Sea Snake Toxicity – StatPearls

Justin Fuehrer; Erwin L. Kong; Heather M. Murphy-Lavoie.

Author Information and Affiliations

Last Update: April 2, 2023.

Continuing Education Activity

Sea snakes, thought to be the most abundant venomous reptiles on the planet, are found in the warm, tropical waters of the Indian and Pacific Oceans but not in the Atlantic Ocean. There are 57 known species of sea snakes and two major subfamilies (Laticaudinae and Hydrophiinae). Sea snakes are not aggressive, although they have been known to bite humans in self-defense or when surprised; this most commonly occurs when fishermen attempt to remove them from fishing nets. Envenomation by sea snakes can be a potentially fatal condition if not appropriately treated, as sea snake venom is a potent neurotoxin with low LD50 values. Subsequent respiratory compromise or drowning can occur owing to the paralysis of the diaphragm and skeletal muscles, respectively. Although not all bites result in envenomation, avoidance of sea snakes is the best approach. This activity outlines the evaluation and management of sea snake toxicity and the role of the interprofessional team in improving care for patients exposed to this venom.

Objectives:

• Describe the epidemiology of sea snake bites.

• Outline the signs and symptoms of sea snake envenomation.

• Describe appropriate treatment strategies for those with sea snake envenomation.

• Review the importance of the medical team in coordinating the care of a patient exposed to sea snake venom.

Access free multiple choice questions on this topic.

Introduction

Sea snakes, thought to be the most abundant venomous reptiles on the planet, are found in the warm, tropical waters of the Indian and Pacific Oceans but not in the Atlantic Ocean. There are 57 known species of sea snakes and two major subfamilies (Laticaudinae and Hydrophiinae). Sea snakes are not aggressive, although they have been known to bite humans in self-defense or when surprised; this most commonly occurs when fishermen attempt to remove them from fishing nets. Envenomation by sea snakes can be a potentially fatal condition if not appropriately treated, as sea snake venom is a potent neurotoxin with low LD50 values. Subsequent respiratory compromise or drowning can occur owing to the paralysis of the diaphragm and skeletal muscles, respectively. Although not all bites result in envenomation, avoidance of sea snakes is the best approach.[1]

Etiology

Sea snakes are not aggressive, although if they feel threatened or surprised, a bite can occur. Fishermen are the most at-risk population for sea snake bites, as contact with sea snakes can occur when fishermen attempt to remove sea snakes from their netting. Much like terrestrial snakes, not all bites result in envenomation.[2] Importantly, sea snakes have small teeth, making it possible for a bite to occur without a person realizing they were bitten until symptoms begin.

Epidemiology

Sea snake bites occur far less frequently than terrestrial snake bites and most commonly occur when fishermen attempt to remove them from fishing nets. The true incidence of sea snake bites is not known as many bites likely occur at sea and in small fishing villages where reporting bites may be difficult. Although sea snake bites occur less frequently than terrestrial snake bites, the potent neurotoxin leads to a high rate of morbidity and, potentially, mortality if not treated rapidly.[3]

Pathophysiology

Sea snake venom contains a potent neurotoxin with low LD50 levels. Several enzymes are present in sea snake venom, including acetylcholinesterase, hyaluronidase, leucine aminopeptidase, 5′- nucleotidase, phosphomonoesterase, phosphodiesterase, and phospholipase A. Sea snake venom acts at both presynaptic and postsynaptic sites. The presynaptic toxin is thought to be due to phospholipase A. This toxin initially causes the release of acetylcholine but, ultimately, the inhibition of acetylcholine release. The postsynaptic neurotoxin is a small protein between 6,000 and 8,000 daltons. This neurotoxin binds nearly irreversibly to the postsynaptic membrane at acetylcholine receptor sites. The net effect of both the presynaptic and postsynaptic toxin is the inhibition of neural impulses which can lead to skeletal muscle paralysis, including paralysis of the respiratory muscles and diaphragm. Other toxins, such as phospholipase A, can cause myonecrosis with resultant muscle breakdown, myoglobinuria, and elevated creatinine and creatine kinase levels.[1]

Toxicokinetics

Sea snake venom is extremely stable. Research has shown that boiling for 30 minutes and dissolving venom in both acidic and basic solutions to a pH range of 1 to 11, respectively, did not significantly change LD50 levels after administration in rats.[1] Therefore, hot water is not indicated for this venom and may, in fact, worsen outcomes by increasing blood flow to the area with the toxins.

