00:01
Alright, those are the African trypanosomes.
Let's take a look at the American trypanosomes.
00:06
Trypanosoma cruzi. Here's a picture of the
blood form, the flagellated form. Slightly
different morphology, doesn't have a nice
undulating membrane, at least to my eye. These
are passed by what I consider to be one of
the most horrid bugs on the planet, the reduviid
bug, better known as the kissing bug. You'll
see why in a moment it's called a kissing
bug. This bug by the way feeds on many mammals
besides humans. And it's quite impressive,
isn’t it? It is not only large, but look
at that proboscis at the very end. It is very
long and very sharp. I would not like to meet
a reduviid, but unfortunately many people
in South America do. These bugs feed at night,
typically they live in the straw that covers
the roof of your home. Many homes in South
America are not fortunate enough to have a
synthetic roof of some kind, they have straw
and reduviid bugs like to live in the straw,
and at night while you're sleeping, what is
the part of you that's exposed? Your face.
01:23
If you sleep on your back, your face is up,
the rest of your body is covered with sheets,
the bugs fall out of the thatched roof onto
your face, they take a blood meal. When these
bugs take a blood meal, they defecate. They
want to make room for the blood that they
have just put into their intestines, so they
defecate. And then they fly away. And guess
what's in the feces? Right, trypanosomes.
So, so far those trypanosomes are sitting
on your skin and they are not getting into
you yet, because the reduviid bug, when it
takes a blood meal is not putting parasites
into you. They come out in its feces. But
what happens when you get bitten by some kind
of a bug? What do you do? You either slap
it or you scratch it. And there you go, you
scratch the bite of the reduviid. You put
the feces into the wound that the bug has
made and you introduce the parasites into
your body. So you’re infecting yourself,
lying in bed at night being bitten on the
face. I think all of this is a horrible scenario
to be honest, but it can happen. Reduviids
by the way, not only will live in the thatched
roof of homes. If you happen to have a regular
roof made of other materials they can still
get in, they live behind pictures that you
have hanging on your walls. Am I scaring you?
You should be! Go check behind the pictures
and then come back and listen. Alright, so
scratching introduces parasites into the bite
wound. Very different from the other parasite
transmissions we've talked about, where the
vector is injecting the parasites; this is
very different, whatever way works I suppose.
03:19
Okay disease caused by American trypanosomes
is called Chagas disease in honor of the man
who discovered the agent. So here we have
an outline of the lifecycle of the American
trypanosomes. Again, they are deposited on
your skin by the reduviid bugs and then you
scratch and introduce the Trypanosoma into
the wound. And then
the parasites will eventually get into your
bloodstream and spread elsewhere. Now two
to four days after you have this bite, swelling
develops at the bite site. This is called
a Chagoma. Again in honor of Chagas, who discovered
the parasite, Chagoma. So if you've gotten
a bug bite at night and a few days later you
get swelling, you can bet that you've gotten
an American trypanosome. Now sometimes the
bugs bite very close to your eye, and you rub
and you rub bug feces into your eye and then
the parasites can get into the mucous membranes
of your eye, it will swell shut. So this little
child in the picture you see, his or her left
eye is swollen shut. When the chagoma or swelling
occurs in the eye, it's called Romaña's sign.
04:44
Again, a telltale sign that you're getting
American trypanosomiasis.
04:51
As this infection proceeds, you develop a
mild disease with fever and typically you
will recover. But some people remain infected
for their whole lives, perhaps 10 to 20 years
after which they develop complications that
will kill them. So, you can be cleared of
infection early on, after a relatively mild
swelling, a chagoma, or you can be persistently
infected and die many years later of complications.
So what happens is that the parasites spread
from that initial bite site that get into
your blood as shown in this illustration,
in most people they’re cleared, but in some
they persist for a long time and they can
spread to different organs as shown in the
bottom. And they can cause damage to nerves
in your gastrointestinal tract. They can cause
megacolon, a swelling of the colon, or megaesophagus,
a swelling of the esophagus, and these cause
gastrointestinal problems which are quite
specific and you can detect on a careful questioning
of the patient. The trypanosomes can also
spread to the heart and cause damage to heart
muscle. So they can be there for many years,
replicating, causing immune reactions that
damage the tissue, and a lot of these individuals,
10 to 20 years after the initial bite on the
face, have a heart attack caused by destruction
of the heart muscle by parasite replication.
06:22
How do you diagnose American trypanosomiasis?
One of the more interesting diagnostic assays
that I've ever heard of is, you take a reduviid
bug which is free of the disease, and you
allow it to bite the patient and a week later
you look at the feces of the bug for metacyclic
trypomastigotes which are shown in this picture.
So you are basically using the bug as an incubator
to see if the trypanosomes are present. Now
if you don’t want to be bitten by a bug,
you can take a little bit of blood into a
blood smear and look for those blood forms
in the microscope, relatively easy to find.
You can stain the trypanosomes with antibodies
and do immunofluorescence, the green color
that is shown here. Or you can use ELISA-based
test to look for antibodies against the parasite,
which we develop in the course of an infection.