This observation is usually ascribed to meeting new allergens or reaching a personal threshold of exposure to common allergens like grass pollen. However, at least in childhood, there is good evidence that susceptibility depends more on whatever causes the Th2 abnormality than on any particular allergen exposures. Other possible explanations for the experience of individuals moving to a new geographic area have been that they leave behind protective parasites and move to more sanitary conditions. However, the protective effect of parasites can be doubted because there are populations, such as the children of the Maldive Islands, where parasites and increasing atopic asthma existed. Interestingly, in this case the increasing commonness of asthma followed some years after a British air base was established on the island. Increased sanitation also has been blamed for increased atopy, but the susceptibility of adults who move seems not to fit the hygiene hypothesis explanation.
An exception to the high incidence of atopic disease in children was seen in the Fore people of New Guinea, where atopic asthma first appeared in 7.3% of adults but only 0.6% of children. The earliest cases were in adults who had returned to the villages after developing asthma while in the European-influenced city. Still, the few affected children belonged to affected adults. There were two households with an affected child in which both parents had developed symptoms within a year of one another. The development of cases first among adults, with eventual spread mainly from affected parents to their offspring, suggests transmission by adult activities Viagra for sale Australia at the beginning of this community’s asthma experience. A later survey of the regional administrative town of Goroka, adjacent to the Fore area that originally had been affected, found that, except for asthma in the child of an affected family, the other 10 cases were in adults who had previously worked or lived in the Fore area. Dust mites were blamed and were found in higher numbers in the dwellings of asthmatic patients.