Eliminating cockroaches drastically reduces household allergens and endotoxins

Researchers at North Carolina State University have shown a relationship between the size of cockroach infestations and the levels of both allergens and endotoxins in those homes, with reducing the number of cockroach infestations through pest control causing significant reductions in allergen and endotoxin levels. The study’s findings suggest that eliminating cockroach infestations could help improve the health of the indoor environment by significantly reducing allergens and endotoxins.

Endotoxins are bacterial cell components that are released when bacteria die. As omnivores that eat almost anything, cockroaches have a rich and diverse gut microbiome. Previous research has shown that cockroaches excrete many endotoxins through their feces, although household pets—and humans—can also excrete endotoxins. The researchers in this study found that a large amount of the endotoxins found in house dust were associated with cockroach droppings.

“Endotoxins are important to human health, as inhalation of these components has been shown to cause allergic reactions,” said Coby Schal, Blanton J. Whitmire Distinguished Professor of Entomology at NC State and co-corresponding author of a paper describing the research. “Previous surveys of US homes have found endotoxin levels to be much higher in homes with self-reported evidence of cockroaches; this association is stronger in low-income homes than in single-family homes.”

The study, conducted in multi-unit apartment complexes in Raleigh, NC, compared estimated cockroach infestation rates as well as allergen and endotoxin levels in cockroach-infested homes. These baseline levels were recorded by capturing settled and airborne dust in homes.

The researchers found significant amounts of endotoxins in infested homes, with female cockroaches excreting about twice as much as males.

“Female cockroaches eat more than males, so more endotoxins are excreted in their feces,” said Madhavi Kakumanu, an NC State researcher in Schal’s lab and co-corresponding author of the paper. He added that more endotoxins were found in kitchens than in bedrooms, as more cockroaches live in kitchens where they find more food.

Infested homes were then divided into untreated homes and homes that received an extermination intervention to eliminate cockroaches. The researchers also included a control group from homes that did not have cockroaches. Cockroach counts and floor dust and airborne dust samples were taken three months and six months into the study.

The results showed that infested houses without extermination had very high amounts of both endotoxins and allergens at all time points.

Meanwhile, in most cases, the infested homes that received the extermination intervention were free of both cockroaches and their allergens and showed a significant reduction in endotoxins.

When you eliminate cockroaches, you eliminate their allergens. Small reductions in cockroaches do not reduce allergen levels because the remaining live cockroaches deposit more allergens. Endotoxins were significantly reduced in homes where cockroaches were eliminated. This paper shows that the cockroach is the most important depositor of endotoxin in contaminated homes.”

Coby Schal, the Blanton J. Whitmire Distinguished Professor of Entomology at NC State

“We also saw that allergens and endotoxins can be airborne,” Kakumanu said.

Schal added that next steps include further examining interactions between cockroach allergens and endotoxins in animal models of asthma, such as mice.

“It is suspected that asthma may be worse because of interactions between allergens and endotoxins,” Schal said. “We want to see if this happens in mice.”

The study appears in The Journal of Allergy and Clinical Immunology: Global. Richard G. Santangelo of NC State, Zachary C. DeVries at the University of Kentucky and Jeffrey Siegel of the University of Toronto co-authored the paper.

Funding for the project came from the Healthy Homes program of the US Department of Housing and Urban Development (NCHHU0053-19, NCHHU0081-24). the Alfred P. Sloan Foundation (2013-5-35 MBE); a pilot project commissioned by the Center for Human Health and the Environment under P30ES025128 from the National Institute of Environmental Health Sciences. the National Institute of Allergy and Infectious Diseases of the National Institutes of Health (award number 1R21AI187857-01); Research Capacity Fund (HATCH) (project NC02639) from the US Department of Agriculture’s National Institute of Food and Agriculture. and the Blanton J. Whitmire Endowment at North Carolina State University.