INTRODUCTION

Tetanus is the disease produced by the Clostridium tetani toxin tetanospasmin within the CNS where it prevents inhibitory interneurons from releasing glycine and GABA. Uninhibited continuous muscular contraction results in either a generalized or focal form of the disease. The toxin load and possibly species susceptibility determines which will develop and the rate of progression of signs.

C. tetani is ubiquitous and survives in the environment for months to years as spores. Inoculation of tissue by a penetrating wound creates the anaerobic environment required for conversion to the toxin-producing vegetative form of C. tetani.

Stick injuries, teething, nail bed infections, bites, and penetrating wounds which quickly heal may go unnoticed by the owner. Snake bite, large burns, and iatrogenic causes such as inadequate sterilization of surgical equipment, poor wound management, IM injections and surgical contamination with ingesta have also been reported as risk factors.

SIGNALMENT

A 7-year-old neutered female English springer spaniel.

CASE PRESENTING SIGNS

Exophthalmos.

CASE HISTORY

Exophthalmos was initially noted, followed 2 days later by the ears appearing more upright and the nostrils flared. The dog seemed stiff, made odd noises when eating and drinking and made a different noise when panting. A claw had been torn 1 week before signs commenced.

CLINICAL EXAMINATION

Clinical signs typically commence 3–18 days after inoculation. Mild generalized tetanus commonly presents as a stiff gait and a rigid stance often described as a ‘saw horse’ posture. The tail may be erect or elevated. Skeletal muscle of the head is generally affected at the same time or soon after, and trismus (‘lockjaw’), retracted lips, erect ears, enophthalmos and protrusion of the third eyelid are easily noticed (Fig. 63.1). Flickering of the third eyelid is produced by intermittent spasm of the retractor bulbi muscles which creates momentary enophthalmos and a passive protrusion of the third eyelid. Laryngeal spasm, dysphagia, constipation and urine retention are possible.

Figure 63.1 Generalized tetanus: retraction of ears and lips, small palpebral fissures.

Severe generalized tetanus results in recumbency and opisthotonus. All muscle groups are affected but extensor tone predominates. Ventilation may be impaired. Stimuli such as light, noise and touch can increase muscle spasticity further.

Focal tetanus presents as rigidity in the inoculated limb (Fig. 63.2). It may remain localized to that limb or spread to the contralateral limb and then to the CNS. Focal tetanus is more common in cats than dogs. Recognition of signs is difficult in the slowly progressive generalized form presenting as stiffness.

Figure 63.2 Focal tetanus in the right hind limb.

Examination of this case detected a stiff gait, ears retracted higher on head, bilateral exophthalmos and less flaccid lips than expected for a spaniel. The tongue was prominent between the mandibles ventrally. There was harsh panting. The temperature was 40.3°C. She could open her mouth and could blink. There were no myotonic dimples. The gait did not improve with exercise. Strength and proprioception were normal. Muscle tone was increased in all limbs.