History and Physical

Physical exam findings revolve around the blockage of neural impulses and muscle breakdown. Paralysis, dysphagia, muscle spasm, respiratory arrest, and dysarthria can occur, and the most common cause of death in sea snake poisoning is respiratory arrest due to diaphragm paralysis or drowning secondary to skeletal muscle paralysis. Because sea snakes have small teeth, bite marks may be difficult to appreciate, and it can sometimes be difficult for the victim to realize they were bitten until symptoms occur. In general, if no symptoms occur within a few hours after the bite, including both neurologic symptoms and muscle pain from myonecrosis, it is possible that the bite was a dry bite with no envenomation.[2] Approximately 50% of bites are dry bites, and only 50% of the time is there a significant envenomation.[4]

Evaluation

Due to the potential for myonecrosis from phospholipase A, creatine kinase levels may be elevated and myoglobinuria present in urine. No specific laboratory or radiographic tests are required for the diagnosis as clinical history including contact with a sea snake, and typical symptomatology is all that is required for diagnosis. Serum electrolytes and creatinine levels may be helpful to monitor for resultant kidney injury but are not required for diagnosis.[5]

Treatment / Management

Treatment is supportive and requires the administration of antivenin as soon as possible when symptoms of envenomation are present. Removal of the patient from the water is paramount, as skeletal muscle paralysis can cause drowning. Respiratory compromise may also occur owing to diaphragmatic paralysis, and patients may require intubation and mechanical ventilation until antivenin is administered and can neutralize the venom. Incision, drainage, and suctioning of the bite area are not indicated as little venom is likely to be removed in this manner, and resultant damage to the skin and possible subsequent infection risks outweigh the benefit of any possible venom removal. A pressure-immobilization bandage can be considered to help prevent systemic circulation of venom. Monitoring urine output should also be considered to evaluate for myoglobinuria, and frequent measurement of serum creatinine and electrolytes should be evaluated, and electrolytes supplemented as needed. In the absence of antivenin, hemodialysis can be considered and, theoretically, could be helpful in refractory cases given the small protein size (6,000 to 8,000 daltons) of the neurotoxin. [1]

Differential Diagnosis

• Cobra envenomation

• Rhabdomyolysis

Prognosis

Due to the low LD50 of sea snake venom, morbidity, and mortality rates are high without appropriate treatment. However, if supportive care, including mechanical ventilation as needed for respiratory compromise and antivenin administration, is done early, the overall prognosis is good.

Complications

Complications of sea snake envenomation can include muscle necrosis and myoglobinuria due to phospholipase A. If significant muscle breakdown occurs, the resultant myoglobinuria can lead to elevated creatinine levels and kidney damage. If antivenin is not administered promptly, significant morbidity up to and including death from drowning or respiratory failure can occur.

Consultations

If available, consultation with toxicology for advice regarding the type and dose of antivenin is warranted. Intensive care unit consultation may also be required if a respiratory compromise occurs and mechanical ventilation is needed. If considering hemodialysis, consultation with nephrology is required.

Deterrence and Patient Education

Sea snakes are not aggressive, but they are quite dangerous; therefore, educating patients and the public to avoid contact with sea snakes could dramatically reduce the incidence of sea snake bites. The group that could be potentially impacted the most by education focusing on prevention is fishermen. As most bites occur when fishermen are emptying or entangling their nets, educating them on identifying sea snakes in endemic areas and avoiding contact with sea snakes could be an important preventative measure. Furthermore, if a sea snake bite does occur, educating the population most at risk about potential adverse outcomes such as paralysis and respiratory arrest is important as this education would help potential victims understand that they need to get to definitive care quickly for antivenin administration.

Enhancing Healthcare Team Outcomes

Recognition and early treatment of a potential envenomation by a sea snake are imperative to a successful outcome. [1] Health professionals who are likely to encounter sea snake envenomation should have the skills needed to identify symptoms of sea snake envenomation and the skills needed to provide supportive care up to and including mechanical ventilation if respiratory muscle involvement occurs. [Level 5]

Review Questions

• Access free multiple choice questions on this topic.

• Comment on this article.

References

1.

Tu AT. Biotoxicology of sea snake venoms. Ann Emerg Med. 1987 Sep;16(9):1023-8. [PubMed: 3307552]

2.

Hornbeak KB, Auerbach PS. Marine Envenomation. Emerg Med Clin North Am. 2017 May;35(2):321-337. [PubMed: 28411930]

3.

Tan CH, Tan KY, Tan NH. Revisiting Notechis scutatus venom: on shotgun proteomics and neutralization by the “bivalent” Sea Snake Antivenom. J Proteomics. 2016 Jul 20;144:33-8. [PubMed: 27282922]

4.

White J. Bites and stings from venomous animals: a global overview. Ther Drug Monit. 2000 Feb;22(1):65-8. [PubMed: 10688262]

5.

