Clinical Information

Overall, allergies to common pets, such as cats and dogs, may afflict up to 20% of the world's population, and the prevalence appears to be increasing over time. A large multicenter study survey in European adults reported an 8.8% sensitization rate to cat (feline, Felis catus [domesticus]) allergens. The assessment of allergy to cats is dependent upon the presence of compatible clinical symptoms in the context of exposure, with support from identification of potential canine specific IgE allergen antibodies either by skin testing or in vitro serology testing. In vitro testing has generally focused on assessing for the presence of IgE antibodies to total cat dander (which contains epithelial proteins) allergen extract.

There is a correlation between total cat IgE allergen antibodies and an increased likelihood of a clinical allergic response. Allergic symptoms can include rhinitis, asthma, and atopic dermatitis. Once an elevated antibody response to total cat dander IgE extract is established, assessment for the presence of IgE antibodies to the most common cat allergenic components will be performed, which can yield additional, potentially useful, information for clinical assessment of allergy and sensitization. During cat component allergen IgE antibody testing, the presence of IgE antibodies specific for potentially allergenic individual proteins, namely Fel d1, Fel d2, Fel d4, and Fel d7, are individually assessed. The determination of the relative amount of IgE antibody to specific components can aid in assessment of the potential strength and type of allergenic response. Co-sensitization to some components, such as Fel d 1 and Fel d 4 may be associated with asthma symptoms.(1)

Fel d 1 is the most clinically important, prevalent, and specific feline component allergen. Fel d 1 IgE antibodies have been observed in up to 95% of individuals with cat allergy. Measuring IgE antibodies to Fel d 1 may have prognostic value in evaluating cat allergy severity. Sixty to 90% of all IgE reactivity to cat dander is against the Fel d 1. Fel d 1 can be readily found in the fur and epidermis of a cat, may become airborne very easily, and can persist in the surrounding environment for several months. In 140 cat allergic patients, where all subjects were suffering from asthma and/or rhinoconjunctivitis, 95.6% of children and 94.4% of adults had IgE against Fel d 1. The IgE levels found in asthmatic children may be higher than the levels in children suffering from rhinoconjunctivitis. Consider avoidance to cat or other environmental exposure to Fel d 1 as well as allergen immunotherapy (AIT). All domestic cats produce Fel d 1. This allergen is also found in other feline species, such as cougar, tiger, and lion.

Sensitization to the serum albumin Fel d 2 cat allergen is associated with increased risks of asthma and allergic rhinitis. Serum albumins are a minor allergen in animal dander and may be most associated with rhinitis but can play a significant role as cross-reacting allergens. Pork/cat syndrome (allergy to cat dander and pork meat) can be mediated by cross-reactive antibodies against pork serum albumin and cat serum albumin (Fel d 2). Less than 20% of individuals with known cat allergy are reactive to Fel d 2. Individuals sensitized to Fel d 2 may show cross reactivity to canine Can f 3 albumin antigen and potentially to other albumins from human, pig, cattle, sheep, horse, mouse, and rat.

Fel d 4 and Fel d 7 are proteins that are members of the lipocalin protein family and are the cat allergens most associated with symptoms of asthma. In the case of Fel d 4, 62.96% (17 of 27) of individuals with cat allergy symptoms had detectable serum IgE antibody to the Fel d 4 antigen. Lipocalin proteins are found in many animal species, and Fel d 4 may cross react with Can d 6 and Equ c 1, while Fel d 7 may cross react with the major dog allergen Can f 1. Fel d 4 and Fel d 7 are produced in all cats.

Table. Specific Cat Epithelium Allergens