Marine Toxins and Human Health

Natural toxins represent an increasing hazard to the seafood consuming public. Toxins are produced by marine algae and are accumulated through the food chain and are ultimately deposited in higher predator fish or filter-feeding bivalves. Toxins may also affect people through the air and drinking water.

Marine and freshwater toxin diseases in human populations are due to the contamination of seafood with a myriad of natural toxins created by minute marine and freshwater organisms such as dinoflagellates found throughout the marine and freshwater world, especially in coral reefs and their surroundings.

In general, the natural marine and freshwater toxins are tasteless, odorless, and heat and acid stable. Therefore, normal screening and food preparation procedures do not prevent intoxication if the fish or shellfish is contaminated.

The marine and freshwater toxin diseases are divided into two groups by their primary transvectors, i.e. those associated with the ingestion of shellfish, and those with fish consumption. In addition, there is a group of marine and freshwater diseases associated with water exposure. The shellfish-associated diseases and those associated with water exposure generally occur with algal blooms or "red tides" while fish-associated diseases are more localized to specific reef areas and/or types of fish.

Paralytic Shellfish Poisoning (PSP), Red Tide/Neurotoxic Shellfish Poisoning (NSP), Diarrheic Shellfish Poisoning (DSP), and Amnesic Shellfish Poisoning (ASP) are primarily associated with the ingestion of contaminated shellfish.

Ciguatera Poisoning and Tetrodotoxin Poisoning (Fugu or Pufferfish Poisoning) occur with the ingestion of contaminated fish.

Aerosolized Florida Red Tide/Brevetoxins, the Blue Green Algae (Cyanobacteria), and Pfiesteria and the Pfiesteria-like Organisms (PLOs) can affect humans through exposure to water droplets or even drinking water contaminated with the organisms and/or their toxins.

The primary toxic effect of the marine and freshwater toxins is to the neurologic system, however, affected individuals usually present a wide range of symptoms resulting in a confusing clinical picture. The acute onset of severe gastro-intestinal distress after eating the contaminated fish occurs within minutes to hours. In the case of PSP, Fugu, and Ciguatera, this gastro-intestinal picture can be accompanied by acute respiratory distress which may be fatal within hours (up to 50% of cases of Fugu and 10% of PSP).

In the case of Ciguatera and ASP, debilitating chronic neurologic symptoms lasting months to years have been reported. The majority of people with Ciguatera, especially in the Caribbean, suffer for weeks to months with debilitating neurologic symptoms, including profound weakness, temperature sensation changes, pain, and numbness in the extremities. ASP has left people with permanent and severe memory loss, even years after their initial illness.

In addition to increasing worldwide seafood consumption, anthropogenic causes may have furthered the spread of the dinoflagellates and their toxins. There is a body of evidence to indicate that man-induced transportation of the cysts or "seeds" of the toxic marine and freshwater organisms such as dinoflagellates, or of the dinoflagellates themselves located inside the 'spat' (young bivalve shellfish sold commercially to global markets for aquaculture) and ship ballast water (international regulations are now changing to require ship ballast water purging in the open ocean prior to docking).

It is hypothesized that human-generated environmental changes such as reef destruction and eutrophication, may be responsible for apparent increased reporting in human cases of marine and freshwater toxin disease as well as increased incidence of red tides reported worldwide. There is even evidence connecting the apparent global increase of algal blooms with Global Climate Changes, such as seen with the El Niño phenomenon.