Ophidiophobia or the fear of snakes, is common in Western civilization. Many stories mention snakes as evil and should be feared. The stories stretch from as back as the Old Testament when Adam and Eve were tempted by the snake all the way to current mainstream pop culture with examples of the famous fear of Indiana Jones of these creatures, to the film Snakes on a Plane. The fear continues to be perpetuated.
The topic of snake bites management in wilderness medicine is dependent on the location. There are approximately 3,000 different species of snakes. There are 375 species of venomous snakes in the world. Worldwide there are 20,000 deaths which occur every year. Most of the deaths are in sub-Saharan Africa and Asia.
The death rate in the United States is 14–20 per year. There have been five reported deaths in Missouri, 1933 by a Timber Rattlesnake, and two copperhead bites in 1965, a copperhead bite in 2014, and recently in 2015 from a cottonmouth. The last patient did not seek medical attention and had a reported lethal dose of oxycodone in his system as well as being legally intoxicated. In fact more people have been killed by dog attacks (32) and lightning (47) in the state during this time period.
In the United States copperheads, cottonmouths, coral snakes, and a variety of rattlesnakes are poisonous. None of the 10 most poisonous snakes live in the United Snakes. The most poisonous is the Belcher’s Sea Snake (Hydrophis Belcheri), which resides in the Ashmore Reef in the Timor Sea off the northwestern coast of Australia. Other top snakes include the Inland Taipans, Common Indian Krait, Phillipine Cobra, the King Cobra, Russell’s Viper, Black Mamba, Yellow Jawed Tommygoff, Multibanded Krait, Black Tiger Snake, and the Jararacussu.
There are five poisonous snakes in the state of Missouri: the Osage Copperhead, Western Cottonmouth, Timber Rattlesnake, Eastern Massasauga Rattlesnake, and the Pygmy Rattlesnake. These snakes all belong to the family Crotalidae, also known as pit vipers. All pit vipers have common characteristics for identification:
Triangular heads
Fangs
Elliptical pupil
Heat sensing pit between eye and nostril
These characteristics allow differentiation between poisonous and non-poisonous snakes (See Figure 1).
Snake venom is used to mobilize prey as well as aid digestion. It is composed of numerous proteins and enzymes. Crotalidae venom is 90% water, 5–15 enzymes, and 3–12 non-enzymatic proteins. Enzymes of snake venom include:
Proteolytic enzymes
Arginine ester hydrolase
Thrombin-like enzyme
Collagenase
Hyaluronidase
Phospholipase A2
Phospholipase C
Lactate dehydrogenase
Phosphomonoesterase
Phosphodiesterase
Acetylcholinesterase
RNase
DNase
5-Nucleotidase
L-Amino acid oxidase
Identification
Identification is essential in treating snake bites. Location where the snake was encountered as well as identification of markings may help guide your treatment. Don’t be surprised if the snake is brought to you by the patient or family for identification.
Missouri’s Poisonous Snakes
Osage Copperhead: (Agkistrodon contortrix phaeogaster)
This is the state’s most common venomous snake. It is pink to orange in color with hourglass-shaped crossbands, which may be dark gray, brown, or reddish-brown. It is found in a variety of habitats ranging from prairies to rocky, wooded hillsides. The species will inhabit abandoned buildings and equipment.
Western Cottonmouth: (Agkistrodon piscivorus leucostoma)
The snake measures 30–42 inches. It is black with a black/cream colored belly. This species is incredibly secretive and shy, but if confronted can be quite aggressive. It lives in cypress swamps, sloughs, drainage areas in the Mississippi Lowlands. Populations can also be in the Ozarks around small creeks and rivers.
Timber Rattlesnake (Crotalus horridus)
This is Missouri’s largest venomous snake, measuring between 36–60 inches. It has a brown dorsal line, a black tale, a slate grey body with black side, and back markings. This species once inhabited the entire states, but now very rare. It is found in mature forests. Its den is often found on rocky, wooded, south facing hillsides, and bluffs.
Eastern Massasauga Rattlesnake (Sistrurus catenatus catenatus)
This snake is light to dark grey or brown in color. It has 28–40 black dorsal blotches. It is 18–30 inches in length. It is almost extinct in the wild due to habitat destruction and persecution. This species lives in the marches and moist prairies in Northern Missouri.
Pygmy Rattlesnake (Sistrurus miliarius streckeri)
It is small bodied (15–20 in). The body of the snake is grayish brown. It has brown dorsal stripe with black blotches on its back. It is found in glades, second growth forests near rock ledges, and in powerline cuts that are cut through dense areas of a forest.
