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Home , Berg adder, Cape cobra, Cobra, Puff adder, Rinkhals, Snouted cobra

Review article — Oorsigartikel

The diagnosis and management of in dogs – a southern African perspective

A L Leisewitza*, R S Blaylockb, F Kettnera, A Goodheada, A Goddarda and J P Schoemana

dogs attack with their mouths. ABSTRACT Standing humans are most commonly Cases of snakebite envenomation are frequently presented to veterinary practitioners in bitten below the knee5,9,18. The different southern . Despite this, no published guidelines exist on how this medical emergency anatomical location of this bite distribu- should be managed. Southern African can be classified into 3 main types tion has important consequences for the based on the main mechanism of action and clinical presentation. A polyvalent outcome of bites, specifically cytotoxic is manufactured in and contains antibodies against the most ones. important southern African snake venoms. The cytotoxic venoms are represented mainly by the puff-adder ( arietans), spitting ( mossabica), black-necked Snakebite is confined almost completely spitting cobra (Naja nigricollis) (in the and ) and the stiletto snake to rural environments and is rarely a 11 (Atractaspis bibronii). These venoms may cause dramatic local swelling, high morbidity and problem in built-up urban areas . low mortality and infrequently require the use of antivenom for survival (the only cytotoxic Hunting dogs and dogs that are inquisi- venoms used to prepare the antivenom are the puff-adder and Mozambique spitting co- tive by nature are especially prone to bra). The neurotoxic venoms (represented chiefly by the non-spitting and ) bites. There is no study to evaluate cause high mortality due to rapid onset of paresis and require antivenom and mechanical snakebite predilection for breed or sex of ventilatory support which is life-saving. The boomslang (Dispholidus typus) and the vine dog. snake (coagulopathic venom) rarely bite humans but dogs may be bitten more frequently. In humans, cytotoxic bites outnumber These venoms cause a consumption coagulopathy and successful treatment of boomslang neurotoxic bites by about 10:15,9,18,21. This is bites requires the use of snake -specific monovalent antivenom. There is no likely to be similar for dogs. Morbidity is antivenom available for treating vine snake (Thelotornis capensis), berg adder (Bitis atropos), high in the case of bites from cytotoxic night adder (Causus spp.), stiletto snake and other lesser adder bites. There are some impor- snake species but mortality is low. The tant differences between the way are managed in humans and dogs. opposite is true of bites due to the neuro- Key words: dog, snakebite, . toxic snake species where mortality is Leisewitz A L, Blaylock R S, Kettner F,Goodhead A, Goddard A, Schoeman J P The manage- high and morbidity is low. It is probable ment of snakebite in dogs – a southern African perspective. Journal of the South African that many snake-envenomated dogs die Veterinary Association (2004) 75(1): 7–13 (En.). Department of Companion Clinical prior to veterinary care. Studies, Faculty of Veterinary Science, University of Pretoria, Private Bag X04, Onderstepoort, 0110 South Africa. SNAKE IDENTIFICATION This can be a daunting task for the novice but some simple, general rules INTRODUCTION species most commonly causing bites in may be helpful in deciding if a southern Snakebite is a common medical their area of practice and be able to iden- African snake is venomous or not. The emergency16 with significant morbidity tify them. Of 175 species of snakes in the following usually indicate a dangerous and mortality in small animal practice in subregion, only a handful are regarded as snake: southern Africa. In Australia, a country poisonous enough to cause death7. There • The snake raises its head from the with similar climatic conditions to south- are some important differences between ground and makes a hood when threat- ern Africa, snakebite is also reported as a humans and dogs in the way snakebite is ened (cobras, Naja spp.; , common presentation20. There is almost managed. Haemachatus haemachatus; black , no veterinary literature addressing this Dendroaspis polylepis). The boomslang problem in dogs in southern Africa. EPIDEMIOLOGY (Dispholidus typus) and vine snake Because the interaction between the pet Being ectotherms (cold blooded), the (Thelotornis capensis) will inflate the and the snake is often not witnessed, the level of activity of a snake is determined front portion of the body. diagnosis of snakebite is most often pre- by the temperature of its environment. • The snake is banded as opposed to sumptive, based on clinical presentation. For this reason the highest incidence of striped along the length of the body. A The snake itself, or a good description snakebite in humans and dogs is during chevron-like pattern dorsally (adders) is of the snake, is usually not presented the warmer summer months5,9,18,21. There an indication of danger. with the patient, necessitating syndrom- is a consistent annual peak in late summer • Heavy bodied snakes with a distinct ic management. Veterinarians should and early autumn in the area served by neck and triangular head (adders). have knowledge of the poisonous snake the Onderstepoort Veterinary Academic It is important to remember that some Hospital (OVAH)16. This is thought to snakes will sham death when threatened aDepartment of Companion Animal Clinical Studies, be due to increased pre-hibernation (particularly the rinkhals) and no snake Faculty of Veterinary Science, University of Pretoria, Private Bag X04, Onderstepoort, 0110 South Africa. activity. should be assumed dead and handled. If bGold Fields Health Services at Leslie Williams Private The most common bite site in dogs is the snake is presented along with the dog, Hospital, PO Box 968, Carletonville, 2500 South Africa. *Author for correspondence. E-mail: [email protected] cranial to the shoulders, especially the advice on identification should be sought Received: July 2003. Accepted: December 2003. face and the loose skin around the neck as as this would be helpful in predicting the

