Details about the Organism

Botulinum neurotoxins are produced by the anaerobic spore forming bacterium Clostridium botulinum and, rarely, by Clostridium baratii and Clostridium butyricum. There are seven neurotoxins (A-G). Illness in humans is usually caused by types A or B or E, or rarely F. Types C, D and E cause illness in mammals, birds and fish. Type G has not been shown to be associated with disease.

All toxins block the release of acetylcholine at the neuromuscular junction, which results in flaccid paralysis.

There are three naturally occurring forms of illness:

• Food-borne botulism, caused by ingestion of pre-formed toxin
• Wound botulism, caused by growth of cells and production of toxin in traumatic wounds
• Intestinal colonisation botulism, usually seen in infants, but also very rarely in adults, caused by growth of cells and production of toxin in vivo.

Deliberate release of botulinum toxin

A deliberate release may involve airborne dissemination of toxin, producing botulism through inhalation. Alternatively, it may involve contamination of food and water supplies either with toxin or with C. botulinum bacteria.

Transmission

Food borne botulism is caused by ingestion of preformed toxin. C. botulinum spores are found throughout the world in soil samples and marine sediments. A normal healthy adult can consume small numbers of spores, for example in raw vegetables and salad products, with no ill effects. However, where food is contaminated before preservation and the spores germinate and grow in anaerobic conditions, toxin is produced which is highly poisonous when ingested. Most cases of food-borne botulism are associated with home preserved meats, fish and vegetables. The disease is rare in the UK, but more common in Southern and Eastern Europe where the practice of home preservation is more widespread. In 1989 the largest ever outbreak of food-borne botulism in the UK affected 27 people who had consumed hazelnut yoghurt. The illness was caused by type B toxin produced by bacteria growing in canned hazelnut conserve that had been inadequately heat-treated and was used to flavour the yoghurt. Between 1989 and 2005 there have been a further five unrelated incidents (6 cases) in the UK.

Wound botulism follows infection of wounds caused by penetrating injuries. C. botulinum spores, which are present in soil, then germinate and produce toxin in vivo. It has also been caused by injecting or sniffing drugs that are contaminated by spores. Wound botulism is now the most common form of botulism in the UK and Eire. There have been >100 clinically diagnosed cases of wound botulism between 2002 and 2007. All cases have been amongst illegal injecting drug users. Further information on wound botulism

Intestinal colonisation botulism occurs in infants of less than two years of age, and most are under 6 months of age. A small number of cases in adults have been reported worldwide. Illness in infants and adults results from ingestion of C. botulinum spores, followed by germination and colonisation of the gut and production of toxin. In the USA infant botulism has been associated with the ingestion of honey, corn syrup, and environmental sources of spores including dust or soil. There were eight cases of infant botulism detected in the UK between 1978 and 2007 - and whilst a route of infection was not detected for the majority of cases, in one case there was a possible exposure to spores in infant formula dried milk and in two others there was an association with spores in the environment.

Other routes of infection

Accidental botulism may follow mis-injection of pharmaceutical preparations of botulinum neurotoxin. Four cases occurred in December 2004 in Florida following cosmetic injection with botulinum toxin that was not approved for human use. There have been no reported cases in the UK.

Inhalation botulism does not occur naturally, but has been demonstrated in model systems and in real cases (three cases were reported in 1962 in veterinary technicians in Germany). Aerosolised toxin is a potential route for deliberate release.

Water-borne botulism may also be caused by ingestion of pre-formed toxin. This route will only pose a risk to humans in some deliberate release scenarios because the toxin is inactivated by normal treatment of mains water supplies. There have been no reported cases of illness in humans worldwide due to contaminated water supplies.

Incubation period

The duration before onset of symptoms depends on the time taken for ingested toxin to reach the target site. In food-borne botulism symptoms usually occur between 12 and 36 hours (median time is 24 hours) after consumption of contaminated food, but can occur as early as 6 - 8 hours or as late as 8 days, depending on the levels and serotype of toxin.

Following aerosol exposure onset of symptoms may be more rapid, although it will probably still take some hours. The onset was 3-4 days after exposure in three cases of accidental inhalation botulism.

Period of communicability

Person-to-person transmission does not occur. Toxin can be detected in the faeces of cases, but normal infection control precautions will prevent ingestion.

Organism survival

C. botulinum is a spore-forming organism. Spores survive well in the environment, and may also survive heat and cooking. Spores do not produce toxin, but in anaerobic conditions they will germinate, and toxin is then produced by the vegetative organisms. The toxin undergoes natural inactivation in surface and drinking water over several days and is destroyed by chlorine. The toxin is inactivated by boiling but may be present in ready-to-eat foods and survive mild heating.

Last reviewed: 18 May 2010