As if tropical parasites weren't scary enough already, Brazilian researchers now report surprising evidence that the parasite that causes Chagas disease can sneak its own DNA into the genetic code of its hosts. In rabbits, the DNA is inherited and appears to sicken offspring. If confirmed, the finding represents a significant advance in understanding the deadly disease.
Chagas disease afflicts more than 20 million people in the Americas, and hundreds of thousands more are infected each year. The disease is difficult to prevent. Stealthy, blood-sucking triatomine bugs bite sleeping victims, contaminating the wound with feces full of Trypanosoma cruzi parasites. As people scratch the insect bite, they inadvertently rub infected feces into the wound. Months of harsh antibiotic treatment can kill the parasites, but some people suffer damage to the heart and intestinal and nervous systems long after the parasites are gone. Doctors don't know why and can't stop or slow the disease's progression.
Chagas researcher and physician Antonio Teixeira of the University of Brasilia in Brazil suspected that an autoimmune response causes the chronic disease. In the 23 July issue of Cell, Teixeira reports findings that back up the idea. Snippets of DNA from T. cruzi mitochondria are lodged in the DNA of previously infected rabbits with chronic Chagas disease but no current infection. Even scarier, all the rabbits' offspring had the T. cruzi DNA and all eventually developed the disease.
Teixeira also found that same parasite DNA in white blood cells from 13 humans with chronic Chagas. The disease may develop in cases where the mixed human and parasite DNA is capable of producing proteins, he says. The hybrid proteins would be recognized by the body as foreign and stimulate an immune system response. But the mixed DNA might not always be functional, Teixeira says, which might explain why only some people suffer the long-term symptoms.
"This report of integration of parasite and human DNA is unprecedented," says molecular parasitologist Dmitri Maslov of the University of California, Riverside. But, "novel phenomena need to be approached with very critical scrutiny," and he advises caution until other labs duplicate the work.