On 8/02/2012 1:39 PM, Carl Clifford wrote:
Andrew,
The problem with Botulism is, that the cause of death is not from
infection by Clostridium botulinum, but from neurotoxins produced by
the bacteria. The botulinum toxins have LD50s of less than 100
nanograms per Kg. Hydrogen Cyanide has an LD50 of only 1-3g/Kg
In Thomas, Hunter and Atkinson's "Infectious Diseases of Wild Birds",
P. 405, they state that natural immunity does not play a significant
role in Botulism, because "The toxin is so poisonous that the amount
required to immunise an animal is much higher than the lethal dose."
They do say that it has been observed that naturally occurring
antibodies to several botulinum neurotoxins were found in several
carrion eating species of birds.
I wasn't actually thinking of acquired immunity. I was thinking more of
evolved immunity. Botulinum toxin (a group of 7 or 8 individual toxins
from /Clostridium botulinum and other related species./) and Tetanus
toxin (from /Clostridium tetani //) /are all proteins, and target
membrane proteins in their action. So mutants resistant to the toxins
should be possible. Indeed while humans, mice etc are very sensitive to
tetanus toxins, dogs, rats, some birds, snakes and amphibians are much
less sensitive and turtles apparently are insensitive to the toxin. Also
there is a range of sensitivities to botulinum toxins in humans with
some humans being insensitive (Schiavo et al Physiol RevJanuary 2000
vol. 80 no. 2 717-766 ). So it should be eminently feasible for ducks
and swans to have evolved immunity or insensitivity to the toxins too.
I suspect that such ducks and swans have been ferreting around in the
ooze for a long time so the question is still, why are they affected,
and has it changed recently. (however you define recently).
Cheers
Andrew
///
/
Cheers,
Carl Clifford
On 08/02/2012, at 3:56 PM, Andrew Hobbs wrote:
Hmm,
Feretting around in the mud is an almost full time occupation for some
ducks and swans so the question that comes to mind is 'why do ducks
and swans suffer from botulism'. I would have thought that it would
have been a sufficiently strong selection pressure to either develop a
different food source, develop an immunity or perhaps botulism is only
a very recent phenomenon in such conditions.
Any ideas?
Cheers
Andrew
On 8/02/2012 12:24 PM, Peter Shute wrote:
Is it possible that the grebes are being poisoned too, but aren't
dying in such visible places?
Peter Shute
-----Original Message-----
From:
On Behalf Of
Carl Clifford
Sent: Wednesday, 8 February 2012 1:52 PM
To: Chris Watson
Cc:
Subject: Re: [Birding-Aus] Botulism poisoning in waterfowl
Chris,
Though Grebes are divers, they feed on crustaceans, fish etc
and tend
not to go poking around in the mud at the bottom of the
ponds. Diving
ducks tend to ferret around in the bottom mud and would be
more likely
to get into the anaerobic layers.
Cheers,
Carl Clifford
On 08/02/2012, at 1:28 PM, Chris Watson wrote:
G'day all,
A bit of a technical question. I've been monitoring the
mortality rate
of a few species at Alice Springs Sewage Ponds after a spike in
botulism poisoning last year.
I'm not a biologist, but what I've learnt is that "c" type
Clostridium
botulinum bacteria reside and breed in anaerobic muds at the
bottom of
the ponds. When we get the warmer weather the amount of bacteria
increases and bottom feeding birds (swans, diving ducks) can stir it
up and ingest it, resulting in the increased mortality that
we witness.
At the moment we are seeing a greater number of dead and moribund
birds around the ponds (mostly Black Swan, Hardhead, and the
occasional Grey Teal).
My question is this; why are the aforementioned species affected but
the grebes (Australasian and Hoary-headed) which are accomplished
divers have not been observed to be affected to this point. In 18
months, I have not found a single grebe carcass or seen any grebes
that seem effected by botulinum toxicity. I am at the ponds at least
twice a week so have a very good idea of the changes in populations
and movements there. We have a fairly stable population of
between 80
and 120 grebes, and I'm surprised that they never seem to be
affected
by this toxin which always seems to take out quite a few swans and
ducks (and the odd stilt and lapwing) each summer. I can only
imagine
that there is some difference in their feeding technique or the
physiology of their digestive tract which keeps them safe from it.
Can anyone enlighten me?
Cheers,
Chris Watson
Alice Springs
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