The protective effect of rural living against atopy in Mongolia.

BACKGROUND: Farm environment in childhood protects against atopy. We investigated in a population-based study in Mongolia the effects of rural living and migration from rural to urban areas on the risk of atopy. METHODS: The screening study data of 9453 subjects, aged 10-60 years, were used for taking the sample for the clinical study in which 869 subjects were examined. Asthma, allergic rhinoconjunctivitis and sensitization were clinically defined and their risk factors analysed by logistic regression. RESULTS: The risks of allergic rhinoconjunctivitis [adjusted odds ratio (OR) 0.43, 95% confidence interval (CI) 0.19-0.98] and allergic sensitization (OR 0.26, 95% CI 0.13-0.55) were the lowest in subjects living in a village from birth and intermediate in subjects who had relocated from a village to a town (OR for rhinoconjunctivitis 0.68, 95% CI 0.36-1.27, OR for sensitization 0.62, 95% CI 0.35-1.12) compared with subjects living in a town from birth. Simultaneous exposure to herd animals and dung heating decreased the risk of atopy. Keeping animals was a risk-factor for asthma only in Ulaanbaatar city. CONCLUSIONS: Continuing farm exposure after childhood may be important in reducing the risk of atopy.

Prevalence of asthma, allergic rhinoconjunctivitis and allergic sensitization in Mongolia.

BACKGROUND: Studies in countries, such as Mongolia, which are in transition from farming to industrial society permit evaluation of the impact of environmental change on atopic diseases. METHODS: In the screening study, questionnaire data were obtained from 9453 subjects aged 10-60 years. In the clinical study, a subsample of 869 subjects (participation rate 50.0%) was examined. A questionnaire-based interview, clinical examination, skin prick tests, spirometry and bronchodilation test or methacholine challenge test were used to define the clinical diagnoses. The prevalences of atopic diseases were evaluated at the population level using two-phase data and sampling weights. RESULTS: The prevalences of asthma, allergic rhinoconjunctivitis and allergic sensitization with 95% confidence intervals were 1.1% (0.3-2.0%), 9.3% (4.0-14.6%) and 13.6% (7.4-19.9%) in Mongolian villages, 2.4% (1.4-3.5%), 12.9% (8.2-17.7%) and 25.3% (17.1-33.6%) in rural towns and 2.1% (1.3-3.0%), 18.4% (13.3-23.4%) and 31.0% (24.5-37.5%) in Ulaanbaatar city, respectively. The prevalence of allergic rhinoconjunctivitis (P = 0.02) and allergic sensitization (P = 0.003) increased significantly with increasing urbanization. CONCLUSIONS: The prevalences of atopic diseases were low in rural Mongolia and increased with increasing urbanization suggesting that rural living environment protects against atopy.

Identification of Tyrophagus putrescentiae allergens and evaluation of cross-reactivity with Dermatophagoides pteronyssinus.

House dust mites are the most common cause of allergic sensitization in respiratory allergic patients in the world. Tyrophagus putrescentiae (TP), which was followed by Dermatophagoides farinae (DF) and Dermatophagoides pteronyssinus (DP), has been reported as the third most common house mite in Korea. We previously reported that many respiratory allergic patients had become concomitantly sensitized to DP, DF and TP. The aims of this study were to identify the allergic components of TP and to evaluate the cross-reactivity between TP and DP. The allergenic components of TP and DP extracts were determined with SDS-PAGE and IgE immunoblotting analysis. The cross-reactivity as evaluated by ELISA inhibition and inhibitory immunoblotting experiments. According the SDS-PAGE, the protein components of the two extracts were somewhat different, although a few components displayed identical molecular weights. The 18 kD protein of TP was the most prevalent allergen in the sera of patients sensitized to TP and DP. Both of the maximum inhibition percentages of optic densities of TP-specific IgE in ELISA with TP and DP extract were 100%, respectively and the 50% inhibitory dose (ID50) of TP extract and DP extract were 0.01 micrograms/ml and 0.02 micrograms/ml, respectively. Maximum inhibition of optic densities of DP-specific IgE in ELISA with TP and DP extracts were 29% and 100%, respectively and the ID50 of DP extract was 0.007 micrograms/ml. On inhibitory immunoblotting of DP specific IgE, 5 micrograms/ml of TP extract completely inhibited 16 kD without inhibiting the other allergic component. Whereas, on inhibitory immunoblotting of TP-specific IgE, 5 micrograms/ml of DP extract completely inhibited all the IgE binding components of TP. These results suggested that the major allergen of TP may be the 18 kD component and we also concluded that TP allergens have a strong cross-reactivity with DP extracts, but that DP allergens only have partial cross-reactivity with TP extracts.