Adder bites in dogs: symptoms, first aid and treatment

Overview

The European adder, Vipera berus, is a venomous snake. It may bite in self-defence if a dog surprises or corners it. In cold climates, bites can occur from the first patches of thawed ground in spring through to autumn.

The amount of venom entering the body during a bite can vary greatly. In a so-called dry bite, no venom or very little is released. Even so, do not wait at home to see whether symptoms develop.

Most treated dogs recover well from a bite. However, severe poisoning can cause internal organ damage or death.

Adders often have a dark zigzag pattern along the back, but entirely dark individuals also occur. Grass snakes and smooth snakes are not venomous. However, searching for the snake is not part of helping a dog that has been bitten.

Causes

Adder venom contains several compounds with different effects on the body. Its composition may vary between individual snakes and geographical areas.

The venom damages blood vessel walls and blood cells. The local tissue reaction causes swelling and pain around the bite. Spread through the circulation can damage the heart, kidneys, nervous system and liver tissue.

Severe poisoning can disrupt normal blood clotting. Excessive activation of clotting can produce many small blood clots throughout the body. Normal clotting may then become impaired, causing internal bleeding.

Movement speeds the spread of venom through a dog's body. Keeping the dog calm and avoiding movement of the bitten area are therefore part of first aid.

Risk factors

A dog may be bitten while sniffing or approaching a snake resting on the ground. Bites often affect the face, neck or lower part of a limb.

On warm, sunny days, adders may bask on paths and roads. Long grass, woodland, heathland and coastal sand dunes are possible places to encounter them.

The consequences may depend on the amount of venom, the bite location, the dog's size and delays in reaching treatment. Venom entering the bloodstream directly can cause an extremely rapid, severe reaction. Swelling of the muzzle or neck can also make breathing difficult.

Typical symptoms

The bite is not always seen, and the snake may no longer be found when symptoms begin. A dog may initially yelp or jump suddenly. Common observations include:

• Rapidly increasing swelling of the muzzle or a limb that is painful to touch.
• Lameness if the bite affects a leg.
• Small puncture marks, although these are not always noticed.
• Being more subdued than usual and reluctant to move.
• Nausea, vomiting or diarrhoea.
• Pale gums, panting or excessive drooling.
• In severe cases, bleeding, profound weakness or difficulty breathing.

Two adjacent puncture holes may be visible at the bite site. Their absence does not rule out a bite, because swelling and pain may be the clearest findings.

Even a dog that initially seems well can develop symptoms later. Always monitor the dog's overall condition as well as swelling around the head.

Complications and consequences

An adder bite can cause circulatory shock. The venom can damage heart muscle cells and cause abnormal heart rhythms.

In a Norwegian follow-up study of 21 dogs, 57% developed abnormal heart rhythms. Severe ventricular arrhythmias were found in six dogs, or 29%. All dogs in the study survived.

Kidney damage may initially be mild and temporary, without an increase in the usual creatinine measurement. However, some dogs may develop prolonged or permanent internal organ damage. Tissue around the bite may die.

Mortality of about 3–4.8% has been reported in dogs bitten by adders. This does not mean that every dog has the same risk. Prompt treatment improves the outlook. The great majority recover fully with treatment.

Internal organ damage may become apparent later as a worsening general condition and an irregular heartbeat. A reduction in swelling alone therefore does not determine whether monitoring is still needed.

An increased tendency for blood to clot may also persist after the acute phase. In a Norwegian study of 28 dogs, this tendency was still increased at 15 days. Its relationship with actual blood clots remains unclear.

Abnormal heart rhythms may still occur on the second day after a bite. In the cardiac study, no arrhythmias were detected at the 14-day check. Troponin had returned to normal at that check in all but one dog.

Diagnosis at the vet

Diagnosis is based on the circumstances, local swelling and pain, and any bite marks. The vet assesses the dog's overall condition and decides what treatment is needed according to symptom severity.

Blood tests may check blood cells, blood sugar, blood proteins and measurements of internal organ function. Heart function is monitored at the same time. An electrocardiogram, or ECG, can reveal an abnormal heart rhythm that is not apparent from the dog's outward condition.

Heart muscle damage can be assessed by measuring troponin in the blood. Of the 21 dogs in the cardiac study, 17, or 81%, had a raised troponin concentration in at least one sample. Raised troponin may be a reason for longer ECG monitoring.

A normal creatinine result does not rule out early, mild kidney damage. Increased albumin, a protein, in the urine may indicate early injury. Other urine markers have been studied to identify damage before routine kidney measurements rise.

In the kidney injury study, abnormal urine markers were detected at 12, 24 and 36 hours after the bite. Differences from healthy controls had disappeared at the 14-day measurement. Repeat samples may therefore complement investigations during the acute phase.

Detection of adder venom in urine and blood has been studied, but the method is still under development. It detected venom up to 24 hours after a bite. This should not be confused with a routine rapid test available at a practice.

