Botulism is an acute poisoning resulting from ingestion of food containing toxins produced by the bacillus Clostridium botulinum. This bacterium can grow only in an anaerobic atmosphere, such as that found in canned foods; botulism is then almost always caused by preserved foods that have been improperly processed. Person to person transmission of botulism does not occur.
Classic symptoms of botulism occur between 12-36 hours after uptake of the botulinum toxin, but they can occur as early as 6 hours or as late as 10 days. They are not caused by the organism itself, but by the toxin that the bacterium releases.
Incidence of botulism is low, but the mortality rate is high if treatment is not immediate and proper. The disease can be fatal in 5 to 10% of cases.The symptoms usually include dry mouth, difficulty swallowing, slurred speech, muscle weakness, double vision, vertigo, vomiting, and severe diarrhoea, along with a progressive muscle paralysis. If untreated, these symptoms may progress to cause paralysis of the arms, legs, trunk, and respiratory muscles. There is no fever and no loss of consciousness.

Botulism is a relatively rare disease. Worldwide, food-borne botulism is the most commonly reported form, but the United States experiences a higher incidence of infant botulism. In the US an average of 110 cases of botulism are reported each year. Infant botulism is possibly under-reported worldwide because it is a relatively recent discovery and diagnosis can be difficult.

Sources:
http://en.wikipedia.org/wiki/Botulism
http://www.who.int/mediacentre/factsheets/fs270/en/
Picture:
http://www.mwra.state.ma.us/germs/botulism.htm