The diagnosis and management of snakebite in dogs--a southern African perspective

Cases of snakebite envenomation are frequently presented to veterinary practitioners in southern Africa. Despite this, no published guidelines exist on how this medical emergency should be managed. Southern African snake venoms can be classified into 3 main types based on the main mechanism of venom action and clinical presentation. A polyvalent antivenom is manufactured in South Africa and contains antibodies against the most important southern African snake venoms. The cytotoxic venoms are represented mainly by the puff-adder (Bitis arietans), Mozambique spitting cobra (Naja mossabica), black-necked spitting cobra (Naja nigricollis) (in the Western Cape and Namibia) and the stiletto snake (Atractaspis bibronii). These venoms may cause dramatic local swelling, high morbidity and low mortality and infrequently require the use of antivenom for survival (the only cytotoxic venoms used to prepare the antivenom are the puff-adder and Mozambique spitting cobra). The neurotoxic venoms (represented chiefly by the non-spitting cobras and mambas) cause high mortality due to rapid onset of paresis and require antivenom and mechanical ventilatory support which is life-saving. The boomslang (Dispholidus typus) and the vine snake (coagulopathic venom) rarely bite humans but dogs may be bitten more frequently. These venoms cause a consumption coagulopathy and successful treatment of boomslang bites requires the use of snake species-specific monovalent antivenom. There is no antivenom available for treating vine snake (Thelotornis capensis), berg adder (Bitis atropos), night adder (Causus spp.), stiletto snake and other lesser adder bites. There are some important differences between the way snakebites are managed in humans and dogs.     

Snake envenomation in dogs in New South Wales

OBJECTIVE: To obtain baseline data on the prevalence of elapid snake envenomation in dogs presented to veterinary practices in New South Wales and to assess attitudes of veterinarians to this clinical entity. PROCEDURE: A mailed questionnaire, sent to all veterinary clinics within New South Wales, was utilised to collect epidemiological information regarding elapid snake envenomation in dogs. RESULTS: A response rate of 68% was obtained and a yearly prevalence of snake envenomation in dogs across New South Wales veterinary clinics was estimated as 0.31%. The most common species reported to be responsible for envenomation within NSW was the Red Bellied Black snake (Pseudechis porphyriacus) followed by the Brown snake (Pseudonaja textilis) and then Tiger snake (Notechis scutatus). The reported envenomation syndromes caused by these common snake species were perceived to be similar for Brown and Tiger snakes but differed for Red Bellied Black snakes. Diagnosis of snake envenomation was based predominantly on the recognition of clinical signs. Specific diagnostic tests, such as venom detection kits, were used infrequently. The most common treatment was reported to be a combination of intravenous fluid therapy and antivenom, and monitoring of response to this treatment was usually through assessment of clinical signs. Survival after antivenom administration was reported to be highest for Red Bellied Black snake species. Survival was perceived to be associated with time between envenomation and presentation to the veterinary clinic and with antivenom administration. CONCLUSIONS: Current attitudes and perceptions of veterinarians have been defined. Diagnosis of species-specific snake envenomation is shown to be made on the basis of clinical signs which are, however, reported as similar for each species. Clearer definition of these envenomation syndromes and identification of accessible diagnostic testing procedures are needed.     

A randomized multicenter trial of Crotalidae polyvalent immune Fab antivenom for the treatment of rattlesnake envenomation in dogs

