Seafood shellfish

Seafood Toxins. Vktually scores of fish and shellfish species have been reported to have toxic manifestations. Most of these toxicities have been shown to be microbiological ki origin. There are a few, however, that are natural components of seafoods. 

The paralytic shellfish toxins (PSTs Fig. 5.2a) include saxitoxin (STX) as well as STX analogs such as neo-saxitoxin (neo-STX), gonyautoxin (GTX), and the decar-bamoyltoxins (Sivonen and Jones 1999). These molecules are of particular concern in marine systems, where they have been implicated in human deaths following the consumption of contaminated seafood (Van Dolah 2000). The causative agents in those cases are several genera of marine dinoflagellates that are common components of red tides (e.g., Alexandrium sp. Homer et al. 1997 Van Dolah 2000). 

AZP, the most-recently characterized marine seafood poisoning, is associated with eating shellfish contaminated with azaspiracids. The first human intoxications attributed to AZP occurred in the Netherlands, and the symptoms included those similar to DSP (i.e., nausea, vomiting, severe diarrhea, and stomach cramps). However, although chemical analyses did not identify significant levels of the diarrhetic shellfish poisons, they identified a new class of toxins (James et ah, 2003a). 

In the U.S., fish and shellfish caused at least one in six food poisoning outbreaks with known etiologies, and 15% of the deaths associated with these outbreaks during 1988 to 1992. This is a marked increase over the preceding decade, when seafood consumption was associated with 10% of foodborne disease outbreaks that had identified etiologies (Ahmed, 1992 Centers for Disease Control and Prevention, 1996 Lipp and Rose, 1997). 

Coupled with successful primary prevention are ongoing monitoring programs for the organisms and their toxins, both in the environment and in the seafood. The molluscan shellfish (i.e., oysters, clams, mussels, and scallops) are the species associated with shellfish poisonings. The absence of characteristics such as abnormal taste, smell, or appearance precludes sensory inspection for these toxins. Instead, ensuring seafood safety relies on testing seawater and the seafood itself The assays used to detect toxins in seafood have evolved as analytic methods and instrumentation have improved. The American Public... 

In addition to recommendations for seawater and seafood testing, shellfish control authorities , which are entities of state or national governments, have the responsibility to determine the risks associated with specific shellfishharvesting waters based on the presence of natural toxins. As a result of routine monitoring, harvesting of seafood from these areas may be limited to certain times of the year or to specific environmental conditions. 

This nonsystematic approach to monitoring has proven inadequate for protecting the U.S. food supply. In response, the FDA enacted the Hazard Analysis and Critical Control Points (HACCP) program of 1997 (U.S. Food and Drug Administration, 1995, 2001). In the U.S., the FDA has established action levels in suspect seafood for the toxins causing some of the shellfish poisonings (see Table 7.3). When an action level is reached, the HACCP plan must be followed to prevent unsafe product from reaching consumers. 

Global seafood safety standards have not been established, and the FDA estimates that more than half of the seafood eaten in the U.S. is imported, from a total of 135 countries. The FDA now requires seafood importers to verify that their overseas suppliers comply with the National Shellfish Sanitation... 

U.S. Food and Drug Administration (FDA) action levels in seafood for the toxins associated with shellfish poisonings. 

Program and that imported seafood is processed under HACCP controls. The World Health Organization also supports the HACCP plan (World Health Organization, 1995). However, because compliance with this program is costly, many countries comply with these standards only for exported shellfish. 

Aune, T. and Yndestad, M., Diarrhetic shellfish poisoning, in Falconer, I.R., ed.. Algal Toxins in Seafood and Drinking Water, Academic Press, San Diego, 1993. Australia New Zealand Food Authority, Shellfish Toxins in Food, A Toxicological Review and Risk Assessment, Australia New Zealand Food Authority, Canberra, 2001. 

Todd, E., Amnesic shellfish poisoning - a new seafood toxin syndrome, in Graneli, E., ed.. Toxic Marine Phytoplankton, Elsevier Science Publishing, 1990b. 

From the human perspective, HABs are problematic because they cause (1) risks to human health, (2) loss of natural or cultured seafood resources, (3) impairment of tourism and recreational activities, and (4) damage to noncommercial marine resources and wildlife. Exposure pathways include (1) consumption of toxic shellfish that have accumulated phytoplankton toxins filtered from the water, (2) consumption of tropical fish that have accumulated phytoplankton toxins (ciguatera), (3) inhalation of aerosolized toxins ejected from the sea surface, and (4) skin contact resulting in irritations due to allergy-like reactions. Harmful health effects from acute exposures have been relatively well studied. Less well known are the health effects resulting from chronic exposures to low toxin levels. This is of particular concern with regards to marine mammals and seabirds. 

Over 100 people got very sick after eating mussels, a type of shellfish.They were disoriented, confused, and some had seizures and memory loss.Three people died. No one knew exactly what was causing the problem but it was clear that scientists needed to find out why— quickly—before other people got sick. Whatever was in the mussels could show up again in seafood if they couldn t find out what it was or where it came from. 

