CPD Article | EQUINE
Clinical signs
There is usually a history of a wound or surgery in
the preceding 1-4 weeks 10 . At first, clinical signs may
be vague with a mild lameness or stiffness and this
may be particularly localised to the contaminated
wound area 8 ; colic may also be noted. The clinical
signs will progress over the next 24 hours with a
more generalized stiff or spastic gait exhibited and
the tonic spasms of the striated muscles 8 can be seen.
The progression of the disease depends on a poor
vaccination status, the extent of infection and the size
and age of the horse 5 . Older and larger animals seem
to be less severely affected 8 . There is no confirmed
incubation period 10 as clinical signs are dependent on
the amount of tetanospasmin toxin that is produced
within the favourable anaerobic environment;
however signs are often evident 10 days after a deep
penetrating wound 2 12 .
Common signs seen are 5,9,10 :
• Trembling, sweating and mild pyrexia,
• Flared nostrils and erect ears,
• “Sawhorse” stance with raised and rigid tail,
• Extensor muscle rigidity that is exacerbated with
external stimulus,
• Enophthalmos and prolapse of the third eyelid
especially after a stimulus,
• “Lockjaw” from the spasm of master muscles
resulting in the inability to prehend or to masticate,
• Dysphagia, ptyalism and laryngeal spasm,
• Recumbency due to marked extensor rigidity
making voluntary movement impossible,
• Respiratory failure due to the spasm of respiratory
muscles and death,
Further complications include: decubital ulcers from
prolonged recumbency, regurgitation or aspiration
pneumonia due to the laryngeal spasm, dysuria due
to hypertonic urethral sphincter and constipation with
gaseous distension as a result of the hypertonia of
the anal sphincter and lack of exercise 8 . Involvement
of the autonomic nervous system results in cardiac
arrhythmias, tachycardia and hypertension.
Diagnostic approach
A detailed clinical examination coupled with the
history of a recent wound and an unvaccinated horse
allows for a presumptive diagnosis 2,9 of tetanus which
is important as an early diagnosis is a significant factor
in improving the treatment outcome 2 . Occasionally
horses may still develop tetanus despite being
vaccinated 5 but this is unusual. Confirmation of the
infection by anaerobic culture or gram staining is not
usually attempted as C.tetani is often found in low
concentrations within the wound and strict anaerobic
culture is required, therefore there is no reasonable
or easy diagnostic confirmation 4 or testing readily
available. Radiographs or thoracic ultrasonography
of horses suspected to have developed aspiration
pneumonia may be of use 5 in case prognosis and
management. Haematology, serum biochemistry and
CSF analysis are usually unremarkable8. There are no
characteristic post mortal lesions that can be ascribed
to the tetanus toxin.
Treatment
Tetanospasmin binding is extremely difficult to combat
and new interneuronal synapses need to develop
to replace those inactivated by the bound toxin8,
therefore recovery from an infection is slow. Treatment
success is based on the following goals 8 : interruption
of toxin production, neutralization of unbound toxin,
muscular spasm control and supportive care.
To stop further tetanospasmin production, the use
a parenteral antibiotic is imperative. The following
systemic antimicrobials can be administered: penicillin,
• Volume 21 Issue 1 | March 2019 •
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