Tag Archives: Paralytic shellfish poisoning

Toxic Algae

 Blooms of toxic algae are nothing new. Toxic algae occur naturally in both fresh and salt water, and algal poisonings have happened many times over the centuries. What is different is the frequency and magnitude of toxic blooms in some areas of the world. Environmental conditions such as changes in salinity, increasing water temperature, and an influx of nutrients can trigger an algal bloom, and once the bloom begins, it can increase exponentially in a short period. As our oceans get warmer, it is likely we will see even more of these toxic blooms in upcoming years. This past summer, a massive bloom of the algae Pseudo-nitzschia that produces domoic acid, a powerful neurotoxin, shut down the Washington state commercial fishing season for Dungeness crab, causing millions of dollars in lost revenue, and this toxic bloom possibly caused the deaths of at least 44 whales in Alaska.

In my next two posts, I will dive into the topic of toxic algae in more detail. There are several species of toxic algae, and I will discuss four types of algal poisonings caused by toxic blooms: Paralytic shellfish poisoning, amnesic shellfish poisoning, poisoning caused by ciguatera toxin, and cyanotoxic poisoning.

     Paralytic shellfish poisoning (PSP) is caused by a microscopic single-celled dinoflagellate algae in the genus Alexandrium. Bivalve shellfish, such as mussels and clams, may feed on these dinoflagellates and concentrate PSP toxins that are not harmful to the bivalves but are poisonous to humans, other mammals, and some birds that feed on these bivalves. Crab can also concentrate the toxin in their viscera.

In my novel, Murder Over Kodiak, Dr. Jane Marcus is working to develop a small, inexpensive kit that would allow a person to dig a bucket of clams and easily test them to make sure they aren’t toxic before eating them. She explains the difficulty of her research to FBI Agent Nick Morgan by telling him that PSP toxins are called saxitoxins, which are produced by dinoflagellate algae. These dinoflagellates do not produce just one toxin, but 21 molecular forms of saxitoxin, and these 21 forms can undergo transformations that can change one toxin into another. The forms vary in toxicity. A person’s stomach acid can change the original saxitoxin into another form that is six times more toxic. Furthermore, some species of bivalves can hold higher levels of the toxin than other species can, and some species, such as butter clams, have the ability to bind the most highly toxic forms of saxitoxin. Steamer clams, on the other hand, transform saxitoxin into one of its less toxic forms.

In my novel, a lady eats toxic clams for dinner and suffers the textbook symptoms of severe PSP. Twenty minutes after eating the infected bivalves, her lips begin to feel numb, and her fingers and toes start to tingle. Soon, she is dizzy and sick to her stomach, her breath coming in short gasps. Forty-five minutes later, she can’t walk or talk and is barely breathing. She stops breathing in the Coast Guard helicopter on the way to the hospital.

Saxitoxins are neurotoxins that block the movement of sodium through nerve-cell membranes, which stops the flow of nerve impulses, causing numbness, paralysis, and disorientation. The toxicity of saxitoxins is approximately 1000 times greater than cyanide, and the symptoms begin to appear soon after consuming the toxic shellfish. There is no antidote for PSP, and there is nothing that can be done to toxic shellfish to render them safe for consumption. Saxitoxins do not dissolve in water, and they are heat and acid-stable. In other words, cooking the bivalves will not break down the toxins. Some shellfish store the toxin for weeks, and others, such as butter clams, can store the toxin for as long as two years. All cases of PSP require immediate medical attention, and some may require life support equipment to save a victim’s life. If the dosage of PSP is low and if proper medical treatment is administered, the symptoms usually diminish in nine hours.

The worst historical account of PSP poisoning occurred in Southeast Alaska in July 1799 when more than 100 Russians and Aleuts died from eating clams and mussels gathered from Peril Straits near Sitka. The most recent cases occurred last summer when two people died in Southeast Alaska, one from eating a cockle and the other from eating a Dungeness crab, and three people became ill in Kodiak from eating butter clams. Cockles tested in Southeast Alaska last summer had a level of PSP that was 2,044 parts per million. Anything over 80 parts per million is considered unsafe for human consumption. PSP also kills sea otters, and it probably is toxic to other mammals. It is known to affect shags, common terns, common murres, Pacific loons, sooty shearwaters, and possibly many other bird species.

As a side note, I am not the first person to use algal toxins as part of the plot of a story, and I am in good company. In 1961, hundreds of crazed birds, mostly sooty shearwaters, attacked the town of Capitola, California, crashing into street lamps and through glass windows and attacking people. These birds normally live offshore, but it is assumed that they dined on small fish that had eaten toxic Pseudo-nitzchia algae, and the birds became disoriented after succumbing to amnesic shellfish poisoning. Alfred Hitchcock based his screenplay The Birds on this incident. I’ll discuss amnesic shellfish poisoning in more detail next week.

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