Cockroaches Rodents Studies examining thresholds of exposure relevant to disease

Public Health Significance of Urban Pests Allergic asthma 25 24 disposition of the individual, and this can explain differences in thresholds reported from different studies. A recent study in a birth cohort in Manchester, England, found that increasing exposure to dust mite allergens was associated with an increased risk of sen- sitization, but that effect was dampened if the children were also exposed to higher levels of endotoxin. However, the modifying effect of endotoxin was only observed in children with a specific genetic polymorphism in a gene for an endotoxin binding receptor Simpson et al., 2006. From this example, it is clear that defining allergen exposure thres- holds is complicated by other environmental exposures and by individual genetic sus- ceptibilities.

1.6.1.2. Cockroaches

To date, exposure thresholds for developing IgE to cockroach allergens have not been well established. However, two studies examined exposure to cockroach allergens and its relationship to the risks of developing asthma and asthma symptoms. In a prospective study of children with allergic parents who lived in the Greater Boston area urban and suburban, those exposed to between 0.05 unitg and 2 unitsg of cockroach allergen Bla g 1 or Bla g 2 were eight times more likely to develop asthma than those exposed to less than 0.05 unitg Litonjua et al., 2001. Those children exposed to 2 unitsg or more were even more likely to develop asthma. A study of inner-city asthmatics in the United States found that asthmatics who were sensitized to cockroach allergens and were exposed to more than 8 unitsg of allergen Bla g 1 had more severe asthma symptoms Rosenstreich et al., 1997.

1.6.1.3. Rodents

Population-based studies on exposure to mouse allergens, sensitization and asthma are limited to cross-sectional studies. One study of rat allergens found that sensitization was common among inner-city asthmatics 22; however, it was not associated with rat aller- gen measured in the house dust at the same time Perry et al., 2003. In the same cohort of asthmatic children, investigators found that those children exposed to greater than the median level of mouse allergen in the kitchen Mus m 1 1.6 µgg were twice as likely to be sensitized to mouse allergen Phipatanakul et al., 2000a. A study conducted in a suburban community where exposure to mouse allergen was substantially lower median Mus m 1: 0.02 µgg in the bedroom also found an increasing risk of sensitization with increasing exposure OR in quartile of exposure Matsui et al., 2004a. A larger effect was seen in an occupational study of exposure to airborne mouse allergens and sensiti- zation to them OR = 1.7 for each increase in quintile of exposure Matsui et al., 2004b. A recent study of the homes of inner-city asthmatics found that many homes had air- borne mouse allergen levels in the range of those found in occupational settings Matsui et al., 2005. Two caveats for application of these thresholds are that the studies do not take into account past exposure to allergens – that is, cross-sectional associations – and that individuals with allergen levels below these thresholds were also sensitized. Although specific monoclonal antibodies have been developed for detecting rat allergens in environmental samples Ferrari et al., 2004, establishing the levels of rat allergen asso- ciated with development of sensitization may be hindered by the cross-reactivity of human IgE antibodies to mouse and rat allergens Spitzauer, 1999; Renstrom et al., 2001.

1.7. Public health recommendations