Objective – To determine clinical efficacy of the Crotalidae polyvalent immune F_ab (ovine) antivenom (OPCA) against progressive crotalid envenomation in the dog as reflected in stabilization or improvement of snakebite severity scores (SSS). Additionally, due to the potential decreased half‐life of the F_ab antibodies in dogs we compared SSS between dogs receiving 2 different dosing regimes. Design – Prospective, clinical trial. Setting – Five veterinary emergency and critical care facilities. Animals – One hundred and fifteen client‐owned Crotalid (rattlesnake) snake bitten dogs in whom worsening of the envenomation syndrome was observed before OPCA treatment. Interventions – In a multicenter randomized clinical trial a single dose (1 vial) of OPCA alone was compared with 2 doses (1/2 vial each) administered 6 hours apart. Standard supportive care was provided in all cases. Measurements and Main Results – Data were available for 115 patients, 9 of which were fatalities. All patients' clinical condition was documented with a standardized SSS system accounting for each major body system. Each fatality received maximum severity scores of 20. The mean severity score of the 115 patients decreased from 4.19 to 3.29 points and there was no difference between the 2 treatment groups. The mean severity score of the 107 patients without fatalities decreased from 4.16 to 2.15. Antivenin‐related acute reactions occurred in 6 dogs (6%), and no serum sickness occurred within the 95 cases contacted at the 2‐week posttreatment follow‐up. Conclusions – In the first randomized trial in dogs of antivenin in the United States, OPCA effectively stabilized or terminated venom effects. There were no statistical differences detected between treatment groups within the study time frame.     

SnakeMap: four years of experience with a national small animal snake envenomation registry

SnakeMap is a national cloud-based, veterinary snakebite registry. It was designed to prospectively collect data of the clinical circumstances and temporospatial information on cases of snake envenomation in dogs and cats. We herein introduce the project and summarise the data from the first 4 years of SnakeMap. The registry is a veterinary community-based online database allowing case entry from veterinary hospitals across Australia. Registry data comprise hospital characteristics, patient characteristics, envenoming snake type, treatment and outcome variables, including time and geolocation of the snake bite. We present summative information on select key variables from the SnakeMap registry (1 July 2015 to 30 June 2019). Twenty-eight hospitals from 6 states/territories entered 624 cases into the registry, including 419 dogs (67%) and 205 cats (33%). Bite time was available in 216 animals of which 90 (42%) were reported to be bitten in the 3 hours between 03:00 pm and 05:59 pm; median bite to presentation interval was 60 (interquartile range [IQR] 30, 211) minutes in dogs and 95 (IQR 41, 238) minutes in cats. Bites occurred in the owner's yard in 356 dogs (85%) and 53 cats (26%). A snake venom detection kit was used in 172 cases (28%) and antivenom was administered in 523 cases (85%). Most animals (n = 534, 88%) survived to discharge (median hospitalisation of 25 [IQR 16, 62] hours). SnakeMap effectively collects relevant clinical data from dogs and cats with presumed snake bite and provides locally specific information on the epidemiology of snake envenomation in small animals.     

Elapid snake envenomation in dogs in New South Wales: a review

Elapid snake envenomation in dogs is a commonly occurring yet poorly described clinical entity. Twelve species of dangerously venomous elapid snakes are found in New South Wales that are capable of causing disease in dogs. Geographical distribution of these species varies, as does their venom composition and systemic envenomation syndromes produced in target species. Elapid venom may be divided into the components of prothrombin activating enzymes, lipases and peptidic neurotoxins. Each species of elapid snake may possess venom components that fit any or all of these classifications. The action of these venom components may result in neurotoxic (pre-synaptic and post-synaptic), haemotoxic (red-cell destruction and coagulation disturbance), cardiovascular, myotoxic and secondary nephrotoxic effects. Marked variability may occur in venom composition between and within snake species, resulting in varying toxicity between species and also potentially unreliable clinical syndromes following envenomation. The existence of certain components consistently within the venom of each snake species allows the broad definition of basic pathological processes and clinicopathological changes resulting from snake species-specific envenomation and these are discussed. Diagnosis of snake envenomation is unreliable if based on clinical signs alone and the use of these signs in conjunction with history, physical examination and laboratory investigation, including snake venom detection kits, is recommended. Treatment of systemic envenomation should be undertaken with initial effective first aid and subsequent administration of snake species-specific antivenom.     

