What do we know about Adder Bites in Dogs?
“Myths and misconceptions”
Harriet Jarvis BVSc (hons) MRCVS of Charter Vets.
The Adder (Vipera berus) is the only venomous snake native to the UK. It is most commonly found in the south and south west of England, western Wales and Scotland where its preferred habitats are sand dunes, heathland, rocky hillsides, moorland and also woodland edges. Here in North Devon we have several suitable habitats, sand dunes are in abundance and Exmoor is also close by. It is a species protected by the Wildlife and Countryside Act 1981; this mean that it is an offence to kill, harm, injure, sell or trade them.
The appearance of the adder is variable but distinctive. They are 40-70cm in length, males range in colour from pale grey to dark brown, females may be olive green, yellow or reddy brown. However, in spite of this colour variation, they are all recognizable by their dorsal zigzag pattern with a V or X shape on the head; the eye is elliptical with a vertical slit. Other snakes native to the UK are the grass snake, the smooth snake and the slow worm, but none of these show the same zigzag pattern.
The adder is a timid and non-aggressive snake, and will only bite when provoked. They hibernate over the winter, emerge in early spring as the ambient temperature increases, mate late April or early May and give birth to live young late in August or early September.
Adder venom in a cytotoxic mixture of enzymes; the adder injects this into its prey in order to subdue it before ingestion.
Adder bites and domestic dogs
The domestic dog is exceptionally curious by nature, especially when young, and will often unintentionally provoke an adder into biting. Most bites are naturally facial or forelimb with 70% of bites occurring between April and July, most commonly in the afternoon; this is likely when the adders are most active.
It has been found that 97% of bitten patients show symptoms; the remaining 3% are presumed to have received ‘dry bites’. All symptomatic patients show local effects. In almost all cases we find swelling and oedema at the bite site, usually within two hours. Other possible symptoms including pain, bruising, bleeding and lameness.
Two thirds of symptomatic patients also show systemic effects. If venom is absorbed into the lymphatic system and then the systemic circulation it will cause a widespread inflammatory reaction leading to symptoms such as lethargy, fever, increased heart and respiratory rates, drooling, vomiting and a wobbly gait (ataxia).
In less than 5% of cases we can see severe systemic effects. These include problems breathing, collapse, convulsions, kidney failure, liver injury, bleeding disorders, shock and an abnormal heart rhythm.
The severity of the clinical signs and the speed of recovery varies depending upon the location of the bite (facial bites are more serious), the size of the patient (small patients tend to be more severely affected), the amount and potency of the venom (it is postulated that the venom is more potent early in the season), the amount the patient moves post bite (movement increases venom uptake into the patient’s circulation), any pre-existing disease within the patient (this may make them more likely to develop severe clinical signs), and the speed of veterinary intervention.
The average time to a full recovery, including resolution of all swelling, is five days; this can however vary from 24 hours to 30 days. Systemic signs are usually resolved within 24 hours, and, most importantly, 96-97% of patients make a full recovery.
What should you do if your dog is bitten?
Importantly, DO NOT PANIC, your dog is highly likely to make a full recovery if treated promptly and correctly. It is important, where possible, to reduce the movement of your dog following a bite; ideally carry your dog or walk quietly back to your vehicle. Ring your nearest veterinary surgery to let us know what has happened and your estimated time of arrival. This enables us to be sure that we have a veterinary surgeon and nurse immediately available to see your dog, and we have had time to prepare our treatments before you arrive. If a bite goes unnoticed, but you see symptoms suggestive later in the day you must ring your vet without delay and seek veterinary attention, even if it is outside of normal opening hours.
What will we do for your dog following a bite?
Our aims of treatment are to support the circulation and preserve organ function, minimize the swelling, provide pain relief, protect against secondary infections, monitor for signs of organ damage during treatment and ultimately to aid a full recovery.
Intravenous fluid therapy (a drip) should be given to maintain blood pressure, protect against shock and maintain the blood flow (perfusion) of the vital organs. We administer the fluids using a catheter placed into the vein, and we can vary, depending upon clinical need and patient weight, the amount and speed of fluid administration using an infusion pump.
Patients are also cage rested to minimize venom absorption into the lymphatic and systemic circulations.
Anti-venom is available and it binds to the enzymes within the venom thereby rendering them inactive and unable to cause damage. This anti-venom may be used in all cases but is especially recommended for potentially serious cases. It should be given as soon as possible for maximum benefit and will show a significant reduction in the degree and duration of the swelling present. The anti-venom can be difficult to obtain and is not licensed for use in animals in the UK. Anaphylaxis (a severe allergic reaction) to the anti-venom is reported in 0.4% of cases.
In cases where anti-venom is not to be used we may give a steroid injection. This is a potent anti-inflammatory drug with a rapid onset of activity. We hope this will reduce the inflammatory reaction within the body and also the swelling present at the bite site. Steroid will diminish the effect of the anti-venom so the two are not used in conjunction.
Adder bites are definitely painful so it is imperative that we provide strong pain relievers. We prefer to use drugs of the opioid class, such as morphine or methadone. These are potent pain killers, which have a sedative effect also; this is helpful in reducing the stress and movement of hospitalized patients. We tend to avoid the non-steroidal anti-inflammatory drugs due to the risk of kidney or liver damage in these patients.
Although bacterial infections directly from the bite are uncommon, tissue death or necrosis can occur around the bite and this increases the risk of secondary infections occurring. Steroid drugs are immunosuppressive so antibiotics would often be used if these drugs are chosen.
During treatment we will monitor these patients for signs of organ damage. As mentioned previously only 5% of patients show more severe clinical signs, but it is important that we monitor all patients for their development. We will regularly monitor heart rate and rhythm and an ECG (electrocardiogram) may be recorded if anything abnormal is heard. Blood pressure can also be monitored and bloods to monitor for ongoing heart muscle damage may be necessary in a very small percentage of cases. Liver damage is reported in 2% of cases and kidney damage in 3.5% of cases; if a patient is not recovering as expected we will run blood tests to look for organ damage and other conditions, such as bleeding disorders.
In summary we should remember that:
- Most adder bites occur between April and July
- Common adder habitats in our region are the sand dunes and Exmoor
- If your dog is bitten, minimize their movement and seek veterinary attention without delay
- The most common signs are significant swelling local to the bite, with systemic signs of depression and lethargy
- Less than 5% of patients display more severe signs
- 96-97% make a full recovery, usually within five days
If you have any questions about issues raised in this article or other health please contact us to speak to a veterinary surgeon.
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