Cockroaches: The Secret Indoor Air Poisoners
A recent study by researchers at North Carolina State University has uncovered a hidden threat to indoor air quality: cockroaches. The study reveals a strong correlation between the severity of cockroach infestations in homes and the presence of allergens and bacterial toxins known as endotoxins. By successfully reducing cockroach populations through pest control, the team found that allergen and endotoxin levels significantly decreased, indicating that eliminating infestations can significantly improve indoor environmental health by reducing harmful biological pollutants.
Endotoxins, which are fragments of bacterial cell walls released when bacteria die, are a concern due to their potential to provoke allergic responses in humans. Cockroaches, with their diverse gut microbiome, shed large quantities of endotoxins through their droppings. Interestingly, while humans and pets can also produce endotoxins, the study found that a significant portion of those detected in household dust originated from cockroach feces.
Coby Schal, the Blanton J. Whitmire Distinguished Professor of Entomology at NC State and co-corresponding author of the study, emphasizes the importance of endotoxins in human health. He notes that past surveys in U.S. homes have found higher endotoxin levels in homes with reported cockroach infestations, particularly in low-income homes compared to single-family homes.
The Study's Methodology
The research was conducted in multi-unit apartment complexes in Raleigh, North Carolina. Scientists measured the scale of cockroach infestations alongside concentrations of allergens and endotoxins in each home. Baseline readings were established by collecting both settled and airborne dust samples before any treatment began.
The findings were striking: infested homes contained high amounts of endotoxins, with female cockroaches producing roughly twice as much as males. Madhavi Kakumanu, an NC State research scholar in Schal's lab and co-corresponding author of the paper, explained that female cockroaches eat more than males, resulting in more endotoxins being shed from their fecal matter. Kitchens, with their abundant food sources, typically contained more endotoxins than bedrooms.
Testing Pest Control's Effectiveness
The infested apartments were divided into two categories: untreated homes and those that received professional extermination to remove cockroaches. A control group of residences with no infestation was also included. Dust and insect samples were collected again at three and six months.
Homes that remained untreated consistently showed high levels of both allergens and endotoxins. In contrast, most units that underwent extermination were cleared of cockroaches and showed substantial reductions in both allergens and endotoxins. Schal explained that small decreases in cockroaches don't lower allergen levels because the remaining live cockroaches deposit more allergens. However, endotoxins significantly decreased in homes where cockroaches were eliminated, confirming that the cockroach is the primary source of endotoxin in infested homes.
Kakumanu added that allergens and endotoxins can be airborne, further emphasizing the impact of cockroach infestations on indoor air quality.
Next Steps: Exploring Health Effects
Looking ahead, Schal plans to investigate the interactions between cockroach allergens and endotoxins in animal models of asthma, such as mice. He suggests that these interactions could potentially worsen asthma symptoms. The research team aims to determine if this is the case in mice, which will provide valuable insights into the health implications of cockroach infestations.
The study's findings were published in The Journal of Allergy and Clinical Immunology: Global, and the research was supported by several grants from the U.S. Department of Housing and Urban Development, the Alfred P. Sloan Foundation, and other organizations.
