When a snake bites • CPT MARCO COPPOLA, DO, MC, USA DAVID E. HOGAN, DO Primary care physicians may More than 3000 species of snakes exist through­ be required to treat snake-bitten patients out the world .. They are found anywhere from and must differentiate between venomous below sea level to above timberline. Worldwide, and nonvenomous snakes. The chief dis­ 300,000 snakebites occur with 30,000 to 40,000 tinguishing characteristics of venomous deaths per year. 1,2 In the United States, 45,000 snakes are fangs and a single row of sub­ snakebites occur with 12 to 15 deaths per year.2 caudal anal plates. The physiologic effects No clinician, whether practicing in a rural or a of snake venom are on the cardiovascular, large, inner city hospital, is exempt from treat­ hematologic, and neurovascular systems. ing snakebites. This article reviews the charac­ The snake-bitten patient first needs sup­ teristics of venomous snakes in the United States, portive treatment and stabilization. Then, the general management of snakebites, and com­ the physician must establish whether enven­ plications associated with envenomation. omation has occurred, grade it, and moni­ Two families of venomous snakes exist in the tor edema around the bite. Local treatment, United States: Elapidae and Viperidae (Table 1).3 broad-spectrum antibiotics, and tetanus The Elapidae family consists of two genera of prophylaxis should be used for all enveno­ coral snakes, Micrurus fulvius and Micruroides mation grades. The decision to administer euryxanthus. Crotalidae, a subfamily of Viperi­ antivenin therapy should be made on clin­ dae, consists of various species ofthe genera Agk­ ical grounds and the envenomation grade. istrodon (cottonmouths and copperheads), Sistru­ Its use, however, can lead to anaphylaxis rus (pigmy and massasauga rattlesnakes), and and anticomplement reactions. Crotalus. The genus Crotalus consists of rat­ (Key words: Snakebite, antivenin, enven­ tlesnakes including the eastern and western dia­ omation) mondbacks, mojave, sidewinder, timber, and prairie rattlesnakes. Venomous snakes exist in all states except Alaska, Hawaii, and Maine.3 Now the serpent was more subtle than any beast of (Figures 1 and 2 illustrate distributions of some the field which the Lord God had made. (Genesis 3:1) common snakes in the United States.4) Dr Coppola is director, Emergency Medicine Residency Pro­ General characteristics gram, and director of research, Medical Department Activ­ ity, Darnall Army Community Hospital, Fort Hood, Tex, and Primary care physicians should have a basic assistant professor, Department of Emergency Medicine, understanding of the general characteristics of Texas A&M University Health Sciences Center, College of snakes. Differentiating venomous from nonven­ Medicine, Temple Campus, Temple, Tex. Dr Hogan is assis­ omous snakebites is a very important step in the tant professor of surgery, director of Disaster Emergency management of the snake-bitten patient. Non­ Medical Services, and undergraduate education coordinator, Section of Emergency Medicine and Trauma, University of venomous snakebites are benign and need only Oklahoma Health Sciences Center, Oklahoma City, Okla. local wound care. Opinions or assertions contained herein are the private In contrast, venomous snakebites are fre­ views of the authors and should not be construed as offi­ quently associated with complications. If patients cial or as reflecting the views of the Department of the Army or accompanying parties can describe the offend­ or the Department of Defense. ing snake, they will provide information important Correspondence to CPT Marco Coppola, DO, Depart­ ment of Emergency Medicine, Darnall Army Community in determining the course of treatment. Hospital, Fort Hood, TX 76544. The two most constant factors differentiating 494 • JAOA • Vol 94 • No 6 • June 1994 Clinical practice • Coppola and Hogan ogous to the human parotid gland. Table 1 Venom is discharged via the Common Venomous Snakes in the United States actions of the external jaw mus­ cle. The amount of venom dis­ Family: Elapidae charged depends on the weight and size of the victim as deter­ Micruroides euryxanthus Arizona coral snake mined by the thermoreceptors.5 Micrurus fulvius American coral snake Because the comparatively large size of a human being overwhelms Family: Viperidae the snake's thermoreceptors, Subfamily: Crotalidae injection of a larger amount of Agkistrodon contortrix American copperhead venom may result. Most aver­ Agkistrodon piscivorus Cottonmouth age-sized snakes discharge between 25% and 75% of their Crotalus adamanteus Eastern diamondback rattlesnake stored venom per strike.6 The Crotalus atrox Western diamondback rattlesnake larger and older snake injects Crotalus