Do Bedbugs Cause Disease?

The second time I freaked out about bedbugs, my landlord suggested I might be overreacting, just a tad. My husband and I had fought back an infestation just five months earlier; now, after finding a single bedbug on my pillow—sated because, I presumed, it’d bitten me—I was demanding that the building respond. “You know they don’t cause disease,” the landlord told me.

Common wisdom holds that bedbugs do not spread diseases to humans, just as my landlord said—or at least that the bugs are so widespread and bite humans so often that if they were carrying dangerous diseases, we’d know it. Most other bloodsucking insects that regularly bite humans, such as mosquitoes and ticks, are vectors for horrifying human pathogens. But recent research suggests that bedbugs might be capable of transmitting human diseases after all—if they’re not quietly doing so already.

Proving that bedbugs transmit human disease would mean demonstrating three key things: first, that those microorganisms can survive and thrive in the body of a bedbug. And recent studies have demonstrated that bedbugs naturally harbor plenty of viruses. The genetic material of several human pathogens—among them MRSA, Bartonella quintana, and hepatitis C—has also been found in bedbugs outside the laboratory.

The second criterion is that bedbugs are capable of transmitting the pathogen. In a laboratory study published in January, Jose Pietri, an associate entomology professor at Purdue University, and his colleagues showed that bedbugs were capable of both contracting and transmitting MRSA while feeding. (They used a membrane contaminated with MRSA to stand in for human skin.) Research from 2014 showed that bedbugs were capable of spreading to mice the pathogen that causes Chagas disease.

And third—the missing piece—transmission must occur in the wild, not just in the lab. “There could be some variables that we’re not understanding” that have prevented us from detecting bedbug disease transmission, Pietri told me. “Or it could simply be that it’s not so common.”

Pietri, like several scientists I spoke with, was drawn to studying bedbug disease-transmission potential because existing research didn’t seem conclusive to him. Scientists first confirmed that insects could act as disease vectors in the late 19th century, and in the decades after, researchers tried to discern whether bedbugs were dangerous too. They attempted to infect bedbugs with microbes; they crushed bedbugs and injected them under a monkey’s skin; they looked at whether a sexually transmitted infection might reproduce in bugs sampled from a West African brothel. None of the experiments directly linked bedbugs to human illness.

With no real-world evidence of human disease transmission and enough failures to make a connection in the lab, eventually many researchers concluded that bedbugs were harmless, at least in this one way. As a 2012 paper put it, “With over 200 million bed bugs biting (and biting multiple times), and without any evidence of any disease resulting, the indications are that the risk of contracting an infectious disease through the bite of a bed bug is almost nonexistent.”

To Pietri, who studies urban pests and vector-borne disease, all of this evidence is not only inconclusive, but out of date. Plenty of bedbugs’ close relatives transmit diseases, so why not bedbugs? “I don’t think it’s a solid scientific argument to say we haven’t seen this thing, so it doesn’t happen,” he told me. “It’s an incomplete picture.”

About 15 years ago, bedbugs were reinvading cities around the world, including New York, after disappearing for decades because of DDT and other pesticides. Amid the growing bedbug panic, Pietri wasn’t the only scientist who started wondering whether bedbugs’ potential as disease vectors had been understudied. The lab that demonstrated bedbugs’ potential as vectors of Chagas disease got the idea from a paragraph-long description of a study from 1912, says Michael Levy, an epidemiology professor at the University of Pennsylvania who led the 2014 study. The team confirmed the century-old results, and found that the bugs’ fecal matter could transmit the disease via mouse skin punctured by a needle or a bite. Technology that allows researchers to more easily identify any microorganism in an insect, such as genetic sequencing, has made it much easier to explore this question. Only in the past five years, Pietri said, have researchers been able to comprehensively survey the viruses and bacteria that a bedbug might carry.

None of the researchers I spoke with thinks that a bedbug is likely to be as harmful a vector as, say, a mosquito. For one, bedbugs don’t fly, are lousy walkers, and must hitch a ride to travel any significant distance. So they have relatively little potential for spreading disease far and wide. “The ecology of the bedbug makes it an unlikely transmitter of disease,” Coby Schal, an entomologist at North Carolina State University, told me. “But is it capable of doing that? Probably so.” In certain places, though—such as hospitals and shelters, where infection rates are high and beds turn over quickly—more significant transmission could be possible. Pietri thinks researchers may simply not be looking in the right places for bedbugs transmitting human disease. Bartonella, a bacterium commonly spread by fleas and body lice but also carried by bedbugs, is especially common among people experiencing homelessness, for instance, but very little research on bedbugs has been done in transient homeless populations. Levy told me he also worries that bedbugs could spread diseases such as Chagas among people sleeping in the same bed in a home.

The bedbug-research community is small, and some within it hold fast to the old wisdom: Bedbugs very likely do not spread disease. If you Google bedbugs, or go to the CDC website, or talk with your friendly local exterminator, you’ll find that’s the consensus. And if bedbugs don’t transmit disease, that could yield important insights, too. One hypothesis is that the bedbug immune system may have evolved to be especially robust because of a brutal copulation ritual that routinely exposes them to microbial invasion. Understanding the mechanism preventing transmission could, for example, help fight transmission by other insect vectors, such as mosquitoes, Pietri said.

If researchers do prove a link between bedbugs and human illness, it would add a new dimension to the already significant torment that the bugs unleash on their hosts. At the same time, the discovery might help marshal more funding toward understanding a pest that’s broadly viewed as a lesser public-health threat than those that clearly spread disease, Levy told me. (In his experience, he said, the sleep center at the National Institutes of Health was the only government agency interested in funding bedbug research.) Better knowledge of bedbugs could be especially important as their numbers and ability to evade treatment continue to grow. Into my own life, they’ve brought insomnia, paranoia, and the itchiest, longest-lasting bites I have ever experienced. Whether or not they spread disease, bedbugs certainly aren’t harmless.