PG.17
muscle contractions and spasms. Tetanus in all species
is usually contracted via a contaminated open wound.
Puncture wounds and foot penetrating wounds carry the
highest risk, but tetanus can be acquired by gastric ulcers
when horses eat manure or highly contaminated soil and
rough feedstuffs that cause wounds in the mouth or gut.
In 30% of clinical cases a wound or history of a wound
cannot be found.
The spores germinate in the dead and injured wound
tissue and produce toxins - tetanospasmin that blocks
transmission at nerve-muscle junctions throughout the
body, and tetanolysin that exacerbates tissue breakdown
and death at the site of initial infection. Travelling at 75
to 250mm a day, the tetanospasmin heads for the central
nervous system where it binds irreversibly to brain cells.
The outcome is muscular spasms and rigidity (which are
extremely painful, last for several minutes, may be severe
enough to fracture bones and persist for 3-4 weeks),
hypersensitivity to touch, light and sound, and eventually
convulsions, respiratory arrest and death.
Reduced intestinal activity, colic and dehydration are
frequent complications. Most cases that are unable to stand
are euthanised on welfare grounds. If the horse (or human)
survives treatment, regrowth of the nerve terminals takes
many months. Unvaccinated horses that recover are
unlikely to develop any significant protective immunity.
TABLE 1.
RANGE OF CLINICAL SIGNS OF TETANUS
Hypersensitivity to sound, touch
Limb spasticity
Stiff neck
Muscle spasms
Restricted jaw movement
Sweating
Dilated pupils
Anxious expression
Trouble swallowing
Increased heart and respiratory rate
Prolapse of third eyelid
Elevated tail
Stiff, erect ears
Fever
Lying down
Treatment requires heroic intensive care and nursing,
including wound care, tetanus antitoxin - (very expensive),
antibiotics, muscle relaxants and sedation, tracheostomy
(and sometimes mechanical ventilation), intravenous
or tube feeding, tetanus vaccination, manual evacuation
of the rectum and urinary catheterisation. The mortality
rate remains high and has not changed in the past two
decades. The solution to the problem of tetanus lies only
in vaccination.
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SEPTEMBER/OCTOBER ISSUE 2020