Allergy to cats is the most common animal-origin allergy in human beings. Worldwide, one in five adult humans, as well as many children, are affected by allergy to cats. Cat allergy in human beings often results in deterioration or breakage of the human-animal bond, resulting in stress and suffering for both the cat and its owner(s), and also is a significant barrier to adoption and ownership of pet cats.
Common recommendations made by human healthcare practitioners for patients suffering from cat allergy are based on reducing or eliminating exposure to the allergen. Restriction of the cat to limited areas of the home, intensive and frequent cleaning or remodeling of the home, including removal of carpets and drapes, and other strategies designed to reduce exposure of susceptible humans to cat-origin allergens, are labor-intensive and inconvenient. Measures involving removal of the cat from the home, including limiting the cat to outdoor living, re-homing, shelter surrender, and euthanasia, are among the heartbreaking sequelae of significant human cat allergy.
Fel d1 is the major allergen produced by cats implicated in human cat allergy. All cats produce this allergen regardless of their breed, coat length, or other physical characteristics, so there is no such thing as a truly hypoallergenic cat. Salivary and sebaceous glands of the cat produce Fel d1, which is then spread all over the cat’s body by grooming and disseminated into the environment by cat hair and dander. The role of Fel d1 in the life of the cat is unknown, but it may act as a pheromone or chemical messenger. Saliva is where the highest concentrations of Fel d1 are found. The small size of the Fel d1 molecule (35-39 kDa) facilitates is prolonged presence in the air and makes it very easy to inhale.
A novel approach to human cat allergy has recently been discovered, and involves treatment of the cat through safe dietary modification: the addition of antiFel d1 IgY polyclonal chicken egg antibody to the food. In this study of 105 cats over a period of 12 weeks, these researchers hypothesized that cats fed this antibody in their diet would demonstrate a significant reduction in active Fel d1 production. Active Fel d1 (aFel d1) is Fel d1 that is capable to binding to IgE in cat-allergic humans, which in turn causes mast cell degranulation and clinical signs of allergic reaction, such as ocular inflammation, sneezing, coughing, wheezing, and various dermatologic manifestations. If aFel d1 produced by the cat is pre-bonded to antiFel d1 IgY when it is secreted into the cat’s saliva, then the binding sites on the aFel d1 molecule are not available to human IgE, and the human hypersensitivity reaction cannot be triggered.
IgY is an avian immunoglobulin equivalent to mammalian IgG. Egg-based IgY products have found to be safe and effective in both human and veterinary medicine, and safety studies in cats involving multiple levels of antiFel d1 IgY, have shown that the antiFel d1 IgY polyclonal egg antibody product can be safely used in cats. Chickens living with cats, such as free-ranging chickens on farms where cats also roam, naturally produce antiFel d1 antibodies.
Cats involved in the study were all healthy domestic shorthair cats ranging in age from 7 months to 17 years; there were 46 neutered males, 3 intact males, 54 spayed females, and 3 intact females. For the first four weeks, the cats were acclimated to the study environment. A two-week control period followed, and then a 10-week test period. All of the cats’ housing and bedding were washed thoroughly prior to the control period and test period to reduce environmental contamination. During the control period, the cats were fed a complete and balanced control diet designed to maintain body weight. During the test period, they received the same diet supplemented with antiFel d1 IgY. Hair was collected from each cat by brushing the cat twice weekly during the control period and once weekly during the 10-week test period. The hair was analyzed for aFel d1 reactivity using ELISA testing. Baseline aFel d1 contents of the subjects’ hair prior to feeding the test diet varied widely.
A steady decrease in levels of aFel d1 was observed in the hair samples beginning with the first week of the test period. From week 3 of the test period onward to the conclusion of the study aFel d1 levels declined relative to the baselines established during the control period, with an average decrease in aFel d1 of 47% (range, 33%-71%). Half of the cats had at least a 50% reduction in aFel d1 from baseline by the end of the study, and 86% experienced a decrease in aFel1 d1 by at least 30% from baseline by the end of the study. Those animals in the quartile with the highest baseline levels of aFel d1 demonstrated a significantly steeper decrease in aFel d1 over time compared to the cats in the other three quartiles.
A previous study demonstrated that reducing Fel d1 levels by just 6.8% of baseline in the home significantly reduced symptoms of nasal allergy in humans. Therefore, a reduction in salivary aFel d1, especially at the levels found in this study with the test diet, should significantly reduce aFel d1 in cat hair and in the environment, without the need to remove the cat from the home. [PJS]