Retrospective Study of Tetanus in 20 Dogs: 1988–2004
The case records of 20 dogs that were treated for tetanus between 1988 and 2004 were reviewed. Young, large-breed dogs were most commonly affected. Twelve dogs had a likely source of infection identified. All dogs were treated with intravenous antibiotics and supportive care, such as muscle relaxants and sedation for muscle tremors and rigidity. Sixteen dogs received tetanus antitoxin. The mortality rate was 50%. Complete recovery in survivors required approximately 1 month.
Introduction
Clostridium tetani is a gram-positive, anaerobic, spore-forming bacillus. 1,2 The spores are ubiquitous and are highly resistant to destruction with routine methods of disinfection. If a wound is contaminated with spores in the presence of an anaerobic environment, the spores may vegetate and produce the neurotoxin tenanospasmin.1 Tetanospasmin is responsible for the clinical syndrome of tetanus.1 Humans and horses are particularly sensitive to tetanospasmin and are thus commonly vaccinated against tetanus in order to prevent clinical disease and associated morbidity and mortality.1–3 In developing nations where vaccination is less frequently practiced, the mortality rate for tetanus in affected people remains high, with some reports as high as 50%.4,5 In horses, a review of 20 cases described a mortality rate of 75%.3
Cats suffer more often from localized tetanus, while dogs are more frequently afflicted with generalized tetanus.6 Clinical signs of tetanus include a stiff gait, prolapse of the third eyelid, and risus sardonicus (i.e., sardonic grin). Unlike people and horses, dogs are not routinely vaccinated against tetanus.1 Previous reports of tetanus in dogs are either single case reports or descriptions of only a small group of affected animals.7–10 The goal of this retrospective study is to evaluate the clinical courses and outcomes for a larger group of dogs with tetanus.
Materials and Methods
The medical records of dogs diagnosed with tetanus between January 1988 and August 2004 at The Cummings School of Veterinary Medicine at Tufts University (n=1) and Medizinische Tierklinik of Ludwig Maximilian University (n=19) were reviewed. As no definitive antemortem test exists for the disease, criteria for a diagnosis of tetanus were characteristic clinical signs without evidence of another neuromuscular disease. Characteristic signs were defined as a stiff sawhorse gait, increased generalized muscle tone, and the presence of risus sardonicus. Information retrieved from the medical records included signalment, duration of signs prior to hospitalization, presenting clinical signs, presence of a potential underlying source of infection, clinical course in the hospital (e.g., use of tranquilizers, antiserum, antibiotics, and nursing requirements), complications, and outcome.
Statistical Analysis
Descriptive statistics were used to analyze the results. Results are listed as mean (± standard deviation [SD]) or median and range, as appropriate. Chi-square analysis was used to evaluate differences between various treatment plans and survival. A P value <0.05 was considered significant.
Results
Signalment
Twenty dogs met the criteria for inclusion in the study [see Table]. Breeds represented included mixed-breed dogs (n=6), the German shepherd dog (n=4), Labrador retriever (n=3), and one each of the dachshund, Dalmatian, German hunting terrier, golden retriever, leonberger, Rhodesian ridgeback, and Kerry blue terrier. Median age at presentation was 3 years (range 6 months to 7 years). Median weight at presentation was 22 kg (range 3.5 to 42 kg). Twelve dogs were intact males, and eight were females (four recently spayed).
Clinical Signs
The median duration of clinical signs prior to presentation at the hospital was 2 days (range 0 to 5 days). Clinical signs at presentation included risus sardonicus (n=20) and appreciable generalized muscle stiffness (n=19). Additionally, 11 dogs had clinical evidence of laryngeal spasm, characterized by moderate to severe upper respiratory tract obstruction, and eight dogs had marked ptyalism.
Potential Sources of Infection
In 12 dogs, a potential source of infection was identified [see Table]. Sources included interdigital abscesses (n=3), infected bite wounds (n=2), and an infected laceration (n=1). Four dogs had undergone ovariohysterectomy within the 14 days immediately preceding the development of clinical signs, and postoperative infection was the suspected cause of infection in these cases. Two puppies had evidence of an oral source of infection (i.e., recent loss of the deciduous teeth). In the remaining eight dogs, the source of infection was not identified.
Treatments
All dogs were treated with penicillin Ga (30,000 IU/kg intravenously [IV] q 8 hours). Additionally, eight dogs were treated with metronidazoleb (10 mg/kg IV q 8 hours). Sixteen dogs received equine tetanus antitoxinc (200 U/kg IV). In 12 of these dogs, an intradermal test dose of antitoxin (0.1 mL) was administered prior to the IV dose. No signs of hypersensitivity to antitoxin were observed in any treated dogs. There was no difference in survival, severity, or duration of clinical signs between dogs treated and not treated with antitoxin.
