Bite wounds in dogs: first aid, assessment and treatment

Overview

A bite can cause injury even when the skin is not broken. A dog should therefore be examined after a fight even if there is no obvious wound in the coat. Small tooth punctures may close quickly. Closure of the skin does not mean that deeper tissue damage has healed.

A bite that penetrates the skin is considered a wound contaminated with bacteria. Bacteria can multiply beneath the skin and spread into surrounding tissues. First aid does not replace assessment of the wound's depth.

A wound treated within six hours has a better chance of healing without complications. However, passing this point does not remove the need for treatment.

Wounds heal through three main phases: inflammation, formation of new tissue and maturation. The inflammatory phase begins with stopping the bleeding. White blood cells start moving into the wound within 30 minutes. They help remove bacteria and tissue debris.

Causes

A dog's teeth and jaws can crush and tear skin and muscle. A sharp canine tooth can create a deep cavity beneath the skin. A small surface hole therefore does not reveal the full extent of the injury. The bite carries bacteria from the mouth deep into the tissue.

Crushed or torn tissue may lose its viability. If the blood supply to skin is interrupted, the skin may die. This tissue death may only become apparent over the following days. An empty space beneath the skin may collect tissue fluid, forming a pocket called a seroma. Fluid in a deep cavity may need a route to drain out.

A cat bite can also injure a dog. Its small, deep punctures easily become infected.

Risk factors

Bites are a common cause of injury in animals allowed to roam freely. Conflict between dogs may involve food, territory or a perceived threat. Competition for an owner's attention may also play a part in a biting incident. Risk is reduced by managing encounters and avoiding situations in which a dog feels forced to defend themselves.

Bites are often found on the head, neck and limbs. The location of the injury affects which structures may be damaged. Major blood vessels, nerves, the oesophagus and the windpipe run through the neck. A bite on a limb can penetrate a joint.

A long coat and dense undercoat can make wounds difficult to find. Delayed detection may leave damage beneath the skin unnoticed. Licking the wound increases contamination and the risk of infection.

Typical symptoms

Only puncture holes or bruising may be visible on the surface. Changes you may notice at home include:

• A small hole or tear in the skin hidden under the coat.
• Pain in or around the wound.
• Swelling and redness.
• Warmth in the skin.
• Pus or other discharge.
• Lameness or reluctance to use a limb.
• Whimpering or other unusual behaviour indicating pain.

Your dog may resist having the painful area touched. The coat may hide injuries in several places. An infected cavity may remain beneath skin that has already closed.

Discharge from a wound being treated may be thin and clear or thick and coloured. Persistent bloody, green or yellow discharge requires reassessment.

Complications and consequences

An untreated bacterial infection can form an abscess. Infection can also spread widely through the soft tissues. In the most severe cases, a life-threatening systemic infection may result. The size of the skin opening alone does not predict this risk.

Rare complications of deep bites include bacterial infection of a joint or bone. Pus may collect in the chest cavity. A bite that penetrates the abdomen may cause purulent peritonitis, an infection of the abdominal lining.

A bite can break ribs or damage internal organs. Penetration of the chest cavity may cause a lung to collapse. A facial bite may damage an eye, ear or the mouth. Serious overall injuries are treated before definitive repair of an individual wound.

A wound managed without closure may contract as it scars. This contraction can restrict joint movement.

Diagnosis at the vet

The vet first assesses the dog's general condition. A visible wound can distract attention from hidden shock. The assessment establishes when the fight happened and where the wounds are. It is not always possible to determine their exact extent while the dog is awake.

Pain relief and sedation or anaesthesia make a safe examination easier. Extensive injuries, or those near the eye, mouth or ear, may require general anaesthesia. Hair is clipped over a sufficiently wide area to reveal all punctures and healthy skin.

The wound may be surgically enlarged to examine damage beneath the skin. The vet looks for cavities under the skin. Damaged muscles, tendons and blood vessels are assessed at the same time. The treatment approach is chosen only after this assessment.

An infected wound may be sampled for bacterial culture and susceptibility testing. These identify the bacteria involved and an effective medicine. Results can take several days. Testing is particularly needed if the infection does not settle with initial treatment.

Tissue viability is assessed before surgical removal of damaged tissue. Blue-black, leathery or white skin may be dead. Tissue of uncertain viability may be monitored and removed in stages.

Treatment

The vet prescribes treatment and medication. Heavy bleeding is controlled with direct pressure. A clean, non-fluffy dressing protects the wound from further contamination. A dog in pain must be handled carefully, as they may bite through fear or pain.

At the practice, flushing removes dirt and reduces the number of bacteria. Flushing also makes deeper tissues easier to inspect. Excessive flushing pressure can force debris into healthy tissue. Dead tissue and foreign material are removed surgically.

A contaminated, infected or deep puncture wound often needs an antibiotic. The medicine may later be adjusted according to culture results. Pain relief is part of wound care. An antibiotic alone does not remove dead tissue or drain an abscess cavity.

