Excerpt from Snake Envenomations, Sea

Synonyms, Key Words, and Related Terms: sea snakes, Hydrophiidae, Pelamis platurus, P platurus, Enhydrina schistosa, E schistosa, sea snake venom, neurotoxins, myotoxins, snake envenomations, sea snake envenomations, sea snake bite, sea snake neurotoxin, sea snake wound, snake bite

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Background: Sea snakes, which comprise approximately 70 species, are the most abundant and widely dispersed group of poisonous reptiles in the world. Most (approximately 50) sea snake species are members of the family Hydrophiidae and are characterized by vertically flattened tails and nostrils with valvelike flaps. Unlike eels, sea snakes have scales but lack gills or fins. While they spend much of their time underwater, they must surface periodically to breathe. They are typically about 1 m in length, but some species may grow to 3 m.

Sea snakes are found predominantly in tropical and subtropical waters in the western Pacific and Indian Oceans, often in protected coastal waters and near river mouths. However, they do thrive in a variety of habitats, ranging from muddy or turbid water to clear waters and coral reefs. The pelagic sea snake, Pelamis platurus, has a remarkably wide geographic range, which reaches the western coasts of North and South America from the Baja peninsula to Ecuador, along with the waters around Hawaii. Sea snakes are not found in the Atlantic Ocean, the Caribbean, or along the North American coast north of Baja.

Generally, sea snakes are not aggressive. They are not thought to strike humans unless provoked, nor do they typically actively pursue swimming prey.

Pathophysiology: The venom apparatus of sea snakes is fairly rudimentary, consisting of 2-4 short hollow maxillary fangs associated with a pair of venom glands. The venom ducts open near the tips of the fangs. The fangs are dislodged easily from their sockets and may remain embedded in the skin of victims.

Nearly 80% of sea snake bites fail to produce significant envenomation, and bites may be inconspicuous, painless, and free of edema. However, sea snake venom is extremely potent, and a complete envenomation by an adult sea snake may contain enough venom to kill 3 adult people. The clinically relevant toxins in sea snake venom are neurotoxins and myotoxins.

The primary neurotoxin causes peripheral paralysis by competitively binding to postsynaptic nicotinic acetylcholine receptors at the neuromuscular junction. Potent myotoxins account for the significant muscle necrosis, with consequent myoglobinemia and hyperkalemia that may occur following envenomation. Sea snake venom does not affect blood coagulation to a significant degree.

Sea snakes are closely related to Australian elapids; some paraspecificity exists between sea snake antivenom and Australian elapid antivenom.

Frequency:

In the US: Hawaii is the only US state where sea snakes are found.

Internationally: Sea snake envenomations occur throughout the serpents' geographic ranges, but accurate data about the incidence of envenomation are not available. Victims most commonly are fishermen bitten while handling nets or after stepping on a snake.

Mortality/Morbidity: Before the development of sea snake antivenom, the mortality rate associated with sea snake bites was approximately 10%. With timely administration of antivenom and aggressive supportive care, the mortality rate currently is much lower, although accurate numbers are not available.

Race: No inherent racial predilection exists for sea snake bites; however, the best-represented races in areas with endemic sea snake populations are the most commonly bitten.

Sex: Males are bitten much more commonly than females, with a male-to-female ratio of approximately 4:1, because of the increased occupational exposure to sea snakes by male fishermen.

Age: Age is a factor in determining sea snake bites only insofar as it occurs with potential recreational or occupational exposure to the serpents.