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Update on tetanus prevention – April 2017

April 23, 2017

Update on tetanus prevention – April 2017

Marcus Allan, BVSc

In a recent vet meeting at the Matamata Veterinary Services Equine Hospital we discussed tetanus, with an emphasis on appropriate preventative recommendations based on current scientific literature.

Tetanus is caused by the bacterium Clostridium tetani, which forms spores that survive in soil. The spores are widespread in the environment and very resistant to being killed. The bacterial spores gain access to the horse’s body through wounds that are contaminated by soil, such as deep puncture wounds, foot abscesses, surgical wounds, the umbilicus in foals and the reproductive tract in mares post-foaling. The bacterium is anaerobic and favours an environment with low oxygen levels such as that found in bruised or traumatised tissues. If conditions are favourable for growth the spores are activated and the bacteria start to multiply. The incubation period of the disease can be several weeks and therefore the original wound may be healed by the time clinical signs of tetanus develop.

  1. tetani produces toxins that bind to the nervous system, resulting in the typical clinical signs of tetanus. These include an exaggerated response to stimuli (hyperaesthesia), rigid posture (“saw horse” stance), stiff gait, elevated tail, difficulty opening the mouth (“lockjaw”), inability to eat (dysphagia), altered facial expression (lips pulled back into grimace, flared nostrils, erect ears, prolapsing or flicking the third eyelid across the eye), generalised muscle spasms, inability to walk, falling over, “star-gazing” (opisthotonus) when lying down and seizures, all of which quickly progress in severity. Affected horses usually die from respiratory failure, or are subjected to euthanasia.

The prognosis for surviving clinical diseased caused by C. tetani is very poor, with 60-85% of affected horses dying or being euthanased. Therefore, disease prevention through vaccination is strongly recommended. However, recommended vaccination protocols vary significantly between countries, prompting our review of the current literature.

There was much discussion about the use of tetanus vaccine (toxoid) versus the anti-toxin. The toxoid stimulates long-lasting immunity but takes at least 2 weeks to start producing immunity and around 6 weeks before strong immunity develops, whereas the anti-toxin provides immediate protection against tetanus that lasts approximately 3 weeks before wearing off. One potential concern with use of the anti-toxin is the possibility of inducing serum hepatitis. This is an immune reaction of the recipient horse to the blood proteins of the donor horse used to create the anti-toxin. The chance of this happening is very low but when it occurs it can be a serious complication. For this reason we prefer to use the toxoid alone whenever possible prior to surgery or when treating a wound; however, if the horse’s vaccination status is unknown it is essential to give the anti-toxin as well to provide that immediate protection. Because the toxoid takes at least 2 weeks to produce some degree of immunity, if the horse is unvaccinated the tetanus bacteria could invade and start producing toxins before the horse’s immune system becomes activated by the toxoid.

Given these facts, Matamata Veterinary Services now make the following recommendations:

  • Unvaccinated horses (or vaccination status unknown)
    • 2 vaccinations 4 weeks apart, followed by a booster dose 1 year later
    • Foals start vaccinations at 3 months of age or older e.g. at weaning
  • Vaccinated horses (maintenance)
    • Booster dose every 3-5 years
  • Horses with wounds (or having surgery)
    • If vaccinated within the previous 3-5 years then boost with vaccine
    • If vaccinated >3-5 years ago (or vaccination status unknown) then boost with vaccine and give anti-toxin simultaneously
      • This should be followed up with a second vaccine at 4 weeks and a booster dose 1 year later for full protection
  • Pregnant mares
    • If vaccinated within the previous 3-5 years then boost with vaccine 4-6 weeks before foaling
    • If vaccinated >3-5 years ago (or vaccination status unknown) then vaccinate 8-10 weeks before foaling so second dose is given 4-6 weeks before foaling
  • New-born foals
    • Give anti-toxin at birth if mare was not vaccinated during pregnancy (or her vaccination status is unknown) or if foal has not received adequate colostrum (regardless of mare’s vaccination status)

Keeping accurate tetanus vaccination records is the best way to ensure appropriate tetanus prevention is given when required. This is not always easy due to horses being moved and sold frequently. Vaccination status should be discussed before horses are moved or sold so the new manager or owner is well-informed and able to make the correct decisions to protect the horse from this devastating disease.