Neurotoxic marine poisoning

Health risks associated with the consumption of sea turtles: A review of chelonitoxism incidents and the presumed responsible phycotoxins

Consuming the meat of some marine turtles can lead to a specific type of seafood poisoning known as chelonitoxism. A recent poisoning event (March 2024) on the Tanzanian island Pemba, resulting in the death of 9 people and hospitalization of 78 others, underscores the need to obtain an up to date overview and understanding of chelonitoxism. Here, we document a global overview of poisoning incidents resulting from the consumption of sea turtle flesh worldwide. All events combined involved over 2400 victims and 420 fatalities. Incidents were predominantly reported in remote regions (often islands) across the Indo-Pacific region. Reported health effects of consuming poisonous sea turtles include epigastric pain, diarrhea, vomiting, a burning mouth and throat sensation, and dehydration. In addition, ulcerative oeso-gastro-duodenal lesions, which occasionally have resulted in hospitalization and death, have been reported. Lyngbyatoxins have been suggested as (one of) the causative agents, originating from the cyanobacterium Moorena producens, growing epiphytically on the seagrass and seaweed consumed by green turtles. However, due to the limited evidence of their involvement, the actual etiology of chelonitoxism remains unresolved and other compounds may be responsible. The data outlined in this review offer valuable insights to both regulatory bodies and the general public regarding the potential risks linked to consuming sea turtles.

Toward Sensitive and Reliable Immunoassays of Marine Biotoxins: From Rational Design to Food Analysis

Marine biotoxins are metabolites produced by algae that can accumulate in shellfish or fish and enter organisms through the food chain, posing a serious threat to biological health. Therefore, accurate and rapid detection is an urgent requirement for food safety. Although various detection methods, including the mouse bioassay, liquid chromatography-mass spectrometry, and cell detection methods, and protein phosphatase inhibition assays have been developed in the past decades, the current detection methods cannot fully meet these demands. Among these methods, the outstanding immunoassay virtues of high sensitivity, reliability, and low cost are highly advantageous for marine biotoxin detection in complex samples. In this work, we review the recent 5-year progress in marine biotoxin immunodetection technologies such as optical immunoassays, electrochemical immunoassays, and piezoelectric immunoassays. With the assistance of immunoassays, the detection of food-related marine biotoxins can be implemented for ensuring public health and preventing food poisoning. In addition, the immunodetection technique platforms including lateral flow chips and microfluidic chips are also discussed. We carefully investigate the advantages and disadvantages for each immunoassay, which are compared to demonstrate the guidance for selecting appropriate immunoassays and platforms for the detection of marine biotoxins. It is expected that this review will provide insights for the further development of immunoassays and promote the rapid progress and successful translation of advanced immunoassays with food safety detection.

Peripheral nervous system and neuromuscular disorders in the emergency department: A review

INTRODUCTION

Acute presentations and emergencies in neuromuscular disorders (NMDs) often challenge clinical acumen. The objective of this review is to refine the reader's approach to history taking, clinical localization and early diagnosis, as well as emergency management of neuromuscular emergencies.

METHODS

An extensive literature search was performed to identify relevant studies. We prioritized meta-analysis, systematic reviews, and position statements where possible to inform any recommendations.

SUMMARY

The spectrum of clinical presentations and etiologies ranges from neurotoxic envenomation or infection to autoimmune disease such as Guillain-Barré Syndrome (GBS) and myasthenia gravis (MG). Delayed diagnosis is not uncommon when presentations occur "de novo," respiratory failure is dominant or isolated, or in the case of atypical scenarios such as GBS variants, severe autonomic dysfunction, or rhabdomyolysis. Diseases of the central nervous system, systemic and musculoskeletal disorders can mimic presentations in neuromuscular disorders.

CONCLUSIONS

Fortunately, early diagnosis and management can improve prognosis. This article provides a comprehensive review of acute presentations in neuromuscular disorders relevant for the emergency physician.

Toxic neuropathies

PURPOSE OF REVIEW

Immunotherapy has had a significant impact on the treatment of an increasing number of cancers as well as in inflammatory, rheumatological and gastroenterological conditions.Recreational nitrous oxide use is now a global epidemic. Linezolid is now recommended for the treatment of drug-resistant tuberculosis (TB); neuropathy is a significant cause of morbidity.Global warming will result in increasing toxin exposure, such as ciguatera, in previously unaffected areas.

RECENT FINDINGS

With increasing experience, the pathophysiology underlying the neuropathic complications of these drugs has become clear with guidelines now available, for the complications of immune check-point inhibitors and nitrous oxide toxicity. The optimum dose and duration of treatment for resistant TB with regimens, including linezolid, has been ascertained.

SUMMARY

Although neuropathic complications with immunotherapy are relatively rare, it is essential that they are recognized and treated early. Nitrous oxide toxicity should be in the differential diagnosis for all patients, particularly those of younger age, presenting with a neuropathy or myleo-neuropathy. Ciguatera toxicity is under recognized and its geographical spread will increase due to global warming. Further research is necessary on the mechanisms and treatment of both acute and chronic effects, which at present, are only symptomatic.