Snakes from Surrounding States
The Texas Coral Snake (Micrurus tener) will grow to 24 inches (61 cm), but some can reach 40 inches (100 cm). Coloration is black, yellow, and red banding. The male are smaller than the females. There are four subspecies.
The Western Diamondback Rattlesnake (Crotalus atrox) can be found in the surrounding states of Oklahoma, Kansas, and Arkansas, as well as the Southwest. The color pattern consists of a dusky gray-brown, but variants including pinkish-brown, brick red, yellow, pinkish, and chalky white are also found. This color is overlaid with a series of dorsal body blotches which are dark gray-brown or brown in color. The tail has two to eight alternating bands of black and with white or gray. The males are larger than the females. They commonly grow to 4 feet (120 cm), but rarely grow up to 6 feet (180 cm).
Which Snake Bit Me?
In treating snake bite patients in Missouri, we must remember that we are boarded by eight states. Identification is important as one may have a patient bitten by a snake not native to Missouri, though there is significant overlap of the species.
Arkansas poisonous snakes
Osage Copperhead
Western Cottonmouth
Timber Rattlesnake
Western Pygmy Rattlesnake
Texas Corral Snake
Western Diamondback Rattlesnake
Oklahoma poisonous snakes
Copperhead
Western Cottonmouth
Timber Rattlesnake
Massasauga
Western Pygmy Rattlesnake
Prairie Rattlesnake
Western Diamondback Rattlesnake
Kansas poisonous snakes
Prairie Rattlesnake
Massasauga
Timber Rattlesnake
Copperhead
Illinois poisonous snakes
Timber Rattlesnake
Massasauga
Cottonmouth
Copperhead
Iowa poisonous snakes
Timber Rattlesnake
Massasauga
Copperhead
Prairie Rattlesnake
Nebraska poisonous snakes
Timber Rattlesnake
Massasauga
Copperhead
Prairie Rattlesnake
Kentucky poisonous snakes
Osage Copperhead
Western Cottonmouth
Timber Rattlesnake
Western Pygmy Rattlesnake
Tennessee poisonous snakes
Osage Copperhead
Western Cottonmouth
Timber Rattlesnake
Western Pygmy Rattlesnake
The Prairie Rattlesnake (Crotalus viridis) is also known as the Hopi Rattlesnake, Western Rattlesnake, and the plains rattlesnake. Originally thought to have seven different subspecies, now it is thought that there are two clades, a western and eastern, with the Rocky Mountains the dividing line. They can grow larger than 3.3 feet (100 cm). The upper body is light brown to green. There are dark, light-bordered blotches along the back.
Management
Prehospital Care
Field care should adhere to the principles of ACLS, remember the ABCs. Monitor vital signs and establish IV access with one large-bore IV. Start crystalloid infusion. Start oxygen if available and monitor the airway. Restrict the person’s activity and immobilize the affected area. This will most commonly be an extremity as most commonly the site on envenomation. The use of a proximal tourniquet is discouraged. This can lead to venous congestion and increased ischemia. No demonstratable benefit has been seen. Cryotherapy (ice packs) is also discouraged as this increased tissue ischemia. If negative-pressure suction devices are available they are beneficial if started within the first several minutes after the bite. Transfer to definitive facility. Do not administer antivenin in the field.
Emergency Department Care
The majority of snake bites are seen by physicians with little experience. If a regional center is available, the patient should be transferred to this facility. Surgical evaluation is recommended. In the emergency room review the ABCs and assess the patient for signs of shock (tachypnea, tachycardia, dry mucous membranes, mental status changes, and hypotension. Laboratory evaluation should include a complete blood count (CBC), Prothrombin time (PT), Partial thromboplastin time (PTT), Fibrinogen, and fibrin degradation products. Tetanus prophylaxis should be performed. Prevention of secondary infections is important. Systemic antibiotic therapy is commonly given to prevent infections of Aerobacter, Proteus, and Pseudomonas. There is debate of the efficacy and utility of antivenin therapy, but it remains the mainstay of significant envenomation.
Envenomation is graded and determines the need for the administration of an antivenin. The grading of pit viper bites is 0–4.
Grade 0 – Visible bite but no envenomation
Grade 1 – Minimal pain and edema less than 25 cm.
