Bed Bugs Medicine
Written by admin on July 5, 2010 – 4:23 PM -Once the scourge of seedy hotels and flophouses, bed bugs are scurrying into new quarters, and even luxury penthouses in New York City’s Upper East Side are within their reach. The city, like several other urban centers, has seen a resurgence in bed bug infestations, which has sparked renewed scientific interest in the bloodsucking pests. To gain a better understanding of the evolutionary adaptations that allow some arthropods such as bedbugs to feed on blood, Jos Ribeiro and coworkers at the National Institute of Allergy and Infectious Disease, Rocky Mountain Laboratories, and the University of Kentucky identified salivary proteins (the so-called sialome) of the common bed bug, Cimex lectularius. They report their results in a new JPR paper (DOI 10.1021/pr1000169).
In the 1940s and 50s, bed bugs were largely eradicated in the U.S. through widespread use of the insecticide DDT. But after the U.S. Environmental Protection Agency banned DDT in 1972, bed bugs began to make a slow but steady resurgence. In the mid-2000s, complaints about infestations in New York City, London, and other large cities skyrocketed, and the pests began showing up in unlikely places such as hospitals, theaters, expensive hotels, and affluent neighborhoods.
Emerging from household crevices to feed primarily at night, the flattened, reddish-brown insects leave behind itchy welts on their sleeping hosts. Because bed bugs are not known vectors for any human disease, they are considered more of a nuisance than a serious health threat. Nonetheless, the bites can cause intense itching and discomfort for those allergic to C. lectularius saliva.
The saliva of blood-feeding arthropods is a complex concoction of vasodilators, anti-clotting agents, and anesthetics that, when injected into the host during feeding, keep the blood flowing and compromise immune defenses. The human body possesses many overlapping mechanisms to prevent blood loss, collectively known as hemostasis. “Because there is such a redundant system in hemostasis, you cannot have a magic bullet to disarm it,” says Ribeiro. “You need to have a magic potion, and that’s what blood-sucking arthropods have in their saliva.”
The ability to feed on blood arose independently multiple times during evolution, and organisms evolved remarkably different strategies to do so. When parasites are forced to switch hosts or when hosts develop antibodies to salivary components, the blood-feeding organism must adapt to changing circumstances. As a result, even two species of mosquitoes that share a common ancestor can have unique sialomes.
Ribeiro and others have investigated the sialomes of mosquitoes, ticks, and fleas, but nobody had examined the composition of bed bug saliva. After characterizing the transcriptome of the salivary glands of C. lectularius, Ribeiro and colleagues analyzed the proteome of bed bug saliva by 1DE and LC/MS/MS. A total of 46 proteins were identified. Although some proteins were common to the sialomes of other blood-feeding arthropods, others were unique to C. lectularius, such as nitrophorin, a heme-containing protein that transports the vasodilator nitric oxide.
Surprisingly, acetylcholinesterase, an enzyme that degrades the neurotransmitter acetylcholine, was strongly expressed in bed bug saliva. “It’s a puzzle to me why acetylcholinesterase is there,” says Ribeiro. “During the evolution to blood feeding, it’s almost like you make a lottery of your genome and try to secrete every protein in saliva to see if it has a beneficial effect.” Ribeiro plans further experiments to investigate the functions of the more enigmatic proteins, including some novel sequences, in bed bug saliva.
In addition to providing insights into bed bug evolution, Ribeiro’s findings could have practical applications. “Many times patients go to the doctor with pustules or allergic reactions of unknown origin,” says Ribeiro. “They deny that they have bed bugs in their house, but often that’s the case. Our results could be used to create a simple test to detect if the person has antibodies against bed bug salivary proteins.”
Philip Koehler at the University of Florida notes that knowledge of the bed bug sialome could assist in developing allergy desensitization vaccines for people who suffer severe reactions to bed bug bites. “This is a significant piece of research that has been needed since the resurgence of bed bugs throughout the world,” he says. “It will serve as a resource for future studies on the effects and treatment of bed bug bites.”
Don’t let the bed bugs bite. C. lectularius ingests a blood meal from a human host. CDC/Harvard University, Dr. Gary Alpert; Dr. Harold Harlan; Richard Pollack. Photo Credit: Piotr Naskrecki
Not only that, “Blood-feeding arthropod saliva is a rich source of pharmacologically active molecules,” says Stephen Wikel at the University of Texas Medical Branch. “These sialomes are potentially very valuable sources for drug discovery.” In other words, someday the bed bug could prove itself more than just an itchy nuisance by providing leads for new drugs such as anticoagulants, vasodilators, and pain and itch inhibitors. Until then, sleep tight.
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