0038-2809 Jl S.Afr.vet.Ass. (2004) 75(1): 7–13 7 clinical course and outcome of the patient. of fur and looseness of a dog’s skin physiological response to blood loss In this regard owners are poor sources of around the neck may make deep and a fall in blood pressure result in reliable information. In most cases, snake- muscle deposition of the venom more fluid retention, haemodilution and a bite is strongly suspected but never con- difficult in dogs as opposed to humans. later fall in haematocrit. In serious cases, firmed, therefore the clinical presentation Human furless skin requires more pain haematocrit should be monitored twice and progression of clinical signs often receptors for protection which are espe- daily. confirms the diagnosis. cially prevalent on the hands. Some In-saline-agglutination-positive, sec- venom components are hyperalgesic. ondary immune mediated haemolytic VENOM TYPES In the few bites involving muscle bellies anaemia (IMHA) has occasionally been There are essentially 3 important groups in dogs (shoulder and gluteal region), observed following bites. It is necessary to of venoms in terrestrial snakes of southern pain has been severe although tissue monitor cases with a falling haematocrit Africa. Each leads to a particular clinical loss was not remarkable. A further with regular in-saline agglutination tests envenomation syndrome. exception is bites by spitting cobras27 (ISA) and look for signs of free haemoglo- 1. Cytotoxic venoms result in progres- which are extremely painful and cause bin in serum or urine. It may be necessary sive swelling. The 3 important snakes significant skin loss (Fig. 4). to treat this complication with glucocorti- in this group are the puff-adder (Bitis • Infection. It is somewhat surprising coids. arietans) and spitting cobras (Naja that secondary bacterial infections are A non-DIC thrombocytopenia is very mossambica, N. nigricollis), with the uncommon in dogs. This is counter- common in puff-adder bites. In the baboon stiletto snake (Atractaspis bibronii) and intuitive as free blood, anaerobic tissue the venom has been shown to contain a night adder (Causus spp.) causing and bacteria from a snake’s mouth potent irreversible platelet aggregation- lesser swelling. would provide grounds for sepsis. inducing component8 that may be associ- 2. Neurotoxic venoms of the family is, however, antibacterial ated with active haemorrhage seen in produce progressive paresis. in action2 and there are few bacteria in humans30 which has also been observed This group is represented by the cobras snake mouths4. In 1 study of infected in a dog at the OVAH. Immune-mediated (snouted, Cape and forest cobras, Naja snakebite wounds only aerobic bacteria platelet destruction may occur as a few annulifera, Naja nivea and Naja melano- which were either Gram positive cocci cases develop intravascular haemolysis as leuca, respectively) and the mambas or Gram negative bacilli were isolated3. a result of secondary IMHA. (Dendroaspis spp.). • Systemic signs associated with massive Typically the leukogram observed in 3. Coagulopathic venoms of the family blood loss and hypotension. Progressive the OVAH following puff-adder bites is Colubridae, which includes the swelling from a puff-adder bite is rapid inflammatory (neutrophilia often with a boomslang and vine snake, produce and associated with haemorrhage and left shift) that is most likely the conse- bleeding. Puff-adder15 and Gaboon oedema (Figs 2, 3). Swelling from a quence of tissue damage and the systemic adder (Bitis gabonica) bites17 may cause Mozambique spitting cobra (Naja inflammatory response syndrome (SIRS) a coagulopathy. mossabica), stiletto snake and night ad- and not of infection. The berg adder (Bitis atropos)12 and der is slower in progression and not rinkhals25 have both neurotoxic and associated with haemorrhage. Swelling Progressive weakness cytotoxic venom. The in a 20 kg dog’s neck following a puff- (neurotoxic envenomation) venom may also have mixed effects. adder bite may contain upwards of half Many cases of neurotoxic envenomation a litre of blood. This is a significant pro- probably die before presentation. The PATHOGENESIS AND DIAGNOSIS portion of the circulating volume and time between when a dog is bitten by a this rapid loss may lead to hypotension neurotoxic snake and the onset of life Progressive swelling (oligaemic shock). Signs associated with threatening collapse is often so short that (cytotoxic envenomation) hypotensive shock include weakness, unless the owner actually observes the The time course of disease following a pallor, tachycardia, hypothermia, re- interaction between dog and snake, we bite in these cases is relatively long. Most duced urine production and eventual suspect many dogs die without veteri- cases will only present several hours after complete collapse. Poor organ perfusion nary care. The time from bite to the onset the bite with the venom effect being and tissue hypoxia may result in multi- of signs is invariably less than an hour and almost exclusively local. Systemic signs ple organ failure. An awareness of these in severe cases less than 30 minutes. Sys- seen are most likely the result of extensive complications has important implica- temic absorption of venom results in pre- fluid extravasation and not due to sys- tions for monitoring and treatment. or post-synaptic blockade at the temic venom absorption. Similar complications have been de- neuro-muscular junction (NMJ)19,26. This The classical presenting complaints are: scribed in humans15. group of snakes have short, fixed front • Local swelling that is typically non- • Upper airway obstruction. Dogs that fangs and venom is deposited superfi- painful. The degree of swelling varies have been bitten around the face or cially in tissues. and may be mild and completely incon- neck region, may develop swelling, • Generalised weakness. Usually the 1st sequential or massive and life-threaten- which causes upper airway compro- neurological signs to become obvious ing (Figs 1, 2, 3). Swelling is usually mise and eventually death by asphyxia- typify bulbar paralysis (loss of the present within 2 hours of the bite, peaks tion (Fig. 3). Cervical swelling may swallowing reflex, paralysis of the between 12 and 24 hours and is signifi- dissect down the trachea into the tongue and jaw) with saliva pouring cantly reduced by 72 hours (without the mediastinal space which may have seri- from the mouth as it cannot be swal- use of antivenom). Swelling is typically ous consequences for cardiac venous lowed (Fig. 5). This is followed by limb located around the head and neck. Bites return as the large veins contained in weakness and finally flaccid paralysis. in humans are typically very painful the cranial mediastinum collapse easily. Breathing is shallow and rapid and the and may be associated with serious • Haematological consequences. Swelling dog’s mucous membranes become tissue loss, both of which are rarely seen is due to the loss of whole blood and this cyanotic and death follows. Similar in dogs. We postulate that the layer does not initially affect haematocrit. The signs have been reported in humans5,9,18.

