Bed bugs suck. Literally.
However, while they are indeed annoying and can keep people awake at night, they have not been regarded as a public-health concern because they have not been documented as transmitters of diseases like malaria, yellow fever, dengue, or others.
However, that status has just changed. A new study from Penn Medicine researchers in the Center for Clinical Epidemiology and Biostatistics demonstrated that bed bugs can transmit Trypanosoma cruzi, the parasite that causes Chagas disease, one of the most prevalent and deadly diseases in the Americas.
In a study published online this week in the American Journal of Tropical Medicine and Hygiene, senior author Michael Z. Levy, PhD, assistant professor in the Department of Biostatistics and Epidemiology at the University of Pennsylvania’s Perelman School of Medicine, and researchers at the Universidad Peruana Cayetano Heredia in Peru conducted a series of laboratory experiments that demonstrated bi-directional transmission of T. cruzi between mice and bed bugs.
In the first experiment run at the Zoonotic Disease Research Center in Arequipa, Peru, the researchers exposed 10 mice that were infected with the parasite to 20 uninfected bed bugs every three days for a month. Of about 2,000 bed bugs used in the experiment, the majority acquired T. cruzi after feeding on the infected mice. In a separate experiment to test transmission from bug to mouse, they found that 9 out of 12 (75 percent) uninfected mice acquired the parasite after living for 30 days with 20 infected bed bugs.
In a third experiment, investigators succeeded in infecting mice by placing the feces of infected bed bugs on the animal’s skin that had either been inflamed by bed bug bites, or scraped with a needle. Four out of 10 mice (40 percent) acquired the parasite by this manner; one out of five (20 percent) were infected when the skin was broken by the insect’s bites only.
“We’ve shown that the bed bug can acquire and transmit the parasite. Our next step is to determine whether they are, or will become, an important player in the epidemiology of Chagas disease,” Levy said.
T. cruzi is also especially at home in the guts of bed bugs.
“I’ve never seen so many parasites in an insect,” said Renzo Salazar, a biologist at the Universidad Peruana Cayetano Heredia and co-author on the study. “I expected a scenario with very low infection, but we found many parasites — they really replicate well in the gut of the bed bugs.”
These days, more people in the U.S. are being infected with T. cruzi than ever before. The Centers for Disease Control and Prevention estimates that the number of Chagas disease cases in the U.S. today could be as high as 300,000.
“If the parasite starts to spread through bed bugs, decades of progress on Chagas disease control in the Americas could be erased, and we would have no means at our disposal to repeat what had been accomplished,” Levy said.
Often referred to as a silent killer, Chagas disease is hard to diagnose in its early stages because the symptoms are mild or absent. The parasites are hidden mainly in the heart and digestive muscle, and over time can cause cardiac disorders and sometimes digestive or neurological problems. In later years, the infection can lead to sudden death or heart failure caused by progressive destruction of the heart muscle. Although there are some drugs to treat Chagas disease, they become less effective the longer a person is infected.
The long asymptomatic period of Chagas disease complicates surveillance for new outbreaks of transmission. In Arequipa, Peru, thousands became infected with the parasite before a case appeared in the hospital. The same could happen in cities in the United States if the parasite were to emerge in the bed bug populations, according to the authors.