Shellfish Poisoning: Causes, Symptoms & Treatment

Mytilism is the medical term for shellfish poisoning. Symptoms may appear in the nervous system and on the skin, in addition to the gastrointestinal tract. Treatment for shellfish poisoning is symptomatic, as no antidotes exist.

What is shellfish poisoning?

Mytilism is a poisoning that is caused by eating shellfish. This shellfish poisoning can be divided into four different forms:

  • Central nervous form
  • Neurotoxic form
  • Diarrheic form
  • Paralytic form.

The subtypes are characterized by different leading symptoms and may in some circumstances merge into each other. In individual cases, the particular form of poisoning may occur only with diffuse boundaries to the other three forms. Sometimes only three forms of shellfish poisoning are distinguished instead of the four mentioned. This classification refers mainly to the anatomical system in which the poisoning symptoms occur. According to this scheme, the allergic and gastrointestinal forms are distinguished from the neurotoxic form. As a rule, the triggering toxins enter the mussels through the water and the food chain. In oysters, however, endogenous toxins are produced during spawning. Putrefactive substances in mussels can also cause poisoning.

Causes

Mussel poisoning occurs primarily after eating mussels and pile mussels. Less commonly, symptoms of poisoning are also observed after consumption of oysters. In neurotoxic poisonings, the poisoning symptoms are caused by neurotoxins. For example, dinoflagellates produce saxitoxin in plankton. The bivalves accumulate this substance in the flesh during plankton filtration. Red and diatom algae, on the other hand, produce domoic acids and are also part of the food chain of various bivalves. The diarrheic form is caused by okadaic acids. Brevetoxins are also found as toxins in mussels and thus can also be the cause of mussel poisoning. Some shellfish poisoning is caused by the putrefaction products that form in shellfish that are no longer fresh. These putrefaction products mainly cause gastrointestinal complaints in humans. Incidentally, that toxins such as those mentioned can be boiled or washed off is a common misconception.

Symptoms, complaints and signs

Symptoms of shellfish poisoning vary with the causative toxin and its dosage. In the gastrointestinal form, the putrefactive products of shellfish trigger gastrointestinal symptoms, the severity of which depends on the dose and the age of the shellfish. Diarrhea and vomiting are the leading symptoms. Chills may accompany them. Allergic shellfish poisoning usually causes harmless skin rashes. The paralytic form caused by neurotoxins is characterized by globus sensations in the throat, sensory disturbances and paralysis. Movement disorders and speech disorders also occur. The patient’s body temperature sometimes rises to life-threatening levels and anxiety sets in and consciousness disorders occur. Respiratory problems are present in the central nervous form. The paralytic form is the most severe form of shellfish poisoning and can cause respiratory or cardiac arrest.

Diagnosis and course of the disease

The physician makes the diagnosis of mytilismus primarily by history. Local occurrence allows the physician to assess the likelihood of each form of shellfish poisoning. The clinical presentation is relatively typical for fish and shellfish poisoning. However, the differential diagnosis between the individual forms of poisoning is often associated with problems in individual cases. The detection of certain toxins in the mussel flesh is considered to confirm the diagnosis, but can only rarely be provided. The course of the poisoning depends strongly on the respective toxin and the severity. Life-threatening courses can occur mainly in the paralytic form. For the other forms, the prognosis is usually more favorable.

Complications

Serious physical symptoms may occur as a result of shellfish poisoning. Usually, accompanying symptoms include diarrhea and vomiting or chills, which, if left untreated, can lead to dehydration and circulatory problems, for example. In severe cases, shellfish poisoning can cause speech disorders and movement disorders.At times, the body temperature rises to a life-threatening level and anxiety and impaired consciousness occur. In the central nervous form, breathing difficulties may occur, and in the paralytic form, respiratory and cardiac arrest may occur. Rarely, toxi infection may occur, in the course of which blood poisoning may occur. People who are already physically weakened or heavily stressed are particularly at risk of such complications. For example, pregnant women, the elderly, small children, patients with a weakened immune system and other risk groups. When treating shellfish poisoning, the prescribed drugs can cause intolerances and allergic reactions. Thus, many antibiotics cause gastrointestinal complaints, skin rashes and physical discomfort. In the context of frequently prescribed occupational therapy, for example, physical overload may occur or the already weakened immune system may be overloaded. In all cases, however, shellfish poisoning can be cured without major complications, provided it is recognized and treated at an early stage.

When should you go to the doctor?

If the affected person experiences severe malaise, nausea or vomiting immediately after or while still eating mussels, a doctor should be consulted. In case of sweating, a pale complexion as well as a sharp drop in blood pressure, a doctor is needed. In acute cases, an ambulance service must be alerted, as the affected person must immediately receive intensive medical treatment. Otherwise, premature death is imminent in the case of shellfish poisoning. Severe diarrhea, stomach pain and cramps are further signs of an irregularity. If there is an increase in body temperature, a feeling of internal heat or dizziness, a doctor should be consulted. Sudden changes in the appearance of the skin, itching or discomfort on the skin should be investigated and treated. If there is paralysis or difficulty breathing, action is also required. If there is a loss of respiratory activity or a sudden loss of consciousness, an emergency physician should also be alerted. In order to ensure the survival of the patient until the ambulance arrives, first aid measures must be taken at the same time by those present. If the above-mentioned complaints occur after or during a visit to a restaurant, a visit to the doctor is also necessary. In some cases, chefs use shellfish to refine or season a prepared meal, so that leftover or tiny pieces of shellfish meat are incorporated into a menu without the knowledge of the affected person.

