Allergy in your practice
An estimated 10 to 15% of dogs have some form of allergy. The most common type of allergy in dogs is atopic dermatitis: a type I or direct-type hypersensitive reaction to inhalation allergens, such as pollen and mites.
A flea allergy is a mixed allergy, a combination of direct-type I and delayed-type IV hypersensitivity, caused by contact with flea saliva. Food allergy where certain food components function as an allergen; contact allergy where the reaction is caused by antigens that come into contact with the skin (carpeting, blankets, shampoo and the like).
The clinical signs of different allergies mentioned above can look similar. However, the treatment of each of these allergies is quite different; this is why the correct diagnosis is important before starting the treatment.
Atopy is one of the most common type of allergy in dogs. Between 3% and 15% of dogs suffer from an atopic condition1. Atopy is hereditary and it can lead to allergies against the pollen of some plants (e.g. grasses, weeds, trees), fungi or various dust and storage mites. Certain breeds appear to be at higher than average risk of developing atopy. Such breeds include the Lhasa Apso, Schnauzer, Alsatian, Boxer, Labrador, Golden Retriever, Poodle, West Highland White Terrier, Cairn Terrier, Jack Russell and Fox Terrier2.
The symptoms of an atopic individual usually manifest themselves before the age of 3 years. The initial symptoms are often mild and are tolerated by owners because they respond well to short-term symptomatic therapy or because they initially only appear at certain times of the year such as pollen allergies in the summer.
1 Hillier, et al. Vet. Immunol. Path. 81 (2001) 147-151
2 Sousa, et al. Vet Immunol. Path. 81 (2001) 153-157
Pruritus without visible skin disorders is the most significant symptom in dogs. This manifests itself in frequent licking or biting of the paws and the rubbing of the head along the floor or other objects. Despite the frequent itching visible clinical symptoms to the head or extremities are observed in 60-70% of the patients. Recurrent ear infections can also be caused by an atopy (in over 75% of the cases1).
1 Paterson S – A review of 200 cases of otitisexterna in the dog. Veterinary Dermatology 14 (2003) 237-267
Sneezing, a discolouration of the fur (from licking) and/or bilateral eye infection are also observed in some patients.
Depending on the duration and the severity of the disorder, the lesions can vary between erythema (redness) to hyperkeratosis (keratinization) and/or lichenification (thickening) of the skin. In addition, other parts of the skin may also show clinical symptoms.
Atopy is often accompanied by seborrrhoea sicca (dry form of excess sebaceous excudate) mixed with skin flakes and superficial pyoderma (skin inflammation) due to bacterial (Staphylococcus aureus or intermedius) or yeast (Mallazesia) infection. When patients are being treated for an atopic dermatitis, they should also be treated for secondary symptoms (e.g. seborrhoea and/or pyoderma).
It is extremely important in the diagnostics of atopic dermatitis to have a systematically prepared clinical history, as well as to adequately record all of the information obtained during the entire process of the examination.
The following aspects are important in the clinical history:
The anamnesis should also include questions regarding the sleeping place (floor covering, pillows, blankets etcetera, in connection with contact dermatitis), the food (food allergy), the presence of other animals (atopy based on animal epithelium) and the vegetation in and around the house. The effect of previously imposed treatments may also produce valuable information.
1 Sousa, et al. Vet Immunol. Path. 81 (2001) 153-157
Skin scrapings microscopic tests, fungal and bacterial cultures must be conducted in order to exclude any ecto-parasitic and infectious causes of the skin problems.
An elimination diet (hypo-allergenic diet, possibly followed by a provocation (challenge) diet, can provide information regarding the likeliness of a food allergy.
Important differential diagnostics for atopic dermatitis are: demodicosis, dermatophytosis, food allergy, idiopathic pododermatitis and trombiculosis (trombiculid mites). If these tests are negative excluded, the probable diagnosis is atopic dermatitis, the next step is to perform an allergy test.
After having diagnosed atopic dermatitis there are several treatment options to be considered.
The elimination of allergens aims to completely avoid contact with the allergens. This method is the fastest way to get results, but is often not an option; this is certainly the case if there is hypersensitivity for multiple antigens or in the case of hypersensitivity to grass, tree pollen or house dust mite which are very difficult if not impossible to avoid, for example.
Symptomatic medication relieves the allergic symptoms from which the patient is suffering fairly quickly, but only for a limited period of time. Unfortunately, most symptomatic drugs have disadvantages, particularly if they – as is the case in atopy – have to be administered for life.
Antihistamines are only slightly effective in dogs (10-15% effectiveness).
Treatment with corticosteroids and cyclosporine is highly suitable to suppress the allergy.
Symptomatic therapies can be useful for the following categories of patients:
Administering Essential fatty acids, such as omega 3 and omega 6 fatty acids, in the diet can lead to a positive result in approx. 10% of the cases.
Allergen specific immunotherapy tries to make the patient less sensitive or not sensitive at all for the substance to which it is allergic by injecting the animal with the allergens in increasingly larger doses and at increasingly longer intervals.
Patients that have symptoms for more than 3 months can be considered for Allergen-specific immunotherapy. The owner should be made aware that this is a lifelong treatment that does not cure the condition completely, but rather keeps it under control.
The results of allergen-specific immunotherapy: a significant improvement (>50%) of the clinical signs occurs in the course of time in 75% of the treated animals; it is assumed in this respect that any pyodermitis (skin infection) and/or seborrhea (dry form of excessive secretion of sebum mixed with flakes of the skin) is treated simultaneously1.
There is essentially no limit to the number of allergens that can be included in the allergen-specific immunotherapy.
The number of allergens also has no influence on the effectiveness of the allergen-specific immunotherapy.
1 Willemse. Tijdschr. Diergeneesk. Deel 129 (2004) 402-408