Ticks and Lyme Disease
Lyme Disease
by Evan Custer, M.D.
Published on this web site June 1998 with author's permission
Lyme disease (LD) is of concern to orienteers, because the disease is
transmitted by tick bites. Ticks are endemic in outdoors terrain, and
therefore we are at high risk for being bitten by a tick. The causative
agent is Borrelia burgdorferi, a type of spirochete-like bacterium, that
lives in the tick. Since Lyme disease can affect the skin, joints, heart,
central nervous system, and other organ systems, we should know as much
about its prevention, diagnosis, and treatment as possible to avoid these
serious sequellae.
Summary
Lyme disease is an uncommon complication that may result from being bitten
by the Western Black-legged tick, Ixodes pacificus. The causative agent is
Borrelia burgdorferi, a type of spirochete like bacterium. If the tick that
bites you is not the Ixodes type, then there is no risk of Lyme disease. If
the tick is of the Ixodes genus, first of all, don't panic. Only a small
percentage of Ixodes ticks are infected. Also, removal of the tick within
24 hours of attachment has shown to reduce or prevent transmission of Lyme
disease. If the tick is of the correct species and has been attached a long
time, your doctor may recommend that the tick be tested for the agent that
causes Lyme disease. If the tick test is negative, it is extremely unlikely
that you were exposed to Lyme disease. If the tick test is positive, this
does not necessarily mean that you have Lyme disease. Even an infected tick
does not always transmit the infection. If you develop an enlarging red
rash (which may occur near the tick bite or elsewhere), fever, malaise,
headache, muscle or joint pain, or other flu-like symptoms in the following
days to weeks, see your physician about further serological testing and/or
antibiotic treatment.
Prevalence and Incidence
The prevalence of infected ticks is highest in New England and the middle
Atlantic states, but also is present in northern California and Oregon. In
California, 172 cases of LD were reported in 1997, up 100% from the 86 cases
reported in 1996. There were 16,461 cases reported nation wide in 1996, so
California has a relatively few number of cases. However, the true
incidence is probably higher because of under reporting.
The good news is that the disease is only carried by a less common species
of tick, and only a small percentage of these ticks are infected with the
spirochete. There are three common ticks found in California. However, the
only species that has found to be a vector for LD is Ixodes pacificus, the
Western Black-legged tick. In a study performed by Robert Lane, an
entomologist at UC Berkeley, of the ticks found in Tilden Park, only 26%
were Ixodes, and 64% were Dermacentor occidentalis, the Pacific Coast tick,
and <1% were the Dermacentor variabilis, the American Dog tick.
In addition, only 0 to 6% of adult ticks were found to be carriers, and 0
to 14% of nymphs were infected. The highest rates were found in places like
Potter Valley in Mendocino County. Therefore, for every 1000 tick bites,
only 260 will be by the Ixodes genus, and of those, less than 3 will be
infected with Borrelia. Also, the tick must be attached to the human for at
least 48 hours before the infection is transmitted. If the tick is removed
within 24-48 hours and before it is engorged with blood, human infection
will be very rare.
Lifecycle
In the spring, tick eggs mature into larvae, which feed on mice. If the
mouse is infected, the larva may pick up the spirochete. After one year,
larvae develop into nymphs (1.0-1.2 mm in size, or about the size of a poppy
seed). Larvae live in leaf litter in damp, well-shaded forests, and don=92t
survive long on a sunny dry trail. Nymphs feed on the dusky-footed wood
rat, deer, and other mammals including domestic pets and humans. Nymphs are
most active in spring and summer. If the wood rat is a B. burgdorferi
carrier, then the nymph may pick up the spirochete during its blood meal (or
pick up more spirochetes if it was already infected as a larva). The
spirochetes multiply in the nymph midgut, but then may pass through the gut
wall into the lymph stream and lodge in its salivary glands. The spirochete
may then be transmitted to a human or other mammal via tick saliva. This
process is believed to take at least 48 hours (11% infected @ 48 hours, 25%
@ 72 hours, and 80% @ 96 hours). Most of the blood meal is not ingested
until the final day. Thus, the nymph remains small and hard to detect until
just before detachment. After another year, a nymph becomes an adult tick
(2-3 mm in size). Adult ticks also feed on mammals and humans. The adult
tick lays eggs and the cycle is repeated. Adult ticks live in brush and
grassland and low vegetation, and most are active from fall to early spring.
Adult ticks must feed for 24 hours to transmit Borrelia burgdorferi to their
victim.
Manifestations
Erythema migrans (EM) is the classic rash of early Lyme disease. It
develops in 60-80% of those who contract LD. It often occurs 7-10 days
after the tick bite, but may occur days to a few months later. EM has a red
annular (ring like) border that gradually expands with partial central
clearing (bull=92s eye rash). It may occur anywhere on the body. It is at
least 5 cm in diameter, with the median size being 15 cm. The rash usually
last 3-4 weeks if untreated, and one week if treated with antibiotics. Note
that most patients will have an inflammatory reaction at the site of the
tick bite cause by tick saliva. This rash does not expand, goes away in a
few days, and is not EM.
