Snake Envenomation

Clinical signs of bites by venomous snakes can vary tremendously, principally depending on the type of snake involved, location and number of bites, and the amount of venom injected. Providers should become familiar with indigenous snakes in deployed areas and seek guidance on specific management recommendations in preparation for deployments. Information on indigenous venomous snakes in each area of operation can be found in the Veterinary Medical Threat Brief from the Medical Detachment Veterinary Service Support or the component command veterinarian.

In general, snakebites by most venomous vipers cause severe pain, variable degrees of local swelling that may spread, and varying degrees of local tissue necrosis. Many MWDs will also develop systemic signs of pain. Some dogs can develop life-threatening complications of envenomation. Conversely, snakebites by most venomous elapids (i.e. cobras, mambas, coral snakes, and taipans) produce minimal swelling but are potent neurotoxins that can progress to life-threatening paresis and respiratory failure. Elapid venom can also cause marked intravascular hemolysis that may require red blood cell transfusions. It is prudent to recommend that any MWD bitten by a venomous snake be evacuated URGENTLY for optimal management. Follow guidelines below while coordinating evacuation.

Unwitnessed envenomation is common. The presence of fang marks does not mean that envenomation has occurred – “dry bites” are common. Approximately 25% of pit viper bites in humans are “dry” and do not cause envenomation.9 Conversely, envenomation may have occurred without obvious puncture wounds evident.

Note: Echinocytosis seen on blood smear evaluation can confirm snake envenomation.

Injection of viper venom typically causes marked localized swelling and edema, intense local pain, and discoloration of the surrounding tissues due to necrosis, with oozing of venous blood. Clinical signs of pit viper envenomation occur within the first 30 minutes from time of bite, but the patient should be observed for delayed effects over 24 hours.9

Systemic signs frequently observed include pain, lethargy, vomiting, weakness, hypotension, tachypnea, tachycardia, ecchymosis, diarrhea/hematochezia, and occasionally neuropathies. Many MWDs will develop laboratory evidence of thrombocytopenia and coagulopathy but true spontaneous hemorrhage is rare.

Injection of elapid venom typically causes rapid paresis that can occur within minutes but may be delayed for up to 24 hours. Paresis can progress to the diaphragm requiring mechanical ventilation. Elapid venom can also cause significant hemolysis that may require a packed red blood cell transfusion. Monitoring for early clinical signs includes serial checks of the patellar reflex, measuring respiratory parameters on a blood gas analysis, and serial evaluations of serum for hemolysis. In addition to respiratory paralysis, life-threatening acute kidney injury can occur with severe hemolysis, therefore kidney values should be monitored if hemolysis develops.

If no clinical signs of envenomation are present, do not administer antivenom and observe the patient for 12-24 hours. Perform baseline database on intake, if any clinical signs develop, and prior to discharge.

In severe envenomation cases, blood products such as canine fresh frozen plasma, packed red blood cells, whole blood, or other interventions may be needed. Refer to the Transfusion for the MWD CPG for guidance.

Patients presenting in or that later develop shock should be treated as recommended in the K9 Shock Management CPG, in addition to receiving antivenom treatment.