8 0038-2809 Tydskr.S.Afr.vet.Ver. (2004) 75(1): 7–13 Fig. 1: The typical presentation following an adder Fig. 2: A young Staffordshire terrier dog died due to asphyxiation follow- bite is a non-painful facial and ventral neck swelling. ing a puff-adder bite. The figure illustrates the massive haemorrhage that Most cases recover without complication and require is responsible for the large swellings seen following adder envenom- no treatment. ation.

The differential diagnosis for flaccid venom injected in spite of a clear bite, injection of these venoms takes longer quadriplegia would include: making it important to withhold treat- than that due to neurotoxicity (may be 1. Polyradiculoneuritis (rarely so acute ment until clear signs of envenomation minutes) or cytotoxicity (hours). Most and seldom severe enough to cause are apparent. patients would be presented to a veteri- respiratory embarrassment). • Other complications. On occasion, focal nary practitioner the next day. 2. Myasthenic crisis (rare). intracranial CNS signs are seen on Severe bleeding is usually the result 3. Tick bite toxicosis. recovery. The complications of mechan- of venom haemorrhagins as well as 4. Organophosphate toxicity (the flaccid ical ventilation can be serious (espe- procoagulant enzymes with boomslang form of the disease or chronic intoxi- cially if improperly applied) and and vine snake venom causing activation cation). life-threatening. The most common of clotting factors II and X23,28 and Gaboon 5. Botulism (rare in dogs). outcome, however, is complete and venom containing a thrombin-like • Local signs. These are usually limited to quick recovery if treatment is early and substance24. Disseminated intravascular mild swelling and the bite marks may be aggressive. coagulation ensues and once coagulation unidentifiable. Exceptions to this are factors are depleted, active bleeding oc- spitting and snouted cobra bites where Bleeding curs. Disseminated microvascular swelling may be significant and necro- (haemotoxic/coagulopathic thrombi may produce multiple organ fail- sis may occur. On occasions a ‘dry bite’ envenomation) ure. Thrombocytopenia may lead to may be delivered by the snake, i.e. no The onset of clinical disease following bleeding from a puff-adder bite. With all

Fig. 3: Puff-adder (Bitis arietans) bites are sometimes severe Fig. 4: Mozambique spitting cobra (Naja mossambica) bites are enough to cause upper airway obstruction. The pitt bull terrier remarkably cytotoxic and associated with severe pain. This small developed upper airway obstruction and had a tracheostomy tube dog sloughed all the skin on the ventral cervical region, ventral chest surgically placed (arrow). Also note the massive swelling cranial and abdomen and ultimately succumbed. to the shoulders.

