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Asymptomatic Lyme Disease: A Ticking Time Bomb?

Asymptomatic Lyme Disease: A Ticking Time Bomb?

Is there a meaningful percentage of patients who contract Lyme disease but have
none of the early symptoms-neither the rash nor the flu-like symptoms (eg, fever,
myalgia, headache, and stiff neck)-and in whom the disease only becomes clinically
evident in a later stage when it is much harder to treat?

For example, if I tell patients who often walk in the woods to watch for a rash
and/or flu-like symptoms (and to seek medical attention if any develop), will a small
percentage of these patients present with a later stage of Lyme disease because they
never had any of the typical early symptoms? Similarly, if I advise patients who have
been bitten by a tick that antibiotics are not needed unless a rash or flu-like symptoms
occur in the next 30 days, might some of these patients also present months
later with serious, late-stage Lyme disease?

—Larry Novik, MD
  Bridgeport, Conn

In 2000, 17,730 cases of Lyme disease were reported in
the United States. The majority of cases were clustered
in southern New England, the eastern part of the Middle
Atlantic states, and the upper Midwest. There is
also a small endemic focus along the northern Pacific
coast.1 The reported incidence of the disease is highest in
young children between the ages of 5 and 10 years and in
adults 50 to 59 years of age. Only a small percentage of
these patients recall the tick bite.

Determining the risk of transmission. Several factors
affect the risk of transmission of Borrelia burgdorferi
to man. The likelihood that a tick will be infected depends
on the stage of the tick and on the region of the country
in which it is found. In endemic areas, 10% to 20% of
nymphal ticks and between 30% and 40% of adult ticks are
infected.2 Additional studies have demonstrated that transmission
does not occur during the first 24 hours of attachment,
and that an infected tick must remain attached to its
host for at least 48 hours for transmission to occur.1 Keep
in mind that these studies involved B burgdorferi; other
tick-borne pathogens, such as Babesia and Ehrlichia, can
be transmitted earlier.

Magid and colleagues3 determined that the probability
of contracting Lyme disease from a tick bite in an endemic
area ranges between 0.012 and 0.05. In 1996, data
were analyzed from 3 trials that involved a total of 600 patients.
The rate of infection following a known tick bite
was 1.4%.4

Incidence of early symptoms. Erythema migrans-
the skin lesion that signals infection with B burgdorferi-is
reported in approximately 90% of patients who have Lyme
disease.5-7 When erythema migrans is present, the diagnosis
is established and the patient is treated with an appropriate
course of an antimicrobial agent.

Data from the Lyme vaccine trial by Steere and
coworkerss7 revealed a seroconversion rate of 0.028% in patients
with no symptoms, while seroconversion was documented
in 0.60% of those with a flu-like illness.

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