Toxic Shellfish Poisoning

作者：admin  点击次数：5  发布时间：2025-05-13

(I) Etiology
Toxic shellfish poisoning is caused by eating certain shellfish such as mussels, clams, snails, oysters, etc. The poisoning is characterized by nerve paralysis, so it is called paralytic shellfish poisoning.
The reason why shellfish are toxic is related to the algae in the seawater. Many dinoflagellate algae in marine plankton are highly toxic. When some shellfish that are originally non-toxic and have always been edible ingest toxic algae, they are poisoned. The poisoned shellfish itself is not poisonous, and there are no changes in ecology and appearance, but when people eat it, the toxins can be quickly released from the shellfish meat and show toxic effects. The toxins carried by poisoned shellfish are collectively called paralytic shellfish poisoning (PSP), which includes a variety of toxins. One of the more important ones is saxitoxin (STX), which is a non-protein toxin with a smaller molecular weight. Pure STX is white, soluble in water, heat-resistant, no change at 80℃, 1h, toxicity reduced by 1/2 at 100℃ for 30min; stable to acid, unstable to alkali, easily absorbed by the gastrointestinal tract. Saxitoxin is a neurotoxin, and its main toxic effect is blocking nerve conduction. The oral lethal dose for humans is 0.5~0.9mg.
The occurrence of shellfish poisoning is often related to "red tide". When red tide occurs, the density of sea poisoning increases and shellfish are poisoned. Poisoning often occurs in coastal countries and regions, and has occurred many times in Zhejiang, Fujian, Guangdong and other places in my country. The shellfish that cause poisoning include clams, clams, conches, and wriggle snails, which are commonly eaten shellfish. Because the toxins of shellfish are mainly accumulated in the internal organs, some countries stipulate that shellfish must be visceral before they can be sold, or that only white muscles are left for consumption.
(II) Symptoms of poisoning
The symptoms of poisoning vary depending on the toxins contained in shellfish. Generally, there are three types:
(1) Neurological type, also known as paralytic shellfish poisoning. Shellfish that cause poisoning include mussels, scallops, clams, and conches. Their toxic components are mainly saxitoxin. The incubation period is 5 minutes to 4 hours, generally 0.5 to 3 hours. In the early stage, there is numbness of the lips, tongue, and fingers, followed by paralysis of the extremities and neck, until motor paralysis, gait staggering, accompanied by dysphonia, salivation, headache, thirst, nausea, vomiting, etc. In severe cases, death occurs due to respiratory paralysis. (2) Hepatic type. Shellfish that cause poisoning include clams, giant oysters, etc., and the toxic part is the liver. The incubation period is 12 hours to 7 days, generally 24 to 48 hours. In the early stage, there is stomach discomfort, nausea, vomiting, abdominal pain, fatigue, and may also have a slight fever, similar to a mild cold. Millet-sized hemorrhagic spots are often seen on the skin, which are red or dark red, and are more common on the shoulder blades, chest, upper and lower limbs. In severe cases, acute liver atrophy, impaired consciousness or coma may occur, with a poor prognosis and many deaths. (3) Solar dermatitis is caused by eating mud snails, with an incubation period of 1 to 14 days, usually 3 days. Initially, redness and swelling appear on the exposed parts of the face and limbs, and there are sensations such as burning, pain, itching, swelling, and numbness. In the later stage, bruises, blisters or blood blisters may appear, which may cause infection after breaking. Fever, headache, and loss of appetite may occur.
(III) Preventive measures
(1) Establish an epidemic reporting and regular monitoring system
① Monitor and forecast the growth of seaweed. The occurrence of poisonous shellfish poisoning is related to "red tides". Therefore, many countries stipulate that during the algae breeding season from May to October, water samples of growing shellfish should be regularly inspected. When the density of seaweed is found to be greater than 2x10'mg/mL, a report of possible shellfish poisoning will be issued, and even the fishing and sale of shellfish in the sea area will be prohibited.
②) Monitor the PSP content in sea shellfish products according to the regularity of the region and period of red tide occurrence. Shellfish from non-toxic to suddenly toxic, or from continuous low toxicity to generally increased, are all dangerous.
(2) Set PSP limits for shellfish meat supplied as commodities. The US FDA stipulates that the maximum allowable limit of saxitoxin in fresh, frozen and head-production shellfish is not more than 80ug/100g, which can be used as a reference. (3) Do a good job in health publicity. Guide the public on safe eating methods based on the characteristics of PSP such as heat resistance, water solubility and high accumulation in the visceral part of the shellfish. For example, before eating, clean and rinse, remove the internal organs, and boil the meat and discard the soup when eating, so as to minimize the intake of toxins.
(I) Etiology
High-histamine fish poisoning is a type of allergic food poisoning caused by eating certain fish containing a certain amount of histamine. Histamine is a decomposition product of histidine, so the production of fish histamine is related to the amount of histidine it contains. Fish with green skin and red meat (such as mackerel, fish, fish, tuna, sardines, saury, bamboo shoots, etc.) contain more hemoglobin in their muscles, so the histidine content is also high. Contamination by bacteria rich in histidine, such as histamine-depleting bacteria, Escherichia coli, Staphylococcus, and Streptococcus, will produce decarboxylase under suitable environmental conditions to decarboxylate histidine and produce histamine. Histamine is easily produced under environmental temperatures of 10~37℃, especially 15~20℃, body salt content of 3%~5%, and weakly acidic pH. Adults who ingest more than 100 mg of histamine (equivalent to 1.5 mg per kilogram of body weight) may be poisoned. If the amount of histamine in fish is calculated to be 1.6~3.2 mg/g, eating 50~100g of fish meat can cause poisoning.
The mechanism of poisoning is that histamine can stimulate the cardiovascular system and nervous system, promote capillary dilation and congestion and bronchial contraction, so that a large amount of plasma enters the tissue, the blood is concentrated, the blood pressure drops, causing a reflex heart rate to accelerate, and stimulating the smooth muscle to cause spasm.
(II) Manifestations of poisoning
The characteristics of histamine poisoning are rapid onset, mild symptoms, and rapid recovery. The incubation period is generally 0.5~1h, and the shortest is only 5min. The main manifestations are flushing, stinging, and burning sensations on the face, chest, and skin of the whole body, conjunctival congestion, accompanied by headache, dizziness, accelerated heartbeat, chest tightness, rapid breathing, and decreased blood pressure. Sometimes there may be urticaria, and some individuals may have asthma. The body temperature is normal. Generally, most people recover in 1~2 days. The prognosis is good, and no deaths have been observed. (III) Preventive measures
(1) Prevent fish from spoiling and deteriorating. Freeze and refrigerate fish during production, storage, transportation and sales to keep the fish fresh and reduce the risk of contamination. When salting fish, the back of thicker fish should be split open to facilitate salt penetration. The amount of salt used should not be less than 25%.