The Toxin Found In Some Seafood That Could Cause Memory Loss

Algae is more than just green stuff that grows on the sides of your fish tank or the decorations within it. As a large group of marine organisms that live in freshwater and saltwater, algae has a key role in the ecosystem as part of the foundation of the marine food chain, primarily as a source of nutrients for small marine animals. When they contain toxins and grow out of control, though, they become harmful algal blooms that pose debilitating or even fatal risks to those who come into contact with them. One algae toxin, domoic acid, can cause memory loss.

Domoic acid was first discovered in algae on the West Coast of the United States in 1991, and of the millions of diatom species, scientists have only found 28 that produce this toxin. Two of these were uncovered in farmed shellfish on Luzon Island in the Philippines during a May 2023 algae bloom, a study of which was published in Diatom Research. This poison can build up in shellfish and isn't destroyed by freezing or cooking. When people consume high amounts of affected shellfish, they may develop amnesic shellfish poisoning, named after the short-term memory loss it causes. Also, the condition presents with abdominal cramps, diarrhea, nausea, and vomiting within the first day, and severe cases can involve confusion, dizziness, and respiratory secretions, among other symptoms.

While cases of ASP are rare, algae blooms are becoming more frequent because of human activities. This trend raises the risk of domoic acid making it to tables and causing the illness. Fortunately, fish and wildlife agencies regularly test seafood as a preventive measure.

The harmful effects of algae aren't restricted to just one type of toxin. Several other toxins can accumulate in seafood and cause various foodborne illnesses when consumed in unsafe amounts. Exposure to saxitoxin, for instance, can lead to paralytic shellfish poisoning. The symptoms of this condition arise within hours and include gastrointestinal discomfort, neurological issues like tingling in the limbs and mental changes, rapid heart action, high blood pressure, and eventually asphyxiation or respiratory paralysis.

Brevetoxin is another poison, and it's known to cause neurotoxic shellfish poisoning. This condition induces gastrointestinal and neurological symptoms such as dizziness, muscle weakness, nausea, tingling in the limbs and mouth, slurred speech, and respiratory discomfort. A fourth toxin is okadaic acid, which can lead to diarrhetic shellfish poisoning. Most people who develop this condition only experience gastrointestinal issues — abdominal pain, diarrhea, nausea, and vomiting — while some also develop chills, fevers, and headaches. Finally, ciguatoxin is a poison that can cause ciguatera, an illness that presents with a wide array of gastrointestinal and neurological symptoms, as well as cardiac symptoms like arrhythmias, high blood pressure, and slowed heart rate.