NEW YORK - A small experiment to see whether uninfected ticks could "diagnose" a lingering Lyme infection in people produced modest results, researchers say.
DNA from the Lyme parasite, but not live parasites themselves, were transmitted to the ticks from just two people out of two dozen who had persistent Lyme symptoms despite treatment.
In animal studies, researchers have successfully used "xenodiagnosis," or diagnosis with another animal, to detect the signs of a persistent Lyme infection in the blood. The technique has also worked in people to detect another parasitic infection, Chagas disease.
But the new report, published in Clinical Infectious Diseases, describes the first attempt to use xenodiagnosis for Lyme disease.
"This is a very initial study, our main objective was to develop the technique in humans," lead author Dr. Adriana Marques of the National Institutes of Health in Bethesda, Maryland, told Reuters Health.
"It is very hard to find evidence of the bacteria itself, not just antibodies, in infected people once the skin rash is gone," she said. This tick method may make that process a bit easier, but only with further research, she said.
For most people who contract Lyme disease, a couple of weeks of antibiotics clear up the infection easily. About four weeks later, patients with no signs of the infecting bacteria in their blood get a clean bill of health.
But 10 to 20 per cent of people who get Lyme disease, which is transmitted through a bite from an infected tick, continue to report having pain, fatigue or aches even when it appears the infection is gone.
The symptoms can last for more than six months and are called Post-Treatment Lyme Disease Syndrome(PTLDS).
In animal tests, mice and monkeys have been infected with Lyme disease then treated until no Lyme bacteria were detectable in their blood. If at that point an uninfected tick bit the animal and Lyme bacteria turned up in the tick, it meant the animal was actually still carrying the infection.
For the new study, researchers tried out the second-bite system on people with PTLDS. Of the 36 participants, 26 had either persistent symptoms after Lyme disease treatment, or still had an itchy, red lesion at the site of the original bite, or had unusually high levels of antibodies against the infection even though treatment seemed to have been successful.
The other ten volunteers were healthy and had never had Lyme disease.
Researchers placed 25 to 30 uninfected ticks on the arm of each person to feed, under a special dressing, and collected the ticks a few days later.
The ticks were then incubated for up to two weeks to allow any potentially transmitted Lyme bacteria to develop, and afterwards researchers did a variety of molecular tests looking for any sings of the bacteria.
None of the ticks from healthy volunteers had evidence of the Lyme bacteria. Researchers successfully harvested usable ticks from 23 participants with a history of Lyme, and 21 had no ticks test positive for signs of bacteria.
For another two people the results were unclear. For one person with persistent symptoms after antibiotic treatment and one person with a persistent rash who had just started antibiotics, the ticks did test positive for fragments of DNA from the bacterium.
"The next step will be to see if the results correlate with persistent symptoms. We can't answer that question right now," Marques said. Right now it doesn't mean anything for the patients' health one way or the other that bacterial DNA was present.
The main objective of the study was to see if this type of xenodiagnosis is safe and appropriate for humans, and the answer seems to be yes since the major complaint from subjects was mild itching, said Justin D. Radolf of the University of Connecticut Health Center in Farmington.
"But the results don't change our understanding of PTLDS," said Radolf, who wrote an editorial accompanying the study.
"There is consensus that post-Lyme disease syndrome as defined in the paper does exist and that it occurs in a minority of people," said Linda K. Bockenstedt of Yale University School of Medicine in New Haven, Connecticut, who coauthored the editorial. "We do not know why this occurs, and the reasons may not be the same for everyone."
The subject is controversial because "chronic Lyme disease" can describe a number of conditions and a constellation of symptoms in people who may never actually have been infected with the bacteria.
"Many chronic Lyme disease patients have been assigned the diagnosis based on symptoms only (not objective signs), and through either misinterpretation of appropriately conducted Lyme (blood tests) or the use of nonvalidated tests," Bockenstedt told Reuters Health in an email.
That could mean that "chronic Lyme disease" is being used as a catchall when in fact another medical condition might underlie the symptoms.
It's hard to say how useful this technique actually is in humans for Lyme disease, Bockenstedt and Radolf write in the journal. The only way to diagnose a persistent infection is by finding live bacteria, which this test did not.