Tetanus is a highly fatal disease caused by the toxin, tetanospasmin from the bacteria Clostridium tetani.
Clostridium tetani lives in the soil as spores and can also be found in the gastrointestinal tract and feces of animals. Infection occurs when wounds become contaminated with these spores. If the conditions in the wound are ideal, the spores germinate, bacteria multiplies and toxins are produced. The spores may be viable for a long time in wounds. The incubation period can vary from several days to several months but it is typically 1-3 weeks. Spores can lie dormant in tissue, long after the wounds have healed.
The toxin travels via nerves and the blood vessels to the central nervous system. Here, it blocks the release of certain neurotransmitters (chemicals which control nerve function) leading to excitatory signals which causes persistent and intense contraction of muscles. This is an important point as it allows us to understand the signs of tetanus
Typical signs of tetanus in horses :
- Over-reaction to normal stimulus
- Spasm of muscles of the jaw – “lockjaw”
- Spasm of the facial muscles – anxious expression
- Contraction of the ocular muscles causing the eyeball to be pulled inwards, leading to the third eyelid becoming more prominent – “3rdeyelid flash”
- Inability to posture to urinate or defaecate – causing urine and fecal retention
- Regurgitation and aspiration of feed
- Difficulty in rising due to prolonged muscle spasms
- The muscle spasms can be so severe that they can cause fracture of the vertebrae
Treatment of tetanus involves intensive care. Therapy usually includes high doses of specific antibiotics, administration of tetanus anti-toxin, reducing anxiety and stress to control muscle spasms, general metabolic and nutritional support.
Recovery can occur, but this depends on the severity of clinical signs and may take 2-3 months.
Vaccination is usually very effective at preventing tetanus. Immunisation with a Tetanus toxoid (2 injections 4 weeks apart), followed by annual vaccinations is recommended. Pregnant mares should be given a Tetanus toxoid 4 weeks prior to foaling. Horses that suffer wounds and which are not vaccinated should receive both a tetanus anti-toxin and toxoid (at different sites) followed by a second toxoid 4 weeks later.