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Original Article in equids: A report of 56 cases G. KAY* AND D. C. KNOTTENBELT† Qatar Petroleum (Medical RAA), PO Box 47, Doha, Qatar; and †University of Liverpool, Leahurst, Neston, Wirral CH64 7TE, UK. Keywords: horse; donkey; mule; tetanus

Introduction et al. 1994). Excellent nursing care is required to support the patient during the period of treatment. This includes Tetanus occurs worldwide and is considered enzootic in many minimising external stimuli (darkened and quiet room, cotton warmer countries in the developing world where vaccination in the ears) maintaining hydration and nutritional status (if programmes for both man and equids are not established. necessary using parenteral means), and, if necessary, external Annually, approximately 800,000 cases of human neonatal physical support, manual evacuation of the rectum and urinary tetanus occur worldwide (Abrutyn and Berlin 1991). catheterisation. Tetanus is a distressing and often fatal disease caused by During an 18 month period between 2003 and 2004 3 protein liberated by the bacterium the Society for the Protection of Animals Abroad tetani of the family Bacillaceae. Equids are particularly (SPANA) hospitalised 56 cases of equine tetanus. This susceptible to the tetanus (Radostits et al. 1994; case series reviews the clinical features and treatment Cullinane et al. 1999). In Morocco, tetanus is a major cause of protocols in this population of equids and attempts to death amongst horses, donkeys and mules. In the developing identify factors that may have an influence on the world, where equids play a key role in the rural economy and outcome of affected horses. the welfare of many families is intimately linked to the welfare of their draught animals, the prevention and treatment of this Materials and methods disease is an important issue. The tetanus bacterium is a commensal of the Equids presenting to SPANA clinics in Morocco with clinical gastrointestinal tract of man and domestic animals and its signs consistent with a diagnosis of tetanus between January spores are highly resistant to environmental changes, acid and 2003 and June 2004 were included in this case series. Cases alkali, and may persist in the soil for many years. The organism presenting in a terminal state were excluded. Locally occurring generally gains entry to the body via wounds. Although deep, differential diagnoses included rabies, equine exertional penetrating wounds, such as punctures of the hoof capsule, rhabdomyolysis, West Nile Fever and musculoskeletal trauma. are more liable to permit proliferation of the tetanus The clinical presentation was assessed for each case and details of age, sex, species, wound location, duration and organism, even superficial wounds can provide suitable severity of clinical signs at presentation, treatment protocol, anaerobic conditions for the development of pathogenic number of days hospitalised, ultimate outcome and any long- numbers of the bacteria (Cullinane et al. 1999). Other term effects were all recorded for each case. Bodyweights were common sites of contamination include the umbilical cord in estimated using a weigh tape for horses using the Ouassat and neonates, retained placentae in mares and surgical wounds. Pearson (1997) nomogram for working donkeys and the Kay The clinical signs of tetanus are attributable to the complex and Pearson (2004) nomogram for working mules. of exotoxins produced by the organism under anaerobic At the time of presentation each case was allocated a conditions. is the major produced by clinical score based on the following criteria: the organism and is responsible for most of the clinical signs. Treatment is typically directed towards elimination of the 1. Mild clinical signs; i.e. nictitans membrane flashing, ears source of the , neutralisation of any unbound toxin, relief pulled caudally, slightly stiff gait but still walking and of pain, establishment of antitoxin immunity and the control eating without difficulty (see Fig 1). of neuromuscular derangements. Penicillin kills the vegetative 2. Moderate clinical signs; i.e. nictitans membrane flashing, form of C. tetani and is indicated in all cases of tetanus (Green ears pulled caudally, limbs stiff and walking with difficulty, trismus and generalised muscle spasm. The animal still *Author to whom correspondence should be addressed. capable of eating and drinking voluntarily albeit slowly. 108 EQUINE VETERINARY EDUCATION / AE / March 2007

offered ad libitum. Animals unable to drink were hydrated by nasogastric intubation with water or an isotonic solution and/or i.v. infusion with acetated Ringers solution after assessment of hydration status. No animals were maintained in slings. Data were extracted from written case records and entered into a table (Microsoft Corp.) then transferred to the minitab statistical program1. Continuous variables were analysed using analysis of variance and the Kruskal-Wallis test as appropriate, and categorical variables were compared using the Chi-square test. A binary logistic regression model examined the effect of species, clinical grade and TAT dose on outcome. A logistic regression model assessed survival as the outcome against clinical Grade 1 and 2 vs. 3, species and dosage of TAT by group.

