In most cases, the onset of symptoms appears shortly after ingestion of the toxin (<30 minutes), with initial signs being gastrointestinal complaints ( nausea, vomiting) and mild paresthesia of the perioral area. The pathogenesis stems from the presence of tetrodotoxin (TTX) in the internal organs of the fugu (the liver, the intestines, and gonads, but also the skin), a powerful heat-stable neurotoxin that blocks sodium channel action, thus diminishing neuronal activity. Multiple dogs in New Zealand were poisoned after eating grey side-gilled sea slugs they found on the beach.Ingestion of pufferfish (called fugu or "river pig" in Japanese), considered to be one of the most delicious fish in Japan, can lead to life-threatening intoxication that is often described in the literature as fugu poisoning. People who have eaten the eggs of horseshoe crab have been poisoned in Thailand. Poisonings from marine gastropods have also been reported in China, Japan, and Taiwan. Ingestions of marine gastropods and thread-sail fish are additional sources of toxicity in Japan. Toadfish are another source of poisoning in Australia. Worldwide, pufferfish are implicated in the poisoning of patients in Bangladesh, Japan, Australia, and India, in addition to the United States. The toxin produced by the Eastern newt is only 1/100th as potent as that of the toxin found in Pacific newts. There is a single species of newt on the east coast, called the Eastern newt ( Notophthalmus viridescens), that contains the toxin. The most toxic newts are found in Oregon. They are distributed along the Pacific coast from Southern Alaska to Baja, Mexico. There are 4 species of Pacific newts of the genus Taricha that contain the toxin. In the United States, the most common sources of poisoning are pufferfish imported from Japan and Mexico, pufferfish mislabeled as another fish, Pacific newts, and the Eastern newt. Poisoning in humans occurs when they ingest tetrodotoxin-containing organisms. Additionally, tetrodotoxin-binding proteins are present in some animals, such as the shore crab, pufferfish, and gastropods. Garter snakes, which do not contain tetrodotoxin, but prey on toxic newts that do, have also acquired this mutation. Therefore, sodium channels in these species are not blocked by tetrodotoxin. Animals that accumulate tetrodotoxin in their bodies have a non-aromatic amino acid substitution that causes the sodium channel to have a low affinity for tetrodotoxin. Normally, sodium channels have an aromatic amino acid chain in the P-loop region of domain I. The exception to this are newts, in which it is still unclear whether the tetrodotoxin is produced endogenously or exogenously due to conflicting results from experiments.Īnimals that contain tetrodotoxin are resistant to the neurological effects of the toxin themselves. Some of these tetrodotoxin-producing bacteria are also a part of the animal’s natural microbiome and is another mechanism of tetrodotoxin accumulation in these animals. The bacteria known to be implicated in the production of tetrodotoxin include members of the following genera: Pseudoalteromonas, Pseudomonas, Vibrio, Aeromonas, Alteromonas, Shewanella, Roseobacter, Raoultella, Actinomycetes, Microbacterium, and Serratia. These captive pufferfish then accumulated the toxin themselves. Some of these captive puffer fish were then fed the livers of wild pufferfish that contained tetrodotoxin. All captive specimens had undetectable levels of tetrodotoxin. This was discovered in an experiment by collecting pufferfish raised in captivity and measuring levels of tetrodotoxin in their organs, particularly the liver. Bacteria produce the toxin and are then consumed up the food chain and accumulate in high doses in high trophic level animals. The animals bioaccumulate the toxin from their diets. The reason that many distantly related taxa have evolved the ability to produce tetrodotoxin is that the animals themselves do not produce the toxin. Other invertebrates that contain the toxin include several starfish species, several species of xanthid crabs, species of the phylum Chaetognatha (arrow worms), species of the phylum Nemertea (ribbon worms), some flatworms, and planarians of the genus Bipalium. Mollusks that contain the toxin include several species of the blue-ringed octopus, species of Niotha gastropods, and species of genus Naticidae (moon snails). In marine vertebrates, the toxin is found in more than 20 pufferfish species and certain angelfish. Of terrestrial vertebrates, the toxin is found in Western, rough-skinned newts of the genus Taricha, the Eastern Newt ( Notophthalmus viridescens), and toads of the genus Atelopus. The toxin is found naturally in a wide variety of vertebrates and invertebrates with no close phylogenetic relationship.
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