Approach
Numerous marine toxins are potentially harmful to humans. Toxins that block voltage-gated sodium channels, including saxitoxin, tetrodotoxin, and conotoxin, can produce rapidly progressive neurological deterioration with loss of airway-protective reflexes and apnoea.[26]
Identification of exposure to marine toxins requires knowledge of potential routes of exposure and recognition of progressive neurological deterioration. Most cases of marine toxin exposure present locally. Knowledge of local marine organisms that produce toxins, the syndromes common for those toxins, and the management of those syndromes is important for healthcare professionals in coastal areas. Travel, the worldwide availability of seafood, and the popularity of marine organism collection make it important for all healthcare professionals to have an awareness of the syndromes produced by marine toxin exposure. Many cases of marine toxin exposure have occurred far from the sea.[12] Global warming is also expanding the risk of marine toxin exposure to historically unaffected regions.[2] Toxic algal blooms and key marine organisms require warm waters. As the temperature of the sea rises, the risk of marine toxin exposure rises with it.[22]
Confirmation of marine toxin exposure is often made through the identification of toxin in the flesh of shellfish or fish by the appropriate authorities.
History
Marine toxin exposures occur as the result of consumption of contaminated seafood or injection of toxins by marine animals as a defense mechanism. It is important to determine seafood exposure and history of shell collection, swimming or wading in the sea, diving, aquarium maintenance, and travel. In the case of contaminated seafood consumption, what seafood was consumed, when it was consumed, where it came from, and how it was prepared are important to identify. Restaurants commonly record the source and lot number of shellfish purchased from commercial sources.
Specific exposures to identify include the following:
Shellfish consumption potentially contaminated by saxitoxin
Puffer fish ingestion
Xanthid crab consumption
Injection of tetrodotoxin from a blue-ringed octopus
Injection of conotoxin from cone snail.
Symptoms:
Oral numbness, anxiety, weakness, difficulty swallowing, difficulty speaking, incoordination, difficulty walking, paralysis, and shortness of breath are commonly reported. Symptoms occur much sooner after exposure and progress more rapidly when the exposure is large.
Nausea, vomiting, and diarrhoea are common.
The development of dizziness, postural near-syncope, syncope, and other symptoms of hypovolaemia can occur.
Extreme pain from cone snail envenomation.
In a patient with neurological complaints and a history of seafood consumption, identification of the timeline is important. Most marine toxins provide rapid onset (within 30 minutes of exposure) and rapid progression of neurological signs and symptoms, with complete recovery within 24 to 48 hours if properly managed.
Physical examination
Vital signs are commonly normal and can be preserved until paralysis produces hypercapnia, hypoxia, and cardiovascular collapse.
Physical examination should focus on identification of weakness and the adequacy of airway protection and ventilation. Early in a marine toxin exposure, the physical examination may be normal. As the syndrome progresses, muscle weakness develops rapidly and can progress quickly. Examination and re-examination should be performed for:
Changes in voice, drooling, and maintenance of the gag reflex
Proximal muscle weakness, weakness of the chest wall, and maintenance of ventilation.
Examination for signs of dehydration should occur in people presenting with vomiting or diarrhoea. Shellfish poisoning from saxitoxin often produces hypertension. Although hypertension is not associated with tetrodotoxin or conotoxin exposure, there have been occasional cases in the literature of patients presenting with hypertension following tetrodotoxin exposure.[27]
Initial investigations
Laboratory studies and imaging studies are usually unrevealing in marine toxin exposures. There are no commonly available tests for the toxins in human blood or urine.
Diagnosis is clinical, based on signs and symptoms, and a history of seafood or shellfish consumption, or a history of shell collection, swimming or wading in the sea, diving, or aquarium maintenance. Confirmation of marine toxin exposure is often made through the identification of toxin in the flesh of shellfish or fish by the appropriate authorities using high-performance liquid chromatography.[28] These studies often take days or weeks to accomplish, making clinical recognition and supportive management key to the initial management of cases of marine toxin exposures.
Other investigations
Pulse oximetry, capnography, serial pulmonary function tests (such as FVC, negative inspiratory force, peak expiratory flow rate, and end-tidal CO₂), and arterial blood tests are useful to evaluate severity of poisoning and monitor for the need for airway control and ventilator support.
Other investigations to consider include:
A chest x-ray in patients with loss of airway control and concern for pulmonary aspiration
A brain CT scan in patients with unclear presentation and possible intracranial event
Serum electrolytes tests in patients with significant gastrointestinal complaints and possible dehydration; these tests may also be useful in evaluating for other causes of paraesthesias.
Emerging investigations
Serum or urine toxin analysis are emerging as potential tests for marine toxin exposure, but these tests are not widely available.
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