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 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 percent 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.
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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.
SOURCE: http://bit.ly/1cPZLio Clinical
Infectious Diseases, online February 11, 2014.
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