0038-2809 Jl S.Afr.vet.Ass. (2004) 75(1): 7–13 9 these bites, bleeding can only occur if the symptomatic should be treated. fluid administration at maintenance action of haemorrhagins cause capillaries • Give as much antivenom as the owner rates. to leak. can afford up to a maximum of 8 vials. 3. Antibiotics are unnecessary unless There is 1 reported case of a boomslang One vial is better than none. there is obvious necrosis (spitting bite in a dog28. Bite site bleeding was • Always give the antivenom intrave- cobra bites). present from the moment of the bite, with nously. 4. Analgesics are not widely used in the systemic bleeding commencing 12 hours • The response to a small test dose does management of progressive swelling later. The dog collapsed approximately 24 not predict the outcome to the main in dogs as pain seems to be minimal. hours after the bite and was bleeding dose and is therefore unnecessary. Potent analgesia (buprenorphine; freely from the gingiva, was pale and • Injection should always be slow. morphine) may be needed in dogs severely anaemic. A case of vine snake • Do not inject locally in or around the bitten by a spitting cobra. envenomation has been reported23. The bite site. 5. If a case deteriorates, aggressive treat- dog showed a mild haemorrhagic ten- Boomslang bite: 1 or 2 ampoules of mono- ment is necessary. Signs of deteriora- dency, an abnormal coagulation profile specific boomslang antivenom. tion include: and made an uneventful recovery on the Puff-adder bite: 5 ampoules of polyvalent • Worsening weakness or depression 3rd day without treatment. Active bleed- antivenom is usually adequate. (a deterioration in habitus). ing due to a puff-adder bite has been seen Gaboon adder bite: up to 20 ampoules of • A rising pulse rate, respiratory rate, at the OVAH. polyvalent antivenom may be necessary. a drop in rectal temperature or pale Vine snake bite: there is no effective anti- mucous membranes with sudden TREATMENT venom. changes in capillary refill time. Adverse effects to South African-manu- • Swelling that begins to impinge on General comments on snakebite factured antivenom and antivenom the upper airway. antivenom manufactured elsewhere are common in • A haematocrit that continues to fall The following snake venoms are used in humans. Adverse effects include a rash, or the appearance of haemoglobi- the polyvalent antivenom manufacturing urticaria, angio-oedema, bronchospasm nuria, haemoglobinaemia or a posi- process by the South African Vaccine and hypotension1. It is recommended in tive ISA test. Producers (Pty) Ltd.: puff-adder, Gaboon humans that atopic individuals be • Evidence of spontaneous haemor- adder, rinkhals, snouted cobra, Cape premedicated with adrenaline1.Atthe rhage. cobra, forest cobra, Mozambique spitting OVAH, adverse effects are rare, but when Recommendations for the management cobra, green mamba (Dendroaspis augus- they do occur they vary from full-blown of the above scenarios are: ticeps), Jameson's mamba (D. jamesoni) anaphylaxis (rare) to more common mild 1. Volume replacement by whole blood and (D. polylepis).