Professor Dave here, let’s talk about Lyme disease.
You may have heard about Lyme disease on the
news or on TV, and wondered what it was about.
Lyme disease is a bacterial infection acquired
by the bite of an infected tick, which classifies
Lyme disease as a vector-borne illness.
As we mentioned in an earlier tutorial, this
means that the infection is transmitted to
humans by a mosquito, tick, or flea.
The disease itself is a little complicated,
presenting itself slightly differently depending
on the person and the stage of disease.
Generally speaking, though, early Lyme disease
symptoms include headache, chills, fever,
fatigue, joint aches, and swollen lymph nodes.
In addition, about 70-80% of infected people
experience a bullseye-shaped skin rash called
erythema migrans.
If left untreated, Lyme disease can spread
to the heart, joints, and the nervous system,
causing symptoms like nerve pain, spinal cord
inflammation, arthritis, facial palsy, severe
headaches, and shooting pain in the tendons,
joints, muscles, and bones.
Because early symptoms are so similar to that
of the flu or other diseases, Lyme disease
can be difficult to diagnose, and isn’t
always reported to state health departments.
There’s still a lot that we don’t know
about Lyme disease, especially in the case
of long-term infections, but let’s get a
closer look and talk about what we do know.
Lyme disease is an infection caused by a corkscrew-shaped
bacterium, also called a spirochete, named
Borrelia burgdorferi.
There are at least 10 related species of Borrelia
that can cause Lyme disease in animals and humans.
Lyme disease was first studied in 1977, when
a cluster of children with arthritis were
found in Lyme, Connecticut.
In 1982, Willy Burgdorfer linked the strange
disease to the spirochete, and the medical
community honored his discovery by naming
it Borrelia burgdorferi.
These bacteria are gram-negative and have
multiple flagella that give them their characteristic
twisting motility.
Genetically speaking, these bacteria have
a linear chromosome, which is quite unusual
in the bacterial world, in addition to a large
number of smaller DNA molecules, or plasmids.
Interestingly, these bacteria don’t have
the usual virulence factors, which are the
factors that many bacterial pathogens typically
have to cause damage, such as toxins or lipopolysaccharide.
Here’s where it gets extra tricky, so pay
close attention.
B. burgdorferi infects a wide range of small
mammals, birds, and lizards.
Ticks, particularly blacklegged ticks, transfer
B. burgdorferi from these vertebrate animals
to humans.
This is the only documented way for humans
to get infected by B. burgdorferi.
Let’s talk more about those ticks.
In the U.S. in particular, the blacklegged
tick, also known as deer tick, or more formally,
Ixodes scapularis, spreads the disease in
the northeast, mid-Atlantic, and north-central
regions of the U.S.
The western blacklegged tick, Ixodes pacificus
spreads the disease on the Pacific coast.
Ticks can attach anywhere on the body, especially
hard-to-see areas.
Most commonly, it’s the smaller, more immature
versions of ticks called nymphs that infect
humans because they’re more difficult to see.
It typically takes 36 to 48 hours of attachment
for the Lyme disease bacterium to be transmitted.
To diagnose Lyme disease, doctors test for
certain antibodies that the body makes in
response to infection.
However, it can take several weeks, or even
longer, for antibodies to develop, which can
lead to a negative test result even if a patient
has been bitten by an infected tick.
To make things more complicated, antibodies
can hang out in the body for months or years
after the infection is gone.
And if that’s not enough, there are multiple
other diseases, viruses, bacteria, and autoimmune
conditions, that can give a false positive
result for Lyme disease.
If all this gives you a headache, you’re
not alone.
However, scientists are working tirelessly
to learn more and develop newer, more accurate
tests to diagnose Lyme disease.
In the meantime, the best thing you can do
is try to limit exposure to ticks, and stay
extra vigilant about checking for them after
outdoor excursions.
So after a hike in tall grass, you know what to do!
