Tetanus in Horses

Tetanus, or lockjaw, is an often fatal disease caused by the anaerobic bacteria (grows in low oxygen conditions), Clostridium tetani. The spores of Cl. tetani are commonly present in the soil and can contaminate puncture wounds, crushing wounds, open lacerations, surgical incisions and the umbilici of foals. Upon gaining entrance to the body, they produce a powerful neurotoxin that blocks neurotransmission, resulting in unopposed muscle contraction and spasm (tetany). Horses often adopt a "saw horse" posture. The incubation period is approximately 8 days (range 3 to 21 days) (1). Spores can also remain dormant in muscles and begin to grow when trauma occurs, making tissue oxygen level low. Horses of all ages can be affected. Horses are the most susceptible of all of the animal species. Tetanus can also affect humans. The disease is not contagious between horses or between horses and humans. The number of horses affected with tetanus annually in Ontario is unknown but would appear to be low (less than 5).

Cl. tetani is present in the feces and intestinal tracts of horses, and humans. Soil contaminated with horse feces commonly contains Cl. tetani spores. Therefore, humans working around horses and horse farms should seek immediate medical attention when injured, especially with penetrating wounds such as those caused by nails. Following a properly administered primary series of tetanus vaccine, virtually all persons develop a protective level of antitoxin (1). Booster vaccines for adult humans are recommended every 10 years (1).

Prevention

Horses should be vaccinated against tetanus using a tetanus toxoid to induce active immunity. Formalin-inactivated, adjuvanted toxoids are readily available and often combined with other vaccines. They appear to be very safe and induce a long-lasting immunity. The American Association of Equine Practitioners recommends (2):

• Foals from non-vaccinated mares should receive their first vaccination for tetanus (tetanus toxoid) between 3 and 4 months of age. The second vaccination should be given between 4 and 5 months of age, followed by a third vaccination between 5 and 6 months of age.
• Foals from vaccinated mares should receive their first vaccination for tetanus at 6 months of age, followed by booster vaccinations at 7 and 8 to 9 months of age. Tetanus vaccination should be repeated annually thereafter.
• Brood mares should be vaccinated annually 4 to 6 weeks before foaling to enhance the concentration of anti-tetanus antibodies in their colostrum.
• Adult non-vaccinated horses or horses with unknown status should receive an initial series of 2 doses of tetanus toxoid administered 3 to 6 weeks apart, followed by an annual booster.
• Adult vaccinated horses (those that have previously been vaccinated with the 2-dose regimen), should receive an annual booster.

Tetanus antitoxin is produced by hyperimmunization of donor horses and then harvesting the antibodies. It is used to administer to unvaccinated horses to induce short-lived, immediate, passive protection. The passive immunity usually lasts only 2 to 3 weeks.

Recommendations

• All horses should be vaccinated for tetanus annually or as recommended by their veterinarian.
• All humans working with horses should ensure that their vaccination status for tetanus is current as recommended by their doctor.
• Proper immunization and wound management should prevent tetanus.

References

1. Tetanus. In: Epidemiology and Prevention of Vaccine-Preventable Diseases - The Pink Book. 7th ed. Waldorf, Maryland, USA: Public Health Foundation, Centres for Disease Control and Prevention, 2003: 49-57.
2. Barnett CD, Brumbaugh GW, Holland RE, Lunn P, Vaala W, Voss ED, Wilson WD. Guidelines for Vaccination of Horses. Lexington, Kentucky, USA: American Association of Equine Practitioners, 2001: 3-4.