Rattlesnake Envenomation

Updated: Dec 14, 2017
  • Author: Sean P Bush, MD, FACEP; Chief Editor: Joe Alcock, MD, MS  more...
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Overview

Background

Rattlesnakes are pit vipers and include the genera Crotalus and Sistrurus. Pit vipers may be identified by a heat-sensing pit anteroinferior to the eye. Rattlesnakes may be identified in all but one species by a rattle at the tip of the tail. Rattlesnakes are indigenous from North America to South America. See the image below.

Juvenile southern Pacific rattlesnake (Crotalus or Juvenile southern Pacific rattlesnake (Crotalus oreganus helleri). Photo by Sean Bush, MD.
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Pathophysiology

Venom is usually injected into subcutaneous tissue via hollow movable fangs located in the anterior mouth. Occasionally, intramuscular or (probably rarely) intravenous injection occurs. Rattlesnake venom is generally composed of several digestive enzymes and spreading factors, which result in local and systemic injury.

Clinically, local effects most commonly predominate, progressing from pain and edema to ecchymosis and bullae. Hematologic abnormalities, including defibrination with or without thrombocytopenia, may result, but serious bleeding is uncommon. [1] Local or diffuse myotoxicity may result in complications such as compartment syndrome [2] or rhabdomyolysis. Other general effects include shock, myokymia/fasciculations, taste changes, and vomiting. Rarely, direct cardiotoxicity or allergy to venom may occur. Some rattlesnakes may exhibit neurotoxicity with minimal local tissue effects (see Mojave Rattlesnake Envenomation).

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Etiology

A large percentage of bites occur when a snake is handled, kept as a pet, or abused. These are considered intentionally interactive bites. Many bites are associated with ethanol use.

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Epidemiology

Frequency

United States

According to the American Association of Poison Control Centers (AAPCC) 2016 Annual Report, 804 rattlesnake envenomation case mentions were reported in 2016, with an additional 994 unknown crotalid envenomations. [3] In total, approximately 6,000 various snake envenomation case mentions were reported in 2016. However, this figure is probably conservative because of underreporting. Rattlesnakes cause the majority of all bites by identified venomous snakes in the United States. [4, 5] Dry bite (ie, no clinical evidence of envenomation) occurs in 10-50% of strikes. The American College of Medical Toxicology established the North American Snakebite Registry (NASBR) in 2013 to collect information about the epidemiology, clinical course, and management of snakebites. Between 2013 and 2015, 14 sites in 10 states entered 450 snakebites into the database. [6]

International

An estimated 300,000-400,000 venomous snakebites occur per year. Although rattlesnakes are not found naturally outside of North America, Central America, and South America, they are imported into zoos, museums, and private collections in other regions of the world.

Sex

Males are bitten more commonly than females.

Age

Young adults are bitten most commonly. [7] Elderly patients may have comorbidities and take medications that may increase the risk of hemotoxicity. [8]

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Prognosis

Before antivenom, estimates of mortality rates ranged from 5-25%.

Since the development of antivenom, rapid EMS transport, and emergency/intensive care, mortality rates have improved to less than 0.28% when antivenom is administered and to 2.6% when antivenom is not administered.

Less specific figures are available for morbidity data, although most patients recover fully after rattlesnake envenomation. The best estimates suggest that rattlesnake envenomation results in tissue loss, deformity, or loss of function in approximately 10% of patients.

Mortality/morbidity

Fewer than half a dozen deaths occur per year as a result of snakebite in the United States; most are caused by rattlesnake bites. Estimates of deaths each year from snakebite range from 30,000-110,000 worldwide. Up to 5 times as many individuals experience permanent morbidity. [9, 10]

US mortality with administration of antivenin is approximately 0.28%. Without antivenin being administered, mortality is approximately 2.6%.

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Patient Education

Call professionals, such as animal control, to move snakes (if it is necessary to move the snake).

Never attempt to handle, possess, or kill venomous reptiles.

For patient education resources, see the patient education article Snakebite.

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