cerastes Sidewinder more, but less-concentrated, Crotalus horridus Timber rattlesnake venom, whereas the younger and Crotalus scutulatus Mojave rattlesnake smaller snake injects less, but Crotalus viridis Prairie rattlesnake more-concentrated, venom. Sistrurus catenatus Massasauga rattlesnake Venom is delivered to the vic­ Sistrurus miliarius Pigmy rattlesnake tim via fangs (Figure 4). All but the coral snakes have hinged fangs venomous from nonvenomous snakes are fangs that fold posteriorly against the upper jaw. Coral and the presence of a single row of subcaudal anal snakes have a fixed pair of fangs that are short­ plates (Figures 3 and 4). Nonvenomous snakes er and fatter than those of Viperidae. Snakes shed lack fangs and have a double row of subcaudal their fangs as they do their skin. Reserve fangs may anal plates. With some exceptions, for example, the be in place at times resulting in one to four fang rat snake, venomous snakes generally have a tri­ marks. angular shaped head. Nonvenomous and the Rattlesnakes are named for their "rattle" American and Arizona coral snakes (M fulvius located on the tail. The rattle is a group of inter­ and M euryxanthus) have a round head that is locking segments formed on the tail each time indistinct from the neck (Figure 3). Venomous the snake sheds. It is erroneous to determine the snakes generally have elliptical pupils. Nonven­ age of the snake by counting the number of rat­ omous and coral snakes have round pupils. Coral tles.4 Snakes shed one to four times a year, the num­ snakes may be easily identified by their red-on-yel­ ber depending on the temperature, climate, mois­ low-on-black circumferential markings. Snakes ture, and the amount of food available. that display red-on-black-on-yellow markings, such as the king snake, are nonvenomous. One Venom need only to remember the following: Snake venom is a complex substance evolved for Red-on-black; venom-lack. immobilizing, killing, and digesting the snake's Red-on-yellow; kill-a-fellow. prey. It is 90% water, 10% protein, and various Characteristic of Crotalidae is a thermore­ trace elements. Table 2 lists some components of ceptor "pit" located between the eyes and nose; venom.5 The proteolytic enzymes in snake venom hence, the term "pit viper." This pit allows the are capable of tissue necrosis; whereas hyalu­ snake to sense gradations in temperature and ronidase, "the tissue spreading enzyme," cleaves locate prey. The thermoreceptor functions well mucopolysaccharide bonds, allowing venom to trav­ with small prey but is overwhelmed by larger ani­ el through tissue. Thrombinlike esterases form mals such as human beings. This feature may in unstable fibrin clots that are easily lysed by part account for the defensive strike of the snake other enzymes in venom.5 resulting in snakebite. The physiologic actions of snake venom are gen­ Venomous snakes have an elaborate enven­ erally directed toward the hematologic, cardio­ omation apparatus, which consists of venom vascular, and neuromuscular systems (Figure 5). glands, ducts, and fangs. The venom gland is anal- The proteolytic action of snake venom wreaks Clinical practice • Coppola and Hogan JAOA • Vol 94 • No 6 • June 1994 • 495 Crotalus atrox -------- Crotalus adamanteus ..... ......... ..... Crotalus horridus Figure 1. Distribution of Crotalus atrox, Crotalus adamanteus, and Crotalus horridus . .. - " ,, Micruroides euryxanthus --- - ---- Micrurus fulvius , --- .......... ... ...... Crotalus viridis ------- Figure 2. Distribution ofMicruroides euryxanthus, Micrurus fulvius, and Crotalus viridis. 496 • JAOA • Vol 94 • No 6 • J une 1994 Clinical practice • Coppola and Hogan consider the possibility of a Crotalidae Nonvenomous "dry bite": a bite without the injection of venom. 2 Also impor- tant is the species and size of the snake involved. Larger snakes inject more venom. The roundhead venom of the coral snakes is predominantly neurotoxic, n whereas the venom of the rat­ tlesnake generally causes hem­ orrhage and tissue necrosis. Pathogens that are normal elliptical eyes round eyes flora of the snake mouth, such ~ ~ as Clostridium, Pseudomonas, or Staphylococcus species, may complicate the wound site with infection. Although extremely rare, anaphylactic and ana- phylactoid shock have also been single plates double plates reported to be a complication of snake envenomation.7 Common signs and symp­ toms of snake envenomation Figure 3. General characteristics of Crotalidae uerslLS nonuenoTrWlLS snakes. (Aoopted from Dowl­ appear in Table 3. One or two ing and coauthors,4 and Podgorny.5) fang marks approximately 0.5 cm to 4.0 cm apart is pathog­ havoc on cell membranes throughout the body. nomonic of a venomous snakebite.3-6 After sig­ Cells undergo lysis or become