Lyme disease is caused by a bacteria (Borrelia
burgdorferi) which is transmitted by ticks. It may be cured
by early diagnosis and appropriate antibiotic treatment, but it
may persist in the human body for years, if not properly treated.
Lyme disease was named for Old Lyme, Connecticut, where the first
cases of Lyme disease were reported. The first case in California
was reported in 1978. It is currently the most commonly reported
tick-borne disease in California, as well as in the United
Is the tick that transmits Lyme disease in San Mateo County?
Yes, the most commonly encountered tick in San Mateo County
during winter and spring is the western
black-legged tick (Ixodes pacificus), a known vector
of Lyme disease. Lyme disease bacteria have been detected in
approximately 3% of western black-legged ticks in San Mateo
County. Infected ticks have been found along recreational trails
throughout the county.
How do people get Lyme disease?
People become infected when they are fed on by infected ticks.
Adult ticks are commonly encountered when people’s clothing
brushes over grass or bushes along the edges of hiking trails.
Nymphal ticks occur on fallen logs and leaf litter in wooded
areas. People can pick them up on their clothes or skin when
leaning against trees, sitting on logs, or playing in fallen
leaves. Nymphs are particularly dangerous because their small
size allows them to go undetected and they may feed on a person
for several days without being found.
If I am bitten by a tick, will I get Lyme disease?
Not necessarily. First, not every tick carries the infection.
Second, laboratory evidence indicates that the bacterium is
usually not transmitted to humans until the tick has fed for at
least 48 hours. The best defense against Lyme disease is to check
for ticks after hiking and to remove ticks as soon as possible
after they attach.
What are the symptoms and signs of Lyme disease?
An early sign of Lyme disease infection often includes a spreading
“bulls-eye” rash which may be accompanied by fever, aches,
and/or fatigue. Symptoms that occur during the later stages of
the disease can include complications of the heart and/or nervous
system as well as severe arthritis. Lyme disease presents itself
with a variety of symptoms and signs in different people. If
infected, you may experience one, both, or none of these
symptoms/stages and they could overlap.
The first recognizable sign is usually a slowly enlarging red
rash, known as erythema migrans (EM), about the size of a
half-dollar or larger. This is noticed in 60–80% of persons who
contract Lyme disease, although some patients never get a rash.
One or more rashes may appear on the body. The rash occurs 3–30
days (average 7–9 days) after the bite of an infected tick. The
rash expands over a period of days or weeks to form a large
circular lesion, often with a central clearing.
Flu-like symptoms may also occur in this stage. These symptoms
may persist, change, disappear, and reappear intermittently for
Often, a tick bite will be followed by a reaction within hours
creating a redness at the site of the bite which does not expand
and disappears within a couple of days. This is not the same as
the spreading EM rash characteristic of Lyme disease.
If Lyme disease goes untreated, patients may experience migratory
pain in joints, tendons, muscles, and bones often without joint
swelling or redness; however, months after onset, arthritis with
marked joint swelling is common. Some infected persons may
develop long-term complications weeks to months after the initial
symptoms. These complications may include disorders of the heart
or nervous system. Abnormalities of the heart include various
degrees of heart block (disturbance of the electrical conduction
system), facial paralysis (Bell’s palsy), and other nervous
system abnormalities may occur.
Is Lyme disease treatable?
Yes. Most cases of Lyme disease can be successfully treated with
antibiotics, but early treatment is important.
Some people may continue to experience symptoms even after they
have been treated for Lyme disease. This is called ‘post-treatment
Lyme disease syndrome’. Researchers believe it may be the
result of residual damage to the body caused during the
Are blood tests accurate in detecting Lyme disease?
The CDC recommends a
two-step process when testing blood for antibodies to the
bacteria that cause Lyme disease.
What does a tick look like?
In California, the western black-legged tick is the primary
carrier of Lyme disease. The adult female is reddish-brown with
black legs, about 1/8 of an inch long; males are smaller and
entirely brownish black. Ticks that have taken a blood meal
(called engorged) will appear much larger, gray in color, and can
reach the size of a pea. Ticks in their immature life stages can
be as small as the head of a pin or poppy seed.
Where is the western black-legged tick found?
This tick can be found on grasses and brush at the edges of
trails and along ecotones (where grass lands and brush meet).
Adult ticks feed on deer, rabbits, lizards, mice, and other
animals. Ticks do not fly, jump, or drop from trees. They climb
to the tips of vegetation, typically along animal trails or
paths, and wait for an animal or human host to brush against them
so they can attach themselves. These ticks have been found
throughout San Mateo County. The District conducts routine
surveys for tick densities and infection rate.
Is Lyme disease only a summertime threat?
NO! It can be contracted during any season of the year. The
different stages of this tick feed at different times of the
year, but are most abundant in winter and spring. The adult ticks
are usually seen November through April. The nymphal tick (an
immature stage) is usually present early spring to late summer,
peaking in mid to late May. Due to the small size of the nymphs,
the chances of having an unnoticed attached tick are increased.
Can pets get Lyme disease?
Yes. Lyme disease has been reported in dogs, rarely in cats,
horses, as well as a number of wild animals. Symptoms may include
fever, loss of appetite, arthritis, intermittent paralysis, and
lack of energy (no rash). The products used for fleas will also
control ticks. Check for ticks and brush your pet after exposure
to ticks. Have your pet examined by a veterinarian if you suspect
it has Lyme disease.
Where can I get more information about Lyme disease?
The California Department of Public Health (www.cdph.ca.gov)
has lots of information on Lyme disease and other tick-borne