Background
Moccasins are new world pit vipers (family Viperidae, subfamily Crotalinae), which may be identified by a heat-sensing pit anteroinferior to each eye, elliptical pupils, a triangular head, and undivided subcaudal scales. See the image below.
Snake envenomations, moccasins. Copperhead (Agkistrodon contortrix). Photo courtesy of Sean Bush, MD. Moccasins comprise the genus Agkistrodon, which includes the cottonmouth (Agkistrodon piscivorus) and copperhead (Agkistrodon contortrix) in the southeastern United States; the cantil (Agkistrodon bilineatus) in Mexico and Central America; the mamushi (Agkistrodon blomhoffii), Siberian pit viper (Agkistrodon halys), and Central Asian pit viper (Agkistrodon intermedius) in central and northeastern Asia; and the Malayan pit viper (Calloselasma rhodostoma) and hundred-pace snake (Deinagkistrodon acutus) in southeastern Asia. See the image below.
Snake envenomations, moccasins. Cottonmouth or water moccasin (Agkistrodon piscivorus). Photo courtesy of Sean Bush, MD. Pathophysiology
Envenomation occurs when the moccasin injects venom via hollow movable fangs located in the anterior mouth. The effects of moccasin envenomation are generally similar to rattlesnake envenomation. However, in most cases, moccasin envenomation is less serious than envenomation by rattlesnakes. For further discussion of more severe pit viper envenomation, see Snake Envenomations, Rattle.
Moccasin venom is complex, with nearly 50 identified components. These can be broken down into 4 major categories:[1]
- Proteolytic enzymes that directly destroy tissue, as happens in digestion of prey animals
- Inflammatory mediators, including histamine- and bradykinin-like factors, that cause pain, erythema, swelling, and occasionally distributive shock
- Fibrinolytic enzymes that cleave fibrin into ineffective D-dimers, resulting in coagulopathy
- Antiplatelet factors that cause thrombocytopenia
Although neurotoxic factors can be detected in moccasin venom, clinically significant neurotoxicity does not occur with envenomation by copperheads or cottonmouths.
Epidemiology
Frequency
United States
Approximately 5,000 snakebites are reported to poison centers each year. Of the venomous snakebites for which the species is known, moccasins are responsible for 42%. The vast majority of these (86%) are copperhead envenomations. In portions of the southeastern United States, copperheads account for 85% of all reported snake envenomations.[2, 3] See the image below.
Snake envenomations, moccasins. Copperhead (Agkistrodon contortrix). Photo courtesy of George Bush. International
An estimated 300,000-400,000 venomous snakebites occur per year worldwide. The proportion of these caused by Agkistrodon species is not known.
Mortality/Morbidity
The American Association of Poison Control Centers (AAPCC) has reported only one death from moccasin envenomation since its first annual report in 1983.[4] Prospective studies of morbidity from moccasin envenomation have not been conducted.[5] However, in two retrospective studies of copperhead victims, patients missed a median of 2 or 6 weeks of work.
Sex
Incidence of snakebite is higher in males than in females.
Age
Young adults are bitten most commonly.[6]
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