Why Fatal Sea Snake Bites Are Unusual

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Banded Sea Krait, Laticauda colubrina, Komodo National Park, Indonesia

On Thursday, a 23-year-old British man was bitten by a “Black Ringed Sea Snake” (also known as a “Banded Sea Krait”) entangled in a fishing net. The fish trawling boat was operating in remote waters off the northeast Australian coast (five hours from land) near Groote Eylandt, the largest island in the Gulf of Carpenteria. Unfortunately, the young man succumbed to his bite before emergency services arrived.

According to Dr. Blanche D’Anastasi, a sea snake researcher based at James Cook University, fishing crews frequently come across sea snakes but this is the first reported sea snake-related death in Australia. And Dr. Bryan Fry, an Associate Professor from the University of Queensland who studies the evolution of venom, says that “by and large they are very gentle animals, and people do go scuba diving with them all the time.”

Sea snakes are commonly found in tropical and sub-tropical waters of southeast Asia, the western Pacific Ocean, and northern Australia. There are 70 known species, 30 of which exist in Australian waters. Although not resident in Australian waters, Banded Sea Kraits (BSKs) are generally seen in shallow waters near coral reefs and mangroves near Queensland and New South Wales. BSKs are unique because they are “amphibious” and come on land to digest food, shed their skin, mate, and lay eggs. Male BSKs can grow to be up to two-and-a-half feet and female BSKs can be up to four feet long; the longest BSK ever recorded was nearly 11 feet in length.

Relief map of Australia showing the State of Queensland. This image was compiled from data acquired by LANDSAT 5 & 7 satellites combined with elevation data.

Although BSK venom is highly toxic, the snake is generally described as non-aggressive. There are more recorded bites from land-based venomous snakes than there are from BSKs. Venom resides in the BSK’s fangs, which it uses to capture prey. The venom of the BSK is a potent neurotoxin that impairs the prey’s ability to move and breathe when injected into the animal (a process called “envenomation“).

When envenomation occurs in humans, bites are often painless and minimal swelling occurs. Symptoms include headaches, sweating, vomiting, body aches, muscle stiffness, and eventually paralysis. As with the eels that the snakes prey on, the paralysis of any muscles involved in breathing or swallowing may be fatal.

In the case of serious bites,  sea snake antivenom can be administered. Antivenom should not be used for all bites because it can cause unpleasant side effects, including allergic reactions to the antivenom serum. Made from the blood of horses that have been immunized against the effects of the venom, the purfied antivenom is injected intravenously to neutralize the neurotoxin.

While BSKs seldom bite humans, the snake that bit the young fisherman was probably stressed and felt threatened after getting ensnared in the trawling net. In general, sea snake bites are rare and envenomation occurs even more infrequently. Only 3% of sea snake bites are ever fatal.

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