What is the role of pet fur aeroallergens in the etiology of allergic diseases?

Updated: Jul 07, 2019
  • Author: Bhumika Patel, MD; Chief Editor: Michael A Kaliner, MD  more...
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Furry pets include, for example, cats does, rodents, ferrets and rabbits. In the United States, 62% of households have one or more domestic pet. [15] The two most common animals are cat and dog; thus, these animals are major contributors to indoor allergen exposure. Cases of sensitization and allergy to rabbit, gerbil, hamster, ferret and other animals are also described in the literature. For this reason, it is imporant to elicit an adequate pet history. [97, 99]

Of the households with a cat, 17% of the individuals who live with them are sensitized based on a positive skin prick test to cat extract. However, only 5% of dog owners have a positive skin prick test to dog extract. [16]   In a study by Arbes et al, all sampled homes in the United States, even those that have never had an animal in the house, contain dog allergen and most contain cat allergen. [17] Furthermore, most homes contain levels that excede the proposed levels for both sensitization and exacerbation of asthma symptoms.

Felis domesticus (Fel d 1), the major cat allergen, is produced primarily in the sebaceous glands and is secreted onto the skin and fur. [18] This allergen also is present in the salivary glands; thus, cats add additional allergen to their fur when they clean themselves. The allergen is carried on small particles and remains airborne for long periods. Thus, decreased ventilation in the home leads to increased levels of cat allergen. Unlike dust mite allergen, cat allergen can be found even at high levels on the walls and other surfaces within the home. [19] The major dog allergens, Canis familiaris 1 (Can f 1) and Canis familiaris 2 (Can f 2), have physical properties similar to those of cat allergens. A truly hypoallergenic cat has not been produced, as published in the lay literature.

An article by Vredegoor et al demonstrates that Can f 1 levels are significantly higher in hair and coat samples in dog breeds referred to as hypoallergenic; that is, they are no less allergenic than any other dogs. Although some variations exist in other characteristics, such as whether a dog was bathed, no measured parameters significantly influenced the conclusions of the study. [20, 21] These data are confirmed by another study by Nicholas CE et al, which indicates that there is no evidence for differential shedding of allergens by dogs grouped as hypoallergenic. [22]

The amount of exposure to an animal allergen necessary to cause sensitization is controversial. The proposed threshold level for sensitization to cat allergen is 1 µg of Fel d 1 per gram of dust, and the level to cause symptoms in susceptible individuals with asthma is 8 µg of Fel d 1 per gram of dust. For dog allergen, the proposed levels for sensitization and exacerbation are greater than 2 and 10 µg/g of Can f 1 per gram, respectively. However, lower levels are reported to be associated with sensitization. Observational studies suggest that high exposure to cat and dog allergen early in life is associated with a decreased risk of pet allergy. [23, 24] However, an earlier study suggests that the opposite is true. [25]

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