Course Content Although many laypeople use venomous and poisonous interchangeably, there are significant differences. Venoms are endogenously produced by the animal and actively introduced into the victim through a wound created by a fang, stinger, pincer, or spike. The clinical scenarios in which these occur are referred to as envenomations or envenomings. Poisonous animals, conversely, deliver their toxins passively; they must be ingested, inhaled, or absorbed transdermally. These toxins are often produced exogenously and accumulate in the host animal through diet or environmental exposure. To further complicate the issue, some animals actively deliver toxins via spraying, smearing, or spitting. An example of these toxungens,
which may also be produced endogenously or taken up from the environment, is the secretions that fire salamanders spit at potential predators. A scoping review of all the ways animals can injure and cause illness in humans would be a Herculean task. Even a summary confined to envenomations worldwide would be massive. Therefore, this course will focus exclusively on the most clinically relevant terrestrial and marine venomous animals native to the U.S., including vertebrates (e.g., snakes, lizards, and fishes) and invertebrates (e.g., cnidarians and arthropods).
SNAKEBITES
In the U.S., there are between 8,000 and 10,000 snakebites annually, resulting in an average of 3.4 deaths each year. 1-6 Approximately 98% of all U.S. snake envenomations are caused by crotalids, also known as pit vipers . Crotalids include rattlesnakes, copperheads, and water moccasins, which are also called cottonmouths . Taxonomic classification changes frequently, but there are currently two copperhead species, two cottonmouth species, and approximately 20 native rattlesnake species. There are also three coral snake species that account for nearly 2% of U.S. snake envenomations, which will be discussed later. Fewer than 1% of venomous snakebites in the U.S. are due to nonnative snakes maintained—legally or illicitly—in zoos or private collections. Snakebites affect all age groups. A study using data from the North American Snakebite Registry (NASBR), administered by the American College of Medical Toxicology (ACMT), found a mean patient age of 34.9 years, with a range of 1 year old to greater than 89 years old. 7 Children less than 13 years old accounted for 28.2% of patients. Contrary to popular belief among herpetologists and other snake enthusiasts, most snakebites do not occur in the occupational setting or in the context of intentionally interacting with the snake. The majority of envenomations occur after the Pit vipers Pit vipers are characterized by large, triangular heads, relatively small eyes, large, retractable and mobile fangs, and a thermoreceptor “pit” located approximately halfway between the eye and the nostril. Pit vipers also have a single row of subcaudal plates distal to the anus, and rattlesnakes will have one or more keratin segments that compose the “rattle” at the distal end. Though some references recommend using the pupil or head shape as a way of distinguishing a pit viper from noncrotalids, it should be noted that both venomous and nonvenomous snakes may have round or elliptical pupils, and pupil shape can change depending on the amount of ambient light. Additionally, many nonvenomous snakes can flatten their heads into a triangle shape when they feel threatened. Experts recommend that people learn to recognize the venomous species in their vicinity using multiple characteristics, rather than rely on single features, rhymes, or mnemonics. Pit viper venom comprises a variety of protein and nonprotein substances. Most crotalid venom contains a mixture of metalloproteinases, collagenase, phospholipases A2, and hyaluronidase that can cause myonecrosis and dermatonecrosis. 9-11 Multiple venom components, for example, serine proteases, disintegrins, metalloproteinases and C-type lectin-like proteins, produce a variety of hematologic effects, resulting in coagulopathy, platelet aggregation, activation or inhibition, or increased coagulation leading to thrombotic complications.
victim accidentally steps on or near a snake or reaches into an area where the snake is located. 7 However, any intentional handling of a snake increases the risk of a bite. Additionally, fewer than 1% of snakebite victims are under the influence of alcohol or other substances of abuse when they sustain the bite. 8 Figure 1. Northern Cottonmouth (Agkistrodon Piscivorus)
Source: Nathan Wells
Figure 2. Timber Rattlesnake (Crotalus Horridus)
Source: Orry Martin Certain crotalid species have unique toxins. Crotalocytin, found in the timber rattlesnake ( Crotalus horridus ), causes platelet aggregation. 9 Mojave toxin is a phospholipase A2 that prevents the presynaptic release of acetylcholine, the neurotransmitter necessary to stimulate muscle contractions. 12 Neurological effects that may be observed can range from subtle, for example, ptosis and diplopia, to profound, for example, skeletal and respiratory muscle paralysis. Mojave toxin is most commonly found in Mojave rattlesnake ( C. scutulatus ) venom, but it has also been identified in the Southern Pacific rattlesnake (C . helleri ) and, less commonly, the tiger rattlesnake ( C. tigris ), the western diamond-backed rattlesnake ( C. atrox ), and the prairie
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