Grade 2 – Moderate pain, edema 25–40 cm, systemic weakness and emesis
Grade 3 – Severe pain, edema 40–50 cm, petechia, and systemic vertigo
Grade 4 – Lethal envenomation, widespread edema, shock, seizures, coma, and renal failure
Antivenins
Antivenins are neutralizing antibodies. Two types of antivenin are available. One was first manufactured in 1956. It is derived from horse serum (Wyeth). The antivenin is purified but still contains other serum proteins that can be immunogenic. The latest version, approved by the US Food and Drug Administration (FDA) in 2000 (CroFab, Savage), is a monovalent immunoglobulin fragment derived from sheep proteins.
The old antivenin may still be available, but it is recommended to use the more specific and purified drug. Even with the newer agent, one must remember while the antivenin maybe life-saving, it also may lead to immediate hypersensitivity (anaphylaxis) and delayed hypersensitivity (serum sickness) reactions and must be used with caution. To achieve maximum efficacy, administer within 4–6 hours of the snake bite.
CroFab is made specifically from venom of the eastern and western diamondback snakes, Mohave rattlesnakes, and the cottonmouth/water moccasin snakes. The purpose of any antivenin is to bind the toxins in the venom and prevent both local and systemic results. Side effects occur in one-third are considered mild to moderate. These include utcaria, pruritus, and rash. Rare side effects include severe rash and uticaria and recurrent coagulopathy. CroFab has been used in Crotalid bites with good effect (reduced fasciotomy) and reductions in antivenin toxicity.
The initial amount of antivenin should correlate with the patient’s presenting grade.
Grade 1 – none
Grade 2 – none
Grade 3 – 2–4 vials
Grade 4 – 5–9 vials
Grade 5 – more than 10 vials
Prior to the administration of antivenin, the patient is tested for sensitivity to equine serum. Intradermal testing is given as 0.2 ml with a ratio of 1:10 or 1:100. A wheal within the first 15–30 minutes is considered a positive test. The patient can also be tested with two drops in the conjunctiva at a ratio 1:1000 ratio. The production of itching and erythema is a positive test. Each vial is diluted in 50 ml of saline and given over 15–20 minutes. Antivenin therapy is continued until progression of symptoms is stopped. Repeated dosing may be necessary.
Surgery is reserved for the development of compartment syndrome initially. Debridement of necrotic tissue may be needed several days after the original bite.
Walker et al. published in 2011 in the American College of Surgeon’s on the management of Copperhead’s specifically. In this article all snakebites from 1995–2010 were reviewed who presented to East Texas Medical Center, Crockett, a level III trauma center. A total of 142 snakebites were treated. Ninety-four were of the Agkistrodon species-contortrix contortrix (copperhead) or piscivorus leukostoma (water moccasin). Three were rattlesnakes, and three were from the Texas coral snake (Micrurus fulvius tener). Forty-two were unidentified pit vipers. The 88 copperhead bites were then reviewed.
Results from the study demonstrated that the most common presenting symptoms were pain and swelling. Eighty-five percent of the patients had grade 1 envenomations. Ten patients had laboratory abnormalities secondary to the snakebite. Forty-four were admitted for observation. The average length of stay for patients admitted was two days. No patients received antivenin, and no patients required surgical intervention. There were no deaths. One patient had edema and ecchymosis that persisted for more than 1 month.
The conclusion from the study was that accurate identification of the pit viper species involved in snakebites is essential. Although envenomation by a rattlesnake (Crotalus species) may require antivenin and uncommonly surgery, a bite by a copperhead (Agkistrodon contortrix) rarely requires any intervention other than observation. The unnecessary use of antivenin should be discouraged.
Conclusion
The treatment of snake bites is essential in wilderness medicine. It is important to follow the ABCs when managing these injuries. Identification of the snake is helpful. Remember that exotic snakes have been imported into the United States and could be the cause of the envenomation. In the case of Copperheads, identification may save the administration of antivenin. Stabilization and transfer for definitive treatment to the nearest medical facility is essential.
Sources
Greenfield LJ, Mulholland MW, Oldham KT, et al. Surgery Scientific Principles and Practice, 3rd Edition. Lippincott Williams and Wilkins. 2001.
Walker JP, Morrison RL. Current management of copperhead snakebite.
J Am Coll Surg. 2011 Apr;212(4):470–4; discussion 474–5.
Photos from the Missouri Department of Conservation
Biography
Brian Biggers, MD, MSMA member since 2010, is a Surgeon in Springfield, Mo.
Contact: biggersb@hotmail.com
Reprinted with permission, Greene County Medical Society Journal.
