Tox in The Land: Amnesic Shellfish Poisoning

A raising issue due to global warming and algal bloom

 

Source: https://c0.wallpaperflare.com/preview/933/930/536/crawfish-seafood-crayfish-cajun.jpg

 

History

  • Domoic acid (DA/DOM), heat-stable toxin, produced by Pseudo-nitzsche, a single-celled, algae-like organism

  • 1958- In a search for new antiparasitic compounds, Japanese scientists discover DA in Chrondria armata, a red algae found in tropical and sub-tropical waters

  • 1961- In Capitola, CA, some nonaggressive, fish-eating seabirds exhibit unusual and aggressive behavior such as attacking humans and crashing through glass windows. Residents were quoted as saying the birds “cried like babies”. Alfred Hitchcock used this frightening event as inspiration for his classic 1963 horror film “The Birds”. Marine scientists now largely believe that the Sooty shearwaters in Capitola were suffering from DA poisoning.

  • 1987- First documented episode of DA poisoning in humans occurs in Canada. The unusual focus of the clinical symptomology on memory impairment leads to the clinical label of Amnesic Shellfish Poisoning (ASP).

  • 1991-1993- First documented episode of DA contamination in the United States occurred on Washington State beaches. During the same period, unusual behavior is noted in seabirds living near Monterey Bay in California.

  • 1998- First documentation of large-scale marine mammal killing from DA poisoning. More than 400 sea lion deaths were attributed to DA exposure. Symptoms included weaving and bobbing, seizures, bulging eyes, disorientation, and ataxia.

  • 2007-2008- Scientists from the Santa Barbara Museum of Natural History recorded high levels of DA in coastal waters and reported an unusual mortality event involving sea lions, dolphins, and birds.

  • Summer of 2015- a massive toxic algal bloom, stretching from central California to the Alaska Peninsula, resulted in a significant impact on coastal resources and marine life.

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Source: https://www.latimes.com/local/education/la-me-ln-sea-lions-dying-20170419-story.html

Mechanism

  • The main vectors of algal toxins to humans are filter-feeding bivalve mollusks and herbivorous finfish that ingest toxic algae, such as mussels, clams, scallops, and oysters. Humans are then intoxicated through shellfish consumption.

 

Source: https://www.researchgate.net/figure/The-toxin-cycle-diagram-illustrating-the-interrelationships-between-harmful-algae-and_fig1_43298267

 

Domoic Acid

  • Domoic acid is structurally related to glutamate and acts as a powerful excitatory neurotransmitter that can cause the death of neurons in the amygdala and hippocampus, which explains the short-term memory loss aspect of the clinical presentation.

  • Pharmacokinetic studies have indicated that DA is well distributed in body water and primarily cleared from plasma through the kidneys

Source: Saeed 2017

Source: https://pakconline.com/what-is-dissociative-amnesia/

Clinical Manifestations

  • Non-specific: nausea, vomit, diarrhea, abdominal cramps

  • Neurologic symptoms: headache, seizures, hemiparesis, ophthalmoplegia, anterograde amnesia, and abnormalities of arousal ranging from agitation to coma. Affected patients were unable to remember events that occurred after DA intoxication and had difficulty recalling new information.

  • Per the original report: “On neuropsychological testing several months later, 12 of the patients had severe anterograde-memory deficits, with relative preservation of other cognitive functions. Eleven patients had clinical and electromyographic evidence of pure motor or sensorimotor neuronopathy or axonopathy. Positron-emission tomography of four patients showed decreased glucose metabolism in the medial temporal lobes. Neuropathological studies in the four patients who died after mussel-induced intoxication demonstrated neuronal necrosis and loss, predominantly in the hippocampus and amygdala”

Episodic Memory & Anterograde Amnesia

  • Episodic memory refers to memory for specific experiences, usually associated with a time, place, and emotion.

  • For example, recalling a birthday party that you attended, who was there, where it occurred, and your own personal interactions there, reflects your episodic memory of that event.

  • In the hippocampus, episodic memories are formed and cataloged to be filed away in long-term storage across other parts of the cerebral cortex.

  • Patient H.M. was unable to recall any events from his daily life after his hippocampal resection.

 

Source: https://www.simplypsychology.org/limbic-system.html

Source: Pulido 2008

 

Management

  • Amnesic Shellfish Poison toxin isn't destroyed by cooking or freezing.

  • There is no antidote for Amnesic Shellfish Poisoning. Medical therapy consists of supportive care.

  • Although evidence is lacking, some experts support administration of activated charcoal to bind any non-absorbed food given the potential for poor outcomes, including permanent short-term memory loss, despite appropriate supportive care.

  • Most important: After the Canadian outbreak, limits on domoic acid concentration in shellfish were rapidly adopted at 20 micrograms per gram of shellfish flesh. These limits based upon the lowest concentrations in mussels found to cause symptoms (200 micrograms per gram of shellfish flesh) reduced by a factor of 10. Wide adoption of the limits on harvested mussels by developed nations has been associated with no further outbreaks on the scale of the Canadian experience.

  • However, the economic hardships can extend beyond fishing-related operations to include other sectors, particularly the hospitality industry, threatening the cultural identities of the affected communities.

Global Warming & Algal Bloom

  • Warming water temperature

    • Toxic blue-green algae prefer warmer water.

    • Warmer temperatures prevent water from mixing, allowing algae to grow thicker and faster.

  • Changes in salinity

    • Climate change might lead to more droughts, which make freshwater saltier. This can cause marine algae to invade freshwater ecosystems. 

  • Higher carbon dioxide levels

    • Algae need carbon dioxide to survive. Higher levels of carbon dioxide in the air and water can lead to rapid growth of algae

  • Changes in rainfall

    • Extreme storms followed by periods of drought can lead to more algal blooms

  • Sea level rise

    • Scientists predict that sea level could rise up to one meter by the year 2100. This would create more shallow and stable coastal water, conditions that are perfect for the growth of algae.

  • Coastal upwelling

    • Coastal upwelling is the process by which winds push surface water offshore and deep water moves towards the coast, bringing nutrients from the ocean floor to the surface. Climate change is expected to alter the timing and intensity of coastal upwelling.

POST BY: RONGYI SUN, MS4

FACULTY EDITING BY: DR. LAUREN PORTER

References

ToxLauren McCaffertytoxicology, tox, shellfish, poisoning