Coral Snake (Micrurus Fulvius Fulvius) Envenomation In Five Dogs: Present And Earlier Findings

The purpose of this study is to report on five cases of coral snake envenomation in the dog to substantiate earlier findings in four dogs reported previously, and to describe any additional clinical features that have not yet been noted. The combined results from both studies allow for a more accurate projection of the frequency of certain clinical signs. Both groups showed signs of lethargy, lower motor neuron weakness (8 of 9 dogs) and varying hematologic changes with hemolysis and hemoglobinuria occurring most commonly (7 of 9 dogs). Cardiac dysrhythmias were recorded infrequently (2 of 9 dogs). Not reported previously was the presence of a subtle bite wound located on the upper or lower lip of three dogs in the present series. An unexpected finding in this second series was the occurrence of an anaphylactoid reaction in one dog presumably attributed to the antivenin. Close examination of the lip might reveal the site of envenomation (as found in 4 of 9 dogs from both studies). Treatment with coral snake antivenin should be given as early as possible and followed by close observation for signs of anaphylaxis. The results of this study substantiate earlier findings and provide for a larger data base for further reference.     

Myotoxicity and nephrotoxicity of common tiger snake (Notechis scutatus) venom in the dog

SUMMARY The myotoxicity and neurotoxicity of common tiger snake (Notechis scutatus) venom are major factors in the pathogenesis of envenomation in the dog. Histological examination of the tissues of experimentally envenomed dogs has demonstrated the importance of muscle damage in affecting the clinical syndrome of tiger snake envenomation. Within one hour of injection of the venom into dogs, there was selective involvement of some muscles. Cardiac and smooth muscles were not significantly affected. The severity of myofibre damage was influenced by the amount of venom injected. Immobilisation under general anaesthesia resulted in significant protection against the myotoxic effects of high doses of venom. Lesions in the kidneys of experimentally envenomed dogs were acute tubular necrosis and the variable presence of a small amount of proteinaceous material in tubules. These lesions, which were similar to those in cases of natural snake bite, were indicative of a direct nephrotoxic effect, which could be complicated by the effects of myoglobinuria. These findings emphasise the need for supportive treatment aimed at maintenance of renal function in the treatment of dogs suffering from tiger snake envenomation.     

Retrospective study of snake envenomation in 155 dogs from the Onderstepoort area of South Africa

A retrospective study was undertaken to evaluate the incidence, signalment, haematological and biochemical changes, therapy, and outcome of dogs presented to the Outpatients section of the Onderstepoort Veterinary Academic Hospital for confirmed snake envenomation. Three hundred and seventy-six records of dogs presented for snake envenomation from 1998 to 2002 were reviewed and 155 were selected on the basis of there being a positively identified snake. The 2 most commonly encountered snake envenomations in dogs were puff-adders (Bitis arietans) and snouted cobras (Naja annulifera annulifera). The majority of cases (56%) occurred in the autumn (March to May), with most being bitten by puff-adders. Dogs were 3 to 168 months old with a median of 36 months. No sex predilection was identified. Ten per cent of cases died because of the snake envenomation. Fifty-seven per cent and 43% of snakebites were puff-adders and cobras, respectively. There was no difference in mortality between the 2 groups of snakes. Of the cobras 60% were the snouted cobra, 14% Mozambique spitting cobra, and 24% rhinkals. Swelling in the area of the bite, usually the face and forequarters, was the primary clinical abnormality. Significant haematological findings were leukocytosis (median 17.3 x 10(9)/l; range 0.4-44), neutrophilia (median 13.6 x 10(9)/l; range 0.3-39.9), band neutrophilia (median 0.4 x 10(9)/l; range 0-5.32), and thrombocytopaenia (median 124 x 10(9)/l; range 3-555). Dogs envenomated by a puff-adder and Mozambique spitting cobra had a greater degree of thrombocytopaenia: median of 68 and 66, respectively, versus 243 for the cobra group. The most commonly used treatments were intravenous fluids, antibiotics and glucocorticoids. Thirty-eight dogs were treated with polyvalent antiserum: 9 for puff-adder envenomation and 29 for cobra envenomation. Only 2 of the dogs that received antisera died, both of them of cobra envenomation. The study concluded that snake envenomation in dogs is associated with high morbidity but moderate mortality rate and that the most significant haematological abnormality is thrombocytopaenia.     

