Howdy,
For those of you who boil and think that you are destroying Clostridium botulinum during the boil process, think again. Clostridium sp. are an anaerobic spore former, and the spores are what you have to worry about.
About 70% of botulism poisoning cases are infants 1 - 8 months old who have eaten honey. Honey often contains (about 1 in 10 tested honey samples) the spores of C. botulinum. These are destroyed in adults by the acidic juices of the stomach. Since the stomach of infants is less acidic than adults, spores are not destroyed and can lead to botulism poisoning. The remaining adult cases of poisoning are overwhelmingly the results of home canning accidents. Never eat from a warped can or a jar with a warped lid. From what I've read as I type this there are about 100 cases of botulism poisoning a year in the USA.
In order to kill off the spores from C. botulinum, you must boil at 239 degrees F for 20 minutes. There are some studies that indicate the boiling must be done under pressure, which would make sense considering the temperature.
C. botulinum produces a toxic protien (exotoxin) which has a neurotoxic effect on humans.
So the big question is why we don't see more cases of botulism poisoning in meads? Well, if there is some kind of botulism infection in your mead or must, you'll know it pretty quickly because these particular bacteria produce a really nasty smell, and a dark discoloration under the surface of the infected media, in this case mead or must.
Also don't forget that the bacteria themselves are anaerobic so the heavy oxygenation of the must during preparation will help to cull them if they are present in your honey.
Cheers,
Oskaar