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Snake Envenomation, Sea
Updated: Nov 6, 2008
Introduction
Background
Sea snakes, venomous elapid snakes that inhabit marine environments, are the most abundant and widely dispersed group of poisonous reptiles in the world. They comprise approximately 70 species, 50 of which are members of the family Hydrophiidae. Sea snakes are characterized by laterally compressed bodies and vertically flattened tails and nostrils with valve-like flaps, giving them an eel-like appearance. Their most characteristic feature is a paddle-like tail, which increases their swimming ability.1 Unlike eels, however, sea snakes have scales but lack gills or fins. Although they spend much of their time underwater, they must surface regularly to breathe. They are typically about 1 m in length, but some species may grow to 3 m.
Sea snakes are found in warm coastal waters, predominantly in tropical and subtropical waters in the western Pacific and Indian Oceans. They are usually found in protected coastal waters and near river mouths. However, they are able to thrive in a variety of habitats, ranging from muddy or turbid water, to clear waters and coral reefs. Most species prefer shallow waters not far from land, around islands. The pelagic sea snake, Pelamis platurus, has a remarkably wide geographic range, reaching the western coasts of North America 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.
Yellow-belly pelagic sea snake.
Generally, sea snakes are not aggressive with gentle dispositions. They are not thought to bite humans unless provoked, and they typically do not actively pursue swimming prey. Sea snakes have been noted to become quite aggressive, when they are taken out of water, exhibiting erratic movements and striking anything near them that moves.2
Pathophysiology
Among this group are species with some of the most potent venoms of all snakes. The venom apparatus of sea snakes is fairly rudimentary, consisting of 2-4 short hollow maxillary fangs associated with a pair of venom-producing 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. Usually, little or no swelling is involved, and it is rare for any nearby lymph nodes to be affected. 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; therefore, some paraspecificity exists between sea snake antivenom and Australian elapid antivenom.
Frequency
United States
Hawaii is the only US state where sea snakes are found.
International
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.
Clinical
History
The diagnosis of sea snake envenomation requires the establishment of the potential for exposure to a sea snake (eg, exposure to water in an area known to harbor sea snakes), identification of symptoms of envenomation, and demonstration of evidence of a bite (eg, multiple puncture wounds or reliable history of observed bite).
Symptoms are attributable to multiple organ systems, with neurological symptoms predominating. They may occur as early as 5 minutes or as late as 8 hours following the bite, but they usually occur within 2 hours. Initial symptoms include generalized aching, stiffness and tenderness of all muscle groups, as well as pain with passive muscle stretching. Trismus is also common. This is followed by progressive flaccid paralysis, starting with ptosis and paralysis of voluntary muscles. Paralysis of muscles responsible for swallowing and respiration can be fatal. Within 8 hours of envenomation, myoglobin, as a result of muscle breakdown, begins to rise in blood plasma; this eventually leads to myoglobinuria with resultant acute renal failure. If muscle breakdown is severe, hyperkalemia may ensue, possibly leading to cardiac arrest.
- Euphoria
- Anxiety
- Malaise
- Drowsiness or mild confusion
- Headache
- Myalgias (typically worse with movement, usually beginning in the afflicted extremity, as well as the neck, within 30-60 min after envenomation)
- Arthralgias
- Ptosis
- Mydriasis with sluggish reaction to light
- Ophthalmoplegia, leading to diplopia
- Failing vision (usually a terminal symptom)
- Sialorrhea
- Trismus
- Facial paralysis
- Muscle paralysis (usually ascending, may be flaccid or spastic)
- Dyspnea
- Nausea, vomiting, abdominal pain, and cramping
- Change in urine color (dusky yellow to reddish brown)
- Oliguria
- Thirst
Physical
Physical examination findings of sea snake envenomation may include the following:
- Fang marks (usually 2 or more small circular dots, which may be difficult to initially identify)
- Local tissue reaction (usually absent or minimal)
- Paralysis (typically ascending)
- Hyporeflexia (progressing to loss of reflexes)
- Hypersalivation
- Trismus
- Bulbar paralysis
- Ptosis
- External ophthalmoplegia
- Dysarthria and slurred speech
- Dysphagia
- Respiratory distress or respiratory failure
- Tachypnea
- Cyanosis
- Apnea
- Cardiac arrest (secondary to hyperkalemia)
- Fever (variable)
- Lymphadenopathy (involving the nodes responsible for draining the site of envenomation)
Causes
- Occupational exposure - Usually fishermen handling nets
- Accidental exposure - Stepping on sea snakes in shallow water
- Nonaccidental exposure - Intentionally handling sea snakes (eg, home aquariums)
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References
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Senanayake MP, Ariaratnam CA, Abeywickrema S. Two Sri Lankan cases of identified sea snake bites, without envenoming. Toxicon. Jun 1 2005;45(7):861-3. [Medline].
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Further Reading
Keywords
sea snake envenomation, sea snake bite, sea snakes, snake bite, Hydrophiidae, Pelamis platurus, P platurus, Enhydrina schistosa, E schistosa, sea snake venom, neurotoxins, myotoxins, snake envenomations, sea snake neurotoxin, sea snake wound
