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):
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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.
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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.