Snake bites are a relatively common occurrence in regional areas of Australia. Within the Tamworth region, Brown snakes are by far the most common. Black snake bites also occur, whilst tiger and whip snake bites are relatively uncommon. There are a number of signs which are typical of a snake bite and, if observed, should be followed by prompt intensive therapy.

Clinical signs of a snake bite

In the vast majority of snake bites, evidence of a bite wound is absent, so it’s important to be aware of the associated clinical signs. Clinical signs observed are largely dependent on the species of snake (and subsequent potency of venom) as well as the dose of venom delivered in the bite.

Pre-paralytic signs

Rapidity of onset of clinical signs following a snake bite is related to the dose of venom received. Generally, onset of signs is faster in dogs (1-6 hours) than cats (15 hours). Additionally, dogs commonly show pre-paralytic signs.

Pre-paralytic signs include:

• transient collapse

• vomiting

• salivation

• lethargy

Pre-paralytic signs may be followed by a seemingly spontaneous recovery. However, the presence of pre-paralytic signs almost invariably means the patient has received a lethal dose of venom, with patients usually deteriorating within hours.

In contrast, cats rarely display premonitory signs, with the earliest signs usually being weakness and ataxia.

Cats

Clinical signs observed in cats vary significantly. Some of these include:

• Weakness

• Ataxia (incoordination)

These are often the earliest signs of envenomation. Other signs also include:

• Mydriasis (dilated pupils)

• Vomiting

• Absence of pupillary reflex (ie pupils do not constrict in light)

• Depression (ie quiet, unresponsive, lethargic, etc)

• Tachypnoea/dyspnoea (increased respiratory rate or difficulty breathing)

• Disorientation

• Pharyngeal paralysis

• Haematuria (blood in urine)

• Coma

• Bleeding from the bite wound

These signs are often transient and inconsistent and may not be present.

Dogs

Envenomated dogs can show an even wider array of clinical signs. Pre-paralytic signs are common. Signs of envenomation include:

• Vomiting

• Severe trembling

• Salivation

• Weakness

• mydriasis (dilated pupils)

• Defecation

• Hindlimb paresis (weakness) progressing to a generalised, flaccid paralysis

• Cyanosis (gums appear blue)

Owners often report that their dog collapsed shortly after the bite but has since recovered. This is related to the presence of pre-paralytic signs and suggests that a lethal dose of venom has been delivered to the dog. Thus, urgent treatment is required.

Treatment

Treatment of snake bites revolves around prompt administration of antivenom and supportive care. Intravenous fluids, antihistamines, adrenaline and respiratory support (supplementary oxygen +/- ventilator) may all be necessary if supportive therapy is to be successful. Hospitalisation for a minimum of 24 hours is usually necessary to ensure adequate monitoring and treatment. Additional drugs (eg atropine; furosemide) may also be necessary during the course of treatment should complications arise. Antibiotics are frequently administered to avoid secondary infections.

Generally, treatment outcome is significantly improved if the animal is hospitalised and antivenom is administered. However, multiple vials of antivenom and mechanical ventilation are often required in severely envenomated animals.

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