Treatment of Tetanus in Horses
The treatment of tetanus in horses requires immediate administration of tetanus antitoxin (50,000 IU intravenously, followed by three additional doses at 48-hour intervals), combined with procaine penicillin (25,000 IU/kg intramuscularly twice daily for 10 days) and muscle relaxants such as acepromazine (0.02-0.05 mg/kg intramuscularly twice daily for 8 days). 1
Pathophysiology and Clinical Presentation
Tetanus in horses is caused by the neurotoxin tetanospasmin produced by Clostridium tetani, a gram-positive anaerobic spore-forming bacterium commonly found in soil and animal excrement. Horses are particularly susceptible to tetanus compared to other domestic animals.
Common clinical signs include:
- Stiffness and muscle rigidity
- Prolapse of the third eyelid
- Hyperesthesia (increased sensitivity to stimuli)
- Dysphagia (difficulty swallowing)
- Respiratory distress
- Recumbency in advanced cases
Treatment Protocol
1. Neutralization of Unbound Toxin
- Tetanus antitoxin: 50,000 IU intravenously, followed by three injections of the same dose at 48-hour intervals 1
- Acts to neutralize circulating toxin that has not yet bound to nerve tissue
2. Elimination of Bacterial Source
- Procaine penicillin: 25,000 IU/kg intramuscularly, twice daily for 10 days 1
- Eliminates C. tetani bacteria at the infection site
- Wound debridement: Thorough cleaning and removal of necrotic tissue from the entry wound
3. Control of Muscle Spasms and Rigidity
- Acepromazine: 0.02-0.05 mg/kg intramuscularly, twice daily for 8 days 1
- Provides muscle relaxation and reduces anxiety
4. Supportive Care
- Intravenous fluid therapy to maintain hydration and electrolyte balance
- Nutritional support via nasogastric tube if dysphagia is present
- Assistance in maintaining quadrupedal position when needed
- Quiet, dark environment to minimize external stimuli that may trigger spasms
Prognostic Factors
Several factors affect prognosis in horses with tetanus:
- Vaccination status: Previously vaccinated horses have significantly better survival rates (p = 0.03) 2
- Response to tranquilizers: Horses that respond well to phenothiazine tranquilizers have better outcomes 2
- Progression to recumbency: Rapid progression to recumbency (within 24-48 hours) indicates a poor prognosis 2
- Early diagnosis and treatment: Timely intervention significantly improves survival rates 1
Mortality Rates
Recent data shows a mortality rate of approximately 23.5% with proper treatment 1, which is significantly improved from historical rates of 75% reported in older studies 2. This improvement likely reflects advances in supportive care and earlier intervention.
Prevention
Given the high susceptibility of horses to tetanus and the improved survival rates in vaccinated animals, annual vaccination with tetanus toxoid is strongly recommended 2. For unvaccinated horses with wounds, immediate administration of tetanus antitoxin provides short-term protection.
Alternative Treatment Approaches
Some studies have explored intrathecal (subarachnoid) administration of tetanus antitoxin, with one older study reporting improved recovery rates (77.5% versus 50%) compared to traditional routes of administration 3. However, this approach carries risks including seizures 2 and is not part of standard treatment protocols.
Important Considerations
- The incubation period for tetanus in horses averages 9 days (range 2-21 days) after injury 2
- Tetanus can develop despite appropriate vaccination in rare cases 4
- Multiple organ systems are affected, requiring broad supportive care
Early recognition and aggressive treatment are essential for improving survival rates in horses with tetanus.