Sex Life of the Schistosome
pspangle at worldnet.att.net
Fri Oct 8 07:28:14 EST 1999
AS> What you MAY have been interpreting as a male surrounded by
females, is some cellular debris around a cercaria that
resulted from your body's immune response, which killed the
cercaria that penetrated your skin at that site.
That's what I first thought. Indeed I interpreted what I first
saw under a microscope (75x) as all cellular debris, although it
sure looked like a miniature seahorse head. The first "specimen"
came from a very thin-skinned blister on my wrist; its whole body
(maybe 3 mm long by 1 mm wide) literally popped out when I
squeezed it lightly.
Alas, I had other things to do at the moment, so I set the
microscope aside and returned to it hours later, but by that time
the creature had dried out and didn't look like much of anything.
With this particular specimen, I don't recall any of the skinny
black creatures which I will call females.
Later attempts to extract specimens from blisters/pustules
yielded bodies (which I will call males), but no heads. It was
with these that I saw the black females (see Figure). Two
specimens of females caught my attention:
The first had about two females, which writhed for a brief time
with a vigor that could not be explained by the motion of the
surrounding lens-cleaner fluid (the only thing I had handy at the
moment to wash away blood).
Left alone, the pustules eventually form a hard white mass that
works its way to the surface of the skin and drops off. One such
mass had slight black specks on it to the naked eye, which under
the microscope were dried-out females entwined in the white mass.
At 75x they looked something like multi-segmented ants, ~3 mm
long and about 0.1-0.2 mm wide, with heads slightly larger than
the body segments. The heads had pincers at the top (see
attached drawing). I can believe that the "pincers" are the
remains of a tail.
The males looked like Figs. b and c of Ref. 1, but with a more
triangular front end. On some I could differentiate a sucker-
like front end, as opposed to a ragged back end. (I now think
these were more "mature" specimens - see below.)
AS> The cercariae of schistosomes do have separate sexes, but
they do not differentiate morphologically until after they
have migrated to the liver. Also, each welt typically
results from the entrance of a single cercaria.
These critters are never going to reach my liver (at least I hope
so). By the time I extracted them, they had been under my skin
from hours to weeks. Is it not possible that they had morphed
and gotten together in that time? At one time, the crooks of my
elbows and knees were one large red rash - plenty of room for
I am the first to admit the inadequacy of my specimen collection
and examination techniques. Obviously more research is required.
Therefore, next June all you academics should put on your bathing
suits and march into the duck pond of your choice, in order to
collect Trichobiharzia ocellata cercariae and properly examine
them at various times after penetration. :)
* Sorry, I don't have a website on which to display the drawing.
I'll email it to anyone to asks (pspangle at worldnet.att.net).
In article <7tfnba$jls$1 at rover.ucs.ualberta.ca>,
al.shostak at ualberta.ca (Al Shostak) wrote:
> Assuming that you do have swimmer's itch, I wonder what you were
> seeing with your microscope. The cercariae of schistosomes do have
> sexes, but they do not differentiate morphologically until after they
> migrated to the liver. Also, each welt typically results from the
entrance of a
> single cercaria. They do not group up prior to penetrating. I think
> highly unlikely that you would have extruded from the pustule, let
> able to identify, a group of females around a male. When the
> the snail the males do not yet even have a gynaecophoric canal. What
> have been interpreting as a male surrounbded by females, is some
> debris around a cercaria that resulted from your body's immune
> which killed the cercaria that penetrated your skin at that site.
> In a subsequent article you mention that you wish to make a
> your local parks board, to convince them to warn swimmers of the risk.
> you do so, I suggest that you educate yourself about the parasite more
> Any general textbook on parasitology will give you information about
> schistosomes. Trichobilharzia is just one genus, but the general
> the life cycles are similar. To address a few of the inaccuracies
> of your postings: (1) The cercariae do not have "pincers"; the forked
> is actually their tail, and it is generally left behind when the
> penetrates skin. (2) Towelling off is not necessarily a simple
> measure. It may remove some cercariae on the surface of the skin, but
> cercariae penetrate many individuals while they are still in the
> Swimmer's itch is a world-wide problem, with no easy solution. If you
> waterfowl and appropriate snails in a lake or pond, there is a good
> some snails will be releasing the cercariae that cause the itch.
> infected waterfowl from visiting the lake, or removal of snails, would
> effective, but is difficult to accomplish in practice. Any claims
> application of certain creams or lotions will prevent the penetration
> cercariae are inconclusive. Recent studies indicate that swimming in
> morning may increase the chances of exposure because the snails tend
> the short-lived cercariae at first light.
> In article <7tbqup$4mv$1 at nnrp1.deja.com>, pspangle at worldnet.att.net
> >In the last few weeks I have become intimately acquainted with
> >Trichobiharzia ocellata - hundreds of them (i.e., I have Swimmer's
> >Itch). When I examine extrusions from the pustules on my legs and
> >under a microscope, I notice that each male T.o. is accompanied by
> >Question: Does the male schistosome carry his whole harem in his
> >gynecophoral canal during his trip from snail to warm-blooded host,
> >do they swim separately and joing up after he has penetrated the
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