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Monday, March 9, 2015

Allergy to furry animals: New insights, diagnostic approaches, and challenges

The prevalence of allergy to furry animals has been increasing, and allergy to cats, dogs, or both is considered a major risk factor for the development of asthma and rhinitis. A workshop on furry animals was convened to provide an up-to-date assessment of our understanding of (1) the exposure and immune response to the major mammalian allergens, (2) the relationship of these responses (particularly those to specific proteins or components) to symptoms, and (3) the relevance of these specific antibody responses to current or future investigation of patients presenting with allergic diseases. In this review by Konradsen et al, research results discussed at the workshop are presented, including the effect of concomitant exposures from other allergens or microorganisms, the significance of the community prevalence of furry animals, molecular-based allergy diagnostics, and a detailed discussion of cat and dog components (J Allergy Clin Immunol 2015; 135: 616-625).

Exposure to allergens from these furry animals is ubiquitous, and the clinician should evaluate all patients with allergic airway disease for sensitization to animal dander. In fact, allergic sensitization to several mammalian animals is prevalent, which might reflect co-sensitization or cross-reactivity. In some countries sensitization to furry animals is associated with more severe allergic disease, which poses extended diagnostic and therapeutic challenges. An important step forward in the diagnosis of allergy to furry animals has been made with the introduction of molecular-based allergy diagnostics, which offer new opportunities for improved characterization. For example, it has been shown that IgE responses to different cat components can be induced through different routes of exposure and are associated with either inhalant symptoms or  food allergy. Cat IgA and other cat proteins carrying alpha-gal are present as minor constituents of cat dander extracts but are better represented in epithelial extracts.  Interestingly, the cross-reactivity between cat and pork albumin is the most consistent.

Although there is clear evidence for the clinical importance of analyzing cat components in relation to both alpha-gal and pork-cat syndrome, the authors believe that future studies will clarify the clinical utility of molecular-based allergy diagnostics in the management of patients sensitized to furry animals. The workshop identified 6 areas for future research related to the specific allergens derived from furry animals that could contribute to our understanding and management of relevant allergic diseases.

Question for the authors:

Based on what is already known about cat allergy, it seems that once an allergy to cat is established, immunotherapy may significantly improve outcomes for patients that suffer from asthma and rhinitis. What is known about cat immunotherapy as it relates to asthma and rhinitis outcomes, regardless of other allergies the patient may have?

Fel d 1 is the most important allergen in cat dander and up to 95% of cat-allergic patients are sensitized to this protein. Subcutaneous immunotherapy (SIT) with cat dander extract has been shown to improve symptom/medication scores for both asthma and rhinoconjunctivitis. In addition, SIT has been shown to decrease skin, conjunctival and bronchial allergen sensitivity and to induce production of IgG and IgG4 antibodies towards Fel d 1. Accordingly, subcutaneous immunotherapy with cat dander extract is considered to be an effective treatment for both allergic asthma and rhinitis. [1-5]

1. Hedlin G, Graff-Lonnevig V, Heilborn H, et al. Immunotherapy with cat- and dog-dander extracts. V. Effects of 3 years of treatment. The Journal of allergy and clinical immunology 1991;87(5):955-64
2. Alvarez-Cuesta E, Cuesta-Herranz J, Puyana-Ruiz J, et al. Monoclonal antibody-standardized cat extract immunotherapy: risk-benefit effects from a double-blind placebo study. The Journal of allergy and clinical immunology 1994;93(3):556-66
3. Van Metre TE, Jr., Marsh DG, Adkinson NF, Jr., et al. Immunotherapy for cat asthma. The Journal of allergy and clinical immunology 1988;82(6):1055-68
4. Varney VA, Edwards J, Tabbah K, et al. Clinical efficacy of specific immunotherapy to cat dander: a double-blind placebo-controlled trial. Clinical and experimental allergy : journal of the British Society for Allergy and Clinical Immunology 1997;27(8):860-7

5. Hedlin G, Wille S, Browaldh L, et al. Immunotherapy in children with allergic asthma: effect on bronchial hyperreactivity and pharmacotherapy. The Journal of allergy and clinical immunology 1999;103(4):609-14

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