Rattlesnake envenomation in 12 New World camelids

BACKGROUND: Rattlesnake envenomation of New World camelids is a seasonal problem with often dramatic clinical signs. HYPOTHESIS: The purpose of this study was to identify the clinical signs, laboratory results, treatment methods, and outcome for rattlesnake envenomation in New World camelids. ANIMALS: Medical records from 1988 to 2004 were searched for New World camelids presented for rattlesnake bite or clinical signs suspected to be related to recent envenomation. Twelve records were identified. METHODS: From these records a retrospective study was performed. RESULTS: Nine camelids presented for acute disease (2/9 arrived dead), whereas 3 presented for subacute onset of disease. Swelling of the lips, head and neck, tachypnea, dyspnea, tachycardia, and lethargy were the most common presenting signs. Snake bites were most commonly located to the muzzle (10/12). Common complete blood count (CBC) and serum biochemical abnormalities were neutrophilia, lymphopenia, increased muscle enzyme activity, hypoalbuminemia, hyperglycemia, hypokalemia, and thrombocytopenia. Treatment included combinations of intravenous fluid therapy, antimicrobials, anti-inflammatory drugs, tetanus prophylaxis, tracheostomy, supplemental oxygen, antivenom, total parenteral nutrition, and nursing care. Five of the 10 animals with acute onset of clinical signs survived, and all animals with subacute presentation died. The mortality rate for New World camelids with severe local tissue reaction and systemic signs of envenomation was 58%. CLINICAL IMPORTANCE: New World camelids that sustain rattlesnake envenomation and severe facial swelling precluding prehension and mastication have a guarded prognosis for survival. Aggressive treatment is recommended to optimize the chances of survival. Animals with less severe local tissue reaction and absence of systemic signs have a better prognosis.     

A retrospective study of 153 cases of undiagnosed collapse, syncope or exercise intolerance: the outcomes

Objectives : To retrospectively assess the long‐term outcome for dogs that were presented with collapse, syncope or exercise intolerance for which an underlying cause is not identified. Methods : The clinical records of animals presenting to two practices were assessed. Dogs which presented for collapse, syncope or exercise intolerance at least 6 months previously and did not receive a definitive diagnosis despite investigation were included. Follow‐up of these cases was carried out by conducting telephone interviews with the owners. Results : One hundred and fifty‐three cases were successfully followed up. Clinical signs had resolved in 64 cases (42%), 35 dogs (23%) were continuing to exhibit clinical signs, although 22 of these had improved without medical intervention. In 17 cases (11%), a diagnosis had subsequently been made or treatment was being administered and 37 dogs (24%) had died. Of the deaths, 18 (12%) were considered to be related to the original presentation. The overall prevalence of death and deterioration related to the problems investigated was 16·2% of cases. Death in boxers was significantly more common than in other breeds (36%). Clinical Significance : Death and deterioration are uncommon outcomes for dogs other than boxers presenting with collapse, syncope and exercise intolerance for which a definitive diagnosis cannot be made.     

Clinical and Therapeutic Aspects of Brazilian Native Bothrops Envenomation in Nine Horses

In this retrospective study, clinical records of nine horses with a diagnosis of Bothrops envenomation were investigated. The accidents were classified as severe (5/9), moderate (2/9), or mild (2/9) according to the adapted bothropic snakebite severity score (BSSS). All snakebites were on the head region. The main clinical signs were local edema, blood coagulation disorders, and respiratory distress. The whole-blood clotting time (WBCT) was prolonged in all horses, and five horses presented with uncoagulable blood. All horses received specific snake antivenom according to the BSSS (six vials for severe, four vials for moderate, and two vials for mild accidents), and emergency tracheotomy was required in six horses because of respiratory distress. One horse died after eight days of hospitalization, whereas the others were discharged after nine days of hospitalization. The BSSS plus the WBCT were useful in determining the prognosis and the amount and frequency of antivenom therapy. Snakebite accidents are emergency cases; therefore, rapid and efficient therapeutic intervention will reflect positively on the prognosis.     

