Botulism

Botulism is a neuroparalytic syndrome manifesting as diffuse generalised flaccid paralysis caused by exposure to botulinum neurotoxin. It can be potentially fatal.

Botulinum toxin is the deadliest toxin due to high lethality and potency. The lethal dose (LD 50) is 1-3 ng of toxin per 1 kg of body mass.

As botulinum toxin injections become more commonplace in a wide variety of medical procedures, it is important to be aware of the potential complication of botulism.

Epidemiology

In the United States, 162 cases of botulism were reported between 2011-2015, most of which were infant botulism (up to 88%). The number of cases per year and relative proportions of cases have been relatively stable for the past 10 years.

Before 1950s, mortality for food related botulism was 60-70%. This gradually fell through the years and between 1975-2009, the mortality was 3%. In 2018, 242 cases of botulism were reported to the CDC.

Clinical presentation

• infantile

  • constipation, loss of appetite, poor latching, muscle weakness, poor head control

• adults

  • bulbar symptoms which progress to symmetric descending weakness of the trunk, smooth muscle and eventual flaccid paralysis

  • blurry vision, diplopia

  • paraesthesia

  • dysphagia

  • dysarthria

  • dysphonia

  • if there is concurrent cellulitis, consider assessing for history/clinical findings of intravenous drug use

Pathology

Clostridium botulinum is a bacteria found in a variety of locations including soil, rivers, sea and dust. The bacteria are also sometimes found in preserved food (vegetables, meat or fish) particularly if it is home-canned. Other bacteria of similar genus which could produce a similar toxin include Clostridium baratii and Clostridium butyricum.

Botulinum toxin has multiple subtypes, namely A, B, E, F, G and H. The majority of cases of botulism are due to subtypes A and B. Whilst most Clostridium botulinum produce a single toxin subtype, there have been reports of some strains producing dual toxin subtypes. Of the subtypes, type A is the most potent, followed by B.

The toxin binds to the presynaptic nerve terminals at voluntary motor and autonomic neuromuscular junctions. The heavy chain of the toxin encourages endocytosis and the light chain of the toxin is cleaved and enters the cytosol. The light chain will target polypeptide complexes which are required for acetylcholine containing vesicles to fuse with the presynaptic membrane. As such, the toxin blocks presynaptic acetylcholine release and inhibits muscular contraction- thus flaccid paralysis.

Aetiology

• food borne

  • improper cooking, preservation or canning techniques

• wound

  • skin break, intravenous drug use

• infant

  • ingest spore in contaminated food or soil such as honey (usually below age of 1 year old)

• iatrogenic

  • botulinum toxin injections (e.g. for cosmesis, migraine, movement disorders)

• bioterrorism

Treatment and prognosis

• antitoxin

  • heptavalent equine serum derived antitoxin (suitable for patients > 1 year old)

  • human derived immunoglobulin (suitable for patients <1 year old)

• supportive care

  • hospital admission

  • respiratory support including consideration of intubation

• wound botulism

  • debridement

  • IV penicillin G (or metronidazole if penicillin allergy)

    • avoid antibiotics for infant botulism due to release of botulinum neurotoxin following cell lysis