A Prospective Study of Allergy Development in 158 Children and 128 Adults With New Extensive Exposure to Furred Animals
Authors: Kewalramani Anu 
Published: October 2008

Millqvist E, Johansson A, Mansson T, Bende M. Clin Exp Allergy. 2007;37(6):948–953

PURPOSE OF THE STUDY. To explore allergy development associated with new extensive exposure to furred animals in adults and children.

STUDY POPULATION. This was a prospective study of 128 parents (age range: 22.4–49.7 years) and 158 children (age range: 1.5–17.9 years) recruited from 68 families through newspaper advertisements in Sweden. These individuals reported that either they would be buying a dog or cat or that at least 1 child in the household would be starting to ride a horse.

METHODS. Subjects were examined before the new exposure and once per year thereafter for 5 years (6 occasions). At each visit, individuals were scored on allergy symptoms. General allergic sensitization was analyzed by Phadiatop (Pharmacia, Uppsala, Sweden), a screening test for allergy to cat, horse, dog, house dust mite, and a few pollen and mold spores. Radioallergosorbent (RAST) testing with relevant allergens was performed to detect allergen-specific immunoglobulin E if screening was positive. Home environmental analyses of furred animal allergens were performed.

RESULTS. Thirty subjects from 5 families dropped out of the study. Of the remaining 256 individuals, 248 were exposed to 1 new animal, whereas 8 were exposed to 2 new animals. At the start of the study, 219 participants (86% [122 children and 97 adults]) were nonsensitized, and 37 (15% [15 children and 22 adults]) were sensitized to ≥1 allergen. Among the 219 nonsensitized subjects, only 1 adult developed sensitization to his new animal. No adults developed sensitization to other animals, and no children developed a sensitization to any animals (their own or others). Ten children and 6 adults became sensitized to other allergens. Of the 37 sensitized participants, 4 children and no adults (4 of 37 [11%]) developed sensitization to their new animals. Four children and 2 adults (6 of 37 [16%]) developed sensitization to another animal, and 1 child developed sensitization to a nonanimal allergen. The relative risk (RR) for developing a new sensitization in presensitized adults and children was 3.8, whereas the RR for developing new sensitization in presensitized children was 7.3. Because of the small sample size, a RR could not be calculated for developing new sensitization for one's own animal. Baseline symptom scores were higher for the presensitized group compared with the nonsensitized group, but the scores did not significantly change over the 5-year period, and no individual developed asthma. The levels of animal dander in house dust were significantly higher at the end of the study for dog and horse.

CONCLUSIONS. For patients over 1 year of age, exposure to a new furred animal did not seem to increase the rate of new allergic symptoms or sensitization over the next 5 years. This result was not affected by the baseline sensitization status of the subjects. On the basis of this study, there is no strong evidence to recommend avoidance of new animals to prevent new allergy development.

REVIEWER COMMENTS. Currently, it is recommended that allergic patients not obtain new pets because of the concern that they may develop new allergies to those pets. This study seems to indicate that pet exposure after 1 year of age does not confer an increased risk of developing new allergy to the pet in presensitized or nonsensitized individuals. The presensitized participants did have a higher risk of developing sensitization in general, but symptom scores stayed the same, indicating no new allergy development within 5 years. It may be interesting to follow this group for a longer period of time to determine if the results stay the same.