The six dogs with wounds or lacerations had their wounds explored, lavaged, and infiltrated with an additional 1000 U of antitoxin. Abdominal ultrasonography was performed in the four dogs with recent abdominal surgery. A uterine stump abscess was identified in one dog. That dog underwent an exploratory celiotomy, with resection of the affected tissues. Anaerobic and aerobic bacterial cultures were obtained in five cases and were positive for Clostridium tetani in the dog with an interdigital abscess.
All dogs received muscle relaxants and sedatives as necessary to control their muscle rigidity. To avoid excessive stimulation, they were kept in a quiet environment. All dogs periodically received diazepamd (0.5 mg/kg IV q 4 to 6 hours). Fourteen dogs also received acepromazinee (0.05 to 0.07 mg/kg IV q 3 to 4 hours), and six dogs also received methocarbamolf (55 to 100 mg/kg IV q 30 to 60 minutes). Upon review of the medical records, acepromazine appeared to control the muscle spasms better, with dogs requiring repeated dosing at approximately 3-hour intervals, in contrast to methocarbamol, of which repeated injections were administered every 20 to 30 minutes.
All dogs received IV fluid support in order to maintain hydration. Nine dogs were fed by syringe. Seven dogs had nasoesophageal feeding tubes placed for enteral feeding. Four dogs were given total parenteral nutrition because of dysphagia and the apparent inability to tolerate oral feedings. All dogs were kept on well-padded surfaces and turned frequently to prevent the development of pressure sores. One dog developed a pressure sore. The bladders of all dogs were expressed every 4 to 6 hours to prevent urinary retention. Urinalyses performed at regular intervals did not document a urinary tract infection in any dog.
Complications
Complications included both those attributable to tetanus and to prolonged recumbency. Complications attributed to tetanus included laryngeal paralysis (n=8), cardiac arrhythmias (n=6), hyperthermia (n=4), and systemic hypertension (n=3). Cardiac arrhythmias that were clinically significant included atrial standstill (n=2), supraventricular tachycardia (n=2) with heart rates of 200 to 300 beats per minute (bpm), and severe ventricular tachycardia (n=2) with ventricular rates of 240 to 300 bpm. One dog with bradycardia died of cardiac arrest; both dogs with ventricular tachycardia developed ventricular fibrillation and subsequently died. The development of arrhythmias was not associated with an increased risk of death in this group of dogs, although not all dogs had continuous electrocardiographic monitoring, so the true incidence of serious arrhythmias was unknown.
Four dogs developed hyperthermia (body temperature >40.5°C) during episodes of severe muscle spasms, which resolved following additional control of the tetany. Four dogs developed hypertension, with peak systolic blood pressure values between 210 and 260 mm Hg (reference range 100 to 120 mm Hg); however, blood pressure was not routinely measured in all dogs during the study period.
Radiographic evidence of pneumonia, which was thought to be secondary to aspiration, developed in nine dogs. Eight dogs had suspected laryngeal paralysis or spasm. Six dogs had transtracheal aspirates performed, which documented suppurative inflammation and intracellular bacteria. Four of the tracheal aspirates had a positive bacterial culture. Cultured organisms included Escherichia coli (n=2), Staphylococcus intermedius (n=2), and Klebsiella spp. (n=1). No dogs required intermittent, positive-pressure ventilation for the treatment of pneumonia or respiratory failure.
Outcomes
Ten dogs survived and were discharged from the hospital. The remaining dogs died or were euthanized. Five dogs died acutely of unknown causes; three dogs died of cardiac arrhythmias; and two were euthanized because of severe clinical signs and a perceived poor prognosis for recovery. Necropsy was performed in nine dogs, and no clinically significant underlying disease was identified in any dog.
The median duration of hospitalization for the survivors was 17 days (range 9 to 30 days). The first sign of improvement in all of the dogs was decreased muscle rigidity in the pelvic limbs. In the surviving dogs, this improvement was noted a median of 9.5 days (range 5 to 12 days) after treatment was initiated. The median time to complete recovery was 34 days (range 26 to 42 days). All dogs that recovered had neither residual neurological deficits nor abnormalities on follow-up examination.
Discussion
This retrospective study evaluated outcomes following a clinical diagnosis of tetanus in 20 dogs. Owing to the small number of affected dogs and the inherent variability in treatment protocols that were encountered in this study, no conclusions could be drawn regarding the best form of treatment. The prognosis for dogs affected by generalized tetanus, however, was guarded, in that the survival rate was only 50%.