Tamiya N, Yagi T. Studies on sea snake venom. Proc Jpn Acad Ser B Phys Biol Sci. 2011;87(3):41-52. [PMC free article: PMC3066545] [PubMed: 21422738]

Disclosure: Justin Fuehrer declares no relevant financial relationships with ineligible companies.

Disclosure: Erwin Kong declares no relevant financial relationships with ineligible companies.

Disclosure: Heather Murphy-Lavoie declares no relevant financial relationships with ineligible companies.

Can sea snakes bite humans?

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It is often said that a sea snake can only bite humans in the thin skin between the fingers or in the ears as its mouth is too small to grab anything else. This story took away the fear of sea snakes from many new scuba divers (and probably some experienced ones too). But is it true or just a myth?

Most sea snakes found in warm coastal waters are highly venomous. The most common snake observed by scuba divers is black and white with the common name of the banded sea snake. It can often be seen swimming over and between the reefs sticking its head in every hole looking for prey. Sea snakes need to breath and can therefore also be observed while free swimming up to the surface for air.

Scuba divers often hear during their open water courses that the snakes are not dangerous for humans as their mouth is too small to bite us. I was told this as well. And I heard this over and over again. I did not question it till I saw a documentary of pearl farmers who are at risk of getting bitten by exactly this banded sea snake that I was told cannot bite.

So workers at pearl farms as well as fishermen do get bitten. The snakes get entangled in fishing nets or hide in the crates where the pearls grow. They then feel threatened when taken out of the sea and bite in self-defense. But – they can’t bite humans, correct?

No, not correct. Sea snakes can indeed bite humans. To swallow their prey, which can be more than twice the size of its neck, the snake has to be able to open its mouth widely. It can obviously do so as well to bite in defense.

However, under normal circumstances a sea snake would never attack a scuba diver, snorkeler or swimmer. Also the fangs of most species are not long enough to reach through wetsuits. As always, treat sea life with respect. Don’t put your hand inside holes in the reef, don’t molest the animals, stay away from mating snakes and don’t block the way of a snake on its way to the surface to breath and you will be fine.

Just recently I met one of the guys who made up this legend many years ago on an island in Thailand. Fascinating how this tale made it around the world and almost every diver has heard it, many believing it.

Sorry for debunking this myth but probably it’s better to know about the dangers and to handle marine life with respect than to erroneously feel safe. Let me repeat, sea snakes are not aggressive; they never just attack without a reason. It would only do so if it feels in danger. If one comes close just let it swim past you. I have done this many times, it’s fine.

When photographing a sea snake and you want to get a nice front shot, swim ahead of the snake, wait for it at a distance and let the snake approach. If it approaches on its own it will not feel threatened and you get your perfect shot. Or alternatively you breath in (and go up) because you now know that they can actually bite you!

Have you heard the story about the small mouth of the sea snakes before? Who told it to you?

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Traveling full-time for 4 years now I explore dive destinations all over the world. I’m a scuba instructor, biologist and underwater photographer. Through my stories, reports and photography I show you the most beautiful destinations, fascinating marine life and hacks to enjoy scuba diving even more.

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Male sea snakes mistook divers for females

Male smooth sea snakes harass divers because they mistake them for females or rivals (and females see them as a refuge from annoying suitors). Herpetologists came to this conclusion after analyzing observations of these reptiles made in the 1990s on the Great Barrier Reef. As noted in the Scientific Reports article, snakes confuse people with snakes because they do not see very well, but if a diver allows them to study themselves, they will quickly realize the mistake and swim away. But an attempt to escape from a snake or brush it off can end in a bite.

Although sea snakes ( Hydrophiinae ) are highly venomous, they rarely bite humans, and if they do, they inject venom only twenty percent of the time. Typically, fishermen encounter attacks by these reptiles during the analysis of nets. However, scuba divers also occasionally complain about sea snakes chasing them, coiling around their limbs and even biting them. The reason for this behavior remains unclear, as the snakes swim up to divers who do not disturb or provoke them. For comparison, terrestrial snakes, when meeting with a person, do not approach him, but try to hide.

A team of herpetologists led by Richard Shine from Macquarie University set out to find out what is behind the “attacks” of sea snakes on divers. The researchers focused on a species that is especially often involved in such attacks – the smooth sea snake ( Aipysurus laevis ). This large, up to two meters long and weighing up to three kilograms, reptile is found in the eastern Indian and western Pacific Oceans, mainly off the coasts of Australia and New Guinea.

