00:01
Borrelia, a bacteria. Borrelia are another example of
spirochetes.
00:07
These are probably one of the larger types of spirochetes
that we know about in human science,
certainly larger than treponemes, the cause of syphilis,
yaws, and pinta.
00:17
The Borrelia however possess numerous axial filaments unlike
other types of spirochetes that have one to three,
they are microaerophilic and they’re very difficult to
culture.
00:30
In fact, as we’ll talk about in a little bit, they can
mostly be diagnosed via dark field microscopy
such as you see on the image on this slide or by serologic
or antibody reactions to confirm an immunologic reaction to
them.
00:45
Today, we’re gonna talk about the two principal human
pathogens,
that being Borrelia burgdorferi and Borrelia recurrentis.
00:54
Borrelia burgdorferi is the cause of Lyme disease and as
such, it is the target of intense human scrutiny
and sometimes, an overabundance of clinical interest. Lyme
disease, Borrelia burgdorferi
which is common in the Northeastern United States.
01:12
I should point out that colorful slide or colorful image on
the preceding slide
was a whole bunch of Borrelia piled up on top of each other,
those spirochetal structures making it look almost like a
sponge.
01:25
That doesn’t necessarily occur in nature but it certainly
made for a beautiful image.
01:30
This image is not so beautiful.
01:32
This is a picture of the United States and every dark purple
spot
that you see is a representation of a county with a reported
case of Lyme disease.
01:43
As you can see, Lyme disease certainly appears to predilect
in the Northeastern part of the country
but there are dark purple dots all over every single state.
Most of those represent cases that were imported,
meaning, acquired from an endemic part of the country, the
North sea, Northeastern part,
and then, a returning traveler going back home
and then, developing the clinical symptoms someplace else.
02:10
The reservoir for Borrelia is the white footed mouse and
then, also in deer
and we’ll talk about the natural life cycle coming up very
shortly.
02:19
The transmission however is the ixodes scapularis tick
otherwise known as the black legged tick
or the deer tick and this image shows an engorged tick,
quite an unreasonable looking beast.
02:33
He’s certainly not something that you would like to discover
stuck to your arm or other parts.
02:38
Let’s look now at the lifecycle of Borrelia burgdorferi as
pertains to the lifecycle of the tick, its primary vector or
host.
02:48
And I’ll point out at the start of this slide that this
entire cycle takes over three years, two and a half or three
years,
the time it takes for an egg to mature into an adult tick.
02:57
the time it takes for an immature or an egg to mature into
an adult tick.
02:58
the time it takes for an immature or an egg to mature into
an adult tick.
03:01
We’ll start off then on the left lower part of the slide
with an adult female tick dropping off its eggs.
03:07
Those eggs will mature into six legged larvae that soon
after this maturation will start looking for their first
blood meal.
03:16
That meal typically occurs from a small rodent, especially
our friend, the mouse,
and it is from that mouse or whatever rodent that the larvae
may first acquire Borrelia burgdorferi.
03:29
At this time however, they are not yet ready to attack or
ingest, and transfer Borrelia to a human being.
03:33
At this time however, they are not yet ready to transfer
Borrelia to a human being.
03:36
Next, over the following season, the winter months, the
larvae will molt
and when they emerge from the winter into the spring, they
will have molted into nymphs
and this means that they are now hungry and looking for
their second blood meal, their second feast if you will.
03:55
Here, most often, the nymphs will actually take their second
meal from another warm-blooded mammal.
04:04
It may be a larger one, it may still yet be the mouse.
04:07
The picture here shows a raccoon and they also may acquire
Borrelia burgdorferi from this second animal host.
04:15
Then, we go through another year, another winter season at
which point, the nymphs are growing and eventually,
maturing into adults and at this point, they are ready for
their third and final blood meal
which may be from a larger animal.
04:31
They’re bigger, they can live higher up, they can drop from
forest leaves, or trees, or branches
onto a taller creature such as a deer or some other hooved
animal.
04:43
However, there are several points at which the tick in its
very stages can transmit Borrelia burgdorferi to the human
being.
04:51
The first is as a nymph.
04:54
Meaning, it’s survived its first winter, it’s turned into
the second stage of the tick
and it’s looking for a second blood meal.
05:01
If that nymph was previously infected from its mouse host
the last season with Borrelia,
it can then transmit Borrelia to the human being by taking a
second blood meal.
05:13
Similarly, the adult can transmit Borrelia to either a human
or a human’s best friend,
the dog as you see there while on a camping trip or hiking
through who knows where.
05:25
So, two stages at which the organism itself can be
transmitted to the human being.
05:32
So, following that inoculation, that injection of Borrelia
burgdorferi into the human being
via the bite of an infected tick either at the nymph
session,
the nymph status, or the adult status, then, the bacteria
enters the bloodstream through the skin,
through that bite and it spreads to multiple organs and the
image here on the right shows
anywhere from the heart, to the lungs, to the kidneys, the
liver, you name it.
06:01
This is where primary infection can absolutely occur driving
then an immune response
followed by disease manifestations.
06:09
The principal clinical symptoms and signs of Lyme disease
are absolutely
caused by the human’s immune reaction to Borrelia
burgdorferi,
not specifically from any action of Borrelia burgdorferi,
although, it does as you see here express a very weak
endotoxin-like activity.