An epidemiological study of snake envenomation in dogs in New South Wales, Australia

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1 An epidemiological study of snake envenomation in dogs in New South Wales, Australia Heller, J. 1,2, Bosward, K.L. 2, Hodgson, J.L. 2, Cole, F.L. 2, Reid, S.W.J. 1, Hodgson, D.R. 2, Mellor, D.J. 1 1 Institute of Comparative Medicine, Faculty of Veterinary Medicine, University of Glasgow, UK. 2 Faculty of Veterinary Science, University of Sydney, Australia. Abstract A cross-sectional mailed questionnaire was delivered to all small animal veterinary clinics within New South Wales (NSW) with the aim of collecting epidemiological information regarding elapid snake envenomation in dogs. A response rate of 68% was achieved and it was estimated that 0.31% of all dogs attending veterinary clinics in NSW were cases of snake envenomation. Red-bellied Black snakes (Pseudechis porphyriacus) (RBBS) were reported to be the most common snake to cause envenomation (44.6% of envenomations), followed by Brown (Pseudonaja textilis) (40.4%) and Tiger (Notechis scutatus) (7.0%) snake species. Despite a reported similarity of clinical signs for the three main species (pigmenturia was the only reported differentiating sign), diagnosis of species-specific snake envenomation was made predominantly based on recognition of these signs (100% of clinics used clinical signs and 25.8% used these signs exclusively). Tests developed specifically for the diagnosis of snake envenomation such as the Snake venom detection kit were reported to be used infrequently (9.9% of clinics). The most common treatment was a combination of antivenom and intravenous fluid therapy (81.8% of clinics). Survival (after treatment) was reported to be lowest for dogs bitten by the Tiger snake (63%) and highest for the RBBS (83.8%). Introduction Snake envenomation in domestic animals is a common clinical entity in veterinary practice within Australia. Descriptions of clinical syndromes resulting from elapid snake envenomations in domestic animals are sparse, as is epidemiological information regarding the prevalence and distribution of snake envenomations in domestic animals and the attitude of veterinarians to this set of disease processes. Objective The objective of this study was to obtain baseline data on prevalence of elapid snake envenomation in dogs presented to veterinary practices in NSW and to assess attitudes of veterinarians to this clinical entity, using a mailed questionnaire. Materials and Methods The questions for the mailed questionnaire were developed specifically for the current study and were based on clinical experience and prior publications. The questionnaire followed a modification of the Total Design Method (Dillman 1991) and comprised 48 questions regarding snake envenomation in dogs. The questions were formatted to request a mixture of estimations of numbers or proportions, frequency-intensity scale estimations and yes/no responses. An other (please specify) open format question was also included at the end of each section to allow for any categories not mentioned. The questionnaire was pre-tested among a group of 20 veterinarians prior to mailing and subsequently mailed to each of the 587 small animal practices registered within NSW. Mailing was undertaken

2 three times, at 0, 3 and 7 weeks and on each occasion, the questionnaire was accompanied by a covering letter and a pre-addressed reply-paid envelope. Comparisons between groups were made using chi-square analysis and significance was assessed at P Results Questionnaire Response A total usable response rate of 68% was obtained. Of the responding clinics, 253 (63.7%) reported that they encountered snake envenomation cases in dogs. The estimated proportion of canine non-revisit cases attributable to snake envenomation at these clinics during the snake-bite season was calculated to be 0.96% (95% Confidence Interval, %) and at all responding veterinary clinics (including those that reported no snake envenomations) was 0.54% (95% CI, %). Noting that the snake season was included as seven months, a revised annual proportion was estimated (assuming rate of consultations are stable year-round) as 0.31% (95% CI, %). Snake species Red-bellied Black snakes were reported to be the most common snake to cause envenomation (reported by 83% of clinics and accounting for 44.6% of envenomations), followed by Brown (74.7% of clinics and 40.4% of envenomations) and Tiger (29.2% of clinics and 7.0% of envenomations) snake species. Envenomation by the lesser-known snakes were reported far less frequently and therefore were unable to be included in the analyses. Clinical Signs The clinical syndromes reported to occur after envenomation by Tiger and Brown snakes were similar with weakness, ataxia and paralysis the most commonly reported clinical signs (Figures 1a,b). The principal difference in the syndrome resulting from envenomation by these two snake species was the presence of pigmenturia (haemoglobin and/or myoglobin within the urine). A significantly greater number of clinics reported that pigmenturia occured always or often in Tiger snake envenomations (48.5%) than in Brown snake envenomations (27.3%) ( 2 1 = 9.165, P = 0.002). Envenomation by the RBBS was reported to result in a different clinical presentation to the above (Figure 1c). was the most commonly noted clinical sign with 82.6% of clinics treating RBBS envenomation reporting pigmenturia to be often or always present, a significantly greater finding than for Tiger snake envenomation ( 2 1 = , p < 0.001). and ataxia were also reported to occur with RBBS envenomation, although paralysis was reported to occur less often than for Tiger and Brown snake envenomations. Diagnosis The only procedure consistently reported to be used for diagnosis of snake envenomation was the assessment of clinical signs. All clinics utilised clinical signs for diagnosis of snake envenomation by the three major species, and diagnosis was reportedly based solely on clinical signs in 25.8% of instances. Other diagnostic modalities, including snake venom detection kits (reportedly used by 9.9% of practices), were utilised infrequently.

