and the underlying bronchial reactivity. For example, controlled studies of the effects of avoidance measures conducted in the homes of patients who were allergic to dust mites have shown significant improvement in both asthma and bronchial reactivity. The effects of avoidance measures on an individual's quality of life, however, remain to be determined.

Research Agenda Item: Conduct longitudinal studies to determine whether long-term allergen avoidance has a positive effect on quality of life.

MAMMALS AND BIRDS

Allergic reactions to mammals and birds are frequent and have been recognized as such for many years. An estimated 100 million domestic animals reside in the United States, the most common being cats and dogs (Knysak, 1989), and from one-third to one-half of homes in the United States have a domestic pet. Although a large number of individuals in the population experience allergic reactions to various animals, the exact prevalence of this common problem has not been determined. Skin test reactions to animal extracts are frequent, but the relationship between sensitization as demonstrated by a positive skin test and the frequency of clinical symptoms is unknown. Nonetheless, exposure to domestic pets, particularly cats and dogs, accounts for most of the allergic diseases caused by mammals.

In addition to exposures to animals kept as pets, individuals may be exposed to mammal and bird allergens in occupational settings. Bird allergens can cause not only allergic rhinitis and asthma but also hypersensitivity pneumonitis. Exposure to rodents among laboratory and animal care facility workers often results in sensitization and allergic symptoms. Farmers, veterinarians, animal health care workers, and zookeepers are also at risk. The prevalence of allergic diseases as a result of these occupational exposures is largely unknown.

Animals and birds are not only a source of allergens but may also serve as vectors, introducing outdoor allergens indoors. For example, pets may carry inhalant allergens such as pollens and fungal spores on their coats.

Cats

Cats are among the most common household pets in urban areas. A survey of 16,204 individuals ages 6 to 74 in the United States showed that 2.3 percent had positive skin prick tests to cat dander extracts (Gergen et al., 1987). Thus, extrapolating from these data, from 6 to 10 million Americans are potentially allergic to cats (Luczynska et al., 1990; Ohman and Sundin, 1987). Approximately one-third of the 2.3 percent of people with positive cat dander reactions have cats in their homes.



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