Results Fig 1: Case 11 showing clinical signs typical of tetanus. Morbidity

3. Severe clinical signs; i.e. capable of standing, but incapable In the 18 months of this study period veterinary surgeons of of walking, severe trismus. Difficulty with prehension, the SPANA clinics in Morocco saw and treated 97,000 equids, mastication and swallowing of food, and drinking and hospitalised 3150. In the same period, 56 equids with a voluntarily. clinical diagnosis of tetanus were hospitalised and treated, 4. Terminal clinical signs; i.e. animal recumbent, incapable of and 8 equids with tetanus were subjected to euthanasia standing, incapable of eating. Animals presenting in this without treatment. The total number of tetanus cases situation were considered candidates for immediate represented 0.07% of the total patient load and 2% of all euthanasia and all but one were not included in this series. hospitalised patients.

In an effort to identify possible associations between the Outcome dose of tetanus antitoxin (TAT) and the outcome, cases were also assigned to one of 3 treatment groups depending on the Mortality for the 56 patients that were treated was 54% (95% dose of tetanus antitoxin TAT they received during treatment. CI, 40–67%). Including the 8 animals subjected to euthanasia at presentation a mortality rate of 59% (CI, 46–71%) was 1. No dose: No tetanus antitoxin administered. All these calculated. Of the 56 hospitalised equids in this series, 26 animals were presented at one clinic that had no access (46%) survived, 18 were subjected to euthanasia and 12 died. to TAT. Hospitalised patients were subjected to euthanasia as a result 2. Low dose: Doses between 1000–19,000 iu. All other of recumbency and inability to eat (9 cases), and recumbency animals treated between January 2003 and December and respiratory distress (3 cases). The majority of animals that 2003. survived were returned to their owners with little or no residual 3. High dose: Doses between 20,000–70,000 iu. All animals effects. However, 2 suffered almost total, nonpruritic, bilaterally treated between January 2004 and June 2004. asymmetrical alopecia during the convalescent period (Fig 2).

All the cases were treated with a standard protocol consistent with those described in the literature. They all received approximately 15,000 iu/kg procaine penicillin i.m. q. 12 or 8 h for a minimum of 7 days (Pearce 1994). Crystalline benzyl penicillin is not available for use in equids in Morocco. All cases received repeated doses of 0.05 mg/kg–0.08 mg/kg acepromazine i.v. To maintain muscle relaxation repeat doses were sometimes required as often as every 2–3 h. Cases with symptoms that could not be controlled by this regimen were treated with 0.05–0.2 mg/kg diazepam by slow i.v. route. Any wounds were systematically cleaned, meticulously debrided and subjected to copious high pressure lavage with tap water. All affected animals were kept in a quiet, darkened stable with ample wood chip bedding. Water and feed were given at Fig 2: Case 12 showing bilateral alopecia after recovery from manger height. A palatable, chopped, complete feed was tetanus. EQUINE VETERINARY EDUCATION / AE / March 2007 109

Vaccination status Heart rate at presentation

None of the animals in this series had been vaccinated against There was no significant difference in the heart rates at tetanus. presentation between those animals that survived and those that died (P = 0.8) Overall mean heart rate at presentation was Species 57 beats/min with a median of 56 and range 40–88 beats/min.

