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Food allergies are reproducible reactions which are caused by the body’s immune system responding to a protein in a particular food. In the case of cows milk allergy (or cows milk protein allergy), the immune system reacts to the milk protein and this triggers an allergic reaction. The reaction can present itself in different ways so it can be difficult to diagnose immediately.
Allergies are different to intolerances; allergies must always involve an immune reaction to a protein whereas an intolerance is a reaction to any food or food product and tend to be more common than allergies. Food intolerances are typically dose-dependant therefore the more of the food component that you are exposed to the worse the symptoms.
Food aversion is different to both allergy and intolerances. With food aversion there is no organic disease present, but a strong dislike to a food leads to the complete avoidance of it. Food aversions are psychological rather than causing clinical symptoms. Simply, allergy is defined as adverse health affects derived from an immune response, or, immunity gone wrong.
Allergy can be quite complex, and no single cause has been identified. The causes of food protein allergies have been attributed to a combination of factors. These causative factors include genetic predisposition, individual immune status, exposure and environmental factors.
Various immunological diseases have been found to be more common in industrialised countries than in the developing world. Studies in third world countries have found that there is an increase in immunological disorders as the country develops and grows ‘cleaner’ The use of antibiotics and antibacterial cleaning agents has also been associated with asthma and other allergic diseases.
Research does suggest the more hygienic we become the less exposure we have in early childhood to common allergens and therefore the more likely we are to develop allergy related symptoms.
Cows milk allergy is the most common food allergy in infants, it currently affects about 2-3% of infants but this has been found to be increasing, some research has suggested that up to 7% of infants may be affected by cows milk allergy. At the age of one year the allergy will still remain in about 45% of patients.
The majority of children will grow out of the allergy by the ages of 3-5 years, however a minority of patients may still have cows milk allergy throughout childhood.
Allergy typically leads to symptoms in one or more of the following three systems:
Cows milk allergy can result in a number of symptoms including skin rash/severe eczema, runny nose/eyes, constipation, diarrhoea, colic, acid reflux, wheezing, constant crying and general distress. The symptoms can either occur one at a time or in a combination. It is rare that all or even a few of these symptoms will be present at once; generally one will appear at a time. One of these symptoms on their own may not necessarily indicate cows milk allergy. It may only be after a significant period of time, when a number of symptoms have been displayed that cows milk allergy may be suspected. Because of the nature of the symptoms it can be difficult to diagnose cows milk protein allergy immediately.
Depending on what type of immune reaction occurs will depend on whether symptoms appear immediately or if they are late/delayed symptoms. The time between exposure to the allergic protein and the display of symptoms will provide an indication of the type of immune reaction that is occurring. Allergic reactions can be either IgE mediated or non-IgE mediated.
In cows milk protein allergy, when the cows milk protein is consumed, the immune system responds to the cows milk protein by releasing antibodies. In cows milk allergy these are called IgE antibodies and they are specific to cows milk protein. These IgE antibodies then bind with mast cells, these are now sensitised. When cows milk protein is recognised in the body for a second time, the cows milk protein binds to the mast cells and an immediated response or reaction occurs.
IgE mediated allergy therefore displays symptoms relatively quickly, and only a small dose is needed for the reaction to occur.
Non-IgE mediated allergy is slightly different. When cows milk protein is first ingested the immune system produces cells called T-cells. These T-cells however are unable to recognise the cows milk protein straightaway, the cows milk protein has to go through certain processing before it can be recognised. This processing can take anywhere up to 24-46 hours. Therefore non-IgE mediated allergy does not display symptoms immediately; instead symptoms have a delayed onset. Non-IgE allergy can also respond to smaller protein fragments than IgE, as well as whole proteins.
Cows milk allergy is often non-IgE mediated or a combination of IgE and non-IgE. Due to this, not all patients will be able to tolerate hydrolysed formulas in these cases amino acid based formulas may be favoured.
If cows milk allergy is suspected, obtaining a detailed medical history is important. It needs to be determined whether or not it is food related. The first onset of symptoms needs to be identified, timing of symptoms and types of symptoms should be identified in order to determine if it is rapid or delayed onset allergy and how severe the allergy is as this may influence the treatment chosen.
Accuracy of diagnosis is essential, if a problem food is left in the diet the symptoms will persist. If foods are removed from the diet unnecessarily, the there may be a risk of nutritional deficiency.
Once doctors have detailed information, they can decide which diagnostic tests may be required. If the symptoms are appearing quite quickly then IgE mediated allergy may be suspected (IgE simply relates to the type of immune response that is triggered), if the symptoms seem to be delayed in appearing then non-IgE mediated allergy may be suspected.
If IgE mediated allergy is suspected then a skin prick test can be carried out.
This test is usually carried out on the forearm or if necessary on the back. A drop of the allergic protein is placed on the skin and the skin is pricked through the trop. If a reaction occurs then the area can become red and swollen almost immediately. This should only by carried out by a doctor or specially trained health care professionals.
The advantage of such a test is that it is quick, inexpensive and the results can be seen quickly. It has been suggested that skin prick testing with food allergens is less reliable than with dust or pollens. It has been suggested now that skin prick testing is only effective in identifying about 50% of IgE mediated allergy.
This is a blood test which can give an indication of which allergens a person is allergic to. A blood sample is taken and the amount IgE antibody specific to a particular antigen is measured. If the levels of the specific IgE antibody are high then this would indicate that the person is allergic to the particular antigen it was for. For example if a person displayed high IgE antibodies specific for cows milk protein it would suggest that person had cows milk allergy.
If test are negative then it does not necessarily mean they do not have an allergy, just that the allergy they may have is not IgE mediated.
For confirmation of cows milk allergy then milk should be excluded from the diet, once symptoms have cleared then the patient may be challenged with cows milk under medical supervision.
The dietary treatment of cows milk protein allergy requires a strict milk protein free diet. Which poses a problem in some infants as standard infant formulas are based on casein or whey protein from cows milk. This can have implications in infants where milk is the only component of the diet up until 6 months of age i.e. sole source of nutrition during this time, and remains a major component of the diet throughout early childhood.
In order to prevent any nutritional deficiencies during infancy a suitable alternative needs offered to ensure that nutrient requirements are met.
This is important as a whole food group is now off limits, the nutrients and energy which infants would normally get from standard infant formulas needs to be replaced. Readily available alternatives such as soya or goat milk are unsuitable in infants. If an infant has cows milk allergy they may have allergy to other animal milk proteins therefore these cannot be used as an alternative.
The formulas developed specifically for cows milk protein allergy are medical foods. Foods for special medical purposes are subject to clinical trials to provide evidence of their effectiveness before they are able to be used in patients. Special medical formulas that are most effective will be hypoallergenic formulas. This means that the formulas will have been subject to clinical trials to prove their effectiveness and safety in severe cows milk allergy patients.
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