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Morphology of swimmer's itch parasite?

Pat Spangler pspangle at worldnet.att.net
Wed Oct 13 09:16:51 EST 1999

I am still trying to understand the parasites that gave me a bad
case of swimmer's itch.  I assume they are Trichobilharzia
ocellata.  However, the picture I have found that is closest to
what I've seen from what I have decysted from my arms and legs is
the bottom picture on the web page


which is listed as "unknown species."  At least the shape of the
head inside the cyst in this picture is the same as what's in me.

However, "my" parasites apparently undergo a transformation after
they enter my skin to a black skinny worm about 3 mm long with a
~heart-shaped head. I know this black object is not a hair or
cellular debris.  Once, when I put a drop of lens-cleaning
solution (the only fluid I had handy at the time) on some
specimens, a few flailed briefly under the microscope with a
vigor that could not be explained by external motion of the

At first I assumed that the larger creature was the male and the
black ones were females (hence my thread on bionet.parasitology
"Sex Life of the Schistosome").  If the "males"* are what bored
into me originally, then the "females"* form within 12 hours.
However, Al Shostak <al.shostak at ualberta.ca> assures me that
morphological differentiation of sexes takes place only in the
liver and does not occur at all when the cercariae get into the
wrong host.

Later specimens seem to indicate that the black creatures form
inside the carcass shell of the "males," but the specimens in me
are drying out, so I'm not really sure. (I am not about to go
swimming in the lake again to gather fresh specimens.)  Could the
black specimens be "metacercariae"?

Any help will be appreciated.

Patrick Spangler

* I use these terms for brevity - I really don't know what they are.

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