Venom
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Venom, the poisonous secretion of an animal, produced by specialized glands that are often associated with spines, teeth, stings, or other piercing devices. Animals use venom primarily for killing or paralyzing prey and for defending against predators. Some venoms also function as digestive fluids. A diverse range of animals employ venom, from various types of insects and spiders to cone snails, scorpions, and some snakes and jellyfish.
Many thousands of people die from venom poisoning each year, with snake bites a leading cause of morbidity and mortality. Venom poisoning in humans is a concern especially for those living in rural tropical regions, where venomous animals are relatively abundant. Most venoms injure humans only when introduced into the skin or deeper tissues, usually through a sting or bite.
Composition and types
- Neurotoxins affect tissues of the nervous system.
- Hemotoxins affect blood and the circulatory system.
- Cytotoxins cause direct destruction of cells and tissues.
- Myotoxins cause damage to muscle tissue.
- Cardiotoxins interfere with the function of the heart and cardiovascular system.
Venoms are mixtures of toxic enzymes and various other proteins that act on the body in different ways. Neurotoxic venoms act on the brain and nervous system and can cause either nervous excitation (characterized by such symptoms as muscle cramps, twitching, vomiting, and convulsions) or nervous depression (with such symptoms as paralysis and weakening or arrest of respiration and heartbeat).
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Hemotoxins affect the blood or blood vessels. For example, some destroy the lining of the smaller blood vessels and allow blood to seep into tissues, producing local or widespread hemorrhages, while others render the blood less coagulable or cause abnormally rapid clotting, leading to circulatory collapse that can be fatal. Still other venoms produce the symptoms of an allergic reaction, resulting in wheals, blisters, and violent inflammation, often followed by death of tissue and muscle spasms.
Venomous animals
Most major animal phyla contain venomous species, but relatively few come into harmful contact with humans. These few include certain types of snakes, such as cobras, mambas, vipers, pit vipers, coral snakes, and rattlesnakes. Most attacks of medical concern are driven by regional groups of snakesâfor example, the common krait (Bungarus caeruleus), Indian cobra (Naja naja), Russellâs viper (Daboia russelii), and saw-scaled viper (Echis carinatus) are often referred to as the âbig fourâ in South Asia.
Certain fishes, including stingrays, weevers, spiny sharks, scorpionfish, ratfish, and some catfish, are venomous. Also widely known for their venomous nature are lizards such as the Gila monster, some scorpions, spiders such as the black widow and brown recluse, and certain social insects, including the bee, wasp, and some ants. Various marine invertebrates, including some sea anemones, fire corals, jellyfish, all cone snails, and sea urchins, are also venomous.
Snakes and spiders inject venom into their victims with their fangs. Fishes use venomous spines, and scorpions and many insects use stings.
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Physiological effects
Venom attacks can range in severity from a simple localized inflammation of the skin to almost immediate death, depending on the animal involved and the potency and mode of action of its venom. An attackâs severity also depends on the victimâs age (children are more severely affected than are adults) and the location of the injury (a venom wound on an arm or leg is usually less serious than a similar one on the head or trunk). See also poison.