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Test results of sea snail sample in a fatal poisoning case in Van Ninh district, Khanh Hoa province, on Sept. 11, 2020

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On September 12, 2020, the Institute of Oceanography under Vietnam Academy of Science and Technology (VAST) received strange sea snail specimens from a fatal poisoning case in Van Ninh district, the central Khanh Hoa province, to determine the name and toxin of this snail.

According to the Department of Food Safety and Hygiene, Khanh Hoa Provincial Department of Health, at 9:00 on September 11, 2020, three local diving fishermen caught some sea snails on the waters of Van Ninh district, Khanh Hoa province. After that, a group of fishermen stopped at Khai Luong Island, Van Thanh commune to give an acquaintance family half of the snails. The three fishermen steamed the remaining snails for food at 16:00. After about 30 minutes, all of them showed symptoms of lip, hand and leg numbness, dizziness, nausea and headache. At 19:00, one of the three victims had worsening symptoms. He was admitted to the emergency room at Tu Bong Regional General Clinic, but was confirmed dead. Around 1 am on September 12, 2020, the remaining two victims were given emergency aid at the Van Ninh District Medical Center, then transferred to Khanh Hoa Provincial General Hospital and were fortunate to survive. The family on Khai Luong Island saw strange snails so only two people ate several snails and had no symptoms of poisoning.

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Samples of sea snails collected from a food poisoning incident in Van Ninh, Khanh Hoa on September 11, 2020 (Photo: Truong Si Hai Trinh) 

Suspecting that the above people were poisoned by eating sea snails, on September 12, 2020, Khanh Hoa provincial health agency collected the remaining snail samples from family on Khai Minh Island and transferred them to the Institute of Oceanography, VAST, to identify the snail species and their toxins.

VAST has invested in three laboratories on food safety and hygiene, including a laboratory on food safety and marine environment (in the central region) at the Institute of Oceanography, Nha Trang, Khanh Hoa. Results of species identification and chemical composition analysis from 30 samples at the Laboratory of Food Safety and Marine Environment (Central Region) were as follows:

- Out of a total of 30 analyzed samples, 29 specimens were identified as Nassarius papillosus and 01 specimen belonging to Nassarius glans.
- A large amount of tetrodotoxin was identified in all specimens of the two above snail species.

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Nassarius pappilosus (Photo: Truong Si Hai Trinh)

Tetrodotoxin is known as a neurotoxin, affecting the central nervous system of humans and animals (research results show that it "blocks sodium ion exchange channels on neuromuscular membranes, stopping the transmission of nerve signals "). With a toxicity many times higher than the marine food safety limit in the analyzed sample, it is estimated that ingesting just 5-10 of the snails containing this toxin could be fatal to a normal person within 30 minutes to a few hours after eating.

Due to its heat-resistant, acid-stable properties, tetrodotoxin does not decompose at high temperatures during processing, so it can remain in processed food products, even frozen or canned products. Poisoning symptoms from eating poisonous sea snails usually appear about 30 minutes after eating, including numbness of the tongue, lip, dizziness, headache, abdominal cramps, nausea, vomiting, difficulty speaking, difficulty swallowing and loss of balance (staggering). In severe cases, the victim has convulsions, foam in the mouth, coma and possibly death due to paralysis of the respiratory muscles. There is no specific antidote for tetrodotoxin poisoning in general and sea snail poisoning in particular. It is necessary to follow the instructions of the health authority and quickly bring the victim to the nearest medical establishment.

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Nassarius glans (Photo: Truong Si Hai Trinh)

In fact, similar poisonings from eating sea snails were reported to be quite common in Pacific countries. The recorded results of sea snail species such as Turban, the top of shells, Trumpet shells, Ivory snails, Oliva are species in danger of being poisonous. Depending on the species of snail, the poison can be saxitoxin or tetrodotoxin.

The origin of toxins in sea snail species is currently unknown and quite complex, not all individuals in the same species contain toxins and toxicity is also very different from individual, geographic region and season. In order to protect health and human life, absolutely not to eat snails that have a history of poisoning or have not been ensured of food safety.

Faced with food poisoning in general, marine food poisoning in particular, marine food hygiene and safety is an issue that needs attention and management.

Translated by Tuyet Nhung
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