This disease is caused by the action of the neurotoxin tetanospasmin, produced during the vegetative growth phase of Clostridium tetani. Other toxins, like tetanolepsin, are also produced, but are clinically insignificant.
Tetanus in dogs is reported with a greater frequency than that observed with cats (factor of 10) but less than horses (factor of 600). Exotoxins are produced locally at the site of the wound and disseminate systemically over time.
Tetanus is usually initiated by a deep penetrating bite or stab wounds which facilitate anaerobic growth of this bacteria, but has been reported from dogs with penetrating oral wounds from eating sharp objects such as bones or wood, surgical sites, puncture wounds, tick bites, and teething.
Clinically affected dogs present 3 - 7 days post infection with initial signs referable to neurotoxicity, such as ocular or facial abnormalities.
Young, large-breed dogs are more commonly affected and present with localized stiffness, often involving the masseter muscles and muscles of the neck resulting in the pathognomonic 'sardonic smile' and locked jaw syndrome which are characteristic of the disease. Hyperesthesia and seizures are observed in advanced cases, and death is by asphyxiation due to respiratory paralysis.
Complications are common and include pressure sores, hyperthermia, and dysuria. Less common complications include transient megaesophagus and hiatal hernia associated with gastroesophageal reflux, aspiration pneumonia, fractures, and laryngeal spasm. A significant inverse relationship exists between development of severe clinical signs and survival, with dogs that show only minor initial signs such as cardiac abnormalities on ECG or hypertension often resulting in euthanasia due to complications.
Diagnosis is based on presenting clinical signs of muscle tremors and rigidity, bacterial culture from wounds and isolation of tetanus toxoid in serum samples.
Treatment usually consists of wound debridement and treatment with metronidazole, sodium ampicillin (25 mg/kg IV every 8 hours), diazepam (0.5 mg/kg IV as needed) and tetanus immunoglobulin (300,000 IU tetanus antitoxin IV, bid).
Intravenous fluid therapy, airway management via tracheostomy (if required), and nursing care are important for recovery. Hyperthermia due to convulsions is common and must be addressed to prevent shock.
Most patients recover within 4 weeks if treated aggressively.
Preventative measures are difficult, but tetanus toxoid, given yearly, especially in working dogs, may limit outbreaks.
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