Ascarid egg resistance

p.darben at qut.edu.au p.darben at qut.edu.au
Wed Feb 7 01:20:11 EST 1996


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"




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