Bites and stings

Disease/Disorder

Anatomy or system affected: Heart, immune system, skin

Specialties and related fields: Emergency medicine, immunology, toxicology

Definition: Injuries from animals or insects.

Bites and stings cause four major types of damage to the victim’s body: physical damage, the introduction of disease-causing organisms, the introduction of poisons (toxins, venoms), and allergic responses, including anaphylactic shock. Often, more than one form of damage is associated with a bite or sting. Alone or in combination, they can be life-threatening, but usually the damage from a bite or sting is minor. A wide variety of organisms can bite or sting, but the most important among them are mammals, reptiles (snakes and lizards), some fish (sharks, rays, moray eels), arthropods (including insects, centipedes, spiders, mites, ticks, and scorpions), and cnidarians (jellyfish, Portuguese man-of-wars, and their relatives).

Bites causing physical damage. Bites delivered by a mammal (most often a dog or cat) are likely to cause the most extensive physical damage. The specialized teeth of mammals, especially carnivores, in combination with powerful jaw muscles, can produce a serious wound. If wounding is in a vulnerable spot or is very extensive, or if the bleeding is not stopped, the physical damage can be fatal. A bite that causes physical damage is almost certain to introduce bacteria, viruses, or other infectious agents. An important example is the rabies virus, but many kinds of organism are dangerous if introduced into the bloodstream, or into the bone marrow of bones broken by the bite. Most mammalian bites do not introduce toxins into the victim. Some shrews have a venom in their saliva, but their small size and secretive habits minimize their threat to human health. Bites from mammals are also of minimal concern with respect to dangerous allergic responses. Physical damage is also the most serious problem in shark and moray eel bites.

Prevention, by avoiding animals prone to bite, is usually readily accomplished. Treatment involves stopping the bleeding, repairing the damage, and preventing infection.

Bites introducing infectious agents. Bites that cause serious physical damage are not the only ones that can introduce infectious agents. Any bite or sting can introduce infection to the victim because it penetrates the first line of defense, the skin. The arthropods are the most important disease vectors. Malaria is caused by a parasitic protozoan (single-celled, animal-type organism) transferred from one host to another by mosquitoes. Lyme disease is caused by a bacterium and is transported between hosts by ticks. Viruses cause yellow fever, and mosquitoes transport the virus to new hosts. Insects and ticks are vectors for a number of other diseases, most of which are introduced to the victim by a bite (including the stabs of blood-sucking arthropods such as mosquitoes).

Prevention of these diseases involves avoiding and/or eliminating the vectors; neither is always possible. Active immunization (stimulating the host to form antibodies against the disease-causing organism) is also used when available. Treatment involves drugs that destroy the disease organism or the use of passive immunization (the injection of preformed antibodies against the disease organism).

Bites and stings introducing toxins. Toxins or poisons are introduced to the victim most often by arthropods (scorpion stings, spider bites), cnidarians (stings), or reptiles (bites). Some mollusks—the cone shell snails, for example—can also inject toxins into a victim. The chemicals involved include enzymes that destroy tissue, neurotoxins that interfere with appropriate nerve cell responses (blocking or stimulating nerve cell signals), and others that interfere with the normal functions of the victim’s body chemistry. Rattlesnakes and their relatives, coral snakes, and the Gila monster (a large lizard) are examples of poisonous reptiles. The brown recluse and black widow spiders are dangerous examples of their group. The sea wasp (a jellyfish) and the Portuguese man-of-war are the best known, but by no means the only, dangerous cnidarians in coastal waters off North America.

Prevention involves avoiding the animals that inject the toxin, which is easily accomplished much, but not all, of the time. Treatment involves injection of antivenin, a solution of antibodies that neutralize a specific toxin. Polyvalent snake antivenoms, which are effective in neutralizing the venom from several species of related snakes, are available. Research on a universal antivenin that inactivates the venom of all snake species, though promising, was still in experimental stages as of 2014. Such research has been underfunded, however, which has slowed the development of new antivenoms and the production of existing antivenoms.