Novel CRISPR/Cas technology in the realm of algal bloom biomonitoring: Recent trends and future perspectives

In conjunction with global climate change, progressive ocean warming, and acclivity in pollution and anthropogenic eutrophication, the incidence of harmful algal blooms (HABs) and cyanobacterial harmful algal blooms (CHABs) continue to expand in distribution, frequency, and magnitude. Algal bloom-related toxins have been implicated in human health disorders and ecological dysfunction and are detrimental to the national and global economy. Biomonitoring programs based on traditional monitoring protocols were characterised by some limitations that can be efficiently overdone using the CRISPR/Cas technology. In the present review, the potential and challenges of exploiting the Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR)-Cas technology for early detection of HABs and CHABs-associated toxigenic species were analysed. Based on more than 30 scientific papers, the main results indicate the great potential of CRISPR/Cas technology for this issue, even if the high sensitivity detected for the Cas12 and Cas13 platforms represents a possible interference risk.

Snake Antivenoms-Toward Better Understanding of the Administration Route

Envenomations induced by animal bites and stings constitute a significant public health burden. Even though a standardized protocol does not exist, parenterally administered polyclonal antivenoms remain the mainstay in snakebite therapy. There is a prevailing opinion that their application by the i.m. route has poor efficacy and that i.v. administration should preferentially be chosen in order to achieve better accomplishment of the antivenom therapeutic activity. Recently, it has been demonstrated that neutralization not only in the systemic circulation but also in the lymphatic system might be of great importance for the clinical outcome since it represents another relevant body compartment through which the absorption of the venom components occurs. In this review, the present-day and summarized knowledge of the laboratory and clinical findings on the i.v. and i.m. routes of antivenom administration is provided, with a special emphasis on the contribution of the lymphatic system to the process of venom elimination. Until now, antivenom-mediated neutralization has not yet been discussed in the context of the synergistic action of both blood and lymph. A current viewpoint might help to improve the comprehension of the venom/antivenom pharmacokinetics and the optimal approach for drug application. There is a great need for additional dependable, practical, well-designed studies, as well as more practice-related experience reports. As a result, opportunities for resolving long-standing disputes over choosing one therapeutic principle over another might be created, improving the safety and effectiveness of snakebite management.

Accidental discovery of a Tetraodontidae (Sphoeroides marmoratus) within a cuttlefish (Sepia officinalis) bought in a fish shop in Italy: risk assessment associated with the presence of Tetrodotoxin

The discovery of a pufferfish specimen (Tetraodontidae) inside a frozen cuttlefish, purchased by a fishmonger, and caught in the Eastern Central Atlantic (FAO 34) is reported. The consumer, who reported this case to FishLab (Department of Veterinary Sciences, University of Pisa) for investigation, was a student of Veterinary Medicine at the University of Pisa. He recognized the Tetraodontidae because he attended practical lessons on fish morphological identification during the course of food inspection and was aware of the risks to human health linked to the Tetrodotoxin (TTX). In this study, the pufferfish was identified morphologically, using the FAO morphological keys, and molecularly, analyzing two markers, the cytochrome oxidase I (COI) and the cytochrome b genes, by DNA barcoding. The pufferfish was identified morphologically as Sphoeroides spp., and molecularly as Sphoeroides marmoratus using the COI gene (99-100% identity values). Literature reports that S. marmoratus from the Eastern Atlantic contains high concentrations of TTX in the gonads and the digestive tract. However, the possible passage of TTX from fish to other organisms linked to contact or ingestion has never been reported. This represents the first case of a potentially toxic pufferfish entering the market inside another organism. The fact that a student observed this occurrence highlights the key role of citizen science in the management of emerging risks.

Chronic Ciguatera Poisoning: A Case Report

Ciguatera is a common marine, toxin-borne illness caused by the consumption of fish that contain toxins that activate voltage-sensitive sodium channels. The clinical manifestations of ciguatera are typically self-limited, but chronic symptoms may occur in a minority of patients. This report describes a case of ciguatera poisoning with chronic symptoms, including pruritus and paresthesias. A 40-y-old man was diagnosed with ciguatera poisoning after consuming amberjack while vacationing in the US Virgin Islands. His initial symptoms, including diarrhea, cold allodynia, and extremity paresthesias, evolved into chronic, fluctuating paresthesias and pruritus that became worse after the consumption of alcohol, fish, nuts, and chocolate. After a comprehensive neurologic evaluation failed to reveal another cause for his symptoms, he was diagnosed with chronic ciguatera poisoning. His neuropathic symptoms were treated with duloxetine and pregabalin, and he was counseled to avoid foods that triggered his symptoms. Chronic ciguatera is a clinical diagnosis. Signs and symptoms of chronic ciguatera can include fatigue, myalgias, headache, and pruritus. The pathophysiology of chronic ciguatera is incompletely understood but may involve genetic factors or immune dysregulation. Treatment involves supportive care and avoidance of foods and environmental conditions that may exacerbate symptoms.

Tetrodotoxin and Its Analogues in Food: Recent Updates on Sample Preparation and Analytical Methods Since 2012

Tetrodotoxin (TTX), found in various organisms including pufferfish, is an extremely potent marine toxin responsible for numerous food poisoning accidents. Due to its serious toxicity and public health threat, detecting TTX and its analogues in diverse food matrices with a simple, fast, efficient method has become a worldwide concern. This review summarizes the advances in sample preparation and analytical methods for the determination of TTX and its analogues, focusing on the latest development over the past five years. Current state-of-the-art technologies, such as solid-phase microextraction, online technology, novel injection technology, two-dimensional liquid chromatography, high-resolution mass spectrometry, newly developed lateral flow immunochromatographic strips, immunosensors, dual-mode aptasensors, and nanomaterials-based approaches, are thoroughly discussed. The advantages and limitations of different techniques, critical comments, and future perspectives are also proposed. This review is expected to provide rewarding insights to the future development and broad application of pretreatment and detection methods for TTX and its analogues.

