Cockroach sensitization and asthma

Public Health Significance of Urban Pests Allergic asthma 19 18 Peak exposures to some allergens – for example, to cat allergens for non-cat owners – may occur in locations outside of the home Custovic et al., 1996b. Due to the lack of large temporal variations in allergen concentrations within one home except in some intervention studies, apportioning the risk from exposure to allergens that occurred early versus late in life is difficult. When considering how accurately a dust sample reflects the allergen that deposits in a lung, the allergen under study must be considered. The particles that mite and cockroach antigens travel on are not easily made airborne; therefore, correlations between dust and undisturbed airborne sampling are poor Platts-Mills et al., 1997; Tovey et al., 1981. Although, cockroach allergens can be carried on particles with a wide range of sizes, depending on the amount of air disturbed de Blay et al., 1997; de Lucca et al., 1999, most of the Bla g 1 allergens tend to be associated with particles greater than 10 µm in aero- dynamic diameter. The recent development of intranasal samplers has detected Bla g 1 in residences with a low level of disturbed air de Lucca et al., 1999, but most research has shown that a considerable disturbance is necessary to measure airborne cockroach allergens Swanson, Agarwal Reed, 1985; de Blay et al., 1997. Exposure to dust mite allergens most likely occurs in close contact with the reservoirs; allergen is probably inha- led either when a person’s head is close to bedding or when children are playing on car- pets Custovic et al., 1999. Vacuum cleaning can also increase exposure de Blay et al., 1991, 1997. To assess exposure to dust mite and cockroach allergens, dust sampling is probably a bet- ter method than airborne sampling. Since dust mite allergens are not measurable without disturbance, the dose–response relationship between exposure and sensitization has been stronger when the exposure was assessed with a settled dust sample than with an air- borne sample Sporik et al., 1990; Platts-Mills et al., 1997. The fact that cockroach aller- gen is associated mainly with larger particles might in part explain why studies have found that relationships among exposure, sensitization and asthma are most strongly associated with exposure in bedrooms, where residents spend prolonged periods of time Sarpong et al., 1996; Rosenstreich et al., 1997; Gruchalla et al., 2005. Previous studies have found variability between the quantity of pet allergen in airborne and settled dust, due in large part to the ease with which the particles on which cat and dog allergens become airborne. Cat and dog allergens have the ability to travel on smal- ler particles and can be detected in air even three hours after disturbance Luczynska et al., 1990; de Blay et al., 1991; Custovic et al., 1996b, 1997. Therefore, previous correlations between airborne samples and dust samples were often poor. Recently, though, a good correlation between a major cat allergen Fel d 1, measured in the air and in the dust, was demonstrated when the airborne samples were collected over a 24-hour period Custis et al., 2003. It is likely that the longer sampling period better reflects an average exposure. Karlsson and colleagues 2002 collected settled dust in a Petri dish over a period of a week and found a good correlation with personal air sampling, and this may provide an alter- native to long-term airborne sampling. These findings could be extended to rodent aller- gens, which travel on particles with similar aerodynamic properties Ohman et al., 1994. 1.3. Cockroaches and asthma 1.3.1. Allergic sensitization to cockroach allergens In the 1960s and 1970s, researchers found that sensitivity to cockroaches was common among atopic populations Bernton Brown, 1967; Kang et al., 1979; Kang Chang, 1985. Specifically, sensitivity to crude extracts of cockroach allergens among allergic indi- viduals ranged from 20 in Boston to 53 in Chicago. Not all cockroach allergen extracts are the same, and this in part explains some of the variation in the prevalence of allergy to cockroaches in the earlier studies. German cockroach whole body extracts correlate well with faecal extracts r = 0.88, P 0.001 Musmand et al., 1995. Specific cockroach antigens that elicit an IgE response in a majority of cockroach-allergic individuals have been identified. Pollart and colleagues 1991b found that twice as many cockroach aller- gic asthmatics had IgE antibodies against Bla g 2 an allergen from German cockroa- ches, compared with those against Bla g 1 an allergen found in several different types of cockroaches. Furthermore, an estimated 60–70 of cockroach-sensitive individuals have IgE antibodies to the allergens Bla g 4 and Bla g 5 Arruda et al., 2001.

1.3.2. Cockroach sensitization and asthma

In many areas of the world, sensitization to cockroach allergens has been associated with asthma Platts-Mills et al., 1997; Eggleston, 2001. In inner cities in the United States, more asthmatic children with cockroaches reported or observed in their home were sensitized to cockroach allergens than those without exposure to cockroaches 75 versus 53, P0.01 Crain et al., 2002. A study of urban, suburban and rural atopic patients found a higher prevalence of cockroach sensitivity among patients with a pri- mary diagnosis of asthma 49.6 than among those with a primary diagnosis of aller- gic rhinitis 30.3 Garcia et al., 1994. Also in this study, no difference was observed between the prevalence of sensitivity to cockroach allergens in urban and rural envi- ronments. T his finding is in contrast to previous studies in Poland and the United States, which reported a high degree of sensitization to cockroach allergens among urban dwelling asthmatics Matsui et al., 2003; Stelmach et al., 2002b. Nonetheless, sensitivity to cockroach allergens appears to be important in the pathogenesis of asthma in areas with cockroaches.

1.3.3. Asthma and the exposure of sensitized individuals to cockroaches