Other acute symptoms include flu-like symptoms, such as fever, malaise,
fatigue, headache, mild neck stiffness, enlarged lymph nodes, muscle and
joint aches. These symptoms usually develop within one month after the tick
bite, and often at the time when EM is present.
Late manifestations include arthritis, neurological and cardiac symptoms.
The arthritis is typically recurrent (about every 3 months), brief (lasting
weeks or months) episodes of pain, swelling and redness of one or a few
joints. Virtually any neurological symptom can be caused by LD, including
neuritis, meningitis, encephalitis, and facial palsy. Heart block can
occur, as well as inflammation of the heart muscle.
Serological Tests
There are a variety of serological tests that can be performed to see if
you have been exposed to Borrelia burgdorferi. However, there is no single
gold standard test that can give you early, reliable evidence of a recent
infection with the Lyme spirochete. There is variable sensitivity (being
able to pick up all of the people who are infected, i.e., it has a low rate
of false negative tests) and specificity (only picking up those who are
infected with the Lyme spirochete and not some other process, i.e., having a
low rate of false positive tests) to these tests. These tests should be
considered as an aid to clinical diagnosis, and if the clinical symptoms
strongly suggest Lyme disease, then a positive test will be confirmatory.
For most people, however, a serological test will not be necessary.
Antibiotic Treatment
Early Lyme disease should be treated with oral antibiotics. There are many
effective antibiotics, but treatment should be for 21 days. Because 99% of
tick bites will not result in LD, prophylactic antibiotics should not be
used. This is not only because of the cost, but because 80% of patients will
develop minor drug reactions, and 6% life threatening drug reactions.
However, if you develop the rash Erythema migrans, you should take
antibiotic treatment.
Prevention
Awareness and knowledge about LD are perhaps the most important factors in
its prevention. Wear a hat, long sleeved shirt, and long pants. Use duct
tape to seal your pants and gaiters to your shoes to prevent ticks from
crawling up your legs. Insect repellents such as DEET can be used on your
skin and permethrins on clothes. After an orienteering event, do a careful
tick search. Have a friend examine your back and scalp.
If you find a tick, remove it by grasping its head with tweezers and
applying gentle traction. Save the tick! Place it in a closed container
such as a 35mm film canister with a cotton ball moistened with water.
Protocol
If an adult tick has been on you less than 24 hours, (or a nymph for less
than 48 hours), and it is not engorged, you are at low risk for getting the
disease, and no serological test and no antibiotic treatment is required.
If the tick has been on you for longer than 24 (or 48 hours for a nymph)
and is engorged, identify the tick species. Most hospital labs can do
species identification. The Ixodes has black legs. If the tick is not
Ixodes, then there is no risk of disease, and no serological test and no
antibiotic treatment is necessary.
If the tick is Ixodes, have it tested to see whether it is infected with
Borrelia burgdorferi.
The Contra Costa Mosquito & Vector Control District, 155 Mason Circle,
Concord, CA 94520, 925-685-9301, will do the test on live ticks only. At
this time, there is no charge.
The Sonoma Public Health Laboratory, 3313 Chanate Road, Santa Rosa, CA
95404, 707-576-4711, will test live or dead ticks, but not dry. They charge
$20.
IgeneX, Inc., 797 San Antonio Road, Palo Alto, CA 94303, 800-832-3200.
They will test live or dead and dry ticks. The cost is $49.00.
BBI Clinical Laboratory, 75 North Mountain Road, New Britain, CT 06053,
800-225-1900 will test live or dead ticks for $39.00
If you develop Erythema migrans, you should be treated with antibiotics,
even if you don't remember being bitten by a tick. Sometimes the tick is so
small that it is not noticed.
If you have been in an endemic area within 30 days of developing clinical
symptoms of Lyme disease (flu like symptoms, arthritis, neurological
symptoms, etc.), you should see your doctor and probably have one or more of
the serological tests performed. If the clinical symptoms are suggestive of
LD, and the serological tests are positive, you should be treated with
antibiotics.
Lyme Vaccine
The FDA advisory panel has recommended that a vaccine Lymerix be approved
for human use. This vaccine is a genetically engineered spirochete surface
protein given so that the patient will make antibodies to the bacterium. It
will be administered as a series of three doses, two a month apart, and one
a year later. In an epidemic area, 13 of 10,936 subjects got Lyme disease
vs. 61 in the unvaccinated control group. The vaccine was 90% effective in
patients under 65 years of age who got all three doses. It is expected that
the FDA will approve this vaccine in the fall of 1998. It probably
initially will be recommended only for those with high risk exposure
(orienteers probably will qualify) and those who live in high risk endemic
areas.
Evan Custer
evancuster@sprintmail.com
Voice: 1-925-254-5628
Fax: 1-925-254-5961
18 Bobolink Road, Orinda, CA 94563-1706
Bay Area Orienteering Club
http://www.baoc.org
baoc@baoc.org or baoc@lists.stanford.edu
Bay Area Orienteering Club Information hot line: 1-408-255-8018
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