* A allergic responses characterised by urti- transfusions to replace lost blood. If monovalent antivenom is produced for caria or angioedema (Fig. 6) and occasion- blood is unavailable, preferably use a boomslang envenomation. Antivenom ally vomiting and diarrhoea. Anaphylaxis synthetic colloid (hetastarch) or lastly comprises pepsin-refined immunoglobu- requires prompt treatment with adrena- crystalloids at shock doses. lins prepared from the serum of horses line, which is life-saving. Milder reactions 2. Intravenous administration of as that have been hyper-immunised with are effectively managed with a single much antivenom as the owner can the various snake venoms. parenteral dose of a short-acting gluco- afford (1 vial may be life-saving but as Appropriate antivenom can prevent corticoid. In humans, serum sickness is many as 8 (or more) vials may be further spread of swelling (cytotoxicity), described and usually occurs about 10 given). Administration even in the prevent the onset of respiratory failure days after treatment. It is characterised late phase of disease may well be help- and reduce the period of ventilation by pruritic skin rash, pyrexia and arthral- ful and should not be withheld. (neurotoxicity) and smother coagulopathic gia10,22,31. Although there is no reason why 3. Cases with upper airway obstruction mechanisms (haemotoxicity). Antivenom this should not occur in dogs, it has never will require tracheostomy tube place- does not prevent necrosis. been specifically diagnosed or suspected ment. In many cases the ventral cervi- at the OVAH. cal swelling is so severe that a tradi- Dose tional tracheostomy tube is too short. A unit of antivenom neutralises a fixed Progressive swelling In such cases an endotracheal tube quantity of venom and has nothing to do (cytotoxic envenomations) (ET) inserted through the ventral cer- with the size of the patient. In view of Most cases of progressive swelling vical surgical tracheostomy site is use- venom / mass ratio, small dogs often are require very little medical attention and ful. If an ET tube is placed by mouth, worse off than large dogs. The dose of recover without treatment. It is important full anaesthesia will normally be nec- antivenom cannot be set in mg/kg or that cases that are showing signs are essary, which is best avoided as many m /kg as for traditional drugs. Guidelines carefully observed for progressive swell- of these cases will need an artificial used in the OVAH for antivenom admin- ing. Antivenom is usually not necessary. airway for longer than a day. A istration are as follows: Despite previous veterinary recommen- tracheostomy tube needs very good • Do not use in dogs showing no clinical dations that antivenom use in puff-adder nursing care (nebulisation to keep signs. bites in dogs was not beneficial, subse- secretions moist, regular suction and • Use in cytotoxic snakebites if the patient quent experience has proven otherwise. daily replacement) to prevent compli- is deteriorating and/or there are evolv- Similar observations have been made for cations such as blockage with dried ing systemic consequences of the bite. humans30. Standard treatment applied at mucous plugs. • All neurotoxic snakebite victims that are the OVAH consists of the following: 4. Critically ill dogs should have intrave- 1. All cases showing swelling (unless nous broad-spectrum antibiotic cover. *Antivenom may be acquired directly from the Antivenom Unit; the contact details are: Tel +27 (0)11 386 6000; Fax resolving) are admitted for observa- Critical illness is associated with +27 (0)11 386 6016; 1 Modderfontein Road, Edenvale, tion. immunosuppression and an increased Gauteng; PO Box 28999, Sandringham, 2131 South Africa. 2. Place a cephalic catheter for crystalloid risk of infection.

