Tetanus

Tetanus in Horses

Tetanus in Dogs

Also known as:

Lockjaw

Description

Tetanus is a rare disease in dogs. The disease pathophysiology is similar to that seen in the horse. The causal agent of tetanus in the dog is the neurotoxin of the gram-positive bacterium Clostridiu tetani. Infection occurs due to contamination of a wound by C. tetani and replication of the bacteria in the anerobic conditions provided by damamged and necrotic tissues. Tetanospasmin (neurotoxin) produced by the bacteria is transported to distant sites via the circulation and intraaxonally along peripheral nerves. This causes inhibition of the release of GABA and glycine from interneurons in the spinal cord and brain, resulting in persistent rigidity of striated muscle.

Because of their high natural resistance to tetanospasmin (compared to the horse and man), affected dogs may have a longer incubation period and clinical signs may be mild. The localised form tetanus that develops in dogs may be difficult to diagnose, particularly if there is no history of trauma.

Diagnosis

A history of trauma and unrelenting muscular spasm in a localised area is often described in cases of tetanus. An obvious wound may help to increase suspicion of tetanus, particularly if the wound is necrotic or infected. An important clinical feature of tetanus in dogs is that of resolution of muscular spasm over a long period of time (weeks or months). In this species, diagnosis is often based on clinical judgement rather than laboratory tests, as these may add little diagnostic information. In occasional cases, C. tetani may be cultured from a wound, but this may be impossible if healing has occurred or the wound is not apparent.

Clinical Signs

The localised form of tetanus seen in dogs may cause differing clinical signs to those seen in other species. A change in gait may be the only reported abnormality. Unlike the generalised spastic paralysis described in horses, dogs may present with a wound to a single limb (often a thoracic limb) and unyielding stiffness or rigidity in the surrounding area. The rigidity may spread to the contralateral limb and then begin to advance cranially, and the disease usually becomes generalised at this stage. Dogs may often display hypersensitivity to even minimal amounts of stimulation. Affected cases have been reported to display caudal displacement of the ears, lateral canthi and commissures of the eyes. Prolapse of the nictating membranes, trismus (excess jaw tone) and retracted lips (risus sardonicus) are other reported clinical features.

Treatment

The approach to treatment in the dog is the same as that described for the horse. it is important however to exercise caution in the intravenous administration of equine tetanus antitoxin as this may cause anaphylaxis if used in dogs.

Noise and external stimuli should be kept to a minimum. The dog should be kept in a quiet, darkened kennel positioned away from other dogs.

In the recovery stage, physiotherapy may be of some benefit.

Supportive nursing care such as catheterisation and/or enemas may be required. Bedding should be thick and changed regularly in order to prevent decubital ulcer formation.

References

• Matthews, B.R and Forbes, D.C. (1984) Tetanus in a Dog Canadian Veterinary Journal May; 26(5): 159–161

• Merck & Co (2008) The Merck Veterinary Manual (Eighth Edition) Merial