Anuric renal failure in a dog after red-bellied black snake (Pseudechis porphyriacus) envenomation

A case of Red-bellied Black snake envenomation resulting in intravascular haemolytic anaemia, rhabdomyolysis and anuric renal failure is described in the dog. A 12-year-old female desexed Golden Retriever was presented with a 15 hour history of profuse salivation, progressive lethargy, obtundence, inappetence and collapse. Significant findings on clinical examination were pallor, icterus, tachypnoea and dyspnoea with increased respiratory sounds and crackles in all lung fields. Generalised abdominal and muscular pain was apparent and dark red-brown urine was present around the perineal region. A diagnosis of Red-bellied Black snake (Pseudechis porphyriacus) envenomation was made and the dog was treated with intravenous fluid therapy, Tiger/Brown snake antivenom, packed red cell transfusions and Intermittent Positive Pressure Ventilation. Continued clinical deterioration occurred and a diagnosis of acute renal failure secondary to myohaemoglobinuric pigmenturia was made 12 hours after admission. Intensive treatment was attempted with diuresis and volume expansion. Oliguria and subsequent anuria ensued and the dog was euthanased due to a grave prognosis and lack of clinical response to treatment. Necropsy examination revealed muscular necrosis, accumulation of fluid in the thoracic and peritoneal cavities, and marked renal tubular necrosis with intraluminal occlusion secondary to pigmentary casts.     

Megaoesophagus in adult dogs secondary to Australian tiger snake envenomation

Four cases of megaoesophagus secondary to tiger snake envenomation are reported. History in all cases suggested megaoesophagus was not present prior to snake envenomation. Diagnosis of megaoesophagus was confirmed by thoracic radiography in all cases. One dog died of respiratory failure. The remaining three dogs recovered, with gradual resolution of clinical signs associated with megaoesophagus.     

Observations on blood coagulation after snakebite in dogs and cats

Blood samples from 13 cases of snakebite, 6 in dogs and 7 in cats, were tested for activated partial thromboplastin time (APTT), prothrombin time (PT) and fibrin/fibrinogen degradation products (FDP). Four cases were tested for fibrinogen concentration. Based on the results of a commercially available ELISA test, 9 cases were caused by tiger snakes (Notechis scutatus) and 1 case by a brown snake (Pseudonaja textilis). Three other cases had clinical signs and increased creatine phosphokinase values which suggested tiger snake envenomation. Although the period post-envenomation varied, results indicated a marked prolongation of the APTT and PT in 5 of 6 dogs. Three of these 5 dogs also had increased FDP values and 3 (of 3 examined) were hypofibrinogenaemic. Clinical manifestations of this coagulopathy were: haematoma formation after venepuncture (3 cases), gingival petechiae (1 case) and hyphaema (1 case). In contrast, there was minimal or no prolongation of the APTT and PT values, and no increase in FDP, in all 7 cats. Furthermore, no cat exhibited clinical signs of a coagulopathy.     

Snake bites recorded by veterinary practices in Australia

Objective To determine the extent of the snake bite problem in domestic animals, its regional significance and the effects of antivenom treatment.
Design A questionnaire was designed seeking information on the number and type of domestic animals referred, whether treated or untreated, type of snakes and management of the bite.
Procedure The survey form was sent to 10% of veterinary surgeons, selected at random throughout Australia.
Results The response of 106 veterinary surgeons revealed that snake bite in domestic animals is frequent, with an estimated 6200 cases reported annually. Bites were more prominent in rural (78%) than urban areas (22%) with brown, tiger and black snakes accounting for 76%, 13% and 6% of cases, respectively. Cats and dogs were the most frequently reported victims. Ninety-one percent of cats and 75% of dogs survived following the administration of antivenom whereas 66% of cats and 31% of dogs survived without antivenom. Overall, in 33% of cases antivenom was not used, and venom detection kits were used in only 1% of cases. A number of drugs were used in various combinations with or without antivenom and intravenous fluids in the treatment of animals with snake bite, but their role in reducing the severity of envenomations was not assessed.
Clinical implications Antivenom significantly improves the chances of survival of domestic animals bitten by snakes.     

Evaluation of castor bean toxicosis in dogs: 98 cases

Castor beans (Ricinus communis) contain ricin. Ricin is a glycoprotein reported to cause hypotension, gastroenteritis, depression, and death. However, few deaths are reported following castor bean ingestion in animals. From January 1987 to December 1998, the American Society for the Prevention of Cruelty to Animals-National Animal Poison Control Center received 98 incidents of castor bean ingestion in dogs. The most commonly reported clinical signs were vomiting, depression, and diarrhea. Death or euthanasia occurred in 9% of the cases. The severity of clinical signs following castor bean ingestion may depend on whether the beans were chewed or swallowed whole.     

