NAME: Clostridium botulinum.
CHARACTERISTICS: A gram-positive (at least in early stage of growth), anaerobic, rod- shaped(3), spore-forming bacillus(1-3). Seven types of C. botulinum toxins exist (A-F)(1,2, 5).Types A, B, E, and rarely F can cause human botulism. Strains consistent with type G were assigned to C. argentinense in 1993. Botulinum neurotoxin is produced when, under anaerobic conditions, C. botulinum spores germinate(3,5,6). In addition to C. botulinum, C. argentinense (formerly C. botulinum type G), C. butyricum, and C. baratii can also produce botulinum neurotoxin.
C. botulinum (botulinum toxin) is defined as a biothreat level A organism by the Centers for Disease Control and Prevention(7). Category A organisms are considered to pose the greatest threat to national security.
PATHOGENICITY: Rare but serious paralytic disease(1,6), caused by a neurotoxin formed during the growth of the spore-forming bacterium C. botulinum (or rarely, C. argentinense, C. butyricum, or C. baratii )(3,5). This neurotoxin binds to the neuromuscular junction and blocks excitatory synaptic transmission by inhibiting acetylcholine release(2,8), causing (flaccid) paralysis(1,5,6), and sometimes fatal respiratory failure(1,2,5,8). The fatality rate of botulism is 5 to 10%(8).
Food-borne botulism: The classic form of botulism is caused by the ingestion of preformed toxin in contaminated food(1,2,4,5). Symptoms include double vision, drooping eyelids (ptosis), slurred speech, difficulty swallowing and muscle weakness that is symmetric and descends through the body (first shoulders are affected, then upper arms, lower arms, thighs, calves, etc.)(1). Death is usually due to respiratory failure(1,2,6,8) and may occur as soon as 24 hours after onset of symptoms(8).
Wound botulism: Occurs by contamination of a wound with spores from neurotoxin-producing Clostridium species in the environment and subsequent germination of these spores and production of toxin in the anaerobic milieu of an abscess(1,4,5). The toxin is released into the bloodstream(1,4) and symptoms may take up to 2 weeks to appear(1).
Intestinal (infant) botulism: Results almost exclusively from spore ingestion and subsequent growth and toxin production in the intestine(1,2,5), affecting infants under 1 year old(1,5,9). The first clinical sign is usually constipation(1,2), but this disease has a wide spectrum of clinical severity, ranging from mild illness with gradual onset, to sudden infant death due to respiratory failure(1,2). With appropriate intensive care, almost 100% of infants with botulism make a full recovery(5). Infants with botulism are lethargic, feed poorly, have a weakened cry, exhibit ptosis, and floppy neck, and may progress to generalised flaccidity and respiratory compromise(2,4).
Adult infectious botulism: Rare(5). Caused by the intestinal colonization of C. botulinum / other neurotoxin producing species, followed by in vivo toxin production in a manner similar to infant botulism(1,2,5). Patients often have a history of immunocompromise, abdominal surgery, bowel disease, or recent antibiotic therapy.
Inhalational botulism: Is not a naturally occurring disease(5), but has occurred in laboratory workers due to inhalation of aerosolized toxin(1). Inhalational botulism leads to neurological symptoms similar to those of food-borne botulism, but with a longer incubation period(5,6).
Iatrogenic botulism: Side effects resulting from the therapeutic intramuscular injection of Botox (purified, diluted A neurotoxin)(5). Characterized by clinical weakness and electrophysiological abnormalities(10,11).
EPIDEMIOLOGY: Sporadic. Family and general outbreaks occur worldwide in association with food products prepared or preserved by means that do not destroy spores and permit the formation of toxin(1,2,5).
INFECTIOUS DOSE: Cells/spores are not normally toxic for healthy adults(2). Botulinum toxin is the most potent toxin known, with an estimated oral or injected toxic dose (serotype A) of 0.001 μg/kg body weight, and an estimated lethal dose by inhalation exposure in humans of approximately 0.07 μg/kg body weight(5,6). Type A toxin is more potent than types B and E and causes the longest lasting disease(9).
MODE OF TRANSMISSION: Food borne botulism: Ingestion of contaminated food containing toxin(1,2,5). Infection is commonly associated with commercially processed foods that had undergone poor processing, storage, and improper preservation(12).
Wound botulism: Contamination of wounds with spores of neurotoxin producing Clostridium species(1,2,5) and is seen almost exclusively in injection drug users, particularly those who partake in injection of black-tar heroin into skin tissue(5,13).
Iatrogenic botulism: Side effect of injection of purified toxin(5).
INCUBATION PERIOD: The shorter the incubation period, the more severe the disease and the higher the case fatality rate(1).
Food-borne botulism: Usually 12 to 72 hrs after ingestion of toxin, depending on the dose(9).
Wound botulism: The median period is 7 days(9).
Adult infectious botulism: Unknown(1).
Intestinal botulism: Unknown(1).
ZOONOSIS: No epidemiological relationship between human and animal botulism has been established(2).
DRUG SUSCEPTIBILITY: Susceptible to penicillin, metronidazole, clindamycin, cephalothin, cefoxitin, cefotaxime, chloramphenicol, tetracycline, erythromycin, rifampin, and vancomycin (with some strain variation)(15,16).
DRUG RESISTANCE: Usually resistant to the aminoglycosides(3), and may be resistant to tetracyclines and cephalosporins (with some strain variation)(16,17). Also resistant to nalidixic acid and sulphamethoxazole-trimethoprim (SMX-TMP)(18).
