Poisonous reptiles are broadly distributed throughout the world. Snakes are cold-blooded animals, which only become active when the environmental temperature reaches about 25-27°C (spring - autumn). The most frequently poisoned animals are hunting dogs (95%).
TOXICITY
The venom is a thick, amber-coloured, odourless fluid. Its chemical composition depends on the physiological state of the reptile and consists mainly of enzymes, non-protein organic compounds and inorganic substances.
The action of the hyaluronidase enzyme is important because this enzyme breaks down tissue collagen, thereby facilitating the spread of the venom.
Kininogenase, an activator of bradykinin, causes vasodilatation, stimulates phospholipase A2 and, consequently, activates the arachidonic acid cascade and an inflammatory response in the tissues involved.
The proteases act as anticoagulants and cause vascular necrosis.
CLINICAL SIGNS
The clinical signs vary depending on the amount of venom injected, the vascularisation of the region affected, the species of viper and the size of the animal bitten.
The most frequently involved regions are the distal parts of the limbs and the muzzle.
The main clinical signs are:
- Very tense bluish-red oedema of the area bitten (when the throat is bitten, the airway can be obstructed and thermoregulation can be damaged because of the respiratory problems);
- Haemorrhagic petechiae and ecchymoses;
- Pale mucosae;
- Intense pain;
- Indicative behaviours: licking or continuous biting of the area involved;
- Sensorial depression;
- Vomiting and diarrhoea with strong abdominal colicky pain;
- Shallow breathing;
- Sweating;
- Muscle tremors;
- Shock;
- Hypothermia, tachycardia;
- Paralysis or convulsions;
- Clotting disorders with severe haemorrhages (in the worst cases);
- Death from liver or kidney failure.
TREATMENT
- Keep the bitten animal still and peaceful, in order to limit the spread of the venom, which is enhanced by muscle activity;
- Shave and clean the bitten area with hydrogen peroxide 20 vol., sodium hypochlorite 10% or potassium permanganate 1%;
- Avoid tourniquets, cutting the wound and aspirating the venom in order not to infect the area;
- Apply ice or cold water;
- Monitor vital signs for at least 24 hours;
- Tracheotomy, if the animal cannot breath because of oedema of the throat;
- Intravenous hydration with physiological saline or Ringer’s lactate solution;
- Prophylactic antibiotics to prevent secondary bacterial infections;
- The administration of antivenom serum is recommended ONLY if symptomatic treatment is not giving good results, since anaphylactic reactions to such serum are common. The serum must be administered by slow intravenous infusion (5-20 ml) and diluted in physiological saline;
- In the case of anaphylactic shock, administer adrenaline (0.1-0.5 ml of solution 1:1000, subcutaneously).
Suggested readings
- Lervik JB, Lilliehook I, Frendhin JH. Clinical and biochemical changes in 53 Swedish dogs bitten by the European adder--Vipera berus. Acta Vet Scand 2010;52:26.
- Ong RK, Swindells K, Mansfield CS. Prospective determination of the specificity of a commercial snake venom detection kit in urine samples from dogs and cats. Aust Vet J 2010;88:222-4.
- Pelander L, Ljungvall I, Haggstrom J. Myocardial cell damage in 24 dogs bitten by the common European viper (Vipera berus). Vet Rec 2010;166:687-90.
- Suchitra BR, et al. Clinical management of snake bite in a dog. Vet World 2010;3:234.
Useful links
Journal of Animal and Veterinary Advances, Snake bite in a dog