Fish is one of the most valuable food groups as it is rich in nutrients such as omega-3 fatty acids that have antioxidant activity. Food allergy to fish is relatively rare in our country, especially compared to the incidence of allergy to other foods such as milk and egg. The prevalence of fish allergy is estimated at less than 0.5% of the general population, which practically translates into a frequency of about one allergic patient per 1000 persons (children and adults).

Fish allergy usually manifests itself in the first 2 years of life. Sometimes it occurs for the first time during the child's first attempt to feed fish (in this case it is concluded that the child's body has had previous contact with the fish allergen through the skin before being fed fish for the first time), while sometimes the onset of the allergy occurs on one of the subsequent occasions when the child is fed fish. The type of fish chosen by the parents to feed the child does not play any role in the occurrence of allergy.

Symptoms appear immediately (usually in the first few minutes) after the food is eaten and may include manifestations from the skin (hives or angioedema), the digestive system (abdominal pain, vomiting, diarrhea), the respiratory system (coughing, runny nose, asthma attack) and, in an advanced stage, the circulatory system (with a drop in blood pressure, manifested by dizziness, visual disturbances, drowsiness and fainting). These are the symptoms of the direct type of fish allergy. As with other foods, fish can rarely cause other types of allergies, such as food protein enterocolitis syndrome. Also, someone who has a direct type of allergy may also show symptoms when their skin comes into contact with fish or even from inhaling fish cooking vapours.

The substance that causes the fish allergy is a protein called parvalbumin. This protein is found in the muscle tissue of all fish without exception, in different amounts for each species (e.g. of the fish that have been studied for their allergenicity, swordfish has a much smaller amount of the protein than cod or sole). In rare cases there may be sensitivity to other fish allergens such as collagen and aldehyde dehydrogenase.

The treatment for fish allergy, like any food allergy, is one and only one: complete avoidance of eating fish. If, despite strict vigilance, accidental ingestion of fish by the child occurs, then appropriate treatment of the symptoms that will occur with drugs such as antihistamines, cortisone and an autoinjector adrenaline device is applied if the severity of the reaction warrants it.

Fish allergy persists for many years or is lifelong for a large proportion of patients. However, up to 20% of patients may eventually develop tolerance (i.e. overcome their allergy). This occurs, as found in a study by our allergy unit, on average about 10 years after the first reaction.

Also, in the allergy unit of the P. & A. Kyriakou Children's Hospital, an innovative approach is applied to patients with fish allergy: a special procedure, called the food challenge test, is used to try to feed them with certain types of fish that are known to contain a smaller amount of the protein that causes the allergy (such fish are, for example, tuna and swordfish). The results show that these fish are tolerated by patients with allergies in more than 90% of cases. In this way, fish allergy patients can incorporate these fish species into their diet and not be deprived of the valuable nutrients of fish.

In addition, a pan-European study on the treatment of fish allergy is currently underway called FAST (Food Allergy Specific ImmunoTherapy). The aim of the study, in which our allergy department is involved, is to discover a safe (in terms of no side effects) and effective treatment for fish allergy. The treatment will take the form of monthly injections (specific immunotherapy) as is currently used to treat other allergic diseases such as hay fever and asthma. However, this will be the first time that this will be possible for a food allergy. The study is currently undergoing clinical evaluation and is expected to produce results soon that will change the lifestyle of fish allergy patients.

Stavroulakis Georgios
ALLERGIST,
Athens Central Clinic
of the Hellenic Police.