27.6.4: Toxin-induced neurological disease

Question 1

True/false: Clostridium tetani prodces toxins constantly and in any environment.

Answer 1

False
* Toxin (tetanospasmin) is only produced under specific circumstances and anaerobic environment.
* The bacterium itself is ubiquitous in soil, ruminant faeces (GI).

Question 2

Incubation period of tetanus

Answer 2

7-21 days

Question 3

Mortality of tetanus

Answer 3

70%

Question 4

Clinical signs of tetanus

Answer 4

• Prolapsed nictitating membrane
• Tight facial expression (Risus sardonicus)
• Limb spasticity (“sawhorse” stance)
• Fixed extended neck
• Tight jaw (trismus)
• Laryngeal spasm (stridor), drooling
• Dysphagia
• Elevated tail head
• Recumbency
• Dyspnoea
• Hyperthermia
• Profuse sweating and tachy/bradycardia (autonomic storms)

Question 5

Treatment of tetanus

Answer 5

• Tetanus antitoxin >10,000 IU IV slow
• Muscle relaxants: dantrolene, methocarbamol, acepromazine
• Magnesium sulphate
• Supportive care: IV fluids and dextrose, quiet environment, thick bedding

Question 6

How does magnesium sulphate help in treatment of tetanus?

Answer 6

Magnesium sulphate:
* Blocks neuromuscular transmission
* Decreased catecholamine release
* Antagonises Ca

Question 7

How does tetanus most commonly enter the horse’s body?

Answer 7

Through dirty/contaminated wounds

Question 8

What should you do if you see a wound and are concerned about entry of tetanus?

Answer 8

• Open the wound, clean and debride it
• Give antibiotics: in human trials, metronidazole performed better than penicillin

Question 9

How do we prevent tetanus in horses?

Answer 9

• Vaccination of pregnant mares 4 weeks before delivery
• Vaccinate foals (first dose = 4-6 months, second dose = 4 weeks later, 3rd dose at 12 months, then biannually)
• In non-vaccinated mares, give foals tetanus anti-toxin at birth

Question 10

Causative agent for botulism

Answer 10

Clostridium botulinum exotoxin