Yeast Cell as a Bio-Model for Measuring the Toxicity of Fish-Killing Flagellates

Harmful algal blooms are a significant environmental problem. Cells that bloom are often associated with intercellular or dissolved toxins that are a grave concern to humans. However, cells may also excrete compounds that are beneficial to their competition, allowing the cells to establish or maintain cells in bloom conditions. Here, we develop a yeast cell assay to assess whether the bloom-forming species can change the toxicity of the water environment. The current methods of assessing toxicity involve whole organisms. Here, yeast cells are used as a bioassay model to evaluate eukaryotic cell toxicity. Yeast is a commonly used, easy to maintain bioassay species that is free from ethical concerns, yet is sensitive to a wide array of metabolic and membrane-modulating agents. Compared to methods in which the whole organism is used, this method offers rapid and convenient cytotoxicity measurements using a lower volume of samples. The flow cytometer was employed in this toxicology assessment to measure the number of dead cells using alive/dead stain analysis. The results show that yeast cells were metabolically damaged after 1 h of exposure to our model toxin-producing euryhaline flagellates (Heterosigma akashiwo and Prymnesium parvum) cells or extracts. This amount was increased by extending the incubation time.

Awareness on tetrodotoxin of illegal activity: forensic issue from a rare homicide case report and literature review

The authors describe an extremely rare case of homicide by injecting tetrodotoxin (TTX) as lethal neurotoxin found in puffer fish. After a thorough investigation, the male victim was found to have a broken stalk from syringe needle in the subcutaneous tissue of left buttock and severe asphyxia confirmed by the main pathological findings at autopsy. During tortuous toxicological analysis，TTX was revealed by ultra high performance liquid chromatography tandem mass spectrometry (UPLC-MS/MS) as well as acute intoxication confirmed from forensic examination. The literature of qualitative and quantitative determination of TTX from human fluids was also reviewed to expect widely acceptable detection strategies. This case highlighted the importance of TTX toxicant with chemical formula name purchased through e-commerce，so as to improve particular emphasis and supervision on harmful substances possibly using hidden information or illegal means. Histopathological and toxicological results demonstrated here provided a reference and other useful information to the challenges of forensic casework. In general, the case report illustrates medico-legal issues of more attention to the possibility of TTX poisoning in rapid death and the need of routine postmortem tox screening in future practice.

The “wing-heeled” traveler

Intoxication syndromes may be travel acquired, and are related to intentional or accidental inhalational or percutaneous exposures or ingestions. Due to their myriad clinical presentations, initial differential diagnosis of such intoxications in returned travelers is broad, and typically requires detailed history and laboratory investigations to disentangle. We herein use a case-based clinical problem solving approach to illumination of a mercury intoxication syndrome, which presented in a 48-year-old VFR traveler to Guyana. Common clinical presentations, differential diagnoses, laboratory investigations, and therapeutic interventions are discussed.

PAR2, Keratinocytes, and Cathepsin S Mediate the Sensory Effects of Ciguatoxins Responsible for Ciguatera Poisoning

Ciguatera fish poisoning is caused by the consumption of fish contaminated with ciguatoxins (CTXs). The most distressing symptoms are cutaneous sensory disturbances, including cold dysesthesia and itch. CTXs are neurotoxins known to activate voltage-gated sodium channels, but no specific treatment exists. Peptidergic neurons have been critically involved in ciguatera fish poisoning sensory disturbances. Protease-activated receptor-2 (PAR2) is an itch- and pain-related G protein‒coupled receptor whose activation leads to a calcium-dependent neuropeptide release. In this study, we studied the role of voltage-gated sodium channels, PAR2, and the PAR2 agonist cathepsin S in the cytosolic calcium increase and subsequent release of the neuropeptide substance P elicited by Pacific CTX-2 (P-CTX-2) in rat sensory neurons and human epidermal keratinocytes. In sensory neurons, the P-CTX-2‒evoked calcium response was driven by voltage-gated sodium channels and PAR2-dependent mechanisms. In keratinocytes, P-CTX-2 also induced voltage-gated sodium channels and PAR2-dependent marked calcium response. In the cocultured cells, P-CTX-2 significantly increased cathepsin S activity, and cathepsin S and PAR2 antagonists almost abolished P-CTX-2‒elicited substance P release. Keratinocytes synergistically favored the induced substance P release. Our results demonstrate that the sensory effects of CTXs involve the cathepsin S-PAR2 pathway and are potentiated by their direct action on nonexcitable keratinocytes through the same pathway.

