Cat Allergies: Symptoms, Causes and Diagnosis

Sensitization to cats is one of the most frequent causes of allergic disease worldwide. The prevalence of sensitization to cat allergens ranges from 10% to 15% among the adult population, and studies have shown that this type of allergies can be linked to an increased risk of asthma. Thus adequate appreciation of this problem and early detection of sensitization are pivotal for further actions.

Causes of Cat Allergies

Even though several substances in cat extracts (such as saliva, urine, or pelt extracts) are considered to be allergenic, the most significant one from a clinical perspective is Fel d 1 (also known as Felis domesticus allergen I). It is a heterodimer with two chains – one containing 70 amino acids, and the other one 90 amino acids. Furthermore, it is the only cat antigen that satisfies the criteria required to be considered a “major allergen”.

This specific allergen is responsible for 90% of the cat-specific antibodies in individuals allergic to cats. Moreover, Fel d 1 is present in different tissues, such as salivary and sebaceous glands. Its production is regulated by hormones, and a single cat is able to produce between 3 and 7 micrograms of the allergen per day.

As all cats stem from the same species, it is not likely that different breeds exhibit certain breed-specific allergen molecules; nevertheless, there is a possibility of variations in relative concentrations of allergens between different breeds of animal (for example, between short hair and long hair breeds).

The level of Fel d 1 is five times higher when the cat is in the room, in comparison to the situation when the animal is absent, lending proof to causal relationship. The majority of the allergen is carried on the large airborne particles (i.e. those larger than 10 micrometers in diameter).

Symptoms

Signs and symptoms of cat allergies are caused by the inflammation of nasal passages; hence they can imitate clinical presentation of the common cold. They include sneezing, nasal congestion, runny nose, postnasal drip, itchy or watery eyes, cough, facial pain, and swollen skin under the eyes.

In addition, cat allergy can contribute to asthma and lead to difficulties in breathing, as well as occasional chest pains. In the clinical milieu, knowledge about the antibody levels targeted at Fel d 1 may be a useful indicator, as increased antibodies (namely IgE antibodies) in children are regarded as a potential risk factor for the development of allergic asthma.

Some individuals are prone to manifesting skin symptoms due to the exposure to cat allergens. Some of the signs are red patches on the skin (also known as hives), itching, and eczema. If a cat scratches or bites an allergic person, swelling of the affected region often occurs.

Diagnosing the Condition

Cat allergy is diagnosed based on the medical and environmental history, signs and symptoms, physical examination, as well as the test results. Allergy testing aims to show if allergic sensitization to the cat is present, with the help of a blood test or a skin test.

Furthermore, contemporary diagnostics of cat allergy via crude cat dander extracts is well established. Although such extracts comprise a myriad of allergenic and non-allergenic components (and thus may be troublesome to standardize), the majority of patients have IgE antibodies directed against Fel d 1.

Reviewed by Susha Cheriyedath, MSc