Puzzlingly, the insects containing human DNA that the researchers sampled were caught far from U.S. homes. "If we sampled in households where people were bitten, this wouldn't be surprising at all," says Stephen Klotz, chief of the infectious diseases section at the University of Arizona in Tucson and one of the study's authors. "But in this situation it was quite a surprise," he says.
Sheba Meymandi, a professor of medicine at the University of California Los Angeles, and the director of the Center of Excellence for the Diagnosis and Treatment of Chagas Disease who was not involved in the study, had a different take on the results. "I'm not surprised at the 38 percent," she says. "The bugs feed on humans in addition to other mammals, so I'm not surprised by the human DNA."
The U.S. prevalence may increase in the future. Observations indicate that the bugs might be changing some of their behaviors, Klotz says. Dogs and raccoons infected with Chagas disease are becoming more common, and the area occupied by infected dogs seems to be expanding north. In one community in Arizona it appears that some of the bugs are taking up residence in households, a strange and worrying development for a species that normally establishes itself in wilderness areas removed from suburban centers. As we encroach more and more on the kissing bug's habitat and remove their usual blood meal sources, such as rodents, says Dorn, the insects—attracted by light—are moving into houses to tap new food sources.
Whereas a Chagas disease epidemic is not likely in North America, the insects do cause severe allergic reactions for some victims. There is also a chance that, as conditions become more favorable with milder winters, Mexican kissing bug species may migrate north, Dorn and Stevens point out, although currently this scenario is only speculation.
To avoid bites, Stevens says, people in infested areas should put up tight-fitting screens and get rid of woodpiles near their homes.
Around 300,000 people, mostly of immigrant background, already live with Chagas disease in the U.S., although awareness of the disease is still rudimentary among the public and physicians. Meymandi calls for an educational campaign among medical students and primary care practitioners. "The disease is here and can be highly lethal, though also highly preventable if diagnosed early," she says.