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Whacky parasite life cycles - your nominations please!

Peter W Pappas ppappas at magnus.acs.ohio-state.edu
Fri Jul 1 05:27:01 EST 1994

In article <2v0gap$e2f at mserv1.dl.ac.uk>,
(David Johnston) daj  <daj at nhm.ac.uk> wrote:
>Hi all,
>as part of our Museum's programme of public events involving its
>scientists, I have been voluntered to give a talk "about parasites"!
>Although I work on Schisto, the only time I see one when I take it out of a
>cryotube and stick it in proteinase K solution to get the DNA out. Hence
>this appeal to those of you with a broader background.
>Under the title "Against the Odds", I want to do 2 things, (1) to get
>across the concept of life cycles, (2) to try to convince my audience that,
>even if they can't get to love parasites like we do, they ought, at least,
>to respect them for the wonderful adaptations they have evolved to maximise
>reproductive success/continuation of the life cycle. I am, therefore
>looking for nominations for your favourite wierd, wonderful and whacky
>adaptations and life cycles to illustrate my talk with; phenomenal
>reproductive output, alteration of host behaviour, parasites of parasites.
>You name it, I would be grateful to hear about it (with follow-up
>references if possible).
>Thanks in advance, I'll be happy to summarise responses
>David A. Johnston
>Dept of Zoology, The Natural History Museum, Cromwell Road,
>South Kensington, London SW7 5DB. England
>(tel 071 9389297, fax 071 9388754, email daj at nhm.ac.uk)

There are, of course, two classic examples that appear in many introductory 
textbooks ---- effects of Dicrocoelium dendriticum on behavior of ants, and 
changes in physical appearance of snails infected with Leucochloridium.  The 
former example is discussed in almost every introductory parasitology text; the
latter is discussed in Cheng's second edition of "General Parasitology."  Evans
et al. published a recent paper in Can. J. Zool. showing the beetles, when 
provided a choice, will preferentially ingest feces containing tapeworm (H. 
diminuta) eggs, and since beetles are the normal intermediate host for H. 
diminuta, this has important implications in transmission dynamics.  We have 
confirmed (and expanded) these data using Tenebrio molitor (MS submitted to 
Animal Behaviour), but as far as I know, no one knows how the beetles actually 
detect the differences in feces with and without eggs.  For reproductive 
potential, there's always the example of Ascaris which is reported to 
produce about 200,000 eggs/day/female, and a single female may contain 
>25,000,000 eggs.  I like another example, and that's Clonorchis.  A single 
worm may produce 4,000 eggs/day, and single redia may produce 50 cercariae, and
an adult may live well in excess of 20 years.  That means that a single worm 
can produce (under idea conditions) about 1.5 x 10 \9/ offspring during its 
life!  Or, how 'bout Giardia --- a single stool sample may contain in excess of
10\9/ cysts, or some of the trypanosomes --- an infected human could contain 
>50 X 10\8/ trypomastigotes.  Hope these few, brief examples are helpful.
Peter W. Pappas, Professor/Chairperson, Department of Zoology,
The Ohio State University, Columbus, OH  43210  USA
E-mail: pappas.3 at osu.edu; FAX (614)-292-2030,
PHONE (614)-292-8088

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