December 10th, 2018
Of the 4500 species of cockroach, approximately 30 are associated with human habitation, and 4 are known to be pests, including the oriental cockroach (Blatta orientalis), German cockroach (Blattella germanica), American cockroach (Periplaneta americana), and brown-banded cockroach (Supella longipalpa). Cockroaches can be found in any building that has a means of ingress, a source of water, food, adequate temperature, and shelter for their survival. Because cockroaches prefer small tight environments, they can be present without the occupant’s awareness until the infestation becomes extensive.
At least 10 allergens have been isolated from the German cockroach B germanica, many of which exhibit extensive cross-reactivity with other cockroach genera, such as Periplaneta, Blatta, and Supella species. A major allergen, Bla g 1, exhibits cross-reactivity with allergens from other insects, including fruit flies and mosquitoes. Produced in the midgut, Bla g 1 is found in cockroach frass (fecal material) and has allergenic activities, as well as the ability to upregulate expression of protease-activated receptors (PARs) and enhance TH2 cytokine production. Because the molecule is a polymer with various numbers of repetitions, its molecular weight is highly variable, and hence concentrations of Bla g 1 are expressed as units per gram of dust rather than micrograms per gram of dust. Another important allergen, Bla g 2, also cross-reacts with mosquito and fungal allergens. With a molecular weight of 36 kDa, Bla g 2 levels in environmental samples can be expressed in micrograms per gram of dust. The other cockroach allergens also have important properties that are described in this practice parameter. Bla g 7 (and Per a 7), which is tropomyosin, is considered to be a panallergen because it cross-reacts with numerous inhalant allergens from arthropods, such as dust mites, and foods, such as crustaceans and mollusks. In addition to allergens, cockroaches also are a source of chitin, which has proinflammatory activities and can induce cells to produce TH2 cytokines.
The health effects of cockroach allergen exposure include sensitization (production of specific IgE), sensitivity (symptoms when sensitized people are exposed), and morbidity in that respiratory diseases get worse with ongoing exposure. Prevention of these health effects requires that exposure be reduced to the lowest levels achievable. A cutoff of 0.04 μg/g dust for Bla g 2 has been proposed as a threshold below which sensitization is prevented, although levels greater than 0.08 μg/g are associated with development of disease and symptoms; however, the evidence for this is based on observational studies of patients exposed to levels greater than and less than these cutoffs. The problem with these types of studies is that the length of exposure causing an increase in risk is unknown, and they do not demonstrate that reduction of cockroach exposure reduces that risk. In addition, use of a specific cutoff does not provide the shape of the dose-response curve.
Patients should be asked whether they have seen cockroaches in their homes. Because it is possible for cockroaches and their allergens to be present without the occupant’s awareness, it also might help to ask patients at increased risk of cockroach exposure to place sticky traps to monitor for occult infestations and to measure Bla g 1 or Bla g 2 levels in a sample of dust obtained by patients from their vacuum cleaners. Levels of greater than 0.04 μg/g Bla g 2 indicate that cockroaches are present or at least that they have been present in the recent past. Such a finding should be used to trigger additional investigation into the cockroach status of the patient’s home.