Allergies affecting dogs

Written by Amelie Krause, Veterinarian
allergies affecting dogs

If a dog regularly scratches itself, we initially think parasites are the cause. However, there are further reasons for itchiness, such as allergies. Even dogs are affected by allergies and the number of allergic illnesses is increasing.

The most significant allergies affecting dogs are flea saliva allergies, environmental allergies (atopy) and food allergies. All three types of allergies emerge with more or less the same symptoms, which is why it can often be difficult to make a diagnosis. As well, several allergies can affect a dog at the same time.

There are still no known breed predispositions for flea allergies, besides dogs of both sexes being equally affected. Flea allergy is mostly caused by the moderately host-specific cat flea (Ctenocephalides felis), although other flea species can also trigger the allergy. A flea allergy can emerge at any age, but not before the age of six months. It is triggered by protein substances in flea saliva. When it bites, the flea both sucks the dog's blood and injects it with flea saliva at the same time. This is either an acute Type I allergy, to which the body reacts within 30 minutes, or a delayed Type IV reaction with symptoms after a few hours or up to two days later. Dogs that sporadically have contact with fleas are mostly affected by allergies, since dogs in regular contact with fleas can develop tolerance.

Atopy (environmental allergy) affects around 15% of the canine population. In contrast to flea allergies, some breeds have a predisposition towards atopy, namely Terriers, Golden Retrievers, Labrador Retrievers, Dalmatians, German Shepherds, Boxers, English Bulldogs, English and Irish Setters and Shar Peis. This illness mostly emerges between one and three years in age, very rarely before the age of six months or with older dogs. One requirement for the outbreak of atopy is the dog's disposition to overreact to an allergen. Such dogs react to harmless environmental substances like pollen, grass, dust mites and mould with severe and inadequate antibody production, which causes a massive inflammatory secondary reaction with tissue damage. These symptoms are the the reaction to observing grasses, for instance, on a seasonal basis. The allergens reach the body via the respiratory tract or skin.

There are no breed or gender dispositions towards food allergies, which can start at any age. A genuine food allergy assumes that a dog can partake of a certain food for an extended period before an overreaction occurs. With healthy animals, there is a immunological tolerance of foodstuffs. However, if the protective function of the intestinal mucosa is reduced, the allergens can overcome the intestinal barrier and trigger an allergic reaction. According to current knowledge, allergens affecting dogs are proteins or protein compounds of a certain size contained in food. Every protein can therefore lead to an allergic reaction, the probability of which increases with the frequency of consumption. The most common triggers of allergies are beef, milk and dairy products, eggs, wheat and chicken. There are immediate and delayed reactions with food allergies, possibly even combinations of the two. Consequently, symptoms can emerge within 30 minutes, a few hours or even days and weeks after consuming the allergen.

Symptoms of allergens

Itching is the main symptom of all allergies. With flea allergies, the bottom half of the body, the lower back, croup, base of the tail, lower legs and stomach are mainly affected by itching. Dogs scratch and rub at these areas, where what is known as a hot spot often emerges: a self-inflicted, inflamed and oozing wound caused by severe itching. Bacteria and yeast fungi like to inhabit these areas too, which further intensifies the itching sensation. The distribution pattern of itching is very similar with atopy and food allergies, which makes it difficult to differentiate between the two. Itchiness affects the head area, paws, armpits, stomach, inner thigh area and ears. Inflammations emerge underneath the paws and between the toes, whilst the whole external auditory canal becomes inflamed when it comes to the ears. Bacteria and yeast fungi often settle on the damaged skin, triggering an infection (secondary) and causing additional itchiness. Regarding food allergies, there can also be gastrointestinal symptoms like vomiting, diarrhoea, flatulence, severe stomach pains and unformed faeces.

Diagnosis of allergies

Since the symptoms of each allergy are very similar, it can be challenging to make a diagnosis. Furthermore, a dog can suffer from several allergies at the same time. In addition, there are no reliable and easily performed tests available to differentiate between different allergies. Hence, an allergy is identified by an exclusion diagnosis. As well, a thorough anamnesis and a personal description can already give some pointers. These include breed, sex, age, age when the symptoms started, location of the itching or skin symptoms, the presence of similar symptoms with the dog's siblings or parents and the season in which the symptoms emerge.

