Botulism

Botulism is a paralytic illness caused by a potent neurotoxin produced by various strains of Clostridium botulinum, and sometimes by Clostridium butyricum and Clostridium baratii bacteria. There are six main kinds of botulism: foodborne botulism, wound botulism, intestinal botulism (infant and adult infectious), inhalational botulism, botulism of unknown source and inappropriate administration of botulinum toxin during its use as a pharmaceutical agent (iatrogenic botulism). All forms of botulism can be fatal and are considered medical emergencies.1 Cases of botulism in any species are important to note because C. botulinum toxin is one of six priority A bioterrorism agents as described by the U.S. Offices of Health and Human Services and Homeland Security. The other five agents include: anthrax, plague, tularemia, smallpox, and viral hemorrrhagic fevers.5

Botulism occurs when animals ingest preformed toxins in food or C. botulinum spores germinate in anaerobic tissues and produce toxins as they grow. Seven types of botulinum toxin, designated A through G, have been identified. Types A, B, E and F cause illness in humans. Type C is the most common cause of botulism in animals. Type D is sometimes seen in cattle and dogs, and type B can occur in horses. Types A and E are found occasionally in mink and birds. Type G rarely causes disease, although a few cases have been seen in humans. Preformed toxins in a variety of sources, including decaying vegetable matter (grass, hay, grain, spoiled silage) and carcasses can cause botulism in animals. The major food sources of botulism toxin are fish, home cured meats, home canned vegetables, and fruit. Eggs, milk and their products are rarely the cause of an outbreak. Most frequently, raw, insufficiently cooked foods or foods not fully salted, cured, dried or smoked are implicated. Humans are usually affected by A, B, E, and very rarely F toxins. Domesticated animals such as dogs, cattle, and mink are affected by botulism C toxin, which also affects birds and has caused massive die-offs in domestic bird flocks and wild waterfowl.

Botulinum neurotoxin (BoNT) is acknowledged to be the most poisonous protein known. This sophisticated nanomachine attacks the nerve endings by binding to their receptors and thus getting access to the inside of the neurons, where it splits protein complexes required for the acetylcholine neurotransmitter release thus causing prolonged muscle weakness. This unique combination of activities underlies the effectiveness of BoNT. Its modular design and the tight interplay between its component modules result in a partnership with consequences that surpass the simple sum of the individual component's action. BoNTs exploit this design at each step of the intoxication process, thereby achieving an exquisite toxicity.



The incubation period after the ingestion of contaminated food in dogs has been from hours to 6 days. The earlier the signs appear, the more serious is the disease. The duration of illness in dogs that recovered has ranged from 14 to 24 days. Clinical signs may include excessive salivation, paralysis in hind limbs progressing to forelimbs; facial paralysis, and paralysis of respiratory muscles resulting in death. Affected dogs may have difficulty in swallowing; lose ability to urinate and defecate; and impaired vision. Death is usually from respiratory paralysis or heart failure. Diagnosis of botulism can be tricky because symptoms mimic those seen in other diseases. Botulism may be confused with myasthenia gravis, drug reactions, nervous system infection or shellfish poisoning. Botulinum toxin can be detected using special systems in about 20-25 minutes. Now, researchers at DOE's Pacific Northwest National Laboratory can detect its presence in five minutes, using the lab's successful Biodetection Enabling Analyte Delivery System, or BEADS combined with optical detection. Treatment involves activated charcoal, respiratory support, and administration of the antitoxin. Early symptomatic detection can prevent up to two thirds of the casualties.6

References

  1. Botulism
  2. C. Greene. Infectious Diseases Of The Dog And Cat.
  3. Botulism
  4. Avian Botulism
  5. Zoonotic Disease & Adverse Event Monthly Surveillance Summary
  6. Principles and Methods of Toxicology (edited by A. Wallace Hayes)
  7. Handbook of Clinical Neurology Volume 91, 2008, Pages 333-368





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