Of the 56 equids in this series, there were 25 (45%) donkeys, Chronicity at presentation 20 (36%) mules and 11 (20%) horses. For comparison, the species breakdown for 12,500 outpatients in 2003 was The majority of animals were presented within 3 days after donkeys, 24%; mules, 46%; horses, 30%. Survival rates did onset of clinical signs (18 animals). Of these, 9 were admitted not vary significantly (P = 0.833) by species (Table 1). between 48 and 64 h after onset of signs, and 9 were actually hospitalised at the time that clinical signs of tetanus became Antitoxin therapy protocol apparent. Survival rate for these 18 animals was 55%. Those presented between 4 and 7 days after onset accounted for Of the 56 animals treated in this case series 14 animals did not 9 animals, and recorded a survival rate of 50%. Only 2 animals receive TAT and 7 (50%) of these survived, 17 were treated presented with a history of more than 7 days since onset of with a low dose TAT either as a single or double administration clinical signs and neither of these animals survived. and 7 (41%) survived, and 25 were treated with the high dose TAT over 2 days and 12 (48%) survived. The survival rate did Sex not vary significantly with total dosage (P>0.8), or with total number of doses, (P>0.185). Table 2 shows the survival of Of the 56 animals treated 26 were male and 27 were female. cases with each antitoxin dose regimen. Details of sex were not recorded for 3 animals. Survival rates did not vary with sex. Severity at presentation Age Twelve animals presented with mild signs of tetanus (Grade 1) and of these 8 (66%) survived. Of the 22 animals presenting Survival rate did not vary significantly with age group. The age with moderate clinical signs (Grade 2), 15 (68%) survived. distribution of surviving and fatal cases is shown in Table 3. Sixteen animals presented with severe clinical signs (Grade 3) and of these 1 (6%) survived. The single surviving case was Wound location admitted in lateral recumbency, unable to rise, but it continued to eat and, therefore, treatment was attempted. One animal Details of wound locations and clinical outcome are indicated in with Grade 4 clinical signs was treated but it failed to survive. Table 4. Many of the animals in this series had no visible wounds at presentation (18/56). At least 12 had injuries that Time to survival were the result of poor management. These included 7 with hobble injuries, 3 with fistulous withers, 1 with a rectal prolapse Clinical signs showed improvement in all survivors by Day 2–3 and 1 with wounds from traditional castration. There was no after hospitalisation, the average hospitalisation time for significant association between survival and wound location. survivors was 30 days. TABLE 3: Survival of equids with tetanus by age group

TABLE 1: Survival by species of hospitalised cases diagnosed Age (years) with tetanus 0–1 2–4 5–9 10–19 20+

Donkeys Mules Horses Total Survived 32484 Fatalities 16863 Survived 11 (44%) 9 (45%) 6 (54%) 26 (46%) Total 4 8 12 14 7 Fatalities 14 (56%) 11 (55%) 5 (46%) 30 (54%) Total 25 20 11 56 TABLE 4: Survival of equids diagnosed with tetanus by wound location TABLE 2: Survival of equids with tetanus by dose of TAT received Site of wound Tetanus antiserum dose rate None Hobble Distal Proximal Nil 1000–19,000 iu 20,000–70,000 iu Total visible injury Head limb limb Other

Survived 7 (50%) 7 (41%) 12 (48%) 26 (46%) Survived 10 34204 Fatalities 7 (50%) 10 (59%) 13 (52%) 30 (54%) Fatalities 841402 Total 14 17 25 56 Total 18 75606 110 EQUINE VETERINARY EDUCATION / AE / March 2007