Even if the symptoms don't indicate a flea allergy, this should be ruled out at the start.

The vet inspects the dog for fleas and flea faeces by using a flea comb. Finding one of the two confirms your suspicion. An intradermal test can also be carried out to make a diagnosis. This involves injecting flea allergens and control substances into the skin on the chest wall and checking for allergic reactions after 15-30 minutes, 4 to 6, 24 and 48 hours. Furthermore, there are blood tests to diagnose flea allergies, although they only inform you of Type I reactions. In addition, what is known as diagnostic treatment is still possible, whereby the dog and all animals living in the household are treated with suitable compounds to tackle fleas. A flea allergy is probable if the attempt at treatment takes effect.

In order to confirm or rule out a food allergy, only an elimination or exclusion diet are sensible options according to the recommendations of dermatologists. With one of these diets, the dog should be fed a source of protein and carbohydrates it has not received up until then for a period of at least eight weeks. Since the dog has not had any contact with these substances, it cannot react to them. During the diet, the dog should not receive anything else to eat. Treats and rewards must be made up of the ingredients of the diet. Dermatologists recommend a self-cooked diet. If it is not possible for the dog owner to prepare food themselves, hydrolysed protein diets are on offer with such small components that the body is unable to recognise them as allergens. It is also possible to provide monoprotein food. The symptoms should improve significantly during the diet. Once they have subsided, you should try to trigger a provocation from your dog by giving it the food it had before the diet. If the symptoms reoccur, this is proof of a food allergy.

Diagnosing an atopy is done clinically by ruling out other illnesses. If the symptoms, age, itching pattern and other factors that indicate an atopy coincide, as well as other causes of itching being carefully ruled out, atopy can be diagnosed. The vet can now carry out specific tests in order to identify the allergens triggering the atopy. An intradermal test that involves injecting allergens into the skin and monitoring reactions is suitable here. An experienced dermatologist should always carry out this test. Equally, an allergy blood test is possible, although this can show false positive reactions.

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Treatment of allergies

The best treatment for allergies is avoiding the allergen that triggers them, although this can be difficult depending on the allergy. Treating a flea allergy involves consistent flea control and prevention. Other animals living in the household should also be regularly treated for fleas so that the allergic dog has as little contact with them as possible. In addition, it is necessary to treat and thoroughly clean the surrounding area for allergy sufferers with existing flea infestations. Should itching be present, it can be treated with specific compounds in order to avoid secondary infections.

It's advantageous to identify the allergen that triggers food allergies (e.g. beef), since the dog can continue to be fed normally by avoiding the allergen. If the allergen cannot be identified or the dog reacts to several sources of protein, a hydrolysed protein diet is possible. Foods with insects as a protein source have also been on the market for some time, which is a new approach to diagnosing and treating sufferers of food allergies. Itching is much worse to treat with substances like glucocorticoids or antihistamines, which are less effective against food allergies than flea allergies or atopy. Secondary ailments like ear or skin infections must be treated additionally.

Treating atopy is a very particular challenge, since it is virtually impossible to avoid the allergen that triggers it. If the itching is limited to a few months of the year, it is possible to treat the dog with anti-pruritic medication during this period. If the dog is affected by itchiness over a longer period, hypo-sensitisation is recommended. This is an immunotherapy whereby the dog is given the allergens it reacts to in increasing concentrations. This stimulates the dog's immune system and develops tolerance to the allergens that trigger itching. Unfortunately this treatment doesn't always have the desired effect. Additional treatment with medication to reduce itching like cortisone, antihistamines, cyclosporin, essential fatty acids or oclacitinib may be possible. Since last year, there has been a new therapeutic agent on the market to tackle itching with atopy. This is a compound with monoclonal antibodies that absorb the substance responsible for causing itchiness and are metabolised like endogenous protein. This form of treatment has been successful up until now and is also very well tolerated.

Preventing allergies

It is difficult to prevent allergies because many factors are necessary for them to emerge. If a dog is already known to have allergies, more can follow. In order to avoid a flea allergy, you should make sure you consistently treat fleas and parasites. As well, it is advised to give a dog several different sources of protein. However, exotic proteins should be omitted, because these can be useful as the basis of a diet should an allergy emerge. Since atopy is a hereditary type of allergy, it is recommended not to breed with animals suffering from the allergy.

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