The geographic mosaic in parallel: Matching patterns of newt tetrodotoxin levels and snake resistance in multiple predator-prey pairs

The Geographic Mosaic Theory of Coevolution predicts that coevolutionary arms races will vary over time and space because of the diverse ecological settings and population histories of interacting species across the landscape. Thus, understanding coevolution may require investigating broad sets of populations sampled across the range of the interaction. In addition, comparing coevolutionary dynamics between similar systems may reveal the importance of specific factors that structure coevolution. Here, we examine geographic patterns of prey traits and predator traits in the relatively unstudied interaction between the Sierra garter snake (Thamnophis couchii) and sympatric prey, the rough-skinned newt (Taricha granulosa), Sierra newt (Ta. sierrae) and California newt (Ta. torosa). This system parallels, in space and phenotypes, a classic example of coevolution between predatory common garter snakes (Th. sirtalis) and their toxic newt prey exhibiting hotspots of newt tetrodotoxin (TTX) levels and matching snake TTX resistance. We quantified prey and predator traits from hundreds of individuals across their distributions, and functional trait matching at sympatric sites. We show strong regional patterns of trait covariation across the shared ranges of Th. couchii and newt prey. Traits differ significantly among localities, with lower newt TTX levels and snake TTX resistance at the northern latitudes, and higher TTX levels and snake resistance at southern latitudes. Newts and snakes in northern populations show the highest degree of functional trait matching despite possessing the least extreme traits. Conversely, newts and snakes in southern populations show the greatest mismatch despite possessing exaggerated traits, with some snakes so resistant to TTX they would be unaffected by any sympatric newt. Nevertheless, individual variation was substantial, and appears to offer the opportunity for continued reciprocal selection in most populations. Overall, the three species of newts appear to be engaged in a TTX-mediated arms race with Th. couchii. These patterns are congruent with those seen between newts and Th. sirtalis, including the same latitudinal gradient in trait covariation, and the potential 'escape' from the arms race by snake predators. Such concordance in broad scale patterns across two distinct systems suggests common phenomena might structure geographic mosaics in similar ways.

Possible food safety hazards of ready-to-eat raw fish containing product (sushi, sashimi)

It is undeniable that with the popularity of sushi and sashimi over the last decade the consumption of raw fish has extremely increased. Raw fish is very appreciated worldwide and has become a major component of human diet because of its fine taste and nutritional properties. Possible hazards concerning fish safety and quality are classified as biological and chemical hazards. They are contaminants that often accumulate in edible tissue of fish and transmit to humans via the food chain affecting the consumer's health. Although their concentration in fish and fishery products are found at non-alarming level of a daily basis period, they induce hazardous outcome on human health due to long and continuous consumption of raw fish. Regular sushi and sashimi eaters have to be aware of the contaminants found in the other components of their dish that often add up to acceptable residue limits found in fish. Hence, there is the urge for effective analytical methods to be developed as well as stricter regulations to be put in force between countries to monitor the safety and quality of fish for the interest of public health.

A Curious Case of Ciguatera Fish Poisoning in the Midwest and a Review for Clinicians

BACKGROUND

Ciguatera poisoning is one of the most prevalent types of fish poisoning, but it is often underreported, leading many health practitioners to be unfamiliar in correctly identifying and treating this toxicity.

CASE REPORT

We present a case of ciguatera toxicity encountered in an emergency department in a Midwest community hospital setting. A 56-year-old woman presented to the ED with symptoms of perioral numbness, generalized pruritis, and hot/cold temperature reversal. Through careful history taking it was determined that the patient had recently returned from vacationing in the Caribbean and had been consuming meals containing various types of fish. A clinical diagnosis of ciguatera toxicity was made, and the patient was treated supportively. WHY SHOULD AN EMERGENCY PHYSICIAN BE AWARE OF THIS?: This topic is important in the realm of emergency medicine because it presents a known toxicologic pathogen in an unsuspecting geographic location. This case highlights the importance of maintaining broad differentials and considering a patient's travel and exposure history to make the clinical diagnosis of ciguatoxin as well as the importance of preventative management to avoid recurrence of symptoms. We review the etiology of this fascinating toxin as well as the clinical implications in the diagnosis and management of this toxicity.

Marine Toxins Detection by Biosensors Based on Aptamers

Marine toxins cause great harm to human health through seafood, therefore, it is urgent to exploit new marine toxins detection methods with the merits of high sensitivity and specificity, low detection limit, convenience, and high efficiency. Aptasensors have emerged to replace classical detection methods for marine toxins detection. The rapid development of molecular biological approaches, sequencing technology, material science, electronics and chemical science boost the preparation and application of aptasensors. Taken together, the aptamer-based biosensors would be the best candidate for detection of the marine toxins with the merits of high sensitivity and specificity, convenience, time-saving, relatively low cost, extremely low detection limit, and high throughput, which have reduced the detection limit of marine toxins from nM to fM. This article reviews the detection of marine toxins by aptamer-based biosensors, as well as the selection approach for the systematic evolution of ligands by exponential enrichment (SELEX), the aptamer sequences. Moreover, the newest aptasensors and the future prospective are also discussed, which would provide thereotical basis for the future development of marine toxins detection by aptasensors.

Marine Tetrodotoxin as a Risk for Human Health

Tetrodotoxin (TTX) is a toxin mainly occurring naturally in contaminated puffer fish, which are a culinary delicacy in Japan. It is also detected in various marine organisms like globefish, starfish, sunfish, stars, frogs, crabs, snails, Australian blue-ringed octopuses, and bivalve molluscs. TTX is produced by marine bacteria that are consumed mainly by fish of the Tetraodontidae family and other aquatic animals. TTX poisoning through consuming marine snails has recently begun to occur over a wider geographical extent through Taiwan, China, and Europe. This neurotoxin causes food intoxication and poses an acute risk to public health. The aim of this review is to present the most recent information about TTX and its analogues with particular regard to toxicity, methods of analysis, and risk to humans of exposure.

