Snake venom

Snake venom is an extremely toxic saliva that often causes paralysis in a snake’s prey. Snakes use venom to subdue their prey and aid in digestion. The glands that produce venom are located on each side of the head and below and behind the eyes. When a snake bites, the muscles in its head squeeze its glands and push the venom into its hollow fangs. If threatened, venomous snakes will also bite humans. Snake bite poisonings are called envenomings. Of the nearly three thousand snake species in the world, only about six hundred are venomous and only about two hundred are very dangerous to people. However, these snakes kill about one hundred thousand people per year. The most venomous snakes are found in Asia, Africa, and Australia.

Medical researchers have developed antivenoms, which contain antibodies that attack and kill the proteins in snake venom. These proteins are responsible for the biological effects experienced by those who have been bitten. Because venom varies among snake species, antivenom does, too. Antivenom is extremely expensive; in the United States, it costs thousands of dollars per vial, and four to six vials are usually needed to treat a person who has been bitten. It is not unusual for an antivenom treatment to cost more than $100,000.

Snake venom has been used to make medicine that is used to treat heart attacks, strokes, and arthritis as well as other diseases and disorders. However, developing new medications from snake venom is time-consuming and expensive.

Background

More than five million people throughout the world are bitten by snakes each year. Of these, more than two million are bitten by venomous snakes. In addition to the estimated one hundred thousand people who die each year from venomous snake bites, many more must undergo amputations and suffer long-term complications from snake venom. Some snake venom is more potent than others. The deadliest venomous snakes live in Africa, Asia, and Australia. The population of venomous snakes in rural areas of these countries is high. They often bite agricultural workers who sometimes die because the closest hospital is many miles away.

The deadliest snake in Africa is the black mamba, which can kill a human being with only two drops of venom. These 8-foot (2.4-meters) long snakes are born with venom already in their fangs, which enables them to quickly kill their prey. Other venomous snakes in Africa are the boomslang, also called the South African tree snake; the cobra (four species of cobra live in Africa); the West African viper; the Gaboon viper; and the puff adder.

Of the venomous snakes in Asia, many live in India, where nearly sixty thousand people die from snake bites each year. Most of these deaths are caused by the Russell’s viper, which is known to bite farmers working in paddy fields. Other venomous snakes in India include the common krait and the infamous king cobra, which swallows its prey whole.

In contrast to Asia and Africa, snake bites in Australia are very rare. The Eastern brown snake, also called the common brown snake, is mostly found in the eastern half of the mainland. Their venom is the second most toxic in the world. The inland taipan, found in the central eastern area, has the most potent venom of any land snake in the world.

The venomous snakes that are native to the United States are not as poisonous as those in other countries, and death from a venomous snake bite in the country is rare. Of the seven thousand people in the United States who are bitten by venomous snakes each year, only about five are killed. Venomous snakes in the country include rattlesnakes, copperheads, water moccasins, and coral snakes.

Overview

Snake venom is unique to a species and in how it kills prey. In general, the five types of snake venom are proteolytic, neurotoxic, hemotoxic, cytotoxic, and myotoxic.

All venomous snakes have proteolytic venom in combination with at least one other type. This type of venom causes a reaction at the site of a snake bite, breaking down tissue and blood vessel walls. Some snakes have more proteolytic venom than others. Rattlesnakes and pit vipers have large amounts of this type of venom.

Neurotoxins affect the nervous system by disrupting the electrical impulses that cause movement. This causes paralysis, brain damage, and loss of consciousness. This type of venom is not especially painful, and occasionally people do not realize they have been bitten until they begin experiencing symptoms. Neurotoxic venom is common among kraits, some cobra species, and coral snakes. The deadly black mamba also has neurotoxic venom.

Hemotoxic venom destroys red blood cells and affects blood clotting, making the blood either too thick to flow or too thin to stop external bleeding, both of which are deadly. It also harms tissues and organs, eventually causing heart attacks and internal bleeding. This kind of snake venom is extremely painful, and people know right away that they have been bitten by a snake. Hemotoxic venom works slowly, though, which gives a person a better chance of getting the medical attention needed to survive. Many types of vipers, including rattlesnakes and copperheads, have hemotoxic venom as do the boomslang and puff adder.

Cytotoxic snake venom kills cells, severely damaging skin and underlying tissue. While not as deadly as neurotoxic and hemotoxic venom, cytotoxic venom often leaves a victim disabled. For example, a person may lose the function of a limb. King cobras and most vipers have this kind of venom.

Myotoxic venom harms the muscular system. It causes tissue death in muscles, preventing muscle contraction. This leads to muscle necrosis, or death. Sea snakes and pit vipers have myotoxic venom.

Many lives have been saved with the use of snake antivenom. This is medication that boosts the immune system’s response after a snake bite. Antivenoms are made by immunizing a host animal, usually a sheep or a horse, with snake venom. These animals have strong immune systems and produce powerful antibodies against snake venom. These antibodies are harvested and then purified. While antivenoms work, their distribution has been affected by weak health systems and inadequate infrastructure in some countries. In Sub-Saharan Africa, the production of antivenom has always been in short supply and is not available for everyone who needs it. Competition from inferior producers has led to some major antivenom producers leaving the country because they could not compete with the lower prices offered by these producers. Their departure has left the country with only a limited supply of an inferior product.

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