Unraveling acronyms: What are ASP, DSP and PSP?

Fresh mediterranean clamsWhether it’s ASP, DSP or PSP, it all comes down to shellfish and biotoxins.

Shellfish poisoning can occur when shellfish contaminated with any of a number of marine toxins are consumed. The individual toxins can lead to a range of conditions and symptoms.

It’s important to remember the algae that produce these toxins are usually present in the water; however, it’s when there is a large algal bloom that it can be problematic. Shellfish feed by filtering the food thorough their bodies. When there is a large toxin-producing algal bloom, more of the toxin is present, therefore, more is filtered through the shellfish. This allows the toxins to bioaccumulate (i.e., the toxins build up in their tissues). Although the toxins don’t cause the shellfish to be sick, consuming these shellfish can cause potentially severe human illness.

Unlike bacterial pathogens, cooking does not kill or neutralize these toxins because they aren’t alive. Similarly, these toxins cannot be detected by sight, taste or smell. There is no antitoxin for these biotoxins.

Health and environmental agencies monitor marine waters for these toxins and for the algal blooms that produce them in an effort to prevent illness. Comprehensive data on the prevalence of these illnesses is hard to come by as cases may often be misdiagnosed or not reported at all, according to the U.S. Food and Drug Administration’s Bad Bug Book.

Amnesic shellfish poisoning (ASP)

ASP occurs when a person consumes shellfish contaminated with domoic acid, which is produced by Psuedo-nitzschia spp. diatoms (diatoms are a type of microscopic algae). Razor clams most frequently are implicated in ASP cases as the algae that produces the toxin typically is found in coastal areas where the clams also are found, according to the Washington Department of Health. Mussels, crabs and oysters also can become contaminated with domoic acid.

In addition to nausea, vomiting, cramps and diarrhea, ASP can cause neurological symptoms including confusion, dizziness, headache, seizures, cardiac arrhythmia and short-term memory loss, which may be permanent. The initial symptoms typically occur within 24 hours with neurological symptoms usually presenting at about 48 hours. Particularly severe cases can lead to death.

Diarrhetic shellfish poisoning (DSP)

Like ASP, DSP is caused by a marine biotoxin produced by algae but in this case, illness is cause by okadaic acid produced by the Dinophysis, a dinoflagellate.

Symptoms include abdominal pain, nausea, vomiting and diarrhea. The Bad Bug Book describes DSP symptoms as usually “mild”.

Paralytic shellfish poisoning (PSP)

Of the illnesses caused by marine biotoxins, PSP may be the cause for the most concern – as the Bad Bug Book states, “The extreme potency of the PSP toxins has, in the past, resulted in an unusually high mortality rate”.

PSP is caused by toxins derived from saxitoxin (in fact, there are 20 toxins related to PSP), according to the Bad Bug Book. Molluscan shellfish can become contaminated as can gastropods, such as moon snails, and crabs that feed on other shellfish.

Many people often associated “red tide” with PSP; however, many non-harmful algal blooms can turn the water a myriad of colors, including red, the Washington Department of Health notes. Additionally, the toxin can be present in water that appears clear or in shellfish after the algal bloom dissipates. Given this, water color isn’t a good indicator of the presence of toxins.

The onset of PSP is quick – typically within a half hour to two hours of ingesting the contaminated shellfish. Symptoms may begin as tingling lips and tongue, tingling fingers and toes, and then followed by the loss of motor control in the arms and legs. Respiratory difficulty occurs and if enough toxin is present, it can paralyze respiratory and chest muscles, causing suffocation. Fatalities from PSP have happened less than a half hour after consumption of the tainted shellfish.

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