Tetrodotoxin and saxitoxin in two native species of puffer fish, Sphoeroides marmoratus and Lagocephalus lagocephalus, from NE Atlantic Ocean (Madeira Island, Portugal)

The presence in EU waters of invasive tetrodotoxin (TTX) -harbouring puffer fishes has been receiving increasingly attention due to potential new threats posed by this potent neurotoxin. The present study investigates the occurrence of tetrodotoxin, saxitoxin (STX), and their analogues in two native puffer fish species from the NE Atlantic. High TTX content was detected by LC-MS/MS in several tissues of the Guinean puffer Sphoeroides marmoratus from Madeira Island (Portugal), reaching concentrations as high as 15 mg TTX kg^-1 in the digestive tract of a male specimen and 7.4 mg TTX kg^-1 in gonads of a female specimen. Several TTX analogues were also detected, including the 4-epi-TTX, 4,9-Anhydro-TTX, 5- 11- deoxyTTX and 6,11-dideoxyTTX. Although at low levels, STX was detected in liver of the Oceanic puffer Lagocephalus lagocephalus. Trace levels of decarbamoylsaxitoxin (dcSTX) were also observed in L. lagocephalus. This study reports the presence of TTX and STX in native fish from EU waters, highlighting the need for a proper understating of the origin, distribution and fate of these toxins in NE Atlantic.

Acute Toxicity Assessment: Macroscopic and Ultrastructural Effects in Mice Treated with Oral Tetrodotoxin

Tetrodotoxin (TTX) is an extremely toxic marine compound produced by different genera of bacteria that can reach humans through ingestion mainly of pufferfish but also of other contaminated fish species, marine gastropods or bivalves. TTX blocks voltage-gated sodium channels inhibiting neurotransmission, which in severe cases triggers cardiorespiratory failure. Although TTX has been responsible for many human intoxications limited toxicological data are available. The recent expansion of TTX from Asian to European waters and diversification of TTX-bearing organisms entail an emerging risk of food poisoning. This study is focused on the acute toxicity assessment of TTX administered to mice by oral gavage following macroscopic and microscopic studies. Necropsy revealed that TTX induced stomach swelling 2 h after administration, even though no ultrastructural alterations were further detected. However, transmission electron microscopy images showed an increase of lipid droplets in hepatocytes, swollen mitochondria in spleens, and alterations of rough endoplasmic reticulum in intestines as hallmarks of the cellular damage. These findings suggested that gastrointestinal effects should be considered when evaluating human TTX poisoning.

Ciguatera fish poisoning in Brazilian traveler to Caribbean

Ciguatera poisoning is the most common form of non-bacterial food-poisoning from fish worldwide. The incidence among Brazilians returning from high-risk regions is unclear because it is not a mandatory reportable disease. We describe a previously healthy 53-year-old Brazilian woman developed Ciguatera fish poisoning while traveling to Havana, Cuba. Physicians and health care professionals should advise travelers to avoid eating ciguatoxic fish species and potentially toxic fish species in the Caribbean islands. Despite the prognosis for most cases is good with a short duration of self-limited symptoms, early recognition of the identifying clinical features of ciguatera can result in improved patient care.

Spatial variability and depuration of tetrodotoxin in the bivalve Paphies australis from New Zealand

Tetrodotoxin (TTX) is a potent neurotoxin responsible for many human intoxications globally. Despite its potency and widespread occurrence in taxonomically diverse species, the primary source of TTX remains uncertain. Paphies australis, an endemic clam found in New Zealand, has been found to contain TTX in several locations. However, it is unknown if this represents endogenous production or accumulation from an external source. To address this question, the concentrations of TTX in whole P. australis and dissected organs (siphons, foot, digestive gland and the ‘rest’) from thirteen sites around New Zealand were determined using liquid chromatography-tandem quadrupole mass spectrometry analysis (LC-MS/MS). Depuration rate of TTX was also investigated by harvesting and measuring concentrations in P. australis maintained in captivity on a toxin-free diet every three to 15 days for 150 days. The LC-MS/MS analyses of the spatial samples showed that TTX was present in P. australis from all regions tested, with significantly (p < 0.001) higher concentrations (15–50 μg kg⁻¹) observed at lower latitudes of the North Island compared with trace levels (0.5–3 μg kg⁻¹) in the South Island of New Zealand. Tetrodotoxin was detected in all the dissected organs but the siphons contained the highest concentrations of TTX at all sites analysed. A linear model of the depuration data identified a significant (p < 0.001) decline in total TTX concentrations in P. australis over the study period. The siphons maintained the highest amount of TTX across the entire depuration study. The digestive glands contained low concentrations at the start of the experiment, but this depurated rapidly and only traces remained after 21 days. These results provide evidence to suggest that P. australis does not produce TTX endogenously but obtains the neurotoxin from an exogenous source (e.g., diet) with the source more prevalent in warmer northern waters. The association of higher TTX concentrations in shellfish with warmer environments raises concerns that this toxin's distribution and abundance could become an increasing human health issue with global warming.

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TTX-containing Paphies australis were maintained in captivity for 150 days and significantly depurated the toxin.

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Thirteen populations of Paphies australis from around New Zealand were collected and tested for TTX.

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All populations tested contained TTX but a significant latitudinal gradient was observed.

