I often see animals in my practice with allergy or hypersensitivity problems. But what are these allergies that bother our pets so much?
Allergies occur when the immune system recognizes a substance as harmful and overreacts against it. These substances are called allergens. Dogs and cats can develop allergies to various substances such as plants, dust, food, medicines and even vaccines, which, when inhaled, ingested or absorbed, stimulate the immune system to produce antibodies. Thus, when the animal comes into contact with this substance again, histamine and other inflammatory mediators are released, resulting in inflammation. The severity of the reaction will depend on the animal's degree of sensitization and the amount of antigens involved, and can range from mild redness or itching to an anaphylactic reaction that can lead to death.
Clinical signs can vary depending on the route of entry (contact, inhalation, ingestion, etc.). Inhalation of allergens, for example, can cause inflammation of the upper respiratory tract, trachea and bronchi, resulting in a runny nose, nasal discharge or asthma. Aerosols, in turn, can reach the eyes, causing conjunctivitis and tearing, while ingesting allergens can cause intestinal imbalances, triggering diarrhea and colic. In contact with the skin, certain allergens can trigger inflammatory processes and dermatitis.
Currently, there has been an increasing number of animals with various allergies, such as atopic dermatitis, food hypersensitivities, flea bite allergies, as well as allergic reactions to vaccines and medicines, which makes this subject vast and complex. Therefore, in this post, we're going to briefly cover two of them and in the future, we'll cover the others.
Let's start with Atopic Dermatitis...
It is a genetically predisposed chronic multifactorial syndrome characterized by skin inflammation and itching, triggered mainly by environmental allergens such as dust and mites, but also food allergens. Around 75% of dogs affected by the disease are between 6 months and 3 years old. The most affected areas are the face (mainly the eyes and mouth), paws, abdomen, inguinal and axillary regions, the tips of the ears, the external auricle, the genital and perianal regions. Excessive scratching or licking of certain areas can cause lesions and secondary contamination, aggravating the condition.
Among the most susceptible breeds are Retrievers, Setters, Terriers, Beagle, Cocker, Shar Pei, Boxer and Bulldog. Some studies have shown that atopic dermatitis is related to a defect in the endothelial cells, which produces flaws in the skin barrier, increasing water loss and susceptibility to irritation. It is also related to certain immune dysfunctions, such as an increase in the concentration of allergen-specific IgE. Depending on the allergen to which the animal is sensitive, atopic dermatitis can be seasonal.
In addition to endothelial cell defects and possible immune dysfunctions, an English study published in 2019 showed that the severity of itching in dogs with atopic dermatitis was directly linked to behavioral disorders such as hyperactivity, coprophagia, excitement and anxiety, among others, which could suggest a link between the severity of itching and psychological stress in dogs suffering from this problem.
Unfortunately, to date, atopic dermatitis has no cure, but it can be managed in several ways. The most common treatment is to avoid exposure to the allergen as much as possible. In traditional medicine, the use of corticosteroids and antipruritic drugs is widely known, but there are alternatives. The use of topical products, such as baths with appropriate shampoos, lotions and creams that promote the restructuring of the skin's lipid barrier, protecting against water loss, also helps to control clinical signs, reducing the animal's discomfort.
In addition, the use of nutraceuticals, such as omega 3, curcumin, PEA and quercetin, among others, can be beneficial. The homeopathic approach is also available, always remembering that homeopathy treats the patient as a whole and not the disease itself, which means that there is no specific homeopathic medicine for atopic dermatitis, but rather for the patient's entire symptomatology. In cases of problematic behavior, therapies that promote stress reduction can also be used, such as Bach Flowers, which help to reduce discomfort and improve the animal's quality of life.
What about food allergies?
These are also widely seen in clinical practice. First of all, let's differentiate between intolerance and food allergy. The former can be understood as a non-immune-mediated adverse reaction, while the latter is mediated by the immune system. Food allergy is known to be a potential cause of various dermatological and gastrointestinal problems in dogs, since around 2% of ingested proteins are absorbed through the intestine in the form of large peptides that can be recognized as foreign by the immune system and can trigger allergic reactions at both the intestinal and dermatological levels. Deficiency of the intestinal mucosal barrier and loss of oral tolerance are risk factors for developing the disease. The foods that most often cause allergies in dogs are chicken, eggs, corn, wheat, soy and milk.
There is no predilection for breed, sex or age, although some breeds are commonly affected. Dalmatians, West-Highland White Terrier, Collie, Shar Pei, Llasa Apso, Cocker Spaniel, Springer Spaniel, Miniature Schnauzer, Labrador Dachshund and Boxer are among the most commonly affected breeds. Although the age varies, research shows that around 33% of cases in dogs occur in animals less than one year old. Therefore, while food allergies can occur at any stage of life, they should always be considered when pruritus (itching) is observed in a young dog.
The main clinical sign is corticosteroid-unresponsive itching, and in 20-30% of cases, dogs and cats have concomitant allergic diseases, such as atopy or flea allergy dermatitis (FAD). Only 10% to 30% of dogs with food allergies show gastrointestinal clinical signs, such as diarrhea and vomiting.
The most widely used test for diagnosing food allergies is the exclusion diet, in which all potentially allergenic foods are removed and a diet of novel foods is provided for a period of 8 to 12 weeks. Alternatively, a diet with hydrolyzed proteins, which are more easily absorbed, can be used. It is important to emphasize that no other foods should be given during the test period, otherwise it will not be possible to conclude which foods are causing the allergy.
After the exclusion period, the diagnosis must be confirmed by individually including the foods previously provided. The result will be confirmed with the return of clinical signs between 1 and 14 days. Once a food allergy has been confirmed, the diet should only be based on foods that do not trigger the allergic process.
Alternatively, the diagnosis can also be made using commercial tests to assess antibodies through saliva. These tests measure IgA and IgM antibodies on the mucosal surface of the intestine to 24 foods commonly eaten by dogs and cats and, based on the results, it is possible to adjust the diet according to the animal's needs. What must be clear is that once the food to which the animal is allergic has been found, it must be excluded from the diet, otherwise the clinical signs will return. Here we can also make use of nutraceuticals, which are of great value in the treatment of food allergies and hypersensitivities, as well as homeopathic treatment, which even makes desensitization possible, improving the symptoms and quality of life of susceptible animals.
REFERENCES:
CHAND, N. Standardized Turmeric and Curcumin In: Gupta, C.R. et al. Nutraceuticals in Veterinary Medicine, Springer, pp.3-23, 2019.
GUEDON, N. & MUELLER, R. Atopic dermatitis in cats and dogs: a difficult disease for animals and owners. Clin Transl Allergy, (2018) 8:4.
HARVEY, N.D. et al. Behavioural Diferences in Dogs with Atopic Dermatitis Suggest Stress Could Be a Significant Problem Associated with Chronic Pruritus. Animals, 2019, 9, 813; doi:10.3390/ani9100813
TIZARD, I. Hipersensibilidade do tipo I. In: TIZARD, I. Imunologia Veterinária. Cap. 28, Elsevier, 9 ed. Rio de Janeiro, 2014.
VERLINDEN, A. et al. Food Allergy in Dogs and Cats: A Review. Critical Reviews in Food Science and Nutrition, 46:259–273 (2006).
https://www.merckvetmanual.com/dog-owners/skin-disorders-of-dogs/allergies-in-dogs
WHITE, S. Update on Food Allergy in the Dog and Cat. World Small Animal Veterinary Association World Congress Proceedings, United States, 2001.
Comments