Boomslang envenomation in 2 dogs in Kwazulu-Natal, South Africa

Although snakebites are frequently seen in small animal practice in South Africa, boomslang (Dispholidus typus) bites are infrequent due to their shy habits. Boomslang venom is a potent procoagulent, causing a consumption coagulopathy and profuse haemorrhage. Boomslang monovalent antivenom is the most effective treatment. This case report describes and discusses 2 small dogs that were presented to a private practice after being bitten by the same boomslang. Boomslang monovalent antivenom administration to both resulted in cessation of bleeding within 45 minutes. One of the dogs developed severe adverse reactions to the antivenom, including vomiting, dyspnoea and nystagmus, which responded well to intravenous cortisone and symptomatic treatment.     

Clinical findings associated with prairie rattlesnake bites in dogs: 100 cases (1989-1998)

OBJECTIVE: To identify clinically relevant variables and treatments for dogs bitten by prairie rattlesnakes (Crotalus viridis viridis). DESIGN: Retrospective study. ANIMALS: 100 client-owned dogs. PROCEDURE: Records of dogs evaluated for rattlesnake envenomation from 1989 to 1998 were reviewed. Analysis was performed to test for significant associations among clinical variables or treatments and cell counts, costs, and duration of hospitalization. RESULTS: Most prairie rattlesnake bites occurred between May and September. Dogs were 3 months to 12 years old (median, 3.7 years); most were bitten on the head in the late afternoon. There was no sex predilection. Median time to evaluation was 1 hour (range, 15 minutes to 13 hours). Swelling in the area of the bite was the primary physical abnormality. Principal initial laboratory findings were echinocytosis, thrombocytopenia, leukocytosis, and prolonged activated clotting time. Ninety-four dogs were hospitalized; 48 were discharged the following day. Antimicrobials and crystalloid fluids, glucocorticoids, antihistamines, and antivenin administered i.v. were the most commonly used treatments. One dog died, and small dogs were hospitalized longer than large dogs. Antivenin administration was not significantly associated with duration of hospitalization but was associated with higher platelet counts after treatment and higher total hospital costs. CONCLUSIONS AND CLINICAL RELEVANCE: Prairie rattlesnake envenomation in dogs is associated with high morbidity rate but low mortality rate. The efficacy of administration of antivenin for dogs with bites from this snake species is questionable.     

Retrospective outcome evaluation for dogs with surgically excised,solitary Kiupel high‐grade,cutaneous mast cell tumours

Published outcomes for dogs with specifically high‐grade mast cell tumours (MCTs), controlled for clinical stage, are few. Clinical outcomes for 49 dogs with Kiupel high‐grade, clinical stage I, cutaneous MCTs were evaluated. Median survival time (MST) was 1046 days; 1 and 2‐year survival rates were 79.3% and 72.9%, respectively. At study end 24 dogs had died, 23 dogs were alive (median follow‐up 980 days) and 2 dogs were lost to follow‐up. Death was considered MCT‐related in 14 of 20 dogs with a known cause of death. Local tumour recurrence developed in nine dogs (18.4%); regional lymph node metastasis occurred in six dogs (12.2%); and a new MCT developed in 15 dogs (30.1%). Tumour location, histologic margin size and use of chemotherapy did not affect MST; increasing mitotic count (P = .001) and increasing tumour diameter (P = .024) were independently negatively prognostic. Six dogs that developed lymph node metastasis after surgery had worse MST (451 days) than 42 dogs that did not develop metastasis (1645 days); (P < .001). Our study suggests that dogs with local surgical control of clinical stage I histologically high Kiupel grade cutaneous MCT may have a long survival time; especially those with smaller tumours and a lower mitotic count. Our results suggest that evaluation of staging information and mitotic count may be equally helpful as histologic grading when making a prognosis; and highlight the importance of not relying on histologic grade alone when predicting survival for dogs with MCT.