Botulism is a paralyzing and potentially fatal disease caused by the botulinum neurotoxins (BoNTs) produced by the Clostridium botulinum bacterium and, less frequently, by C. baratii and C. butyricum. This disease affects both humans and animals, but there are no documented cases of direct transmission between an animal suffering from botulism and a human.
What are the types of botulinum toxins produced by C. botulinum?
There are seven types of BoNTs classified from A to G on the basis of their immunological properties. Human botulism is mainly associated with the toxin types A, B and E, and more exceptionally F. Animal botulism is most often due to types C or D in poultry and cattle and types A, B, and C in horses.
What are the transmission routes for botulism?
There are 3 different forms of botulism:
- foodborne botulism: caused by ingesting the BoNT toxins produced during anaerobic proliferation (i.e. in the absence of oxygen) of the bacterium in food
- infant botulism: caused by the colonization of the intestine by C. botulinum and by the production of toxins in situ
- wound botulism: caused by the proliferation of bacteria in a contaminated wound.
What are the symptoms in humans?
The symptoms vary according to the type of botulism and the degree of exposure to the BoNT. They usually appear between 6 and 36 hours after exposure in the case of foodborne botulism and within 4 to 8 days in the case of an infected wound.
For all types of botulism, the first symptoms are:
- double or blurred vision
- difficulty of speaking and swallowing
- dry mouth
The neurological effect is afebrile (i.e. it is not accompanied by fever) and is characterized by visible acute paralysis in the region of the face, head, throat, chest and in the extremities. Respiratory insufficiency can lead to death.
What are the symptoms in animals?
Depending on the amount of toxin ingested, symptoms may be mild to severe (or even fatal). Mild symptoms are usually gastrointestinal, while severe symptoms include lateral decubitus (the animal is turned on its side), paddling movements, progressively worsening dyspnea (breathing difficulties), and dysphagia (swallowing difficulties).
How is botulism diagnosed?
Biological diagnosis is based on the detection and typing of botulinum toxin(s) in serum (human or animal) and on the detection of toxin(s) and/or neurotoxigenic Clostridium in stool (humans or animal). In the case of animals, organs like the liver and the kidney, as well as the stomach (or rumen) contents can also be used for diagnosis. The final diagnosis can be supported by the detection of BoNT and/or neurotoxigenic Clostridium in the suspect food.
What analyses are performed in the laboratory?
Botulinum toxins and toxin-producing bacteria are detected by means of a mouse bioassay (lethality test). Typing of the toxin is performed by seroneutralization tests by the use of specific antitoxins. The (neurotoxigenic Clostridium) bacterium is detected in the stool of patients and in suspect foodstuffs by enrichment culture followed by a qPCR molecular method. This can be done for samples of feces, organs (liver, kidney, etc.), gastric content, animal foodstuffs and water. In the case of serum samples, only the presence of toxin is analyzed. A negative result does not allow to exclude botulism.
How is botulism treated?
Botulism can be treated with an antiserum. This will not eliminate the effects of the disease but can prevent further neurological damage.
Which food products are at risk?
Foodstuffs typically associated with botulism are fermented fish products and homemade preserved food (such as smoked meat and vegetables) stored at room temperature. Infant botulism is principally associated with spores present in honey. Foodborne intoxications often concern small groups of two or more people, but larger outbreaks associated with restaurant visits are also possible.
Monitoring in Belgium
In Belgium, according to the data collected since 1988 by the NRC based at Sciensano, human botulism is a fairly rare disease. Only 19 cases of foodborne botulism have actually been confirmed since 1988. Of these, 15 were identified as cases of type B botulism, one case as type A (associated with the consumption of a dish of potatoes with onions and ham) and two cases for which neither the type nor the origin could be identified. Type B botulism is predominant in Belgium.
Monitoring in Europe
According to the monitoring data of the ECDC, 91 confirmed cases were reported in Europe in 2014 by 16 EU/EEA countries. Thirteen countries had no cases. The notification rate was therefore 0.02 cases per 100,000 inhabitants. Most of the confirmed cases were notified by Romania (31 cases), Poland (17 cases) and Hungary (12 cases). In Europe, in 2014, the male-female sex ratio observed was 1.9 and the most affected age groups were males aged 0-4 and 45-65 years and females aged 0-4 and 25-44 years.
In addition to cases of foodborne botulism, a botulism epidemic among drug users was identified in December 2014 in Norway and in Scotland. In February 2015, 23 cases of botulism were reported, 8 in Norway and 15 in Scotland. The suspected source of the infection was contaminated heroin.