Bites and stings causing allergic reactions. Any bite or sting can cause an allergic response in the victim, because all introduce large foreign molecules, called antigens. These are often proteins, and they stimulate a response in the victim’s immune system. If the response is more than that needed to destroy the antigen, it is called an allergic response and the foreign protein is called an allergen. The allergic response may simply be a nuisance causing minor inflammation, but it is exceptionally dangerous if it escalates into anaphylaxis. Anaphylaxis is a hyperreaction to a foreign substance in which the heart rate increases; bronchioles in the lungs constrict, making breathing difficult; and blood pressure drops. If symptoms continue, the victim may go into shock and even die. The toxins introduced by venomous arthropods, reptiles, cnidarians, and mollusks are often allergenic, even causing anaphylaxis, but even nonpoisonous or minimally toxic materials such as the venom introduced in a bee or wasp sting can cause life-threatening anaphylactic shock in sensitive people. A painful sting for people not sensitized to the foreign material becomes a threat to the life of a sensitized, hypersensitive person.

Prevention, by avoiding the allergen, is the preferred defense against allergic reactions. If avoidance is not possible or cannot be assured, the injection of small amounts of the substance to which an individual is hypersensitive, followed by increasingly larger doses, is sometimes effective in desensitizing the individual. Treatment of severe anaphylactic reactions involves the injection of adrenaline. Antihistamines, taken orally or injected, are used in less severe situations.

Bibliography

California Academy of Sciences. “Universal Antidote for Snakebite: Experimental Trial Represents Promising Step Forward.” ScienceDaily, 28 May 2014, www.sciencedaily.com/releases/2014/05/140528105256.htm. Accessed 25 Oct. 2017.

Dossenbach, Hans D. Beware! We Are Poisonous! How Animals Defend Themselves. Woodbridge, Conn.: Blackbirch Press, 1999. Dossenbach examines some of the world’s most poisonous animals and shatters some myths about creatures long perceived as dangerous. Includes a bibliography.

Foster, Steven, and Roger A. Caras. A Field Guide to Venomous Animals and Poisonous Plants: North America, North of Mexico. Boston: Houghton Mifflin, 1994. Containing excellent information and bright color pictures, and written for an easy understanding, this book should be in any nature enthusiast’s library.

Halstead, Bruce W., and Paul S. Auerbach. Dangerous Aquatic Animals of the World: A Color Atlas. Princeton, N.J.: Darwin Press, 1992. Spectacular gallery of animals as diverse as polar bears and sea anemones. A natural history of the envenomation, or wounding apparatus, with slight detail on range, and none on life cycles. The excellent color photos are augmented by fine drawings of the anatomy of the dangerous parts of animals.

Harvey, Alan L., ed. Snake Toxins. New York: Pergamon Press, 1991. Discusses various topics, such as immunology of snake toxins, dendrotoxins, the structure and pharmacology of elapid cytotoxins, the influence of snake venom proteins on blood coagulation, and amino acid sequences and toxicities of snake venom components. Includes an index.

Hsu, Jeremy. “Defanging Snakebites.” Scientific American, vol. 313, no. 6, 2015, pp. 14–16. Environment Complete, search.ebscohost.com/login.aspx?direct=true&db=eih&AN=110842085&site=eds-live. Accessed 25 Oct. 2017.

Krohmer, Jon R., ed. American College of Emergency Physicians First Aid Manual. 2d ed. New York: DK, 2004. A comprehensive guide that details the treatment and techniques, in text and photographically, of a range of emergencies. Bites and stings are covered specifically.

Nagami, Pamela. Bitten: True Medical Stories of Bites and Stings. New York: St. Martin’s Press, 2004. Nagami describes strange and often gruesome true cases of bites and stings, resulting infections, and treatments.

Silverstein, Alvin, et al. Bites and Stings. New York: Scholastic, 2002. A young adult book that covers information about bites and stings from insects, pets, wild animals, sea creatures, and plants. Body reactions, transmittable diseases, treatment, and protection are also covered.

Spiders and Other Arachnids. http://spiders.ucr.edu. Site provides links to information about the spider, scorpion, bee, wasp, and ant species worldwide whose bites cause morbidity and mortality.

Tu, Anthony T., ed. Reptile Venoms and Toxins. New York: Marcel Dekker, 1991. In twenty-four contributed chapters, thirty-seven international specialists describe the latest developments in research on snake venom-including different types of venoms and toxins, actions, antidotes, and applications-and summarize what is known to date on Gila monster and frog toxins.