Treatment and therapy

Mytilismus cannot be treated causally, but only symptomatically. For example, if there is respiratory distress, providing the patient with oxygen may be indicated. If symptoms of the gastrointestinal tract are present, dehydration may occur. If necessary, this dehydration is compensated for by the intravenous administration of fluids. In order to eliminate toxins from the body as quickly as possible, the water balance should be kept relatively high. The excretion of toxins with the urine is stimulated in this way. If dermatological symptoms occur, ointments and compresses are used to relieve itching. Anxiety can be relieved via the specific administration of sedatives. However, the condition of the cardiovascular system plays a crucial role in this process, as heart failure may occur if not considered. Pumping the stomach is usually no longer effective when the first symptoms appear, as the toxins are already absorbed into the blood within two to five hours. If paralysis has developed that does not resolve on its own within the next few days, physical therapy may be indicated to regain mobility. Occupational therapy may also make sense in this context. If persistent speech problems are present, then a speech therapist is usually consulted.

Outlook and prognosis

The prognosis for shellfish poisoning depends on the exact toxin, site of action, and dose. Many shellfish poisonings are considered harmless. For example, poisonings that affect only the digestive tract are usually well survived. At most, dehydration as a result of diarrhea is dangerous here. Permanent damage is not to be feared with this form of mytilism. This form of poisoning is mostly caused by okadaic acid. In other forms of shellfish poisoning, the prognosis is much worse.Domoic acid, ciguatoxin and saxitoxin are much more dangerous and can cause respiratory and circulatory problems, respectively. There is both the possibility for affected persons to survive the poisoning despite serious symptoms. In other cases, the condition can become life-threatening, which is especially the case with high doses of ingested poison. In these cases, poisoned individuals must be treated as quickly as possible. As the duration of poisoning without help and treatment increases, so does the mortality rate. Shellfish poisoning that is treated and survived leaves no secondary damage. Complete recovery with temporary physical debilitation is usually the result. It should be remembered that shellfish poisoning has nothing to do with the immune system and can occur every now and then.

Prevention

Shellfish poisoning can be prevented. For example, mussels from unclean waters should not be consumed. In general, mussels should always be soaked in pure water before consumption to detoxify their toxins. In the summer months, a general avoidance of mussels is advisable, as many algae form in the warm season and mussels thus come into increased contact with their toxins in the summer.

Aftercare

Because shellfish poisoning is associated with a serious course of infection of the gastrointestinal tract, final, complete recovery of the patient does not occur for several weeks. During the follow-up period, the patient should consistently pay attention to the correct selection of foods that are gentle on the stomach and intestines. During this time, food should also be prepared in a way that is very gentle on the stomach and intestines. Foods with an increased risk of germs, such as raw meat, raw egg products or fish, should be avoided. Gastrointestinal rehabilitation is advisable as part of the follow-up treatment. This is usually done with the help of preparations containing live lactic acid bacteria, which are taken for several weeks to stabilize and build up a healthy intestinal flora. Since the immune system and the gastrointestinal tract have been weakened and impaired, the organism is very susceptible to further infections and diseases caused by bacteria and germs. Follow-up examinations with the treating physician must therefore be carried out very promptly, if necessary, as a result of renewed gastrointestinal complaints. If diarrhea reoccurs, the patient’s stool should be examined in the laboratory. Through follow-up examinations, the physician will diagnose whether gastritis has developed from the shellfish poisoning. This would then require appropriate medical and drug treatment.

What you can do yourself

There is no antidote for shellfish poisoning. Self-help measures must therefore focus on prevention as well as on the therapy of the individual symptoms. If mussels cause gastrointestinal problems, this is usually because the food was no longer really fresh when it was eaten and putrefactive substances have already formed. Those who prepare mussels themselves should therefore always buy them fresh and use them the same day. Certain symptoms of poisoning, however, result from neurotoxins that the mussels accumulate in their flesh. There is little room for preventive action here. However, this phenomenon occurs less frequently with oysters than with other mussel species. So for those who don’t want to give up completely, the risk of neurotoxic poisoning can be reduced by eating only oysters and avoiding mussels and pile mussels. Nausea, diarrhea and vomiting usually represent rather harmless symptoms of shellfish poisoning. In mild cases, these accompanying symptoms can also be treated with over-the-counter medications from the pharmacy. In addition, the affected person should allow himself rest and make sure that he makes up for the loss of fluids, which is often associated with diarrhea. In addition to water, unsweetened tea or vegetable broth should be drunk. Since the electrolyte balance is often also disturbed, nibbling salty cookies can be helpful. If paralysis, speech disorders, anxiety, impaired consciousness or breathing difficulties occur, a doctor must be consulted immediately. In this case, the patient’s life is in danger, as severe forms of shellfish poisoning can lead to respiratory or cardiac arrest.