Although domestic dogs (Canis familiaris) are among the most abundant of household pets, the prevalence of clinically relevant allergic diseases caused by dogs is lower than that for cats. Still, sensitivity to dog allergens can be a major cause of allergic symptoms (and even severe manifestations such as asthma) in susceptible individuals, and it is thought that up to 20% of the population in Western countries exhibits some kind of allergy to dogs.
Major Dog Allergens
Three major dog allergens have been described in the literature – Can f 1 (Canis familiaris allergen I), Can f 2 (Canis familiaris allergen II), and serum albumin (also known as Can f 3). They can be found in saliva, urine, serum, and dander of the dogs. Can f 1 is a major dog allergen that accounts for approximately 50% of patients allergic to dogs and it exhibits dimeric structure.
Can f 1 is predominantly associated with large dust particles (larger than 9 micrometers in diameter) due to their aerodynamic specificities, albeit small particles (smaller than 5 micrometers in diameter) also comprise almost 20% of the total allergen load in the air. There is also evidence of a dog allergen that can cross-react in 25% of Fel d 1 allergic patients (i.e. patients allergic to cats).
Dander from all dog breeds– including poodle – is allergenic with notable differences in the number and quantity of allergens. It has been shown that skin tests conducted in different patients can vary across various dog breeds, although one study has shown that such variations did not correlate with the patient’s own perception of specific breed allergy.
Hence even though different dog breeds have anecdotally been considered “hypoallergenic” by patients and dog breeders alike, breed-specific allergens have not been isolated. Several studies have probed for potential quantitative or qualitative differences in allergen production between various dog breeds with contradictory results for hair length and protein patterns.
Exposure to dog allergens and subsequent symptoms are dictated not only by the concentration of allergens in hair, but also by shedding and some other exposure-determining elements. Symptoms usually appear during the exposure to the animal or shortly after, but they can linger even when the dog is absent (as the dander remains on furniture or clothing).
Symptoms that point to an allergic reacting appear when the dog is close and include watery eyes, sneezing, runny nose, and congestion. In addition, skin allergy symptoms (such as itchy skin and hives) can also be a part of the clinical presentation. Furthermore, chronic exposure to dog allergens can lead to allergic sensitization and subsequently contribute to the development of bronchial hyper-reactivity and asthma in children.
Diagnosing Dog Allergies
Commercial skin prick test extracts are commonly employed for the diagnosis of dog allergies, and are usually prepared by extracting specific allergens from natural sources. However, extracts may differ apropos their allergen contents due to variability of extraction methods and starting material, which can in turn have a negative influence on the overall accuracy of the diagnostic method.
Recombinant Can f 1 and Can f 2 are immunologically functional and can be used for diagnostic purposes, as they can bind IgE found in dog-allergic patients by immunoblotting, and inhibit the binding of IgE antibodies to their innate counterparts in the extract of dog allergen.
It has to be emphasized that, even though Can f 1 levels in hair samples are related to breed, there is a tremendous variability (up to four orders of magnitude) between distinct dogs of the same breed. This may indicate variation between individual dogs, but might also be determined by less apparent factors such as grooming habits.
Reviewed by Susha Cheriyedath, MSc