Shellfish Toxicity

Shellfish Toxicity

Shellfish toxicity refers to poisoning caused by eating shellfish including clams, oysters, mussels, or scallops. Molluscan shellfish often contain marine biotoxins which can cause food poisoning. Marine biotoxins are produced by microscopic algae in very small amounts which are normally harmless. However, in the presence of abundant sunlight, warm temperatures, and water that is rich in nutrients, these algae rapidly reproduce. Molluscan shellfish feed on these algae, both good and bad, from the surrounding water. The toxin-producing algae continue to accumulate in the tissue of the shellfish. These biotoxins do not harm the shellfish but can cause serious illness in humans and other mammals.
It is important to note that cooking shellfish will kill the algae that produce the biotoxins. However, the toxin still remains in the cells of the shellfish. Toxicity levels also vary in different species of shellfish. Mussels have a tendency of accumulating toxins the fastest. Varnish clams are known to absorb toxins at the highest levels. Varnish clams and butter clams can store toxins for a longer duration of time in comparison to other species.

Types of Shellfish Toxicity

There are four main types of shellfish poisoning which are listed below:

• Paralytic shellfish poisoning ( PSP): This type of shellfish poisoning is caused by consuming shellfish which have been contaminated by chemicals that are derived from saxitoxins and gonyautoxins. Saxitoxin attacks the nervous system and can cause gastrointestinal illness. The symptoms of paralytic shellfish poisoning include burning, tingling, lack of coordination, drowsiness, slurred speech, choking feeling in throat, and dryness of mouth. The symptoms typically appear within 30 minutes of consumption. Severe poisoning can cause fatal damage in the form of muscle paralysis and respiratory failure, and eventual death.

• Amnesic shellfish poisoning (ASP): This type of shellfish poisoning is caused by the consumption of shellfish that has been contaminated by Domoic acid. The early symptoms of this type of shellfish poisoning include abdominal pain, vomiting, and diarrhea. These symptoms are followed by neurological symptoms such as mental confusion, headache, disorientation, dizziness, memory loss, seizures, and visual disturbances. Severe poisoning can also cause paralysis and death.

• Diarrhetic shellfish poisoning (DSP): This type of shellfish poisoning is caused by consumption of shellfish that has been contaminated by Okadaic acid. Okadaic acid is a toxin that can cause persistent diarrhea. The symptoms of this type of shellfish poisoning appear within an hour of consumption and last for a day or two. Typical symptoms of diarrhetic shellfish poisoning include nausea, abdominal pain, vomiting, and diarrhea.

• Neurotoxic shellfish poisoning (NSP): This type of shellfish poisoning is caused by consumption of shellfish that has been contaminated by brevetoxins. The symptoms of neurotoxic shellfish poisoning are quite similar to those of paralytic shellfish poisoning. Typical symptoms of this type of shellfish poisoning include numbness in mouth, legs, and arms, poor coordination, dryness of mouth, drowsiness, slurring of speech, vomiting, nausea, and diarrhea. It normally takes two days to recover from the symptoms of neurotoxic shellfish poisoning.

Treatment for Shellfish Toxicity

The treatment for shellfish poisoning varies depending on the type of toxins consumed. Most of these forms of poisoning are associated with vomiting and diarrhea which can result in depletion of bodily fluids. Drinking enough fluids that contain electrolytes is recommended. In cases of severe poisoning hospital treatment is required, especially if the infected people have low immunity.
 
References:

• “Shellfish toxicity: human health implications of marine algal toxins” by K.J. James, et al. Published in July 2010, Volume 138, Issue 07 of Epidemiology and Infection, accessed on 20 May 2015. Retrieved from: https://dx.doi.org/10.1017/S0950268810000853