10 0038-2809 Tydskr.S.Afr.vet.Ver. (2004) 75(1): 7–13 5. In very ill patients a high level of the limbs or begins to show shallow to clot in a test tube or there is laboratory nursing care is required for assess- breathing or reduced respiratory effort, evidence of significant coagulopathy ment of urine production (urinary an intravenous general anaesthetic is (prothrombin index less than 50%, partial catheter), regular turning, toilet care administered and an ET tube placed. thromboplastin time more than double of artificial airways and attention to An AMBU bag or a closed circuit the control). nutrition (by naso-gastric or oesopha- anaesthetic machine allows manual Be aware of haematoma formation at gostomy tube) if the patient does not ventilation followed by as much injection sites and gain peripheral venous eat for longer than a day. Monitoring antivenom as the owner can afford access so that possible bleeding is more and pharmacological management of given slowly intravenously (over easily controlled. Fresh whole blood or blood pressure is helpful. about half an hour). While this is being fresh plasma transfusion may be neces- 6. The treatment of Mozambique spitting done a mechanical ventilator can be sary. Monitor urine output in case of renal and other spitting cobra bites is some- set up (Figs 7A, 8). Ventilation (bag or failure. what different from the typical puff- mechanical) may be required for 6–12 Heparin is contraindicated as venom- adder bite. Haematoma formation hours while antivenom is reversing induced thrombin is resistant to its does not occur and hypovolaemic paralysis. In the OVAH general anaes- action29. Fibrin-stabilising drugs may shock is unusual. There is extreme thesia with pentobarbitone (or the convert a DIC with a good prognosis to pain (much like Hyalomma tick bites) more expensive propofol by continu- one with a bad prognosis. Thrombolytics and often large areas of skin necrosis. ous rate infusion) is maintained for would aggravate the situation. These cases should be given anti- 6–12 hours before attempting to wean In humans, antivenom is effective even venom and a large area around the the dog off the ventilator. Good nurs- in late-stage disease when active haemor- bite site should be shaved in anticipa- ing care is necessary and includes rhage is well established15 and the same tion of slough. The problems that keeping the body temperature nor- observation has been made in the OVAH. require management relate to pain, mal, regular turning, maintenance fluid, electrolyte and protein loss that intravenous fluid and bladder care. Venom ophthalmia occur through the large wounds. The use of prophylactic antibiotics is Ocular envenomation is caused by Secondary infection is a potential risk. controversial and most likely unnec- squirted venom from the spitting cobras Treatments that are generally not rec- essary. and the rinkhals. All cases seen at the ommended include: OVAH had large corneal erosions, oe- Is it worth trying to treat these cases with- 1. Corticosteroids. There is no rationale dema and severe chemosis. Venom is a out a mechanical or manual ventilator? for the use of these drugs. They may caustic (basic) agent that forms soaps with No, as ventilatory support is crucial to worsen muscle weakness, enhance the lipids of the corneal cell membranes success in spite of using antivenom. catabolism and cause immunosup- and disrupts glycosaminoglycan ground pression. An indication for 1 dose of a Is it worth trying to treat these cases with- substance, causing softening of the tissue short-acting steroid would be a mild out antivenom? and devitalisation of corneocytes. These adverse reaction to antivenom. Yes, as ventilatory support is life-saving actions may continue after liberal ocular 2. Non steroidal anti-inflammatory but this strategy is not encouraged. irrigation13,14. Treatment involves the use drugs are contra-indicated in volume- In 2 cases of human enven- of liberal amounts (around 1 per eye) of challenged patients. Use morphine- omation, up to 19 vials of antivenom had a sterile isotonic irrigation agent (such as like drugs if analgesia is required. no effect in reversing NMJ blockade and Ringers lactate). Pain is intense and the 3. Antihistamines. long-term ventilation was required. Once dog may well require sedation to allow 4. Under no circumstances should large complete flaccid paralysis has become proper irrigation. Before using any other incisions be made in an attempt to established it seems the antivenom has topical agent, the cornea should be drain venom or the haematoma. minimal effect6. stained with fluorescein. Topical corti- When humans are bitten in muscle, It is clear from our experience at the costeroids should not be used in the fasciotomy may be indicated to relieve OVAH that some dogs develop obvious presence of corneal ulceration but oral pressure and prevent necrosis (com- local swelling and even skin necrosis in corticosteroids are beneficial in managing partment syndrome). Although this is addition to neurotoxic effects, requiring chemosis. A sterile uveitis and/or hypo- theoretically possible in the dog ventilator support. This dual neuro- and pyon frequently develops within a day. (bitten in a muscle belly surrounded cytotoxic effect may be ascribed to the Topical antibiotics are indicated and by fascia), the authors have never felt snouted cobra in our hospital (Figs 7B, 9). atropine assists in pain management. the need to perform this procedure. The complications associated with Pain is as a result of the loss of corneal The management of such large open these bites usually relate to mechanical epithelium which stimulates the ophthal- wounds would require expensive ventilation or acute adverse antivenom mic branch of the trigeminal nerve, specialist ICU facilities. reactions. The haematological conse- causing a reflex miosis. The spasm of the quences seen in cytotoxic envenomations iris muscles drives the pain response felt Progressive weakness are not a feature of neurotoxic bites. by the patient. Effective relief can be (neurotoxic envenomations) achieved by paralysing the iris with All dogs suspected of having been bit- Bleeding atropine that will cause cycloplegia and ten should be very carefully observed and (haemotoxic envenomations) mydriasis. Epinephrine has similar but no treatment should be initiated until it is Antivenom is more important in the far weaker effects. The longer the time obvious that signs are present. The ap- bleeding syndrome than in the syn- interval between envenomation and proach at OVAH to managing symptom- dromes of progressive swelling or pro- treatment the longer the period for which atic cases is as follows: gressive weakness where good suppor- treatment will be required (possibly 1. Place an intravenous catheter for tive measures alone may be life-saving. weeks). The cornea is a resilient tissue venous access. Antivenom is indicated if there is active and has a remarkable ability to regener- 2. As soon as the dog becomes weak in bleeding (internal or external), blood fails ate.

