Safety Hazards with Marine food Products

MBT lec 11

IntroductionFish and shellfish can become contaminated from their natural environment or from subsequent handling or processing.

Fish and shellfish act as intermediate hosts for a number of parasites that can infect humans

Water polluted with sewage is a particular problem with filter-feeding molluscan shellfish such as oysters and mussels.

which are often eaten raw or after only light cooking. These feed by filtering nutrients from large volumes of their surrounding water, at the same time accumulating microorganisms from their environment.

Since shell fish are mainly harvested from shallow coastal waters where sewage contamination is likely to be greatest, they are commonly contaminated with pathogenic bacteria and viruses of human (and animal) enteric origin.

Vibrio parahaemolyticus Fish from warmer coastal waters can often be contaminated with the bacterium

Vibrio parahaemolyticus and can be transferred to other fish both at the market and in the home.

Vibrio parahaemolyticus cause an intestinal infection that is characterized by lower gastrointestinal distress such as diarrhea and cramps. In some cases, nausea, vomiting, fever and headache may also be present.

Occasionally, this disease may manifest itself as a dysentery-like illness with bloody or mucoid stools, high fever and a high white blood cell count, but normally the disease has a duration of only two to three days.

Illness with Vibrio parahaemolyticus is most common during the summer months and is requently associated with consumption of oyster.

V. parahaemolyticus is readily killed by thorough cooking but an be spread to cooked fish by inadequate separation of raw and cooked products.

Vibrio vulnificus Vibrio vulnificus is a bacterium in the same family as those that cause cholera. It

normally lives in warm seawater and is part of a group of vibrios that are called "halophilic“

Vibrio vulnificus is associated with seafoods, particularly oysters.Which are often eaten uncooked.

V. vulnificus can cause disease in those who eat contaminated seafood or have an open wound that is exposed to seawater.

Among healthy people, ingestion of V. vulnificus can cause vomiting, diarrhea, and abdominal pain.

In immunocompromised persons, particularly those with chronic liver disease, V. vulnificus can infect the bloodstream, causing a severe and life-threatening illness characterized by fever and chills, decreased blood pressure (septic shock), and blistering skin lesions. V. vulnificus bloodstream infections are fatal about 50% of the time.

V. vulnificus can cause an infection of the skin when open wounds are exposed to warm seawater; these infections may lead to skin breakdown and ulceration.

Persons who are immunocompromised are at higher risk for invasion of the organism into the bloodstream and potentially fatal complications

Vibrio cholerae Vibrio cholerae is often transmitted by water.

But foods that have been in contact with contaminated water also serve as a vehicle of infection.

These would naturally include fish from contaminated water or washed with it after being caught.

Relaying Numbers of pathogenic bacteria in their tissues can be reduced by

transferring the shellfish to clean coastal waters (relaying) or

by holding them in tanks in which the water is recirculated and disinfected with ultraviolet light (a processknown as depuration).

While this is an effective and well proven procedure for bacteria, it is far less so for viruses which seem to persist much longer in shellfish.

Algae Intoxications Fish can also be the cause of a number of different intoxications where

cooking does not eliminate the problem.

These toxins are often the products of algae.

When these algae are consumed by filter- feeding shellfish or small herbivorous fish, the toxin accumulates in the flesh which may then be consumed and accumulated by larger carnivorous fish.

Ciguatera Ciguatera is an example of this where the toxin (ciguatoxin) is produced by

the dinoflagellate alga Gambierdiscus toxicus and then amplified through the food chain.

This particular condition occurs only with fish from tropical and subtropical regions but other types of dinoflagellate intoxication occur in cooler climates.

Usually this follows an algal bloom where environmental conditions lead to a sudden proliferation of the toxin-producing algae.

Ciguatera Ciguatera presents primarily as an acute neurologic disease manifested by a

constellation of gastrointestinal (diarrhea, abdominal cramps and vomiting), neurologic (paresthesias, pain in the teeth, pain on urination, blurred vision, temperature reversal) and cardiovascular signs and symptoms within a few hours of contaminated fish ingestion.

The pathneumonic symptom of Ciguatera intoxication is hot/cold temperature reversal, although not all patients report this.

Acute fatality, usually due to respiratory failure, circulatory collapse or arrhythmias, ranges from 0.1% to 12% of reported cases; presently in the Pacific, the mortality is less than 1%. Lethality is usually seen with ingestion of the most toxic parts of fish ie. the liver, viscera

The symptoms of Ciguatera poisoning, especially the paresthesias and weakness, can persist in varying severity for weeks to months after the acute illnes

Limiting Contamination In many fish products, salt is an important factor in limiting the growth of

pathogens.

For example, pre-salting is a common practice in fish drying where it helps accelerate drying while limiting the growth of bacteria during the process.

