There are few living things on earth that can set our nerves more on edge than the aptly named bed bug (Cimex lectularius). Even if you've never had the displeasure of being their unwilling blood bank, you probably know someone who has. Since at least the 1990s, bed bugs have started to resist the pesticides we've long used against them and stormed back from near-extinction to once again become a common household pest.
Much as bed bug infestations are a nightmare to deal with, though, it's long been thought that they pose little physical danger to us. They don't seem to carry any diseases - scientists have exhaustively looked for pathogens they could theoretically host and infect us with, like HIV and Hepatitis B, but come up short. But a new study published Monday in PLOS-One suggests that we've been missing the whole picture. Bed bugs might not sicken us though their cooties, but they might be making us ill though the histamines they poop out into our homes.
Researchers at North Carolina State University examined homes in an apartment complex long plagued by bed bugs in Raleigh. They tested the indoor dust of homes visibly infested with bed bugs as well as those that weren't (and other control homes elsewhere), then came back for the same tests after a professional pest company had successfully eradicated the infestation through heat treatments and pesticide.
They were specifically looking for histamine, a compound that our bodies naturally produce to marshal the immune system into action. Recent research had shown that bed bugs also produce histamine - and shoot it in the air via their poop. As expected, bed bug-infested homes had more histamine, but the researchers were surprised by the scale: Some homes had levels up to 20 times higher than those seen in non-infested homes. More surprising, the levels of histamine stayed practically unchanged by the three-month mark, when the researchers stopped testing.
"We want to be careful. We don't want to sound the alarm, saying 'Everyone's in big trouble if you've had bed bugs.' But there is a potential - a massive potential for health consequences," lead author Zachary DeVries, an entomologist and post-doctoral research scholar at the university, told me.
While histamine is essential to keeping our immune system primed against foreign invaders, it's also one of the major instigators behind people's allergic symptoms, including asthma. DeVries notes doctors even regularly use histamine to provoke reactions in our skin and breathing when testing for possible allergies. But the implications of being exposed to chronic airborne histamine are unclear.
"It's opened a whole new avenue of research into bed bugs," DeVries said. "We've got to identify if there are health consequences from exposure to histamine in household dust, because this is a realm that no one's looked at — we've never had reason to look at histamine outside our bodies."
At this point, DeVries and his team venture an educated guess that the dangers of bed bug histamine might at least rival those caused by allergic reactions to cockroaches and dust mites. But unlike cockroaches, bed bugs love to stick close to us, meaning their effects could be even more potent. We also have a very intricate relationship with histamine, with receptors found in a variety of different cells and tissues. So aside from causing symptoms on its own, a constant dose of bed bug histamine might worsen our sensitivity to other allergic triggers, the study authors speculate.
And the durability of histamine post-eradication is just as troubling. "Of all the treatments, [heat treatment] was the most likely to degrade and get rid of the histamine. And because it didn't, I don't think any of the current treatments we have are going to eliminate it from the home." DeVries said. Bleaches and powerful vacuums might be able to get the job done, he added, but those are still just guesses for now.
Another lingering question is how exactly bed bugs make histamine in the first place. According to DeVries, there's some indication that it's partly a metabolic byproduct of the blood they suck out from us. But bed bugs also somehow produce histamine on their own. As for why, the best guess is that histamine acts as a signalling pheromone to other bed bugs, letting them know that a location is suitable for resting their weary six legs with their brethren.
There's some evidence showing bed bugs could make us sick in a different way, by transmitting the parasite that causes Chagas disease through their faeces. So far, however, that link hasn't been shown with humans, just lab animals. But even if the link were real, it would really only matter to people living in South and Central America, where Chagas is endemic.
The implications of DeVries and his team's research are much wider, since bed bugs are a global problem. But while the blood suckers are unswayed by nationality or income, DeVries notes that poorer neighbourhoods are hit hardest by them, since they're less able to devote the resources, which include chemical and non-chemical approaches, needed to control them. That also means their potential dangers, like those of so many environmental contaminants, will affect the poor and disadvantaged all the more.
"Until now, bed bugs have been - I hate to use the word - neglected when compared to other pests like German cockroaches. Because we don't consider them to be pests of medical importance, despite the fact that they cause plenty of problems," he said. "We think our research raises some serious questions about that assumption."
For now, DeVries and his colleagues are eager to get started on the hard work that lies ahead.
"The next step for this research is a massive, large scale epidemiological study, where we're taking a huge cohort of people and we're looking for differences between those with and without bed bugs, and with and without histamine levels," DeVries said. "We're going to need to see if there are increases in asthma, increases in hospital visits, any number of things that might be associated with bed bugs."