A logistic regression model considering survival as the series of 20 cases and 66% reported by Steinman et al. (2000) outcome and clinical Grades 1, 2 and 3, species and dosage of in a series of 3 cases. TAT by group, confirmed a strong association between survival A higher mortality rate in this series would be expected and clinical grade at presentation (P = 0.001) whilst the effect given the negative vaccination status of all the animals. Also, of species and dosage of TAT were not significantly related to the majority of the equids in Morocco are in poor to very poor survival (P>0.4). body condition and parasite control programmes are nonexistent suggesting a poor immune status of most of the Discussion animals. Finally, most patients were admitted more than 48 h after onset of clinical signs and 12 were admitted 4 days or The bacterium is an obligate anaerobe. more after onset of clinical signs. Notably, no previous Under anaerobic conditions its spores germinate and produce treatment had been administered in any of theses cases. The three exotoxins (tetanospasmin, tetanolysin and relatively low mortality rate in this series is puzzling given these nonspasmogenic toxin). These pass to the ventral horns above factors, however although the mortality rate reported in of the spinal cord either by haematogenous spread or directly our series (including the 8 animals subjected to euthanasia at along peripheral nerves. Clinical signs of tetanus arise when presentation) is lower than that reported by Green et al. (1994) tetanospasmin binds to the gangliosides GT and GD1b in the they are not significantly different (P = 0.21). Mortality rates central nervous system (Hathaway 1990). This binding is vary quite markedly in reports from the human literature with almost irreversible and thus accounts for the prolonged nature 55–86% mortality reported by Neequaye and Nkrumah (1983); of the signs. The tetanospasmin acts inside nerve terminals the figures in the present study are in line with that variation. and blocks neurotransmitter release via its activity on soluble There is no definitive ante mortem test for tetanus, nor any N-ethylmaleimide-sensitive factor attachment receptor post mortem findings pathognomonic for the disease. In (SNARE) proteins (Grumelli et al. 2005). The effect is amplified addition, finding microscopic evidence of the bacteria or its by the second exotoxin, tetanolysin which causes further toxin at the site of a wound is an unreliable diagnostic tissue necrosis by the breakdown of leucocytes at the site of indicator. A biological assay for premortem diagnosis is infection, and by the third exotoxin, nonspasmogenic toxin, possible in some cases by injecting infected material into the which may block transmission in peripheral neuromuscular tail base of mice and observing for onset of clinical signs. As junctions (Cullinane et al. 1999). The overall effect is the this is not a possibility in Morocco, diagnosis was based on continued stimulation of motor and reflex arcs which results in clinical signs alone. The lack of a history of trauma or the characteristic muscular spasms and contractions, obstetrical incident could not be used to rule out a diagnosis hyperesthesia and eventually convulsions, respiratory arrest of tetanus as in many instances there was no indication of and death seen in patients with tetanus (Mayhew 1989). trauma and the histories received from owners of working Establishing the site of infection and exposure of the area equids are very imprecise. Clinical signs of advanced tetanus to aerobic conditions coupled with penicillin therapy are major are fairly specific and the presence of spasm or prolapse of the cornerstones for the prevention of further toxin production. nictitating membrane and the presence of generalised tetany The infected site in many of the cases in this series could not are reliable indicators of early tetanus. be identified, but in Morocco, where working equids are Despite the almost irreversible effects of the toxin, its frequently hobbled, pastern and cannon lesions from ill fitting binding by high doses of TAT have been reported to be an or ill designed hobbles are probably one of the major portals effective adjunct to therapy along with penicillin and of entry. establishing aerobic conditions at the infected site. Therefore, Although tetanus is a preventable disease, this relies the use of TAT in the neutralisation of unbound exotoxin forms heavily upon effective vaccination programmes. The an important part of the treatment protocol but published adjuvanted tetanus toxoid vaccine is highly immunogenic, but dosages and routes vary widely and evidence on which to base effective vaccination requires at least 2 injections 2–4 weeks such therapy is scarce. The antitoxin probably prevents apart. Booster vaccinations at 12–24 months are usually continued binding of gangliosides and so prevents recommended. The vast majority of the equids in Morocco are deterioration in the clinical signs. Recommended doses range not vaccinated at all. from a single administration of 5000–2.5 x 106 iu/animal The prognosis for survival is reported to depend on several followed by lower doses over 5 days. The best effects are factors including the immune and vaccination status of the probably achieved in the earliest cases (Cullinane et al. 1999). host, the dose of clostridial organism inoculated, and the For 18 months from 2002–2003 TAT was only sporadically availability and duration of aggressive treatment and available in Morocco. Therefore the use of antitoxin in the supportive care (Green et al. 1994). One study reported an treatment of these cases was somewhat arbitrary. In 2004 association between survival and previous prophylactic SPANA decided to assess the efficacy of using higher dose TAT vaccination with tetanus toxoid (P = 0.03), and stated that over 2 days as opposed to a single or multiple lower doses. none of the nonvaccinated horses in their series of cases Therefore, all cases treated in 2004 were given 50,000 iu over survived. (Green et al. 1994). The mortality rate in this series 2 days. The first 30,000 iu were given i.v. followed a day later was 54%. This compares favourably with rates from previous by 20,000 iu i.m. Green et al. (1994) reported that all 5 of the case series such as 75% reported by Green et al. (1994) in a surviving equids in their series of 20 tetanus cases had EQUINE VETERINARY EDUCATION / AE / March 2007 111

