Canning your own foods at home is a great way to preserve extra food, and provide meals for your family. If the process is not carried out correctly, however, it is also a potential source of botulism. There are many descriptive names for botulism: Shaker Foal Syndrome (horses), Limberneck (ducks), and Floppy Baby Syndrome (humans). If treatment is not started quickly, botulism can be fatal.
Causative agent: Clostridium botulinum
Clostridium botulinum is a ubiquitous saprophyte found in the soil worldwide. It is an anaerobic, Gram-positive, spore-forming bacillus. The spores are highly resistant to heat and disinfectants. The spores can remain dormant for years in the environment. The vegetative stage can only grow in aerobic conditions, with high water content, and a pH of greater than 4.6.
Nearly all species are susceptible to botulism, including mammals, birds, reptiles, and fish. Interestingly, dogs and pigs are relatively resistant to the toxin. There is a vaccine for horses available in the US.
3 Forms of Botulism
There are three forms of botulism: foodborne, infant, and wound botulism.
Foodborne intoxication usually occurs when the preformed toxin is ingested in food or water. The spores can also invade anaerobic tissues and grow and produce toxin (wound botulism). The bacteria can also survive in the gastrointestinal tract of immature animals (infant botulism).
Mechanism of Action of Botulism Toxin
C. botulinum has the ability to produce seven serotypes of exotoxin (Types A-F and M). Only Types A, B, E, and F cause botulism in humans. Type A is most common in North America, and Type B is most common in Europe. Botulism toxin is the most acutely lethal toxin known to humans; only 1 nanogram per kilogram (1 part per trillion) can kill a human. This makes botulism a concern for bioterrorism as well. The toxin will not penetrate intact skin but can be absorbed through broken skin or mucous membranes.
Botulism toxin is a potent neurotoxin that irreversibly binds to the endplates of neurons. It is dose dependent. The larger the dose, the quicker and more severe the clinical signs are. Signs can be seen as soon as 2 hours after ingestion, or up to 8 days with very small doses or wound infections. While the toxin is not contagious between individuals, it is common to see outbreaks when everyone in the family eats the same food.
Clinical Signs of Botulism
Often the first signs noted are vomiting and abdominal pain. This will progress to a symmetric, descending flaccid paralysis. Early signs could include drooping eyelids, slurred speech, and muscle weakness. In animals, hind limb weakness is often the first sign noted. Flaccid paralysis of respiratory muscles will eventually lead to death.
Knowing the toxin type is important when selecting antiserum for treatment, as there is no cross-protection against other types. Antiserum is only effective when the toxin is circulating in the blood; it cannot reverse the toxin once it is bound to the nerve.
Foods Commonly Associated with Botulism
C. botulinum grows best in non-acidic foods, especially home-canned vegetables and meats. The absence of oxygen in canned foods is the ideal culture media for the bacteria. Foods must be canned at 250°F for 20 minutes to destroy the spores. The toxin can be destroyed by heating foods to 176°F for 5 minutes. Raising the pH of the food, or increasing salt content can inhibit the growth of the bacteria.
Livestock is commonly exposed to the toxin when small animal carcasses are unknowingly incorporated into hay or bagged silage at the time of cutting. There is often outbreaks of botulism within the herd when this happens.
Honey has been implicated in infant botulism. The CDC recommends not giving honey to children under 1 year of age.