The schistosomes of course are examples of the
non-segmented flukes. And there are four different
schistosomes which cause significant human disease.
Again, these are rather small worms and we'll talk
about these in a separate lecture. They are
schistosoma mansoni, and that's the worm form
of course. Schistosoma haematobium. This is the egg
form. It's obviously not a worm but it's in egg form
that's stable in the environment. Schistosoma
japonicum, in the egg form in submucosal tissues.
And Schistosoma mekongi, another egg form. So we had
one photograph of the actual worm and three different
egg forms for these schistosomes. I want to talk a
little bit about how these parasitic infections
are transmitted. So first we're going to focus on
those that are transmitted from parasites being in
the feces. So lets zoom in on this. So in the
first case, the mode of exit for both of these
categories is feces. So, the parasite is shed in
the feces. For some this is reintroduced into humans
by eating. So this is called fecal-oral contamination.
It can happen if food or water becomes contaminated
with fecal material. So cryptosporidiosis is an
example of a parasite infection that goes from
human to human by fecal-oral contamination. It can
also go from animal to human. And there are
other examples of this kind of transmission here.
Amebiasis, Giardiasis, Strongyloidiasis, Ascariasis,
Trichuris infection and the pork tapeworm. Those are
all transmitted human to human by fecal-oral
contamination. Then there are other examples of
fecal-oral passage involving animal to human.
Toxoplasmosis for example, from cat feces to human.
Visceral larva migrans, from dog feces to humans.
If you ever walk around on a deserted beach
that's not well cleaned and there are wild dogs
walking around, you better make sure you wear shoes.
Because the dog tapeworms are in the dog feces
and they can get into your feet and cause visceral
larva migrans. Now there are also examples of
parasites that are shed in the feces but that
enter your skin. An example is strongyloidiasis,
coming from a dog or a cat
hookworm or schistosomiasis.
Lets now look at other modes of transmission and
we'll focus in on these. As I told you, many
parasites are transmitted by the bite of an
arthropod. And sometimes the parasite leaves the
host by an arthropod bite and then it enters another
host by the same kind of bite. From human to human
examples include lymphatic filariasis, leishmaniasis,
malaria or onchocerciasis. But the parasite bite
can go animal to human as well. Trypanosomiasis
(sleeping sickness or Chagas disease), leishmaniasis,
the disease can go from an animal to a human. And
finally there are some parasitic infections
that are acquired by eating inadequately cooked meat.
So there is no mode of exit here. The parasites are
within the animal typically in the muscle tissue.
And when you eat them undercooked you get infection.
Examples of these are trichinosis, toxoplasmosis,
the beef, pork and fish tapeworms. So the bottom line
here folks is that you really need to cook your
food well. Otherwise, you could be risking a
parasite infection. Finally there's a whole new mode
of transmission of parasites we haven't talked about.
This is by blood transfusion. The malarias,
trypanosomes, toxoplasma, leishmania, babesia.
These are all potentially transmitted in the blood.
So, those countries that check for these parasites
you're certainly better off than in countries where
these are not checked for because there have been
ample numbers of transmissions documented where
these go from one person to another via donated blood.