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This study provides further evidence of an exogenous source of TTX in marine bivalves.

First detection of tetrodotoxin and high levels of paralytic shellfish poisoning toxins in shellfish from Sicily (Italy) by three different analytical methods

Paralytic shellfish toxins (PST) and tetrodotoxin (TTX) are naturally-occurring toxins that may contaminate the food chain, inducing similar neurological symptoms in humans. They are co-extracted under the same conditions and thus their combined detection is desirable. Whilst PST are regulated and officially monitored in Europe, more data on TTX occurrence in bivalves and gastropods are needed before meaningful regulations can be established. In this study, we used three separate analytical methods - pre-column oxidation with liquid chromatography and fluorescence detection, ultrahigh performance hydrophilic interaction liquid chromatography (HILIC) tandem mass spectrometry (MS/MS) and HILIC high resolution (HR) MS/MS - to investigate the presence of PST and TTX in seawater and shellfish (mussels, clams) collected in spring summer 2015 to 2017 in the Mediterranean Sea. Samples were collected at 10 sites in the Syracuse Bay (Sicily, Italy) in concomitance with a mixed bloom of Alexandrium minutum and A. pacificum. A very high PST contamination in mussels emerged, unprecedentedly found in Italy, with maximum total concentration of 10851 μg saxitoxin equivalents per kg of shellfish tissue measured in 2016. In addition, for the first time TTX was detected in Italy in most of the analysed samples in the range 0.8-6.4 μg TTX eq/kg. The recurring blooms of PST-producing species over the 3-year period, the high PST levels and the first finding of TTX in mussels from the Syracuse bay, suggest that monitoring programmes of PST and TTX in seafood should be activated in this geographical area.

New Invasive Nemertean Species (Cephalothrix Simula) in England with High Levels of Tetrodotoxin and a Microbiome Linked to Toxin Metabolism

The marine nemertean Cephalothrix simula originates from the Pacific Ocean but in recent years has been discovered in northern Europe. The species has been associated with high levels of the marine neurotoxin Tetrodotoxin, traditionally associated with Pufferfish Poisoning. This study reports the first discovery of two organisms of C. simula in the UK, showing the geographical extent of this species is wider than originally described. Species identification was initially conducted morphologically, with confirmation by Cox 1 DNA sequencing. 16S gene sequencing enabled the taxonomic assignment of the microbiome, showing the prevalence of a large number of bacterial genera previously associated with TTX production including Alteromonas, Vibrio and Pseudomonas. LC-MS/MS analysis of the nemertean tissue revealed the presence of multiple analogues of TTX, dominated by the parent TTX, with a total toxin concentration quantified at 54 µg TTX per g of tissue. Pseudomonas luteola isolated from C. simula, together with Vibrio alginolyticus from the native nemertean Tubulanus annulatus, were cultured at low temperature and both found to contain TTX. Overall, this paper confirms the high toxicity of a newly discovered invasive nemertean species with links to toxin-producing marine bacteria and the potential risk to human safety. Further work is required to assess the geographical extent and toxicity range of C. simula along the UK coast in order to properly gauge the potential impacts on the environment and human safety.

Advances in DNA Barcoding of Toxic Marine Organisms

There are more than 200,000 marine species worldwide. These include many important economic species, such as large yellow croaker, ribbonfish, tuna, and salmon, but also many potentially toxic species, such as blue-green algae, diatoms, cnidarians, ctenophores, Nassarius spp., and pufferfish. However, some edible and toxic species may look similar, and the correct identification of marine species is thus a major issue. The failure of traditional classification methods in certain species has promoted the use of DNA barcoding, which uses short, standard DNA fragments to assist with species identification. In this review, we summarize recent advances in DNA barcoding of toxic marine species such as jellyfish and pufferfish, using genes including cytochrome oxidase I gene (COI), cytochrome b gene (cytb), 16S rDNA, internal transcribed spacer (ITS), and Ribulose-1,5-bisphosphate carboxylase oxygenase gene (rbcL). We also discuss the application of this technique for improving the identification of marine species. The use of DNA barcoding can benefit the studies of biological diversity, biogeography, food safety, and the detection of both invasive and new species. However, the technique has limitations, particularly for the analysis of complex objects and the selection of standard DNA barcodes. The development of high-throughput methods may offer solutions to some of these issues.

Preliminary Results on the Evaluation of the Occurrence of Tetrodotoxin Associated to Marine Vibrio spp. in Bivalves from the Galician Rias (Northwest of Spain)

Tetrodotoxins (TTX) are a potent group of natural neurotoxins putatively produced by symbiotic microorganisms and affecting the aquatic environment. These neurotoxins have been recently found in some species of bivalves and gastropods along the European Coasts (Greece, UK, and The Netherlands) linked to the presence of high concentrations of Vibrio, in particular Vibrio parahaemolyticus. This study is focused on the evaluation of the presence of Vibrio species and TTX in bivalves (mussels, oysters, cockles, clams, scallops, and razor clams) from Galician Rias (northwest of Spain). The detection and isolation of the major Vibrio spp. and other enterobacterial populations have been carried out with the aim of screening for the presence of the pathways genes, poliketide synthase (PKS) and non-ribosomal peptide synthetase (NRPS) possibly involved in the biosynthesis of these toxins. Samples containing Vibrio spp. were analyzed by biochemical (API20E-galery) and genetic tests (PCR-RT). These samples were then screened for TTX toxicity by a neuroblastoma cell-based assay (N2a) and the presence of TTX was further confirmed by LC-MS/MS. TTX was detected in two infaunal samples. This is the first confirmation of the presence of TTX in bivalve molluscs from the Galician Rias.

