) intimidation, using a noisemaker such as a rattle, hissing or expand their bodies so they look bigger than they actually are); 2) defecating when they are attacked to gross out their attackers; 3) feigning death; 4) getting attackers to harmlessly attack the snakes tail.



Snakes and Humans

It is pretty to safe to say that most people dislike or hate snakes. Even ones who have a fondness for them arguably like them because there is an element of danger associated with them. For a long time snakes have been regarded as symbols of evil and the devil and been linked with qualities and emotions like lust and deceit. It was a snake after all that tempted Eve in the Garden. Even Albert Schweitzer, who went out of his way not to step on insects, had no compunction about shooting a snake.

Tropical biologist Alexander Skutch wrote "the serpent is stark predication, the predatory existence in its boldest, least-mitigated form. It might be characterized as an elongated, distensible stomach, with the minimum of accessories...not even teeth that can tear its food." Many scientist think that a fear of snakes may instinctual and related to the dangers presented by poisonous snakes and large constrictors to our human, or even primate, ancestors. Harvard biologist E. O. Wilson said, "The brain appears to have kept its old capacities, it channeled quickness. We stay alert and alive in the vanished forests of the world."

Sometimes snakes are killed for their skins, which are used to make boots, purses wallets, amulets and charms Snake bones and body parts are taken as cures for a variety of ailments People who handle snakes a lot often use a special curved rod that looks like a golf club shaft attached to a hook. With these handlers can pick snakes and keep them at a safe distance.

Snakes usually go out of their way to avoid humans. Few species are aggressive. Most instances of aggressive behavior occur if a snake is cornered, surprised, harassed or attacked. To avoid an encounter with a snake look before stepping over logs and don’t poke around crevices, hollow logs or burrows. It is also a good idea to wear sturdy boots, thick socks and long pants if walking in an area with snakes.

Snakes are often caught and handled with a “snake hook” that keeps the snake beyond striking distance. When transported they are placed first in a thick sack and they placed into darkened crates.

Most snakes in zoos and snake farms have been bred in captivity and are used to being handled. If they appear nervous they might have a cloth hood placed over their heads. Some are quite happy to crawl into their darkened crates.

Snakes can be helpful to humans by eating pests such as rats. They also be a nuisance, sneaking into hen houses and eating eggs. Some great medical discoveries have come from snake poison. Merck sells a blood thinner based on the venom of the deadly saw-scaled viper. A protein from another Asian viper has shown great promise in inhibited the spread of melanoma cells.

Snakes Bites and Fatalities


snakebite

Symptoms of poisoning arise in only about half the people bitten by venomous snakes and many of those that do have symptoms recover with no treatment at all. Of those who get poisonous bites, children are more likely to die of suffer an injury than adults because they are not as strong as adults and they are injected with larger amounts of poison in relation to their body size. Since the venom takes approximately a month to replenish itself, a snake while not strike a human being unless it feels it has to.

The severity of snake bite has a lot do with the amount of venom injected. About 25 percent of all snake bites are dry (meaning no venom is injected) and another 25 percent involve the injection of only small amounts of venom. About 25 percent are severe but not life threatening. The remaining 25 percent are potentially lethal and require antivenin.

Snakes kill more people than any other animal. They kill around 20,000 people a year, many times more than all the people killed by sharks, crocodiles, elephants, tigers, hippos, pit bulls and rottweilers combines. Most snakebite victims are barefoot farmers in tropical Asian countries like Burma, Thailand and India there are large populations of rodents and rodent-consuming snakes and large numbers of poor farmers who sleep on the ground and work in rice fields that attract rodents and rodent-eating snakes. Population pressures have increased the number of snake bites while rubber boots and antivenin have reduced the number of fatalities.

What to Do When Bitten by a Venomous Snake

Victims of snake bites are recommended to stay calm and warm and, if possible, elevate the affected limb, and get to a hospital or clinic as quickly as possible. Doctors used to recommend applying a tourniquet or immersing the swollen area in ice water to stem the spreading of venom to the rest of the body. These techniques are no longer recommended in part because the resulted in needlessly lost digits and limbs. The tourniquet cut off blood circulation and the ice water caused frostbite. Cut-and-suck methods are also no longer in vogue.


snake bite tissue necrosis

Doctors are told that the following steps should be taken in case of snake bite, until the patient is taken to hospital: 1) It is important to re-assure the patient and keep the bitten part immobilized to prevent absorption of venom and reduce the pain; 2) Do not perform suction or slitting of the wound; 3) Remove accessories such as rings and anklets in case swelling occurs. 4) The patient should be given paracetamol 1000 mg to relieve pain. 5) Aspirin or aspirin containing analgesics or alcohol should not be given.

Antivenins

Antivenins are medicines made from snake venom that are used to treat snake bites. They work by triggering the body’s natural defenses to stops the venom’s harmful effects, and are species specific, meaning that victims have to take antivenins for the species of snake that bite them. Locally produced antivenins are better than imported ones because the toxins they fight better match the snakes that are found locally and lesser amounts are needed to cure a victim. Side effects of high does include high blood pressure, breathing problems and itching.

Antivenins are serums that are produced today pretty much they same way they were half a century ago: by repeatedly injecting venom into horses (and sometimes sheep) until they develop a resistance and then collecting and processing their blood. The venom is milked from snakes every couple of weeks. Giving horses and sheep increasingly higher doses of the venom trigger the production of antibodies. The fortified blood or plasma is then harvested and purified to isolate the serums, which is done through a complicated series of steps that must be overseen by a technician.

The amount of antivenin a victim needs varies from case to case and doctors need to have some experience with snake bites to know what to do. Antivenin contains a great deal of horse or sheep proteins and many people develop rashes or have reactions to these proteins and other impurities. Sometimes people die from anaphylactic shock caused by a reaction.

Antivenin is expensive. A hospital in the United States pays $200 for each vial and patients are often charged double that price. An average patient received 17 vials. Moreover each vial can take a staff member up to 30 to 40 minutes to prepare into the required reconstituted solution, which is required. Because antivenin is so expensive, doctors often try to use other treatments before resorting to it.

Drug companies have few incentives to come up with alternatives to antivenin because the market is small and the risks and cost are high. Much of the research into snake bite remedies is taking place in countries that have snake bite problems. Scientist at the Vittal Mallya Scientific Research Foundation in Bangalore, India, for example, have developed an antivenin that is effective in small doses and is made cheaply by injecting snake venom into hens and processing proteins collected from the hens eggs. Not only is method cheap it produces antivenins that have fewer side effects than traditional horse-serum based antivenin.

Image Sources: Wikimedia Commons

Text Sources: National Geographic, Natural History magazine, Smithsonian magazine, Wikipedia, New York Times, Washington Post, Los Angeles Times, Times of London, The Guardian, Top Secret Animal Attack Files website, The New Yorker, Time, Newsweek, Reuters, AP, AFP, The Economist, BBC, and various books and other publications.

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© 2008 Jeffrey Hays

Last updated November 2012

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