Depending on the circumstances, the wound may be closed, left open or closed later. An infected or heavily contaminated wound is generally not sealed immediately. In some situations, a lightly contaminated wound can be closed after 24–72 hours. A severely infected wound may need a longer wait.

Closure more than five days after injury is called secondary closure. By then, new tissue called granulation tissue has already begun to form in the wound. A wound left open heals with repeated dressing changes and cleaning as needed. Treatment must not stop just because the skin surface looks clean if deeper infection persists.

A drain, or drainage tube, may be placed in a deep cavity. It carries fluid out and helps prevent an abscess from forming. Removal may be scheduled for 2–3 days later. The timing is assessed according to the wound's condition.

At home, prevent licking with a protective collar or suitable covering. Keep stitches and the surrounding skin clean and dry. Clean away discharge around the drain as instructed. Restrict your dog's exercise during recovery.

In a healthy wound, fibroblasts, the cells that build connective tissue, begin to appear after about three days. They later produce collagen. New capillaries bring blood into the wound. The growth of capillaries and fibroblasts forms granulation tissue.

Granulation tissue is easily damaged because it contains many blood vessels. Dressings should not tear it away. The early new surface cell layer is also delicate. Damaging it slows healing.

The surface of a well-closed surgical wound may be covered with new skin cells within 48 hours. Skin cells in an open wound need healthy granulation tissue beneath them. Excessive drying slows the formation of the surface cell layer. The dressing chosen by the practice therefore maintains a suitable wound environment.

The wound gains strength as collagen fibres reorganise. Maturation can continue for up to two years. Most healed wounds remain 15–20% weaker than the original tissue. Healing of the visible surface therefore does not mean that the original strength has returned.

Adequate nutrition and energy support healing. Lukewarm tap water may be used for rinsing as instructed. Hydrogen peroxide can damage healthy tissue.

Strong chlorhexidine solution harms healing tissues. Surgical skin cleansers containing detergents are unsuitable for flushing inside a wound. Extensive skin loss may prevent surgical closure. As healing begins, the wound should become less painful.

Granulation tissue is generally relatively resistant to infection. Defence cells in the wound also release growth factors that promote healing.

The fibroblasts that repair a wound need an adequate supply of oxygen to function.

Prevention

Uncontrolled roaming increases the risk of encounters. A lead helps you keep control of your dog in public places. Do not approach an unfamiliar loose dog with your own dog. Your dog's friendliness does not predict how the other dog will react.

Carefully managed introductions to other dogs when a dog is young support safe encounters. Training basic skills can reduce the risk of fights. Recognise situations involving conflict over food or territory early. Preventing licking helps avoid further infection of an existing wound.

Keep rabies vaccination up to date too.

Important for dog owners

Record when the injury happened, details of the animal that bit your dog and what occurred. Examine the coat calmly, but do not probe a puncture or try to measure a cavity's depth. If touching the area hurts, leave the examination to the practice. A dog in pain may bite even a familiar person. Protect your own safety.

On discharge, keep the instructions for wound cleaning, medication, the protective collar, drain removal and follow-up checks. Check daily for redness, warmth, swelling, discharge and pain. Tell the practice about deterioration or inadequate pain relief. Do not add cleaning products, creams or human painkillers yourself.

Frequently asked questions

Does a small bite puncture need a vet?

Yes. Even a small hole may be associated with extensive damage beneath the skin. A bite wound always needs veterinary assessment. Do not judge its true depth from the visible surface alone or wait for swelling and pus to reveal the problem.

Can there be damage without broken skin?

Yes. The pressure of a bite can crush tissues beneath the skin even if the skin appears intact. After a fight, the dog is also examined for pain and other injuries. Your dog's general condition, breathing and use of a limb are important observations to report to the practice.

Why is the wound not always stitched immediately?

A heavily contaminated or infected wound is generally unsuitable for immediate, sealed closure. It may be managed open or closed later, once it is cleaner. This avoids sealing an infection out of sight beneath the skin.

What is a drain and when is it removed?

A drain is a tube placed in a wound cavity to allow fluid to escape. Removal may be planned for 2–3 days later. Follow the practice's plan and report persistent heavy discharge or worsening pain before removal.

Can I clean the wound with hydrogen peroxide?

Do not use it on your own initiative. Hydrogen peroxide damages healthy tissue and is unsuitable for flushing wounds. Use only the products and cleaning method recommended by the practice. Examining and opening deep bite wound cavities, and carrying out any necessary surgery, are always a vet's responsibility.

Is an antibiotic enough to treat a bite wound?

It may be a necessary part of treatment, but damaged tissue and cavities often need other care too. Treatment includes cleaning, removal of dead tissue and, when needed, placement of a drain. The vet examining the wound decides which medicine to use and whether surgery is necessary.