Cockroaches secretly poison your indoor air

Endotoxins are parts of bacterial cell walls that are released when bacteria die. Because cockroaches consume a wide range of substances, they host a diverse gut microbiome. Previous studies have shown that these insects secrete large amounts of endotoxins through their droppings. Although humans and household pets can also produce endotoxins, researchers found that a significant portion of those detected in household dust originated from cockroach feces.

“Endotoxins are important for human health, as inhalation of these components has been shown to elicit allergic responses,” said Coby Schall, distinguished professor of entomology at UNC and co-author of the study. “Previous surveys in American homes have found that endotoxin levels are significantly higher in homes with subjective evidence of cockroach presence; this association is stronger in low-income homes than in single-family homes.”

How was the study conducted?

The research was conducted in multi-unit apartment complexes in Raleigh, North Carolina. Scientists measured the extent of the cockroach infestation along with the concentrations of allergens and endotoxins in each home. To determine baseline readings, settled and airborne dust samples were collected before any treatment began.

The results revealed that infested homes contain high amounts of endotoxins, with female cockroaches producing almost twice as much as males.

“Female cockroaches eat more than males, so more endotoxins are eliminated from their feces,” explained Madhavi Caccomanu, an NC State researcher in Schaal’s lab and co-author of the paper. She pointed out that kitchens usually contain more internal toxins than bedrooms, because they provide abundant food sources for cockroaches.

Pest control effectiveness test

The infested apartments were divided into two categories: untreated homes and those that received professional extermination to remove the cockroaches. The researchers also included a control group of residences in which there was no infection. Dust and insect samples were collected again after three and six months.

Homes that remained untreated consistently showed high levels of allergens and endotoxins throughout the study period. In contrast, most extermination units were cleared of cockroaches and showed significant reductions in both allergens and endotoxins.

“When you eliminate cockroaches, you eliminate their allergens,” Schall said. “A slight decrease in the number of cockroaches does not reduce allergen levels because the remaining live cockroaches deposit more allergens.” “Endotoxins decreased significantly in homes where cockroaches were eliminated. This paper shows that the cockroach is the most important repository of endotoxins in infested homes.”

“We have also seen that allergens and endotoxins can be airborne,” Cacomano added.

Next steps: Exploring health impacts

Schaal noted that future research will look at how cockroach allergens and endotoxins interact in animal models of asthma, such as mice.

“There is an implication that asthma can be made worse due to interactions between allergens and endotoxins,” he said. “We want to see if this is the case in mice.”

The research was published in Journal of Allergy and Clinical Immunology: International. Co-authors include Richard J. Santangelo of North Carolina State, Zachary C. DeVries of the University of Kentucky, and Jeffrey Siegel of the University of Toronto.

Funding was provided by the US Department of Housing and Urban Development’s Healthy Homes Program (NCHHU0053-19, NCHHU0081-24); The Alfred P. Sloan (35/5/2013 MBE); A pilot project from the Center for Human and Environmental Health under P30ES025128 from the National Institute of Environmental Health Sciences; National Institute of Allergy and Infectious Diseases of the National Institutes of Health (Award No. 1R21AI187857-01); the HATCH Research Capacity Fund (Project NC02639) of the USDA-National Institute of Food and Agriculture; and the Blanton J. Whitmire Foundation at North Carolina State University.