Nociceptors: thermal allodynia and thermal pain

The sensation of pain plays a vital protecting role, alerting organisms about potentially damaging stimuli. Tissue injury is detected by nerve endings of specialized peripheral sensory neurons called nociceptors that are equipped with different ion channels activated by thermal, mechanic, and chemical stimuli. Several transient receptor potential channels have been identified as molecular transducers of thermal stimuli in pain-sensing neurons. Skin injury or inflammation leads to increased sensitivity to thermal and mechanic stimuli, clinically defined as allodynia or hyperalgesia. This hypersensitivity is also characteristic of systemic inflammatory disorders and neuropathic pain conditions. Mechanisms of thermal hyperalgesia include peripheral sensitization of nociceptor afferents and maladaptive changes in pain-encoding neurons within the central nervous system. An important aspect of pain management involves attempts to minimize the development of nociceptor hypersensitivity. However, knowledge about the cellular and molecular mechanisms causing thermal hyperalgesia and allodynia in human subjects is still limited, and such knowledge would be an essential step for the development of more effective therapies.

A Case Series of Puffer Fish Poisoning

Puffer fish poisoning caused by tetrodotoxin, a potent neurotoxin, is uncommon in Hong Kong. We report a total of seven cases of puffer fish poisoning with different levels of severity. Two of them developed respiratory distress and subsequently required endotracheal intubation and respiratory support while the others presented with numbness and mild weakness. Most of them experienced perioral numbness as the first symptom. The mean time of symptoms onset was approximately 94 minutes. All of our patients survived the intoxication.

Evaluation of tetrodotoxins in puffer fish caught along the Mediterranean coast of Spain. Toxin profile of Lagocephalus sceleratus

Although consumption of Tetraodontidae species is prohibited in the EU, intoxications are still reported. The evaluation of tetrodotoxins (TTXs) by mass spectrometry (LC-MS/MS and LC-HRMS) and a screening immunoassay (mELISA) in tetraodontid fishes caught along the Western Mediterranean Sea revealed high concentrations of TTXs in Lagocephalus sceleratus while no TTXs were identified in L. lagocephalus and Sphoeroides pachygaster individuals. The high TTXs content found in the L. sceleratus analysed herein demonstrate the occurrence of highly toxic puffer fish in the Western Mediterranean Sea. Being L. sceleratus a recent invasive species in the Mediterranean, surveillance, risk assessment and risk management measures are necessary. The strategy used within this research work could be a valuable tool for future food safety monitoring.

Detection of Tetrodotoxin Shellfish Poisoning (TSP) Toxins and Causative Factors in Bivalve Molluscs from the UK

Tetrodotoxins (TTXs) are traditionally associated with the occurrence of tropical Pufferfish Poisoning. In recent years, however, TTXs have been identified in European bivalve mollusc shellfish, resulting in the need to assess prevalence and risk to shellfish consumers. Following the previous identification of TTXs in shellfish from southern England, this study was designed to assess the wider prevalence of TTXs in shellfish from around the coast of the UK. Samples were collected between 2014 and 2016 and subjected to analysis using HILIC-MS/MS. Results showed the continued presence of toxins in shellfish harvested along the coast of southern England, with the maximum concentration of total TTXs reaching 253 µg/kg. TTX accumulation was detected in Pacific oysters (Crassostreagigas), native oysters (Ostreaedulis) common mussels (Mytilusedulis) and hard clams (Mercenariamercenaria), but not found in cockles (Cerastodermaedule), razors (Ensis species) or scallops (Pectenmaximus). Whilst the highest concentrations were quantified in samples harvested during the warmer summer months, TTXs were still evident during the winter. An assessment of the potential causative factors did not reveal any links with the phytoplankton species Prorocentrumcordatum, instead highlighting a greater level of risk in areas of shallow, estuarine waters with temperatures above 15 °C.

Urinary Excretion of Tetrodotoxin Modeled in a Porcine Renal Proximal Tubule Epithelial Cell Line, LLC-PK₁

This study examined the urinary excretion of tetrodotoxin (TTX) modeled in a porcine renal proximal tubule epithelial cell line, LLC-PK₁. Time course profiles of TTX excretion and reabsorption across the cell monolayers at 37 °C showed that the amount of TTX transported increased linearly for 60 min. However, at 4 °C, the amount of TTX transported was approximately 20% of the value at 37 °C. These results indicate that TTX transport is both a transcellular and carrier-mediated process. Using a transport inhibition assay in which cell monolayers were incubated with 50 µM TTX and 5 mM of a transport inhibitor at 37 °C for 30 min, urinary excretion was significantly reduced by probenecid, tetraethylammonium (TEA), l-carnitine, and cimetidine, slightly reduced by p-aminohippuric acid (PAH), and unaffected by 1-methyl-4-phenylpyridinium (MPP+), oxaliplatin, and cefalexin. Renal reabsorption was significantly reduced by PAH, but was unaffected by probenecid, TEA and l-carnitine. These findings indicate that TTX is primarily excreted by organic cation transporters (OCTs) and organic cation/carnitine transporters (OCTNs), partially transported by organic anion transporters (OATs) and multidrug resistance-associated proteins (MRPs), and negligibly transported by multidrug and toxic compound extrusion transporters (MATEs).