SUSCEPTIBILITY TO DISINFECTANTS: The vegetative state is susceptible to disinfectants such as 70% ethanol, 0.1% sodium hypochlorite, and 0.1N NaOH(19). Spores may be resistant to disinfectants. Toxins are inactivated (more than 99.7%) by 20 minutes exposure to 3 mg/L free available chlorine (FAC; similar to the military disinfection procedure), and 84% inactivated by a treatment of 20 minutes at 0.4 mg/L FAC (similar to municipal water treatment procedures)(6).
PHYSICAL INACTIVATION: Toxin is destroyed after heating for 5 minutes at greater than 85°C(1,8,9). Toxins are detoxified in air within 12 hours and following exposure to sunlight within 1 to 3 hours(9). Spores are highly resistant to heat(2) and desiccation(2); therefore, it is recommended to sterilize with dry heat (2 hours at 160°C) by autoclaving (20 minutes at 121°C, 1 atm pressure) and/or by irradiation(9).
Food borne botulism: Can be diagnosed by demonstration of toxin in serum(1,2,5,8,15), stool(1,2, 6,8), gastric aspirate(1,2,5) or implicated food(1,2,5), or by culture of C. botulinum from a patient's gastric aspirate or stool in a clinical case(1,5). The mouse bioassay is the most reliable method for detection of botulinum(5,6,8).
Adult infectious botulism: Can be diagnosed by demonstration of C. botulinum (or other neurotoxin producing species) and/or toxins in a patient's faeces or in autopsy specimens(1).
Intestinal (infant) botulism: Since the toxin is rarely found in the sera of infants(1,2), faeces should be examined(1). An ELISA has been developed for the detection of A and B toxins in children's faecal samples(2).
Inhalational botulism: Aerosolized toxin can not usually be identified in serum or faeces, but may be detected by ELISA from nasal swabs(8).
Note: All diagnostic methods are not necessarily available in all countries.
Foodborne botulism: Within 1 hour of ingestion of suspected food, the recommended course of action is a gastric lavage(1,2), or enemas(1), and the administration of a cathartic (sorbitol)(1). In some cases intravenous administration of AB or ABE(1,2,6,8) botulinum antitoxin(1,2,5,6,8) is required, and assisted ventilation if respiratory failure occurs. Treatment may be required for weeks or months(5).
Infant botulism: Requires meticulous supportive care(1). Instead of antitoxin which can cause sensitization and anaphylaxis(1,6,8), an investigational human-derived botulinal immunoglobulin (BIG) is available for the treatment(1) and assisted respiration is given if required(1,5).
PROPHYLAXIS: Individuals known to have eaten contaminated food should be purged with cathartics(1), given a gastric lavage and high enemas(1), and may be given equine botulinum AB or ABE antitoxin(1,6).
LABORATORY-ACQUIRED INFECTIONS: Rarely reported(5).
SOURCES/SPECIMENS: Food products, and clinical materials such as serum/blood, stool, vomit, and gastric aspirates(5). For wound botulism: wound exudates, debrided tissue, or swab sample. Other sources include, nasal swabs from inhalational botulism patients, and environmental samples (soil, surface water)(1,2,6,9).
PRIMARY HAZARDS: Exposure to the toxin. The toxin may be absorbed after ingestion, or following contact with the non-intact skin, the eyes, or mucous membranes, including the respiratory tract(5). Inhalation of the toxin has occurred under laboratory conditions(5,6).
SPECIAL HAZARDS: None.
RISK GROUP CLASSIFICATION: Risk Group 2(21).
CONTAINMENT REQUIREMENTS: Containment Level 2 facilities, equipment, and operational practices for work involving infectious or potentially infectious materials, animals, or cultures.
PROTECTIVE CLOTHING: Lab coat. Gloves when direct skin contact with infected materials or animals is unavoidable. Eye protection must be used where there is a known or potential risk of exposure to splashes(19).
OTHER PRECAUTIONS: All procedures that may produce aerosols, or involve high concentrations or large volumes should be conducted in a biological safety cabinet (BSC). The use of needles, syringes, and other sharp objects should be strictly limited. Additional precautions should be considered with work involving animals or large scale activities(19).
SPILLS: Allow aerosols to settle, and, while wearing protective clothing, gently cover the spill with paper towels and apply appropriate disinfectant starting at the perimeter, working inwards towards the centre. Allow sufficient contact time before clean up(19).
DISPOSAL: Decontaminate before disposal, using steam sterilisation, incineration, or chemical disinfection(19).
STORAGE: In locked, leak-proof containers that are appropriately labelled and secured(19).
REGULATORY INFORMATION: The import, transport, and use of pathogens in Canada is regulated under many regulatory bodies, including the Public Health Agency of Canada, Health Canada, Canadian Food Inspection Agency, Environment Canada, and Transport Canada. Users are responsible for ensuring they are compliant with all relevant acts, regulations, guidelines, and standards.
UPDATED: September 2010.
PREPARED BY: Pathogen Regulation Directorate, Public Health Agency of Canada.
Although the information, opinions and recommendations contained in this Pathogen Safety Data Sheet are compiled from sources believed to be reliable, we accept no responsibility for the accuracy, sufficiency, or reliability or for any loss or injury resulting from the use of the information. Newly discovered hazards are frequent and this information may not be completely up to date.
Public Health Agency of Canada, 2010