The effect of pet ownership on the risk of allergic sensitisation and bronchial asthma.

An increasing volume of evidence suggests that early contact of children with the allergens of furred pets (especially those produced by cats) may determine a lower risk of developing allergic sensitisation to these materials. A possible explanation of this data is that an early inhalation of high levels of the major cat allergen Fel d 1 induces the production of IgG and IgG4 antibodies with a "protective" effect. Other authors have shown that the prevalence of allergic sensitisation to cats, in adults, is reduced in those patients exposed to the lowest and highest levels of the allergens. On the contrary, the risk of developing sensitisation to cats is significantly higher when the patients were exposed to intermediate levels of Fel d 1. Moreover, epidemiological studies have demonstrated a relatively low prevalence of cat allergy (about 10%) in some countries where rates of cat ownership are high. This data confirms the role of indirect exposure to pet allergens in inducing allergic sensitisation. Clothes of pet owners have been indicated as the carriers for the dispersal of these allergens in pet-free environments. However, it is important to point out that exposure of highly sensitised patients to relevant amounts of pet allergens (such as in a pet shows/shops) may determine a dramatic exacerbation of nasal and/or bronchial symptoms.

Sensitization to horse allergens without apparent exposure to horse. Report of two cases.

It has been well established that occupational exposure to horses increases the risk of allergic sensitization to horse hair, on the contrary very few data have been published in individuals without direct contact with horses. We describe two cases of severe respiratory symptoms triggered by a single direct exposure in two patients with only 4-5 previous short contacts with horses during the entire their life, since they live in urban area of Naples. Cutaneous and serological diagnostic tests showed significant sensitization to horse dander other than some common inhalant allergens. Our report suggests that, in already (but unaware) horse-sensitized patients, the last direct contact with a horse has triggered severe respiratory symptoms. Passive carriage of horse allergen by the clothes of individuals in contact with horses/horse environments or a cross-reactivity between horse allergen (a lipocalin) and the major allergens (also lipocalins) of several furred animals are likely to explain our findings. Some other considerations can be derived by the clinical observation. First, it is likely that allergic sensitization to horse allergens could be more frequent than expected also in subjects without direct exposure to horse because of living in urban areas. Secondly, individuals suspected to be highly atopic or those already sensitized to some pet dander should be tested by SPTs/radio-allergo-sorbent test before the introduction of a pet indoors or, in the case of a big animal as the horse, a direct horse contact/entering into environments containing a horse.

Focus on cat allergen (Fel d 1): immunological and aerodynamic characteristics, modality of airway sensitization and avoidance strategies.

The increasing frequency of pet ownership (especially cats) in many industrialized countries has raised the level of exposure to the allergens produced by these animals. Moreover, it is likely that modern energy-saving systems and the wide use of upholstered furniture has resulted in closer contact between cats (and their allergens) and humans. Many different methods have been developed to quantify the main cat allergen (Fel d 1) in settled dust and in ambient air. The threshold levels of cat allergen inducing sensitization or triggering respiratory symptoms in sensitized patients have been calculated in settled dust, but airborne amounts of Fel d 1 probably represent a more reliable index of allergen exposure. Noticeably, the amount of Fel d 1 may be relatively high also in confined environments where cats have never been kept. It has been demonstrated that clothes of cat owners are the main source for dispersal of allergens in cat-free environments. This fact may be of relevance, because recent studies have shown that allergic sensitization to cats is more likely to develop in children exposed to moderate levels of this allergen than in children exposed to high amounts of Fel d 1. The ubiquity of cat allergen may justify the common observation that allergen avoidance is often insufficient to reduce the risk of developing allergic sensitization and/or symptom exacerbation in highly susceptible patients. Further efforts are needed to improve the efficacy of Fel d 1 avoidance strategies to try to reduce the risk of allergic sensitization to this allergen.