April 17, 2025 Author : Saraiva da Cunha (infectious diseases) Botulism is a serious, potentially fatal disease caused by botulinum toxin, a neurotoxin produced by the bacterium Clostridium botulinum . It is a rare disease. In European Union countries around 200 cases occur per year on average. Described for the first time in the early 19th century, in Germany, botulism has three main forms , which differ mainly in the mode of infection: foodborne, wound and infant botulism . Clostridium botulinum and botulinum toxin Clostridium botulinum is an obligate anaerobic bacteria, that is, it only multiplies in the absence of oxygen. In unfavorable conditions, Clostridium botulinum forms spores, which are a protection and inactive form that allows it to survive . Clostridium botulinum spores occur naturally in the environment all over the world. They can be isolated from soil, dust, marine sediment, fruit and vegetable surfaces, among others. They can also be transported in the air. Spores are very resistant to the environment and last for many years. They are destroyed by heat at 120°C for at least 5 minutes. When the spores encounter favorable conditions, they germinate and the active bacteria produce botulinum toxin . Favorable conditions include: Lack of oxygen; pH 7 or higher; Temperature between 25ºC-37ºC Botulinum toxin is responsible for botulism, a disease that, although not very common, can be fatal. There are eight types of botulinum toxin – A to H. Types A, B, E, F and, more rarely, G and H can cause disease in humans. This bacterial toxin is one of the most lethal substances known. It has no odor or taste. When ingested, it is resistant to stomach acidity and digestive enzymes. Botulinum toxin is inactivated: By exposure to chlorinated water for 20 minutes; By exposure to fresh water for 3-6 days; By heat at temperatures above 85ºC. Botulinum toxin is a neurotoxin , that is, it acts on the nervous system. It affects the function of peripheral nerves, which stop releasing neurotransmitters (acetylcholine), paralyzing the muscles, which become flaccid and unable to contract . Mode of infection and types of botulism Botulism occurs as a result of three main modes of infection that give rise to the various types of the disease: By ingesting food contaminated with botulinum toxin: foodborne botulism It almost always occurs in small outbreaks related, most frequently, to the consumption of preserved foods and other processed foods, which were prepared from foods contaminated by spores and have not been subjected to adequate treatments to eliminate them. This way, the spores found favorable conditions (humidity, nutrients and absence of oxygen) to germinate and produce toxin. By ingesting food contaminated with Clostridium botulinum spores Once ingested, the spores germinate and produce toxins, causing: Infant botulism in children under 1 year of age, due to their digestive immaturity. Intestinal botulism in adults , which is rare because the digestive system is resistant to colonization by spores, with the exception of children under 1 year of age. By contamination of deep wounds with spores: wound botulism Mainly associated with the injection of illicit substances but may occur in other circumstances in which wounds are a favorable environment for contamination and germination of spores. Rarer modes of infection include: Inhalation of botulinum toxin, for example in laboratory accidents or bioterrorism events. Adverse effects of the medical or cosmetic use of botulinum toxin, which are rare and give rise to iatrogenic botulism. Symptoms and treatment All types of botulism vary in severity and can be fatal. Symmetrical descending muscle paralysis and vision changes (with dilated pupils) are the most characteristic and common symptoms of the different types of the disease. In foodborne botulism , symptoms generally begin 18-36 hours after ingestion of the toxin, but the incubation period can vary from a few hours to 2 weeks. There is no fever. Nausea, vomiting, abdominal pain, and diarrhea may precede or be simultaneous with symptoms of paralysis. In wound botulism , the incubation period is about 10 days (range 7 to 21 days). Fever may occur and there are no digestive symptoms. Infant botulism usually begins with constipation, difficulty breastfeeding, drooping eyelids, and moaning. When paralysis affects the respiratory muscles and diaphragm, it increases the likelihood of respiratory failure and also the mortality rate. The diagnosis of botulism is based on epidemiological data, clinical symptoms and laboratory tests that allow the detection of botulinum toxin in biological samples from the patient and in suspected foods. Botulism treatment needs hospitalization, in the most severe cases in intensive care, and is based mainly on support measures and the administration of antitoxin . In Portugal, the Direção Geral de Saúde has drawn up a rules about use of antitoxin for healthcare professionals (Norma 002/2025 of 31/01/2025). Full recovery of botulism takes weeks to months, and 5%-10% of severe cases are fatal, despite the medical resources now available. Preventing botulism There is no vaccine to prevent botulism, although this possibility is being investigated. Prevention measures include all actions that allow avoiding exposure to Clostridium botulinum s pores or botulinum toxin , including: Always keep food at the appropriate temperature and humidity conditions, in closed containers and comply with expiration dates; Do not eat raw fruits and vegetables without washing them well first; Cook food thoroughly; Follow the appropriate heat treatments (temperature and time) when preparing homemade preserved food; Discard canned food if they are swollen, as this could be a sign of gas production by bacteria, including Clostridium botulinum. Discard any preserved or processed foods whose packaging or appearance does not appear normal; Do not give honey to children under one year old; Seeking medical attention for deep open wounds is the primary preventive measure for wound botulism. Sources European Centre for Disease Prevention and Control. Botulism . Kobaidze K, Wiley Z. Botulism in the 21st century: A scoping review. Brown Hospital Medicine. 2023;2(2).doi: 10.56305/001c.72707 Pegram PS. Botulism. www.uptodate.com Meet the infectious diseases clinical team from Hospital da Luz network. The content published in the Health Guide is intended for the general public and is provided for informational and educational purposes only. It does not replace individual medical assessment, diagnosis, or personalized clinical advice from a qualified healthcare professional. The content is produced or reviewed by physicians and other healthcare professionals at Hospital da Luz and is based on the knowledge available at the time of publication or the most recent update, as indicated at the beginning of each item.