Shine and his colleagues analyzed data collected at the end of the last century by one of the authors of the study, Tim P. Lynch. From May 1994 to July 1995, he made 188 half-hour dives in the south of the Great Barrier Myth, during which he counted smooth sea snakes, recorded their behavior and noted all the cases when they pursued and attacked him. In addition, Lynch determined the sex of the reptiles encountered by their size (females are larger) and coloration features (females are grayish-blue and males are brown).

In total, Lynch encountered smooth sea snakes 158 times during his dives. Many of the reptiles showed interest in it and slowly swam up to study it better. At the same time, the behavior of snakes depended on their gender: if out of 58 males encountered, 35 approached the diver, then among females this proportion was much lower: 35 individuals out of 100. Male snakes often swam up to the diver several times in a row (females almost never did this) and spent more time next to him than females (p<0.0025). Also, males more often tried the water next to the diver with their tongue or touched his clothes and skin with it. Interestingly, outside the breeding season, Lynch almost did not see males on the reef, and female interest in him remained consistently low throughout the year.

Thirteen individuals, seven males and six females, were particularly aggressive. They quickly approached Lynch and pursued him (however, there were no attempts to bite the diver). Three males even wrapped themselves around the diver’s limbs, just as they wrap around the bodies of females during courtship. All such cases occurred during the breeding season. According to the diver’s observations, males “attacked” him immediately after an unsuccessful attempt to catch up with a female or a conflict with another male, and females – when they tried to escape from a male.

Thus, smooth sea snakes do approach and chase divers, and this is mostly done by males. Usually, reptiles slowly approach a person and study him. However, sometimes snakes, again mostly males, quickly swim up to the diver, stay close to him and wrap themselves around his limbs. According to Schine and his co-authors, the observations made by Lynch indicate that male snakes are interested in divers because, when highly aroused, they mistake them for females or rivals. This may be due to the fact that sea snakes do not see very well, and the chemicals with which they find partners do not remain on the substrate, as in the case of land snakes, but dissolve in water. At the same time, females swim up to people, because they perceive them as shelters from annoying boyfriends. This may be true of other species of sea snakes seen chasing divers.

When a diver approached by a sea snake behaves calmly, it soon realizes the mistake and swims away. However, if you try to swim away from the snake, it will start to catch up, and if a person also panics and starts to brush off the reptile, it will bite. This means that the best strategy for a diver who has caught the attention of a sea snake is to remain still and let it explore itself with the help of receptors on the tongue.

Two-colored bonitos ( Hydrophis platurus ), sea snakes from the Indian and Pacific Oceans, cannot drink salt water and must make do with rain water. Scientists have found that during the dry season, characteristic of a tropical climate, they suffer from thirst and wait for heavy rain to drink from the freshwater “lenses” formed on the surface of the ocean.

Sergey Kolenov

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Sea snake bite

Sea snake bite is dangerous. It is often said that she can only bite people between the fingers or behind the ear, as her mouth is too small to capture anything larger. This story comes from the fear of many new divers (perhaps some of the more experienced divers too).

Let’s find out if this is true or just a myth?

Most reptiles living in warm coastal waters are highly poisonous. The most common black and white with a common name is the Asia Minor sea snake. She is often seen swimming between reefs in search of prey.

They must breathe, so they can be observed on the surface.

Divers often say that aquatic reptiles are harmless to humans because their mouths are too small to bite. I was told that it is. And heard it over and over again. I did not question the theory until I saw real pearl farmers who are at risk of being bitten by this particular ribbon sea snake, which is said to be unable to bite.

However, pearl farm workers and fishermen are bitten by them. They get tangled in fishing nets or hide in boxes where pearls grow. Feeling threatened when they are taken out of the sea, they bite in self-defense. But – they can’t bite people, right?

No, not correct. The bite of a sea snake is quite real, they can bite people. In order to swallow their prey, which is more than twice the size of their neck, it must open its mouth wide. This is obviously rather biting for defense purposes. jellyfish pose a big threat.

However, under normal conditions, the reptile never attacks a scuba diver, snorkeler or swimmer. The fangs in most species are not powerful enough to pierce a wetsuit.

Always treat the inhabitants of the sea with respect. Don’t put your hands inside the reef holes, don’t touch the animals, stay away from mating animals, don’t block their path to the breathing surface, and you’ll be fine.

Poisonous snake in the black sea

Driver legends

Just recently I met one of the guys who came up with this legend many years ago on the island of Thailand. This fascinating story has spread all over the world, almost every diver has heard it, and many believe it.

Debunking this myth is important, as it is better to be aware of the dangers of marine life than to mistakenly feel safe. Let me reiterate, sea snakes are not aggressive; they never attack for no reason. They will only attack when they are in danger.

If one of them is approaching, let her swim past.