Endotoxins are bacterial cellular components that get released when bacteria die. As omnivores that will eat just about anything, cockroaches have a rich and diverse gut microbiome. Previous research has shown that cockroaches shed a lot of endotoxins through their fecal matter, although house pets – and humans – can also shed endotoxins. The researchers in this study found that a large amount of the endotoxins found in household dust was associated with cockroach feces.
“Endotoxins are important to human health, as inhalation of these components has been shown to provoke allergic responses,” said Coby Schal, the Blanton J. Whitmire Distinguished Professor of Entomology at NC State and co-corresponding author of a paper describing the research. “Past surveys in U.S. homes found endotoxin levels much higher in homes with self-reported evidence of cockroaches; that association is stronger in low-income homes than in single-family homes.”
The study, held in multi-unit apartment complexes in Raleigh, N.C., compared estimated cockroach infestation sizes as well as allergen and endotoxin levels in homes infested by cockroaches. These baseline levels were tabulated by capturing settled and airborne dust in homes.
The researchers found significant amounts of endotoxins in infested homes, with female cockroaches excreting about twice the amount that males excreted.
“Female cockroaches eat more than males, so more endotoxins are shed from their fecal matter,” said Madhavi Kakumanu, an NC State research scholar in Schal’s lab and co-corresponding author of the paper. She 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 receiving an extermination intervention to eliminate cockroaches. The researchers also included a control group of homes that had no cockroaches. Cockroach counts and floor and airborne dust samples were taken three months and six months into the study.
The results showed that infested homes without extermination had very large amounts of both endotoxins and allergens at all timepoints.
Meanwhile, in most cases, infested homes that received the extermination intervention were rid of both cockroaches and their allergens, and experienced significant declines in endotoxins.
“When you eliminate cockroaches, you eliminate their allergens. Small decreases in cockroaches don’t lower allergen levels because the remaining live cockroaches deposit more allergens,” Schal said. “Endotoxins significantly decreased in homes where cockroaches were eliminated. This paper shows that the cockroach is the most important depositor of endotoxin in infested homes.”
“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.
“There exists the implication that asthma can be worse due to interactions between allergens and endotoxins,” Schal said. “We want to see if that is the case in mice.”
The study appears in The Journal of Allergy and Clinical Immunology: Global. NC State’s Richard G. Santangelo, Zachary C. DeVries at the University of Kentucky and Jeffrey Siegel of the University of Toronto co-authored the paper.
Funding for the work came from the U.S. Department of Housing and Urban Development Healthy Homes program (NCHHU0053-19, NCHHU0081-24); the Alfred P. Sloan Foundation (2013-5-35 MBE); a Pilot Project awarded 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 U.S. Department of Agriculture National Institute of Food and Agriculture; and the Blanton J. Whitmire Endowment at North Carolina State University.
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Note to editors: The abstract of the paper follows.
“Indoor Allergens and Endotoxins in Relation to Cockroach Infestations in Low-Income Urban Homes”
Authors: Madhavi L. Kakumanu, Richard G. Santangelo and Coby Schal, North Carolina State University: Zachary C. DeVries, University of Kentucky; Jeffrey Siegel, University of Toronto
Published: Oct. 23, 2025 in The Journal of Allergy and Clinical Immunology: Global
DOI: 10.1016/j.jacig.2025.100571
Abstract:
Background: Cockroach allergens are well recognized as important risk factors in the development and prevalence of allergic rhinitis and asthma in children, especially in low-income urban households. The German cockroach gut hosts a diverse community of highly abundant microbes, including Gram-negative bacteria that shed large amounts of endotoxins in cockroach feces.
Objective: To delineate the causal relationship between the presence of cockroaches in homes and levels of household endotoxins.
Methods: In laboratory-assays, we measured the amount of endotoxin produced by cockroaches. In-home monitoring estimated the size of the cockroach population in each home and quantified cockroach allergen Bla g 2 and endotoxin levels in household dust and on HVAC filters. An environmental intervention was implemented in a subset of the infested homes to eliminate cockroaches. Bla g 2 and endotoxin levels were quantified for 6-months post intervention.
Results: Large amounts of endotoxin are excreted by female (2,900 EU/mg feces) and male (1,400 EU/mg) cockroaches. At baseline, household dust and HVAC filters in infested homes had significantly higher levels of allergen (Bla g 2) and endotoxin than in uninfested homes. Environmental intervention resulted in significant declines in cockroaches as well as allergen and endotoxin levels. In contrast, cockroach numbers and allergen and endotoxin concentrations remained high in infested-control homes.
Conclusion: Cockroaches are a significant source of both endotoxins and potent allergens, potentially resulting in co-exposure of asthmatic children to both.
END