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Various mammals seem to get away with eating parts of carcasses that we would prefer to not even touch, and that we assume will make us sick.
Because of that, I assume botulinum toxin is more dangerous to humans than many animals.

Is that right so far - can they handle more of some toxins compared to us?
Or are they better in avoiding harmful substances based on more suited olfactory sense?
Or are we just more afraid?

Assuming the differences exist - what is the cause for it?
Are there plausible explanations in terms of evolutionary pressure?

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    $\begingroup$ How do you come to the conclusion that is is more dangerous for us? Botulinus is a strict anaerobic bacteria, so you will not likely find it on relatively fresh carcasses. $\endgroup$ – Chris♦ Sep 21 '14 at 16:09
  • $\begingroup$ Humans have a tendency to can things and put food in jars, which is more or less a recipe for botulism. Vultures have a huge list of fascinating adaptations for eating rotting carcasses but that's an answer for a different question. $\endgroup$ – Resonating Sep 21 '14 at 16:34
  • $\begingroup$ @Chris Yeah, I was not that sure with it - that's why I called it assumption. So part of it is the "Or are we just more afraid?"... And right, the vultures deserve a separate question! $\endgroup$ – Volker Siegel Sep 21 '14 at 16:50
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    $\begingroup$ It's an interesting question other than your assumption about botulinum toxin, which is incorrect and seemingly irrelevant. Perhaps you should remove it. sciencedirect.com/science/article/pii/… $\endgroup$ – canadianer Sep 22 '14 at 19:22
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    $\begingroup$ From a food safety point of view, you don't get botulism from "carcasses" (meat). Common botulism vectors are plants, especially the parts growing around dirt (making homemade garlic oil is a really bad idea), and honey (a danger to infants, adults can stomach the spores and they can't form a colony of living bacteria in honey). So, if there are animals which come frequently into contact with botulism, they aren't vultures. Actually, I might have to write an answer about that... $\endgroup$ – rumtscho Sep 23 '14 at 10:21
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Because of that, I assume botulinum toxin is more dangerous to humans than many animals.

Couldn't find too many examples but, there are some things to consider (according to [1]):

  • there are seven distinct types of toxin with variable action among animals
  • different dose / effect intensity ratio between toxin types
  • toxins A, B, E and F cause disease in humans
  • toxin C and D are more common to birds, cattle, horses

And here are some numbers:

  • cattle median lethal dose: 0.388 ng /kg [2] of C type toxin
  • mouse median lethal dose ( 12.88 times more than cattle): 5 ng/kg [2] of C type toxin
  • human median lethal dose: 1 ng/kg [1] of A type toxin

When it comes to carcasses toxicity, there are some papers to consider:

are they better in avoiding harmful substances based on more suited olfactory sense?

Not if we are talking about nonproteolytic B, E and F type bacteria. Indeed, Clostridium botulinum, proteolytic type A, B and F types produce odor [3].

Or are we just more afraid?

I don't see how fear could (significantly) influence pharmacodynamics and pharmacokinetics of the toxin.

References:

  1. CIDRAP - Center for Infectious Disease Research and Policy. Botulism. Available from http://www.cidrap.umn.edu/infectious-disease-topics/botulism
  2. Moeller RB, Puschner B, Walker RL, Rocke T, Galey FD, Cullor JS, Ardans AA. Determination of the median toxic dose of type C botulinum toxin in lactating dairy cows. J. Vet. Diagn. Invest. 2003 Nov;15(6):523-6. PubMed PMID: 14667014.
  3. P. Kendall. Botulism. Colorado State University Extension. Available from http://www.ext.colostate.edu/pubs/foodnut/09305.html
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  • $\begingroup$ I think he means 'fear' in the sense that humans worry about botulism, and vultures apparently do not. Some explanations: vultures are less affected by botulinum toxin, vultures aren't exposed, and vultures just don't worry about things. Seems to be a blend of 2 and 3, but it's interesting to point out that in certain temperature/time windows carcasses might be poisonous to humans but not to vultures, due to differences in relative toxicity/toxin type. A faulty assumption is sometimes right. $\endgroup$ – Resonating Sep 22 '14 at 23:52
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You seem to not understand how botulism works. It is impossible for vultures (or anybody else) to get botulism from a carcass.

First, you have spores. They are ubiquitous in nature, and you have probably eaten lots of them. They are especially common on vegetables growing around/in dirt, like garlic. The spores are

  • indestructible when using common cooking methods
  • dormant under normal food storage conditions
  • not dangerous to humans above 1 year of age. They remain dormant in the human body and get excreted without causing anything.

Then, you have botulinum bacteria colonies. To get a colony going, you need to take some spores and cut off the oxygen supply. For example, storing raw garlic in oil provides both a possible contamination route and a perfect growth environment.

The bacteria themselves are - easy to kill off with heat - not prone to establishing a colony in your body.

The problem with the bacteria: Once there has been a colony, it starts producing the toxin. This toxin is very poisonous even in minute amounts, and stays around to harm you even after you have killed the bacteria which produced it (e.g. with acid). It is not especially heat stable, certainly not as stable as the spores.

So, the way you get botulism is:

  • Start out with food contaminated by the spores (meat is rarely such food, vegetables are more common. Of course, cross contamination in your kitchen is possible.)
  • Cut off all oxygen supply for some time. A colony forms.
  • Sterilizing the food by placing it in boiling water for some time doesn't matter, the spores will survive it easily. (This is why industrial food is canned at much higher temperatures, and safe home canning recipes are quite acidic).
  • eat the food after it has been stored with the colony inside.

So, vultures don't have any special resistance to botulism toxin, they just don't come in contact with it.

On a side note, there are quite a few other pathogens which are common in meat, and vultures are probably more resistant to them than humans. But it is normal for bacteria to be able to only make one species, or a small range of species sick. Just ask the poor medical researchers trying to heal human disease in mouse models - there are huge differences.

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