Able to control myself no longer . . .
I've just submitted my PhD thesis on the structure and chemical
resistance of ascarid and oxyurid nematode eggs (with a special interest
in developing an ovicidal compound) and have amassed quite a volume of
literature and information on the subject.
The problem of the chemical resistance of the nematode egg-shell has
caused a great deal of stress for a while now. Many treatments work quite
well (such as non-polar solvents) but are difficult to use in the
environment (volatility, toxicity). Physical treatments like heat also
work quite well but are similarly difficult to maintain. The two major
resistance barriers in the egg-shell are the chitinous layer (which acts
to keep out a lot of non-polar compounds, as well as some detergents) and
the lipid layer (which stops the passage of most water soluble agents).
My research was therefore directed at a two component treatment - one to
overcome each structure. The treatment works quite well and is reasonably
safe, but more suited, once again, to controlled areas, such as animal
pens. I hope to be able to publish my results once we get the commercial
confidentiality agreement sorted out (I love commercial funding:(.
A subject which puzzled me was the use of the hypochlorite irritability
test for _Ascaris_ egg viability. I've spoken with others on this topic
(sorry I haven't gotten back to you Fredrik - internet access has been
difficult). This test supposedly relies on the increased motility of
nematode larvae when the eggs are suspended in a solution of hypochlorite
(as a result of the penetration of the hypochlorite into the egg). As far
as I can tell, the body of literature states that the egg-shell
(specifically the lipid layer) is impervious to hypochlorite -
concentrated solutions were regularly used to "deshell" (remove the
chitinous and uterine layers) eggs without harming the embryo within, and
ovicidal and electron microscopic studies I have performed seem to
support this. When I first heard of the test, I put the results down to
increased activity due to warming by the microscope lamp, but since this
is now a respected test, I assume there must be more to it. Can anyone
out there illuminate the subject (sorry) ?
One area which appeared interesting is the use of ovicidal fungi.
Researchers such as Lysek, Sterba and the like have been regularly
publishing the ovicidal effects of fungi (eg. Verticillium
chlamydosporium) since the 1960's. The rate of killing is slow (over
months) but these might represent a means of lowering the egg burden in a
continuous manner.
just some thoughts
Peter Darben
School of Life Science
QUT, Brisbane, Oz
"No longer making the world safe from pig worms - you're on your own no
folks"
