NEW FRONT AGAINST LYME DISEASE
By Sean Henahan, Access Excellence
New information on the bacterium that causes
Lyme disease will provide a much needed boost to efforts to
design diagnostic tests and vaccines for the disease, report
researchers from the National Institute of Allergy and Infectious
A team of NIAID researchers conducted studies showing that
Borrelia burgdorferi, the Lyme disease bacterium, changes its
protein coat before being transmitted from ticks to humans and
other mammals. This adaptation likely evolved to ensure that the
bacteria can be transmitted to and thrive in two very different
hosts, ticks and mammals, the researchers note.
"This new finding underscores why investment in basic
research is so important. This specific adaptation of the Lyme
spirochete that has now been identified will assist efforts to
diagnosis and prevention of this illness," noted NIAID Director
Anthony S. Fauci, M.D.
Previous studies have shown that when a tick first becomes
infected, the Lyme spirochetes settle in its midgut and make a
surface protein called OspA. The current research reveals that
when an infected tick subsequently attaches to a warm-blooded
mammal and begins feasting on blood, two environmental
cues--something in the blood itself and an increase in
temperature --signal the spirochete to stop producing OspA and
make OspC surface protein instead.
"We believe that OspC is critical for the dissemination and
transmission of Lyme spirochetes during tick feeding," comments
lead investigator Tom G. Schwan, Ph.D., a microbiologist with
NIAID's Rocky Mountain Laboratories (RML) in Hamilton, Mont.
This suggests that OspC is the first abundant surface protein
the immune system encounters when spirochetes enter the body.
This could explain why people rarely make an antibody response to
OspA and why they develop antibodies to OspC early on. The lack
of OspA and the possible shutdown of OspC by spirochetes after
entry into humans may play a role in the persistent infection
characteristic of the disease. it may also help the spirochetes
evade the human immune
response, said Dr. Schwan.
This finding confirms the utility of using OspC assays while
doing confirmatory diagnostic
tests with the Western blot technique, a method that detects
antibodies to specific proteins. The study also has implications
for researchers that have been developing vaccines based on
OspA. Future vaccine efforts may include both OspA and OspC,
notes Edward McSweegan, Ph.D., Lyme disease program officer for
The current research also may help explain a previously
observed lag time between the time the tick attaches and the time
the disease is transmitted, usually after the second day. This
lag time in transmission during early tick feeding had been
attributed solely to the spirochete's location in the midgut.
But the new research suggests that the change to OspC begins
while the spirochete is still in the midgut and may be required
for the spirochete to migrate out of that location.
While the tick is feeding on the host's blood, the
spirochetes multiply, pass through the
midgut wall to the tick's bloodlike fluid, invade the salivary
glands, and are transmitted to the animal or human host in tick
"This entire phenomenon takes time, during which both ticks
and spirochetes first warm to approximately 37 degrees C when
ticks attach to the host's skin, " the researchers note.
The researchers demonstrated that the spirochetes produce
OspC at 32 degrees C to 37 degrees C, but not at 24 degrees C.
Merely raising the temperature, however, does not cause the
switch. This change also requires some as yet unidentified
signal or nutrient in blood.
Last year, some 13,000 people in the U.S. developed Lyme
disease, the CDC estimates. The spiral-shaped Borrelia
burgdorferi bacteria are passed on to people through the bites of
infected black-legged ticks. Lyme disease primarily affects
people living in the northeastern and upper north-central United
States, and along the northern Pacific Coast.
For more information, see the complete research article, in
the April 1, 1995 issue of the Proceedings of the National
Academy of Sciences by Dr. Schwan et al.
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Transmitted: 95-04-10 19:39:45 EDT
Related information at other Web sites
The U.S. Army's Report on Ticks and Diseases
The National Institute of Allergy and Infectious Diseases Web Server