WORLD OF MICROBIOLOGY AND IMMUNOLOGY Lyme disease355•
LLyme diseaseYME DISEASE
Lyme disease is an infection transmitted by the bite of ticks
carrying the spiral-shaped bacterium Borrelia burgdorferi.
The disease was named for Lyme, Connecticut, the town
where it was first diagnosed in 1975, after a puzzling outbreak
of arthritis. The organism was named for its discoverer, Willy
Burgdorfer. The effects of this disease can be long-term and
disabling unless it is recognized and treated properly with
antibiotics.
Lyme disease is a vector-borne disease, which means it
is delivered from one host to another. In this case, a tick bear-
ing the B. burgdorferiorganism literally inserts it into a host’s
bloodstream when it bites the host to feed on its blood. It is
important to note that neither B. burgdorferinor Lyme disease
can be transmitted from one person to another.
In the United States, Lyme disease accounts for more
than 90% of all reported vector-borne illnesses. It is a signifi-
cant public healthproblem and continues to be diagnosed in
increasing numbers. More than 99,000 cases were reported
between 1982 and 1996. When the numbers for 1996 Lyme
disease cases reported were tallied, there were 16,455 new
cases, a record high following a drop in reported cases from
1994 (13,043 cases) to 1995 (11,700 cases). Controversy
clouds the true incidence of Lyme disease because no test is
definitively diagnostic for the disease, and the broad spectrum
of Lyme disease’s symptoms mimic those of so many other
diseases. Originally, public health specialists thought Lyme
disease was limited geographically in the United States to the
East Coast. Now it is known that it occurs in most states, with
the highest number of cases in the eastern third of the country.
The risk for acquiring Lyme disease varies, depending
on what stage in its life cycle a tick has reached. A tick passes
through three stages of development—larva, nymph, and
adult—each of which is dependent on a live host for food. In
the United States, B. burgdorferiis borne by ticks of several
species in the genus Ixodes,which usually feed on the white-
footed mouse and deer (and are often called deer ticks). In the
summer, the larval ticks hatch from eggs laid in the ground and
feed by attaching themselves to small animals and birds. At this
stage, they are not a problem for humans. It is the next stage,
the nymph, that causes most cases of Lyme disease. Nymphs
are very active from spring through early summer, at the height
of outdoor activity for most people. Because they are still quite
small (less than 2 mm), they are difficult to spot, giving them
ample opportunity to transmit B. burgdorferiwhile feeding.
Although far more adult ticks than nymphs carry B. burgdor-
feri, the adult ticks are much larger, more easily noticed, and
more likely to be removed before the 24 hours or more of con-
tinuous feeding needed to transmit B. burgdorferi.
Lyme disease is a collection of effects caused by B.
burgdorferi. Once the organism gains entry to the body
through a tick bite, it can move through the bloodstream
quickly. Only 12 hours after entering the bloodstream, B.
burgdorferican be found in cerebrospinal fluid (which means
it can affect the nervous system). Treating Lyme disease early
and thoroughly is important because B. burgdorferican hide
for long periods within the body in a clinically latent state.That ability explains why symptoms can recur in cycles and
can flare up after months or years, even over decades. It is
important to note, however, that not everyone exposed to B.
burgdorferidevelops the disease.
Lyme disease is usually described in terms of length of
infection (time since the person was bitten by a tick infected
with B. burgdorferi) and whether B. burgdorferiis localized or
disseminated (spread through the body by fluids and cells car-
rying B. burgdorferi). Furthermore, when and how symptoms
of Lyme disease appear can vary widely from patient to
patient. People who experience recurrent bouts of symptoms
over time are said to have chronic Lyme disease.
The most recognizable indicator of Lyme disease is a
rash around the site of the tick bite. Often, the tick exposure
has not been recognized. The eruption might be warm or itch.
The rash, erythema migrans (EM), generally develops within
3–30 days and usually begins as a round, red patch that
expands. Clearing may take place from the center out, leaving
a bull’s-eye effect; in some cases, the center gets redder
instead of clearing. The rash may look like a bruise on people
with dark skin. Of those who develop Lyme disease, about
50% notice the rash; about 50% notice flu-like symptoms,
including fatigue, headache, chills and fever, muscle and joint
pain, and lymph node swelling. However, a rash at the site can
also be an allergic reaction to the tick saliva rather than an
indicator of Lyme disease, particularly if the rash appears in
less than three days and disappears only days later.
Weeks, months, or even years after an untreated tick
bite, symptoms can appear in several forms, including fatigue,
neurological problems, such as pain (unexplained and not trig-
gered by an injury), Bell’s palsy (facial paralysis, usually one-
sided but may be on both sides), mimicking of the
inflammationof brain membranes known as meningitis(fever,
severe headache, stiff neck), and arthritis (short episodes of
pain and swelling in joints). Less common effects of Lyme
disease are heart abnormalities (such as irregular rhythm or
cardiac block) and eye abnormalities (such as swelling of the
cornea, tissue, or eye muscles and nerves).
A clear diagnosis of Lyme disease can be difficult, and
relies on information the patient provides and the doctor’s
clinical judgment, particularly through elimination of other
possible causes of the symptoms. Lyme disease may mimic
other conditions, including chronic fatigue syndrome (CFS),
multiple sclerosis (MS), and other diseases with many symp-
toms involving multiple body systems. Differential diagnosis
(distinguishing Lyme disease from other diseases) is based on
clinical evaluation with laboratory tests used for clarification,
when necessary. A two-test approach is common to confirm
the results. Because of the potential for misleading results
(false-positive and false-negative), laboratory tests alone can-
not establish the diagnosis.
Physicians generally know which disease-causing
organisms are common in their geographic area. The most
helpful piece of information is whether a tick bite or rash was
noticed and whether it happened locally or while traveling.
Doctors may not consider Lyme disease if it is rare locally, but
will take it into account if a patient mentions vacationing in an
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