received antitoxin i.v. and were amongst only 7 that had tetanus simply because of its lower economic value to the received antitoxin by this route. No problems have been owner and to its hobbling. Our results also indicated a trend for encountered using TAT via the i.v. route in this series horses to be presented earlier in the course of the disease than The economic implications of using high doses of TAT either donkeys or mules, which is another indicator of the without evidence to indicate the increased chance of a more better management afforded to the horses. favourable outcome are important. The use of TAT Surviving animals were hospitalised for approximately one administered into the subarachnoid space has also been month and left the clinic with no or few remaining visible advocated. A study by Muylle et al. (1975) reported a recovery neurologic deficits. The 2 donkeys that developed marked, rate of 77.5% in horses treated with 30,000–50,000 iu TAT nonpruritic, generalised alopecia were interesting. Skin intrathecally. Such success has not been repeated in cases scrapes for ectoparasites were negative. No hair regrowth was reported by Green et al. (1994) and Steinman et al. (2000) detected at discharge and both these animals were then lost where recovery rates using intrathecal TAT varied from 0–33%, to follow up. It might be assumed that the alopecia was part nor has it been demonstrated to be useful in human neonatal of a stress response to the disease and to prolonged tetanus (Neequaye and Nkrumah 1983). Therefore the hospitalisation. advantages of the intrathecal route seem to be questionable. Readers may wish to be reassured that TAT and other An important finding of this study was that there was no medications were stored correctly in the SPANA clinics in association between treatment group and outcome (P>0.8). Morocco and an appropriate cold chain maintained from point This suggests that TAT may be neither beneficial nor of purchase. economically justifiable in the treatment of tetanus in working Clearly, a prophylactic vaccination campaign for working animals in the developing world. Early diagnosis, nursing care, equids in Morocco would be desirable, however the vast high doses of parenteral penicillin and establishing aerobic majority of owners are illiterate and are often difficult to conditions at the infected site are probably the most important access with no contact details. The challenges of getting aspects of treatment. them to return with their animals for follow-up vaccination Acepromazine administration appeared to be beneficial in between 14 and 30 days after initial vaccination seem controlling muscular spasm and so preventing physical insurmountable. exhaustion. The relaxing effects appear to be helpful in allowing an affected animal to drink spontaneously and Acknowledgements possibly even eat succesfully. These 2 factors are thought by many clinicians to indicate a better prognosis and so from a The authors would like to thank both SPANA Morocco and the clinical perspective this drug can be viewed as particularly team of SPANA Moroccan vets without whose valuable indicated in cases of tetanus. Adverse effects of repeated and cooperation this study would not have been possible. We are long term use of phenothiazine ataractic drugs have been also very grateful to Peter Cripps for his assistance with the described and include tachyphylaxis, anaemia and statistical analysis of the data. splenomegaly (Landvaal 1958) but these problems were not observed in the cases presented here. Manufacturer’s address Of all the clinical factors that were recorded for this series of cases the only one which has a clear association with 1Minitab 14, Minitab inc., State College, Pennsylvania, USA. prognosis is the severity of clinical signs at presentation. Those animals with clinical signs categorised as Grade 1 or 2 at References presentation had over 60% survival rate, compared to those Abrutyn, E. and Berlin, J.A. (1991) Intrathecal therapy of tetanus: A with severe clinical signs (Grade 3) where the survival rate was meta analysis. J. Am. med. Ass. 266, 2262-2267. less than 10% (P<0.001). Cullinane, A.A., Bernard, W., Duncan, J.L., Smith, I.M. and Timoney, F. Factors such as sex, age, and chronicity at presentation (1999) Infectious diseases. In: The Equine Manual, Eds: A.J. Higgins had little relationship with prognosis. Heart rate at and I.M. Wright, W.B. Saunders, London. pp 65-70, 979-980. presentation appears to have little value as a prognostic Green, S.L., Little, C., Baird, J.D., Tremblay, R.M. and Smith-Maxie L. indicator, except where elevated above 80 beats/min. (1994) Tetanus in the horse: A review of 20 cases (1970-1990) J. The species breakdown of the equids in this case series vet. int. Med. 8, 128-132. indicates that the donkey is slightly overrepresented. The fact Grumelli, C., Verderio, C., Pozzi, D., Rossetto, O., Montecucco, C. and that 45% of this case series were donkeys and only 20% were Matteoli, M. (2005) Internalization and mechanism of action of horses suggests a species predisposition in donkeys. However, clostridial toxins in neurons. Neurotoxicology 26, 761-767. this may reflect the greater value of the horse and mule, and Hathaway, P. (1990) Toxigenic clostridia. Clin. Microbiol. Rev. 3, 66-70. the correspondingly greater care that the owner is likely to take Kay, G. and Pearson, A. (2004) Estimating the liveweight of working in their management. A study on hobble injuries in working mules in Morocco from certain body measurements. Vet. Rec. 154, 85-88. equids showed a greater percentage of donkeys suffered from Kay, G. and Ouassat, M. (2003) Experiences with a hobble distribution hobble lesions than horses (Kay and Ouassat 2003). As hobble programme in Morocco. In: Proceedings of 4th International lesions account for 30% of all the animals with visible lesions Colloquium on Working Equines, Eds: A. Pearson, D. Fielding and in this series it seems possible that the donkey is predisposed to D. Tabaa, SPANA, London. pp 190-191. 112 EQUINE VETERINARY EDUCATION / AE / March 2007

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