Histamine is a chemical compound that the human body naturally produces that can cause inflammation and alert the immune system to threats. Normal reactions to histamine production include allergic reactions with side effects such as a rash or difficulty breathing. A previous study showed links between excess histamine, particularly in patients with histamine intolerance, and health effects such as headaches, gastrointestinal problems, irregular heart rate and asthma.
Sudip Gaire, a post-doctoral fellow at the UK Institute of Entomology (http://entomology.ca.uky.edu/), and Zach DeVries, assistant professor of entomology, led the study, which looked at bed bugs’ histamine excretion across the country at different life stages of the beetles, different populations and different time periods, and the effects that blood feeding had on the pests’ histamine production. The UK-based team also worked with researchers from North Carolina State University on the project.
The Journal of Medical Entomology recently published the study showing that bed bugs can produce large amounts of histamine, with a single bed bug producing more than 50 micrograms of histamine in just one week. Researchers found that in a hypothetical infestation of 1,000 bed bugs, the bugs could produce up to 40 milligrams in a week. That adds up to more than 2 grams of histamine per year, not even counting natural population growth or the larger infestations that often occur in the real world.
“That’s a lot that you can actually see, and we don’t see that with any other containment,” DeVries said. “When we’re talking about pesticides, allergens, or anything else in our home that an invading organism produces, it’s always on a microscopic level, not something you can actually hold in your hands.”
Another important discovery was the role bed bug diets play in histamine production. The researchers compared histamine production across three different diets, including blood-fed, saline-fed, and starved bed bugs. The researchers found that blood-fed bed bugs produced “significantly higher” levels of histamine compared to the other groups.
“Blood is the main factor in histamine production, but we don’t know exactly how they produce the histamine,” Gaire said.
While bed bugs are a common problem in homes around the world, scientists don’t usually consider them a major risk to human health, aside from their bites, since they are known not to transmit pathogens. However, the problem of high-level histamine production poses a new potential risk from the pest. While scientists do not know the specific health effects of histamine produced outside of the human body, such as that produced by bed bugs, DeVries, Gaire and their fellow entomologists suspect that bed bugs’ high histamine secretion may have negative clinical implications. The effects of such narrow, often direct, exposure to histamine, which is commonly seen in bed bug infestations, are also unknown, DeVries said.
“It’s not just the fact that they produce histamine, but they produce it right next to where you generally spend most of your time in our homes, which is our beds or sleeping areas,” DeVries said.
Gaire said close exposure to histamine is not only a problem for humans, it can also affect agriculture. Poultry coops are a common site for bed bug infestations, with bed bugs living near chickens in infested facilities, Gaire said. In previous studies, researchers found that histamine had a negative effect on egg production, but Gaire said more research is needed to find out what specific effects the histamine produced by bed bugs has on egg production.
DeVries said the research also has implications for social justice.
“Anyone can get bed bugs, but only those who have the tools and resources can truly get rid of the problem. There is a significant portion of the population that either doesn’t have the money or resources to do it, and so they have to deal with bed bugs themselves,” DeVries said. “So we have disadvantaged communities that not only have to deal with bed bugs, but maybe the health consequences of it.”
DeVries and Gaire said that while their study answers important questions, scientists need to do more research before sounding the alarm. To answer some of the remaining questions, DeVries, Gaire and others at the UK Department of Entomology plan to continue research on this topic, addressing things such as histamine distribution, mechanisms of histamine production in bed bugs, the clinical relevance of histamine and mitigation strategies in examine households. DeVries received funding for the study through the 2019 National Institutes of Health Director’s Early Independence Award, which will fund similar future studies through 2024.
Research reported in this publication was supported by the Office of the Director of the National Institutes of Health under grant number DP5OD028155. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health.