The more classical approach to assess the presence of marine biotoxins in seafood is the in vivo mouse bioassay. It is based on the administration of suspicious extracted shellfish samples to mice, the evaluation of the lethal dose and the toxicity calculation according to reference dose response curves, established with reference material. It provides an indication about the overall toxicity of the sample, as it is not able to differentiate among individual toxins. This is a laborious and time-consuming procedure the accuracy is poor, it is nonspecific and generally not acceptably robust. Moreover, the mouse bioassay suffers from ethical implications and it is in conflict with the EU Directive 86/609 on the Protection of Laboratory Animals. Despite the drawbacks, this bioassay is still the method of reference for almost all types of marine toxins, and is the official method for PSP toxins. 

In our program to provide consumers with safe, high quality products and respond to critical national and international needs to eliminate major impediments to expanding markets, a primary seafood utilization issue is the area of marine toxins that continue to present serious economic problems to the fishing industry and impact consumers. Ciguatera is one of the most treacherous and common forms of seafood poisoning in tropical waters. Also, sporadic outbreaks of PSP in shellfish from most of the major growing areas of North America... 

Over the last eight years, most of the estimated cases of world-wide poisoning in humans due to the three major kinds of seafood toxins that are found in fresh and unspoiled marine organisms, namely, paralytic shellfish poison (PSP-saxitoxins/ gonyautoxins), ciguatoxin(s), and tetrodotoxin, (13-16) were caused by ciguatera (Table I). 

A third concern is the industry s ability to compete with clam products harvested from the East Coast, Canada, Japan and Korea. To successfully compete, we must establish a reputation for a safe and wholesome quality product. To this end, Alaska has become a member of the National Shellfish Sanitation Program which allows us to participate in interstate marketing. In addition, the state has instituted a seafood certification program. 

In summary, from the stanc int of risks and benefits, the benefits far outweigh the risks. Tliere are many health benefits to be derived from eating fish and shellfish as long as the nutritional quality is assured. Seafood and fresh water fish, as well as shellfish, are excellent foods. They are a renewable... 

Fish Products. As explained earlier, it is unlikely that paralytic shellfish toxins have an impact on the utilization of fish products from the point of view of the suitability of fish as food, except perhaps in cases where whole fish are eaten with little processing. Fish simply are unable to accumulate the toxins in their muscle tissues. But the toxins do appear to have an impact on the marketing of fish products, related to consumer wariness of seafood products in general during red tide and PSP incidents. The media blitz surrounding these incidents often leaves consumers unaware of which particular seafood items to be cautious. Consequently, finfish as well as shellfish products have been avoided during these episodes (25). 

Cyanobacterial toxins (both marine and freshwater) are functionally and chemically a diverse group of secondary chemicals. They show structure and function similarities to higher plant and algal toxins. Of particular importance to this publication is the production of toxins which appear to be identical with saxitoxin and neosaxitoxin. Since these are the primary toxins involved in cases of paralytic shellfish poisons, these aphantoxins could be a source of PSP standards and the study of their production by Aphanizomenon can provide information on the biosynthesis of PSP s. The cyanobacteria toxins have not received extensive attention since they have fewer vectors by which they come in contact with humans. As freshwater supplies become more eutrophicated and as cyanobacteria are increasingly used as a source of single cell protein toxic cyanobacteria will have increased importance (39). The study of these cyanobacterial toxins can contribute to a better understanding of seafood poisons. 

Molluscan shellfish play an important role in human nutrition and the world economy (Wild and Lehrer, 2005). Table 4.2 provides data on the worldwide production/catch of various molluscan shellfish species for 2005. The most widely available species are oyster, squid, clam, mussel, and scallop. Aquaculture has become an important contributor to the production of molluscan shellfish with the exception of the cephalopods. However, the popularity and frequency of consumption of various molluscan shellfish varies widely across various countries and cultures. Accurate information on comparative consumption patterns for molluscan shellfish in various countries does not exist. Molluscan shellfish are consumed as freshly cooked or even raw seafood items particularly in coastal communities. But mollusks also are consumed as processed foods in a variety of forms. 

The prevalence of allergies fo specific foods is unknown for the most part. Good estimates exist of the prevalence of milk allergy in infancy (Hosf and Halken, 1990) and peanut and tree nut allergy throughout the life span (Sicherer et ah, 1999). However, the prevalence of allergies to seafoods including molluscan shellfish is not precisely known. 

Sicherer et ah (2004) conducted a nationwide random telephone survey of the prevalence of seafood allergies in the United States and a standardized questioimaire. Responses were categorized on the basis of convincing symptoms and self-reported physician confirmation of the allergy. The survey involved 14,948 individuals with 67 reporting reactions to molluscan shellfish including scallops, clams, oysters, and mussels. The self-reported prevalence in this study population was 0.4%. 

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