Biooxidation of Ciguatoxins Leads to Species-Specific Toxin Profiles

Ciguatoxins (CTXs) contaminate fish worldwide and cause the foodborne illness ciguatera. In the Pacific, these toxins are produced by the dinoflagellate Gambierdiscus toxicus, which accumulates in fish through the food chain and undergoes oxidative modification, giving rise to numerous analogs. In this study, we examined the oxidation of CTXs in vitro with liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis using reference toxins, and found that CTX4A, CTX4B, and CTX3C, which are produced by the alga, are oxidized to the analogs found in fish, namely CTX1B, 52-epi-54-deoxyCTX1B, 54-deoxyCTX1B, 2-hydroxyCTX3C, and 2,3-dihydroxyCTX3C. This oxidation was catalyzed by human CYP3A4, fish liver S9 fractions, and microsomal fractions prepared from representative ciguateric fishes (Lutjanus bohar, L. monostigumus, and Oplegnathus punctatus). In addition, fish liver S9 fractions prepared from non-ciguateric fishes (L. gibbus and L. fulviflamma) in Okinawa also converted CTX4A and CTX4B to CTX1B, 54-deoxyCTX1B, and 52-epi-54-deoxyCTX1B in vitro. This is the first study to demonstrate the enzymatic oxidation of these toxins, and provides insight into the mechanism underlying the development of species-specific toxin profiles and the fate of these toxins in humans and fish.

Risks for public health related to the presence of tetrodotoxin (TTX) and TTX analogues in marine bivalves and gastropods

Tetrodotoxin (TTX) and its analogues are produced by marine bacteria and have been detected in marine bivalves and gastropods from European waters. The European Commission asked EFSA for a scientific opinion on the risks to public health related to the presence of TTX and TTX analogues in marine bivalves and gastropods. The Panel on Contaminants in the Food Chain reviewed the available literature but did not find support for the minimum lethal dose for humans of 2 mg, mentioned in various reviews. Some human case reports describe serious effects at a dose of 0.2 mg, corresponding to 4 μg/kg body weight (bw). However, the uncertainties on the actual exposure in the studies preclude their use for derivation of an acute reference dose (ARfD). Instead, a group ARfD of 0.25 μg/kg bw, applying to TTX and its analogues, was derived based on a TTX dose of 25 μg/kg bw at which no apathy was observed in an acute oral study with mice, applying a standard uncertainty factor of 100. Estimated relative potencies for analogues are lower than that of TTX but are associated with a high degree of uncertainty. Based on the occurrence data submitted to EFSA and reported consumption days only, average and P95 exposures of 0.00-0.09 and 0.00-0.03 μg/kg bw, respectively, were calculated. Using a large portion size of 400 g bivalves and P95 occurrence levels of TTX, with exception of oysters, the exposure was below the group ARfD in all consumer groups. A concentration below 44 μg TTX equivalents/kg shellfish meat, based on a large portion size of 400 g, was considered not to result in adverse effects in humans. Liquid chromatography with tandem mass spectroscopy (LC-MS/MS) methods are the most suitable for identification and quantification of TTX and its analogues, with LOQs between 1 and 25 μg/kg.

Surveillance of marine fish for ciguatera toxin at fish markets in Bangkok, Thailand

Background: Ciguatera intoxication is a form of food poisoning. It is caused by the consumption of certain warm-water fish that have accumulated ciguatera toxin (CTX) through the marine food chain. Ciguatera fish poisoning (CFP) is a global disease, which although common, has been largely ignored in Thailand. This may be attributed to lack of confirmatory tests and seemingly nonspecific clinical presentations.

Objective: We studied CTX contamination in marine fish sold at Bangkok markets.

Methods: A surveillance of CTX in fish using the Cigua-Check assay has been conducted in Bangkok, the center of seafood marketing in Thailand. Here, there are several types of fish. Some come from domestic fishing and others are imported from Indonesia, Myanmar, or India.

Results: A random survey at three fish markets in Bangkok revealed two samples possibly contaminated with ciguatera toxin from a total 227 fish samples (of 21 fish species). This is the first report of finding CTX contamination in fish meat sold in Bangkok.

Conclusion: It is possible that these CTX-positive fish were caught from other countries. Even though the positivity (0.88%) is lower when compared with studies of other endemic areas (5.0% in Hawaii and Pacific Islands), this finding should raise awareness of the possibility of facing rare CFP intoxication from fish obtained at local Thai markets.

Harmful Algal Blooms and Public Health

The five most commonly recognized Harmful Algal Bloom related illnesses include Ciguatera poisoning, Paralytic Shellfish poisoning, Neurotoxin Shellfish poisoning, Diarrheic Shellfish Poisoning and Amnesic Shellfish poisoning. Although they are each the product of different toxins, toxin assemblages or HAB precursors these clinical syndromes have much in common. Exposure occurs through the consumption of fish or shellfish; routine clinical tests are not available for diagnosis; there is no known antidote for exposure; and the risk of these illnesses can negatively impact local fishing and tourism industries. Thus, illness prevention is of paramount importance to minimize human and public health risks. To accomplish this, close communication and collaboration is needed among HAB scientists, public health researchers and local, state and tribal health departments at academic, community outreach, and policy levels.