Sensitization to cat without direct exposure to cats

Background: Allergy to pets, particularly cats, is one of the most important determinants of asthma and asthma-like symptoms in many parts of the world. Cat allergen is found in homes and public places without cats. Objective: The purpose of the study is to investigate the prevalence of sensitization to cat on the island of Tristan da Cunha where cats have been eliminated since 1974. Methods: A cross-sectional survey was conducted in 1993 on all residents on the island including allergy skin testing. Dust samples were collected from 20 homes on the island for measurement of house dust mite and cat allergens. Results: Positive skin test reaction to cat was present in 57 (20.1%) of all islanders and in six (12.8%) of those born in or after 1975, 1 year after cats had been exterminated. Five of these six residents were born within 5 years of extermination of cats; two of these had attended school outside the island. A low level of cat allergen (Fel d 1) was found in only one out of 20 homes even though house dust mite allergens (Der p 1 or Der f 1) were found in all homes. Conclusion: Sensitization to cat allergen occurs on the island of Tristan da Cunha where there is no direct exposure to cats. This is due either to the persistence of the allergen after the removal of the animal or to the allergen being brought in on visitors' clothing.