3 a) Always Often Sometimes Never b) c) RESPONSE Figures 1a),b),c) Clinical signs reported by veterinary clinics for a) Tiger (N=74), b) Brown (N=189) and c) Red-bellied Black (N=210) snake envenomations in dogs.

4 Treatment The most commonly reported treatment options for snake envenomation were intravenous fluid therapy and antivenom administration, and this combination was used by 81.8% of all clinics. Monitoring of snake envenomation cases was predominantly performed by assessment of clinical signs with almost all clinics reporting this as routine practice. Survival Survival after treatment was reported to be greatest for dogs envenomed by RBBS (83.8% survival), followed by Brown snake (70.4%) and then tiger snake (63.0%). Survival was perceived by all responders to be associated most strongly with time between envenomation and presentation. Administration of antivenom was also perceived to contribute to survival by 98.8% of responding clinics and the development of renal failure secondary to envenomation was reported as a negative association with survival by 71.3% of respondents. Discussion This paper represents the first wide-scale study investigating current practice regarding occurrence and management of snake bite in dogs amongst veterinarians in NSW. The response rate elicited (68%) is favourable in comparison with previous mailed questionnaires and is well above the a priori assumed response rate of 50%. One of the primary findings from the current study is that RBBS account for a far greater number of envenomations within NSW than previously reported in other areas of Australia (Mirtschin et al 1998). In addition to the finding that the envenomation syndrome produced by the RBBS occurs as commonly as any other snake envenomation syndrome in dogs within NSW, the current study reveals that, although to a lesser degree than other snake species, it is possible for RBBS envenomation to cause mortality in dogs (survival was estimated to be 83.8% after treatment) which is previously unreported. It was also found in the current study that diagnosis of snake envenomation within NSW is based mainly on the recognition of clinical signs. Reliance on clinical signs for diagnosis may be problematic as marked variation in envenomation syndromes have been shown to occur both between and within species of snakes (Chippaux et al 1991). Furthermore, within the current study it has been shown that the clinical signs relied on for diagnosis are non-specific. and ataxia were reported as occurring always or often by over 50% of clinics for all three major snake species, and pigmenturia was reported as the only differentiating clinical sign between these species. Almost all of the clinical signs were classed as occurring sometimes, often or always by more than 75% of clinics for all three major snake species. These findings may reflect perceived ambiguity and overlap of the clinical syndromes associated with snake envenomation by different snake species. The current study has defined the yearly proportion of cases attributable to snake envenomation in dogs within NSW and shown a greater reported contribution of RBBS to the disease burden than was known previously. It has also elicited knowledge of veterinarians regarding clinical signs and current practice for diagnosis and treatment, along with estimates of survival of dogs when envenomed by snakes encountered within NSW. The results of this study demonstrate the need for clearer definition of the clinical signs associated with snake envenomation by different snake species, and also emphasise the necessity of relevant clinicopathological or other testing for accurate diagnosis of the apparently varied clinical entities associated with snake envenomation.

5 References Chippaux, J.P., Williams, V. and White, J. (1991). Snake venom variability: Methods of study, results and interpretation. Toxicon 29, Dillman, DA. (1991). The design and administration of mail surveys. Annual Review of Sociology 17, Mirtschin, P.J., Masci, P., Paton, D.C. and Kuchel, T. (1998). Snake bites recorded by veterinary practices in Australia. Australian Veterinary Journal 76, Acknowledgements This study was funded by the Canine Research and Veterinary Foundation of New South Wales. The authors also wish to thank all veterinarians who participated in the mailed questionnaire. Jane Heller is currently funded by DEFRA.