In smoked fish, a minimum salt content of 3% in the water phase and an internal temperature of at least 63oC during smoking have been recommended in order to control Clostridium botulinum.

Clostridium botulinum Clostridium botulinum is a Gram-positive, rod-shaped bacterium that produces several toxins. The best known are its neurotoxins, subdivided in types A-G, that cause the flaccid muscular paralysis seen in botulism.

 Types A, B, E, and F cause botulism in humans, while types C and D cause botulism in animals and birds. Type G was identified in 1970 but has not been determined as a cause of botulism in humans or animals.

Foodborne botulism results from the ingestion of pre-formed toxin in food. Botulinum toxin can be found in foods that have not been properly handled or canned and is often present in canned vegetables, meat, and seafood products

Problems with Clostridium botulinum have been encountered with some traditional fermented fish products.

These rely on a combination of salt and reduced pH for their safety.

If the product has insufficient salt, or fails to achieve a rapid pH drop to below 4.5, C. botulinum can grow.

Clostridium botulinum Botulinum toxin is a neurotoxin, thus it affects the nervous system and is

characterized by descending, flaccid paralysis that can cause respiratory failure.

Foodborne botulism produces symptoms beginning in 6 to 36 hours, though some can even start after two weeks. Symptoms include double and blurred vision, slurred speech, difficulty swallowing, dry mouth, diarrhea, nausea, and muscle weakness that descends through the body.

Recovery occurs with prompt administration of antitoxin and respiratory intensive care. Deaths that occur within the first two weeks of botulism are often the result of pulmonary or systematic infection and failure to recognize the disease.

Often the symptoms of foodborne botulism are mistaken for symptoms associated with stroke, chemical intoxication, myasthenia gravis, and Guillain-Barre syndrome

SCOMBROID

Scombroid, one of the most common fish poisonings, occurs worldwide in both temperate and tropical waters.

The illness occurs after eating improperly refrigerated or preserved fish containing high levels of histamine, and often resembles a moderate to severe allergic reaction.

Fish that cause scombroid have naturally high levels of histidine in the flesh and include tuna, mackerel, mahimahi (dolphin fish), sardine, anchovy, herring, bluefish, amberjack, and marlin.

Histidine is converted to histamine by bacterial overgrowth in fish that has been improperly stored (>20°C) after capture. Histamine and other scombrotoxins are resistant to cooking, smoking, canning, or freezing.

SCOMBROID

Symptoms of scombroid poisoning resemble an acute allergic reaction and usually appear 10–60 minutes after eating contaminated fish.

They include flushing of the face and upper body (resembling sunburn), severe headache, palpitations, itching, blurred vision, abdominal cramps, and diarrhea. Untreated, symptoms usually resolve within 12 hours.

Rarely, there may be respiratory compromise, malignant arrhythmias, and hypotension requiring hospitalization. Diagnosis is usually clinical. A clustering of cases helps exclude the possibility of fish allergy.

Fish contaminated with histamine may have a peppery, sharp, salty, or bubbly taste but may also look, smell, and taste normal.

The key to prevention is to make sure that the fish is promptly chilled (below 38°F) after capture. Cooking, smoking, canning, or freezing will not destroy histamine in contaminated fish.

Parasites in raw, frozen, and smoked fish Human pathogenic parasites occur in several species of fish that may be cold-

smoked, including gadoids, salmonids, sole or flounder, grouper, halibut , herring, mackerel, mullet, sablefish, sprat, small tunas, and turbot.

Parasites are also identified as a potential hazard in some invertebrates that may be cold-smoked or cold-smoked and dried, including octopus, squid, snails, and crabs/crayfish.

Several species of salmonid parasites, such as Anisakis spp. (a nematode or roundworm), Diphyllobothrium spp. (a cestode or tapeworm and Nanophyetus salmincola are of public health concern 

ll wild-caught Pacific salmon (Oncorhynchus spp.) are considered to have A. simplex larvae present. Prevalence reached more than 75% in fresh U.S. commercial sockeye salmon (O. nerka), chum salmon (O. keta), coho salmon (O. kisutch), and king salmon (O. tschawyscha) (Myers 1979; Deardoff and Overstreet 1991)

Parasites Freezing raw fish prior to smoking remains the most effective way to

ensure that viable parasites are not present in cold-smoked products consumed by the public. It is essential, therefore, that raw fish potentially containing viable parasites be frozen and held in that state for a period of time that assures destruction of all viable parasites in that fish species.

The Fish and Fishery Products Hazards and Controls Guide recommends a temperature below -4 oF (-20 oC) for 7 d or -31 oF (-35 oC) (internal) for 15 h to kill the parasites of concern