0038-2809 Jl S.Afr.vet.Ass. (2004) 75(1): 7–13 11 Fig. 5: Bulbar paralysis following neurotoxic snake bite. Note the tongue Fig. 6: Adverse reactions to the use of polyvalent anti- paralysis and anisocoria. This dog was unable to swallow and was serum are fairly common but mild. Following a large dose minutes away from requiring a general anaesthetic, tracheal entubation given intravenously to this small dog bitten by a cobra, and assisted ventilation. moderate facial angio-oedema and hyperaemia devel- oped. Such reactions are independent of antivenom dose.

Fig. 7: Bites from the snouted cobra (Naja annulifera) are classically neurotoxic. Treatment of these cases requires intravenous anti-serum and mechanical ventilation (A). Occasionally signs of cytotoxic injury are seen as illustrated in (B) where a well circumscribed area of tissue necrosis can be seen medially on the front leg.

Fig. 8: Neurotoxic bite victims require mechanical ventilation for up to Fig. 9: Following a bite from a snouted cobra (Naja annulifera), 12 hours following the use of antivenom. Smaller patients have a worse this dog developed classic neuromusucular junction blockade prognosis. and required a large dose of antivenom and assisted ventilation. A few days after this 2 large areas of skin necrosed on the lateral chest wall – probably the bite site. Snouted cobra (Naja annulifera) bites may be associated with obvious cytotoxic effects.

12 0038-2809 Tydskr.S.Afr.vet.Ver. (2004) 75(1): 7–13 CONCLUSIONS 4. Blaylock R S 2001 Normal oral bacterial 18. McNally S L, Reitz C J 1987 Victims of There are many similarities in terms flora from some southern African snakes. snakebite. A 5-year study at Shongwe Onderstepoort Journal of Veterinary Research Hospital, Kangwane, 1978–1982. South of clinical presentation, treatment and 68: 175–182 African Medical Journal 72: 855–860 outcome between dogs and humans 5. Blaylock R S 1982 Snake bites at Triangle 19. Minton S A 1990 Neurotoxic snake enven- following a venomous snakebite. Key Hospital January 1975 to June 1981. Central oming. Seminars in Neurology 10: 52–61 differences include: (1) the way a diagno- African Journal of Medicine 28: 1–10 20. Mirtschin P J, Masci P,Paton D C, Kuchel T sis is made (humans can usually provide 6. 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