Blood pressure measurement may form part of the assessment. As well as local swelling, the vet considers breathing, circulation and digestive signs.

A concurrent inflammatory response throughout the body may complicate interpretation of early urine markers. A raised research marker therefore does not always identify the cause of injury unambiguously.

In a study of 29 bitten dogs, an increase in the inflammatory marker CRP was common. Creatine kinase, or CK, which is associated with muscle injury, was also often raised. Results are considered alongside the clinical condition and other organ-specific investigations.

Blood venom testing also produced false-positive results in the study, so urine appeared to be a more useful sample. Development of venom testing therefore does not yet remove the need for a clinical assessment based on symptoms.

Treatment

The vet prescribes treatment according to the dog's condition and test results. Common components include rest, intravenous fluids and pain relief. The airway is kept open despite swelling.

Fluid therapy supports circulation and internal organ function. Giving a dog in shock water to drink does not replace intravenous treatment. Shock can impair swallowing and absorption of fluid from the gut.

For severe poisoning, the vet may use antivenom, also called antiserum, containing antibodies against adder venom. Antiserum can cause a harmful hypersensitivity reaction, so administration requires monitoring. Tell the practice if your dog has received antiserum previously.

Corticosteroids are not an antidote to adder venom. Routine corticosteroid treatment has not shown a clear benefit for recovery from Vipera berus bites. Nor is there clear evidence of harm from corticosteroids specifically in Vipera berus bites. The vet decides whether to use them in special circumstances, such as treating a reaction to antiserum.

Antibiotics are mainly needed if the bite area becomes infected or bacteria are suspected of spreading into the bloodstream. Dead tissue may need surgical removal. Cases other than very mild ones are often monitored in hospital for at least 24 hours.

Monitoring for organ damage may require 36–48 hours of hospital care and intravenous fluids. Continuous ECG monitoring may continue for about 48 hours. This allows treatment for an abnormal heart rhythm to begin promptly if one develops.

Severe pain may be relieved with opioid painkillers given by the vet. Supportive care and monitoring of venom effects continue even when a dog receives antiserum.

Some antiserum products contain antibodies produced by horses.

Prevention

In areas where adders live, keep your dog under control and, where possible, on a lead on the path. Avoid allowing your dog to sniff around places where snakes have just been seen. On sunny days, an adder may be warming itself on the path too.

Before visiting an unfamiliar walking area or holiday location, check local adder sightings and risk spots. Nevertheless, preventing every bite is difficult. Being prepared for first aid and keeping emergency veterinary contact details available help you arrange assistance quickly.

Do not try to catch or touch the snake after a bite. Approaching it may expose the person helping to a bite as well.

Important for dog owners

Do not massage, suck or cool the bite site yourself. Do not apply a tourniquet or any other tight bandage over the bite. Keep your dog's movement to a minimum while arranging transport.

Do not give painkillers or corticosteroids at home without a vet's explicit instructions. In shock, a non-steroidal anti-inflammatory medicine can increase the risk of kidney injury. Even if a first-aid tablet has been given, the dog still needs immediate veterinary treatment.

Follow-up blood samples are often taken a few weeks after initial treatment. Report new weakness, breathing difficulties or any other deterioration to the treating practice without delay.

Avoid exertion at least until the agreed check, which may be at about 14 days. A longer restriction on exercise, of about a month, may be needed according to the treating vet's assessment. Report sudden neurological signs or breathing difficulties immediately during follow-up, because possible signs of blood clots need assessment.

Frequently asked questions

Must I see a vet even if my dog seems well?

Yes. Every suspected adder bite needs prompt veterinary assessment. Apparently good health initially does not prevent serious symptoms developing later. Keep your dog resting and, if possible, carry them to the vehicle, because movement speeds the spread of venom.

Can I give a corticosteroid tablet for an adder bite?

Do not give medicines at home without specific veterinary instructions. Corticosteroids are not an antidote to adder venom, and a tablet does not replace veterinary treatment. Routine use has not shown a clear benefit for recovery in bitten dogs. The vet assesses any special circumstances individually.

Should I cool or squeeze the bite site?

Do not massage, suck or cool the bite site yourself. Do not use a tourniquet or any other tight bandage over the area either. The key first aid is to keep the dog and bitten area as still as possible and arrange prompt veterinary treatment.

Can an adder bite damage the heart without visible heart symptoms?

Adder venom can damage heart muscle cells and cause abnormal rhythms. Assessment based on the outward severity of the bite did not predict arrhythmia severity in the follow-up study. The vet may therefore use ECG monitoring and troponin measurement even when swelling is the most obvious finding.

When can my dog return to normal exercise?

Avoiding vigorous exercise for about a month after a bite is recommended. Recovery requires rest even when swelling starts to improve. Follow-up samples are often recommended after a few weeks because effects of venom or antiserum may be delayed. The vet determines when your dog can return to exertion according to their individual situation.