All horses are at risk of development of tetanus, an often-fatal disease caused by a potent neurotoxin elaborated by the anaerobic, spore-forming bacterium Clostridium tetani. Tetanus toxoid is a core equine vaccine and should be included in equine immunization programs for every horse annually.
Clostridium tetani organisms are present in the intestinal tract and feces of horses, other animals, and humans, and are ubiquitous and abundant in soil. Spores of Cl. tetani survive in the environment for many years, resulting in an ever-present risk of exposure of horses and people at equine facilities. Tetanus is not a contagious disease, but rather is the result of Cl. tetani infection of puncture wounds (particularly those involving the foot or muscle), lacerations, surgical incisions, exposed tissues such as the umbilicus of foals, and the reproductive tract of the postpartum mare (especially in the event of trauma or retained placenta).
Vaccines currently available are formalin-inactivated, adjuvanted toxoids. Tetanus toxoid is a potent antigen that rapidly induces strong serological responses. Circulating antibodies are able to mediate complete protection against tetanus. It is generally accepted that tetanus toxoid administered per manufacturer recommendations is both safe and efficacious.
All tetanus toxoid vaccines are labeled for annual (12 month) revaccination. Extending the time-interval for annual revaccination beyond the manufacturer’s recommendation is not advisable due to a veterinarian’s liability if label recommendations are not followed.
There are no challenge studies that have been published to document the onset or duration of immunity induced by tetanus toxoid products available for use in horses in the United States. Conclusions regarding the efficacy of products used in the U.S. are based on serologic responses in laboratory animals and field experience per the USDA APHIS 9-CFR. This is because antibody alone has been demonstrated to mediate protection against tetanus. Tetanus has rarely been documented in vaccinated horses in the U.S. Tetanus toxoids are highly efficacious such that documented cases of tetanus most often occur when incomplete or ineffective vaccination has occurred. Survival of horses infected with Clostridium tetani organisms is strongly associated with previous vaccination.
Adult horses, previously vaccinated against tetanus: Annual vaccination is recommended. Horses that sustain a wound or undergo surgery ≥ 6 months after their previous tetanus booster should be revaccinated with tetanus toxoid immediately at the time of injury or surgery. Note: The severity of the wound does not predict the risk for development of tetanus: superficial wounds have resulted in clinical tetanus in horses.
Adult horses, previously unvaccinated against tetanus, or of unknown vaccinal history: A 2-dose series of tetanus toxoid with a 4- to 6-week interval between doses is recommended. Protective concentrations of immunoglobulin are usually attained within 14 days after the second dose of vaccine. These horses should be vaccinated annually thereafter.
Pregnant mares previously vaccinated against tetanus: Annual vaccination, 4 to 6 weeks prior to foaling, both to protect the mare from either foaling-induced trauma or retained placenta, and to enhance concentrations of colostral immunoglobulins to protect their foals.
Pregnant mares unvaccinated against tetanus or of unknown vaccinal history: Administer a 2-dose primary series of tetanus toxoid with a 4- to 6-week interval between doses. Revaccinate 4 to 6 weeks before foaling.
Foals of mares vaccinated against tetanus in the peripartum period: Administer a primary 3-dose series of tetanus toxoid beginning at 4 to 6 months of age. A 4–6-week interval between the first and second doses is recommended. The third dose should be administered at 10 to 12 months of age.
Foals of unvaccinated mares or mares of unknown vaccinal history: Administer a primary 3-dose series of toxoid beginning at 3 to 4 months of age. A 4- 6week interval between the first and second doses is recommended. The third dose should be administered at 10 to 12 months of age. Serologic data indicates that a 3-dose initial series produces a more consistent anamnestic response in all foals, regardless of the age at which the series is initiated. Tetanus antitoxin is indicated to provide passive immunity in situations where a foal is born to a non-vaccinated mare and is at risk of tetanus infection (see information above regarding tetanus antitoxin above).
Horses recovered from naturally infection with tetanus: Such horses should be vaccinated annually.
Revised – 2021