After a kissing bug finishes gorging itself on supper, it resembles “a tiny football,” says insect ecologist Lucia Orantes. “A tiny football full of blood.”
Split that turgid football in two (revealing innards that, according to Orantes, bear an uncomfortable resemblance to blood sausage) and you’ll find a treasure trove within. Mixed in with the kissing bug DNA is a bounty of foreign DNA—from the blood of the insects’ recent victims, perhaps… or from the dangerous Trypanosoma cruzi parasites that cause Chagas disease.
Today, in the journal PLOS Neglected Tropical Diseases, Orantes and her colleagues report that researchers can now figure out where kissing bugs live, which parasites they carry, and who or what they’re biting—crucial intel for preventing future Chagas outbreaks—all by reading the gigabyte of genetic information contained within a single inch-long insect.
About 70 million people across the Americas are at risk of contracting Chagas disease, which may affect up to one million U.S. residents. Though Chagas often begins with mild, fever-like symptoms, the disease can severely compromise organ function if left untreated. Those in poor, rural communities—the same populations with limited access to healthcare and medical resources—are often most susceptible to the disease.
But Chagas would be a virtual nonentity if not for the nighttime antics of the kissing bug, a bloodsucking insect native to the southern United States, Mexico, and Central and South America that derives its name from its penchant for nipping at faces. After taking a blood meal from a sleeping person, the kissing bug unabashedly defecates before fleeing the scene of the crime. These fresh droppings are often rife with T. cruzi—and if the feces are rubbed into a person’s eyes, mouth, or any break in the skin (including the insect’s recent bite mark), Chagas parasites can enter the human body.
Multiple factors—including the source of a kissing bug’s last blood meal, where the insect chooses to spend most of its time, and the strain of T. cruzi parasite the bug houses in its guts—can heavily influence the probability of contracting Chagas. It’s a challenge for scientists to keep track of so many variables at once. But all of them have one thing in common: the kissing bug itself.
To capitalize on this commonality, a team of researchers at the University of Vermont led by Orantes and Sara Helms Cahan set out to interrogate the bloodthirsty bugs. “Kissing bugs are living carriers of information of all the components that contribute to the spread of disease,” Helms Cahan explains.
The researchers’ strategy? Asking kissing bug guts. With every blood meal, these insects essentially upload a mouthful of DNA from the humans and wildlife they bite and the hidden parasites the animals’ bodies may harbor.
Orantes, Helms Cahan, and their colleagues extracted DNA from 61 kissing bugs collected from Central America, one of the regions where Chagas is particularly prevalent. They focused on two parts of kissing bug anatomy: the abdomen, including the contents of the insects’ internal organs, and the legs. From the two sets of DNA, the researchers learned that the insects they’d amassed represented four distinct geographical regions––each with its own little lineage of kissing bugs. But even more importantly, the legs, which the researchers presumed to be bona fide bug, served as a reference point for the abdominal DNA. By filtering out all the sequences common to both body parts, the researchers were able to distinguish which DNA belonged to the kissing bugs—and which DNA denoted something else entirely.
Once purged of kissing bug DNA, the abdominal sequences left behind told Orantes and her team that the bloodsucking insects had been awfully busy. They’d taken blood meals from humans, as expected—but also from chickens, dogs, and ducks. And two different strains of T. cruzi parasites plopped out in their poop.
Puzzling out where the bugs originate, or what sorts of animals they’re biting, means researchers may be able to pinpoint bug colonies for containment or destruction. By the time kissing bugs reach communities of people, it’s often too late to take action—but powerful genetic technology could quickly and effectively track the bugs’ movements backwards in time.
The researchers also found a great deal they didn’t initially expect. For instance, the sheer amount of information contained within the bugs was dizzying, Orantes notes: With only 20 or so milligrams of tissue—the weight of about 30 grains of sugar—the researchers had coaxed several million fragments of DNA out of each insect.
“It’s amazing how much DNA you can get,” Orantes says. “Very little tissue can yield a lot of information.”
A good portion of the DNA recovered from the bugs’ guts was actually bacterial—the insects’ own version of a gut microbiome. Depending on where the kissing bugs hailed from, different bacterial species populated their abdomen—a striking parallel to what’s seen in humans. Except, that is, when T. cruzi was around. Strangely, there seemed to be a relationship between these tiny tenants and Chagas parasites: All of the infected bugs’ gut microbiomes looked similar.
It’s still unclear whether there’s a common set of gut microbes that allow T. cruzi to set up shop, or if the presence of the parasites shapes the surrounding bacterial community; this is something that Helms Cahan hopes to uncover in future work. For now, this interaction adds yet another factor that may affect how Chagas disease is controlled in the future.
“[This method] is a great use of new technology,” says Ravi Durvasula, an infectious disease specialist at Loyola University Medical Center who was not involved in the new study. “It’s highly efficient and yields a lot of data quickly, and really gives you a comprehensive look at all of the things going on in the insect.”
However, Durvasula points out, this method alone won’t make or break the transmission of Chagas. For that, the team will need to combine its work with other techniques. Luckily, many researchers—including Durvasula—are studying ways to use kissing bugs’ own bodies against them. For instance, knowing which gut microbes are most compatible with T. cruzi could help scientists develop bacteria that produce antiparasitic compounds. If a kissing bug is tricked into swallowing them, the bacteria can become Trojan Horses, eradicating parasites from within while the insect itself remains unscathed. An outbreak could be curbed without having to shoot the messenger.
Given the complexities of Chagas transmission, scientists could use every bit of intel they can get. And, as the liplocking linchpins at the center of it all, kissing bugs may just be the most willing to spill their guts—if one just knows how to ask.
Correction: This article previously misstated the amount of genetic information contained within a single kissing bug. Each bug contains about 1 gigabyte of information. The total number of bugs in the study amassed about 37 gigabytes of information.