Venom

This article is about the class of biotoxins. For other uses, see Venom (disambiguation) and Venomous (disambiguation).

Venom is any of a variety of toxins used by certain types of animals, for the purpose of defense and hunting. Generally, venom is injected by such means as a bite or a sting, while a poison is absorbed by ingestion or through the skin.

Wasp sting, with droplet of venom

The animals most widely known to use venom are snakes, some species of which inject venom into their prey through hollow fangs; spiders and centipedes, which also inject venom through fangs; scorpions and stinging insects, which inject venom with a sting (which, in insects such as bees and wasps, is a modified egg-laying device – the ovipositor). Many caterpillars have defensive venom glands associated with specialized bristles on the body, known as urticating hairs, and can be lethal to humans (e.g., that of the Lonomia moth). Venom is also found in a few reptiles besides snakes, such as the gila monster and Mexican beaded lizard. Other insects, such as true bugs [1] and many ants, also produce venom. Venom can also be found in some fish, such as the cartilaginous fishes – stingrays, sharks, and chimaeras – and the teleost fishes including monognathus eels, catfishes, stonefishes and waspfishes, scorpionfishes and lionfishes, gurnard perches, rabbitfishes, surgeonfishes, scats, stargazers, weevers, carangids, saber-toothed blenny, and toadfish. In fact, recent studies have shown that there are more venomous ray-finned fishes than all other venomous vertebrates combined. There are many other venomous invertebrates, including jellyfish and cone snails. The box jellyfish is widely considered the most venomous creature in the world.[2] Some mammals are also venomous, including solenodons, shrews, the slow loris, and the male platypus.

Because they are tasked to defend their hives and food stores, bees synthesize and employ an acidic venom (apitoxin) to cause pain in those that they sting, whereas wasps use a chemically different venom designed to paralyze prey, so it can be stored alive in the food chambers of their young. The use of venom is much more widespread than just these examples, of course.

Venomous vs. poisonous

There is a difference between organisms that are "venomous" and those that are "poisonous", two commonly confused terms applied to plant and animal life. Venomous, as stated above, refers to animals that deliver (often, inject) venom into their prey when hunting or as a defense mechanism. Poisonous, on the other hand, describes plants or animals that are harmful when consumed or touched. A poison tends to be distributed over a large part of the body of the organism producing it, while venom is typically produced in organs specialized for the purpose. One species of bird, the hooded pitohui, although not venomous, is poisonous, secreting a neurotoxin onto its skin and feathers. The slow loris, a primate, blurs the boundary between poisonous and venomous. From patches on the inside of its elbows it secretes a toxin, which it is believed to smear on its young to prevent them from being eaten; however, it will also lick these patches, giving it a venomous bite.

Snake venom

Main article: Snake venom

Snake venom is produced by glands below the eye and delivered to the victim through tubular or channeled fangs. Snake poisons contain a variety of peptide toxins. Snakes use their venom principally for hunting, though the threat of being bitten serves also as a defense. Snake bites cause a variety of symptoms including pain, swelling, tissue damage, low blood pressure, convulsions, and hemorrhaging (varying by species of snake).

Doctors treat victims of a venomous bite with antivenin, which is created by dosing an animal such as a sheep, horse, goat, or rabbit with a small amount of the targeted venom. The immune system of the subject animal responds to the dose, producing antibodies to the venom's active molecule; the antibodies can then be harvested from the animal's blood and applied to treat envenomation in others. This treatment can be used effectively only a limited number of times for a given person, however, as that person will ultimately develop antibodies to neutralize the foreign animal antibodies injected into him (anti-antibody antibodies). Even if that person does not suffer a serious allergic reaction to the antivenom, his own immune system can destroy the antivenin before the antivenin can destroy the venom. Though most people never require even one treatment of antivenin in their lifetime, let alone several, people who work with snakes or other venomous animals may. Fortunately, these people often develop antibodies of their own against the venom of whatever animals they handle, and thereby are protected without the assistance of exogenous antibodies.

Aristolochia rugosa and Aristolochia trilobata, or "Dutchman's Pipe," are recorded in a list of plants used worldwide and in the West Indies, South and Central America against snakebites and scorpion stings. Aristolochic acid inhibits inflammation induced by immune complexes, and nonimmunological agents (carrageenan or croton oil). Aristolochic acid inhibits the activity of snake venom phospholipase (PLA2) by forming a 1:1 complex with the enzyme. Since phospholipase enzymes play a significant part in the cascade leading to the inflammatory and pain response, their inhibition could lead to relief of problems from scorpion envenomation.

See also

• Toxin
• Poison
• Toxinology
• Schmidt Sting Pain Index
• Venomous mammals
• Venomous fish
• Big Four (Indian snakes)
• Envenomation
• Venomous animals (category)

Bibliography

• Leo Smith and Ward C. Wheeler. 2006. Venom evolution widespread in fishes: A phylogenetic road map for the bioprospecting of piscine venoms. Journal of Heredity 97(3): 206-217.
• Lans C, Harper T, Georges K, Bridgewater E. 2001. Medicinal and ethnoveterinary remedies of hunters in Trinidad. BMC Complement Altern Med. 2001;1:10. Epub 2001 Nov 30. http://www.biomedcentral.com/1472-6882/1/10