A source or presumptive source of infection was identified in 12 dogs in this study. In people and horses, the source of tetanus is commonly a puncture wound, although infection during childbirth or of the umbilicus is also a possibility in people.2–5 In the present study, four of the dogs recently underwent ovariohysterectomy; in one of these dogs, a uterine stump abscess was identified and resected. The uterus is considered a sterile environment, so the actual relationship to ovariohysterectomy was unclear. Surgical or postoperative contamination may have been a potential source of infection.
Clinical signs of tetanus may develop between 3 and 18 days after an injury, as found with the dogs described in this report.1,9 All of the dogs reported here developed generalized tetanus, with full body rigidity within 2 to 3 days of initial hospitalization. Localized tetanus was not observed in any dogs of this study.
Treatment of tetanus classically involves antitoxin and antimicrobial therapy, wound management, and supportive care.1 Wound management has included surgical exploration and lavage to remove small pieces of debris, such as wood fragments, that may be an ongoing source of infection. Six dogs in this study had wounds treated in this fashion. Antimicrobial therapy is aimed at eliminating any remaining clostridial infection, although it is ineffective against the spores. Antibiotics with activity against anaerobes (e.g., penicillin, potentiated-penicillin, metronidazole, clindamycin) have historically been used. All dogs in the current study received IV penicillin, and eight dogs also received metronidazole.
In this report, antitoxin was used in 16 dogs following an intradermal test to detect hypersensitivity reactions. There were no statistically significant differences in survival, severity of clinical signs, or duration of clinical signs between dogs treated with antitoxin and those that did not receive antitoxin.
Complications were common in the study reported here and included pneumonia, cardiac arrhythmias, and hyperthermia from severe muscle spasms. In people, autonomic dysfunction is associated with a poor survival rate.11 Arrhythmias have previously been reported in two dogs with tetanus.8 Autonomic instability, which is characterized by hypertension, hyperthermia, tachycardia (or other arrhythmias), profuse sweating, and increased urinary catecholamine excretion, has been identified in humans with tetanus.12,13 Bradycardia is also occasionally noticed in humans with tetanus, which suggests dysfunction of the parasympathetic system or basal nucleus, leading to excessive vagal activity.14,15 In the study reported here, cardiac arrhythmias were not associated with increased mortality, but because continuous electrocardiographic monitoring was not performed, the true incidence of serious arrhythmias was not documented. It would seem prudent to monitor dogs with tetanus for the development of arrhythmias.
Clinical improvement was seen in surviving dogs within 5 to 12 days, and full recovery occurred in all survivors. Based on the small sample size, no obvious positive prognostic indicators were identified; however, outcomes were poor in animals with severe arrhythmias and evidence of aspiration pneumonia. Failure to improve within 7 days’ time does not preclude continued supportive care of dogs with tetanus, as some dogs in the current study required almost 2 weeks for improvement to occur.
Limitations of this study included its retrospective nature and inherent variation of treatment strategy for the affected dogs. Of the five dogs that died suddenly, in which no cause was identified, a fatal arrhythmia may have been involved. No morphological abnormalities were found on these dogs on necropsy, making autonomic dysfunction (e.g., arrhythmias) more likely as the cause of sudden death. Although efforts were made to statistically evaluate differences between survivors and nonsurvivors, no differences were identified. This was most likely because of the small sample size and the 16-year duration of the study, during which advances in critical and nursing care may have affected the outcomes of some of the dogs.
Conclusion
Tetanus was diagnosed in 20 dogs, 10 of which survived. All survivors had no permanent complications, although time to complete recovery was lengthy (average of >1 month). All survivors required prolonged treatment and nursing care. Prospective studies evaluating differences in outcomes in relation to the choice of antibiotics, use of different antispasmodic drugs, and the use of tetanus antitoxin are warranted; but such studies may be difficult because of the rarity of the disease in small animals.
Penicillin G; Mega Jenapharm Durchstechfl, 10, Mibe Vertriebsges. mbH, Jena, Germany
Metronidazol; B. Braun, Infusionslösung, B. Braun Medical AG, Jena, Germany Metronidazol; Baxter Health Care, Deerfield, IL 60015
Equine Tetanus Serum; WdT Wirtschafts-genossenschaft deutscher Tieraerzte e.G., Garbsen, Germany Equine Tetanus Antitoxin; Fort Dodge Laboratories, Ft. Dodge, IA 50501
Diazepam; AbZ-Pharma GmbH, Germany Diazepam; Hospira Incooperation, Lake forest, IL 60045
Vetranquil 2%; Wirtschafts-genossenschaft deutscher Tieraerzte e.G., Garbsen, Germany Acepromazine Maleate; VEDCO, St. Joseph, MO 64507
Ortoton K.I.S.; Injectionsloesung, Bastian-Werk GmbH, 81245, Muenchen, Germany Methocarbamol; Baxter Health Care, Deerfield, IL 60015
