Pest allergens and asthma: the hidden health cost of untreated infestations

The cockroach allergen problem

German cockroaches (Blattella germanica) — the primary species in Metro Vancouver multi-unit residential buildings — produce allergens in their feces, shed exoskeletons (frass), saliva, and body parts. The major cockroach allergens (Bla g 1, Bla g 2, Bla g 4) are heat-stable proteins that persist in the environment long after cockroaches are eliminated. In homes with heavy infestation histories, allergen levels remain elevated for months to years unless active remediation (deep cleaning plus HEPA vacuuming) is performed after pest elimination. The epidemiological evidence is strong: the National Cooperative Inner-City Asthma Study (NCICAS) found that cockroach allergen sensitisation combined with high allergen exposure was associated with significantly higher asthma morbidity than either factor alone. A similar pattern has been documented in urban environments across North America and Europe. The BC Lung Association identifies cockroach allergen as one of the top modifiable indoor asthma triggers in urban BC housing. For Metro Vancouver's rental housing stock — particularly older buildings with connected wall voids where German cockroach populations move between units — this is not a theoretical concern. Cockroach allergen levels in infested Metro Vancouver multi-unit residential units routinely exceed the threshold for sensitization and trigger exposure.

Rodent allergens

The major mouse allergen, Mus m 1, is a urinary protein secreted in large quantities by male mice. It is airborne at room temperature — a mouse-infested room has detectable Mus m 1 in the air — and persists in settled dust for months. The rat urinary allergen Rat n 1 has similar properties. For households where mice have been active (attic, crawlspace, kitchen), Mus m 1 persists in insulation, flooring, and settled dust even after the mice are eliminated. Remediation — removing contaminated insulation, HEPA vacuuming, treating settled dust — is the correct post-elimination approach for asthmatic households. Rodent droppings also carry hantavirus (Sin Nombre virus in BC) and leptospirosis risk — separate from the allergen concern. Disturbing dried rodent droppings without respiratory protection (N95 minimum) during cleanup is the primary hantavirus exposure risk in BC. See the BC CDC guidance on rodent cleanup before disturbing any accumulation of dried droppings.

Dust mite amplification

Pest infestations — particularly rodent infestations — create conditions that amplify dust mite populations. Mice leave urine and feces in carpet, insulation, and wall voids. This organic material is consumed by mould, which in turn supports dust mite population growth. In Metro Vancouver's damp climate, a rodent-infested home with any accessible fabric or carpet can develop dust mite levels far above background within a single season. Dust mites (Dermatophagoides pteronyssinus and D. farinae) are among the most potent indoor allergens — their fecal particles and body fragments are primary asthma and rhinitis triggers. Mite populations drop dramatically with humidity control and HEPA vacuuming, but they require the organic substrate (which a rodent infestation provides) to be removed first.