Introduction
A bite is an injury inflicted by the teeth of a human or animal. Bite wounds can take a number of forms including lacerations, puncture wounds, and crush or degloving injuries. The most common mammalian bites are associated with humans, dogs, and cats.
Pathophysiology
Human Bites
- Human bites are either:
- Occlusal injuries — inflicted by actual biting, or
- Clenched-fist injuries ('fight bites') — sustained when a clenched fist hits a person's teeth, often during a fight, causing small wounds over the dorsum of the hand or metacarpophalangeal joints).
- Most human bites occur on the hand. Men are most frequently bitten on the hand, arm, and shoulder. Women are most frequently bitten on the breast, genitalia, leg, and arm.
Dog Bites
- Dog bites characteristically involve puncture wounds from the canine teeth which anchor the victim whilst the other teeth bite, shear, and tear the tissues, causing structural damage. Adult dogs have very powerful jaws. These can inflict high pressures which, in addition to the shearing forces delivered during a bite can cause deep, open cuts, crush wounds, devascularisation, and soft-tissue avulsion. In some cases, a body part may be torn off by a dog bite. The severity of a dog bite depends on the type and size of dog, with breeds such as Rottweilers, German Shepherds, and pit bull terriers able to cause significant damage.
- Dog bites are the most common mammalian bites treated in emergency departments. In the UK, around a quarter of a million people per year present to minor injury and emergency departments with dog bite injuries. Children are more often bitten by dogs than adults (with a peak incidence of 5–9 years of age).
Cat Bites
- Cats have fine, sharp teeth and, despite having a weaker bite than dogs, inflict deep puncture wounds inoculated with saliva, and are capable of penetrating bone, joints, and tendons. Fluids can only drain from the small skin puncture wounds, therefore infections such as abscesses and osteomyelitis are more common with cat bites.
Complications
Bacterial Infection
- Wound infection
- Infective complications resulting from a bite wound include abscesses, tenosynovitis, septic arthritis, osteomyelitis and systemic spread (for example sepsis, meningitis, endocarditis, and organ abscesses)
- Human bites are most commonly infected by Streptococcus spp, Staphylococcus aureus, Haemophilus spp, Eikenella corrodens, Bacteroides spp and other anaerobes
- Most animal bite wound infections are polymicrobial and contain a mixture of aerobic and anaerobic organisms
- Tetanus (Clostridium tetani)
- Tetanus can occur after an animal bite or human bite, especially in puncture wounds or those containing devitalised tissue, dirt, or foreign bodies; however, tetanus after a human bite is extremely rare
- Syphilis
- Syphilis transmission via a human bite has also been reported
- Cat-scratch disease (Bartonella henselae)
- Cat-scratch disease may follow a bite or scratch from a cat or dog, and presents with a mild infection at the wound site 3–14 days after the injury, followed by lymphadenopathy and symptoms including fever, malaise, headache, and poor appetite. Lymph glands near the scratch become swollen, and swelling may persist for several months; occasionally the eyes, brain, heart, and other organs can be affected
Viral Infections
- Blood-borne viruses e.g. hepatitis B and C, HIV
- There is the possibility of viral transmission through human bite wounds, although the risk is low
- Rabies
- Rabies is an acute viral encephalomyelitis that is almost always fatal. It usually occurs after a person is bitten or scratched by an animal with rabies (most commonly a dog). The risk of contracting rabies in the UK is very low, as there is no indigenous rabies in terrestrial animals, but bats anywhere in the world can carry rabies-like viruses, therefore are considered to be a rabies risk
Structural Damage
- Scarring and disfigurement
- Traumatic amputation
- Tendon and joint capsule damage
- Fractures
- Neurological damage
Psychological Effects
- Anxiety and depression
Wound Assessment
- Document how and when the bite occurred.
- For human bites
- Who was bitten, and by whom.
- Whether the skin was broken or blood was involved.
- The nature of the bite (i.e. occlusal or clenched fist).
- For animal bites
- The type of animal (domesticated or wild) and its state of health or any unusual symptoms.
- Whether the attack was provoked.
- Mechanism of injury.
- For human bites
- Monitor vital signs if the bite is particularly traumatic, or sepsis is suspected.
- Examine the bite using gloves, bearing in mind that deep layers of tissue may move with positional changes after the bite injury, disguising the true depth of the wound. Document the following (record both positive and negative findings as there may be future litigation):
- The location of the wound. Photographs or diagrams may be useful.
- The size and depth of the injury.
- The type of wound (for example laceration, puncture, abrasion, crush, haematoma, avulsion, amputation).
- The degree of crush injury, devitalised tissue, nerve or tendon damage, and involvement of muscle, bones, joints, or blood vessels. Examine wounds overlying a joint through the full range of motion to detect retracted injuries and tendon rupture.
- Neurovascular function in the area distal to the bite — check pulses and sensation.
- The range of movement of any adjacent joints.
- Any lymphadenopathy.
- The presence of any foreign bodies (for example teeth) in the wound.
- Any signs of infection (for example redness, swelling, induration, necrotic tissue, purulent discharge, pain, localised cellulitis, lymphangitis, lymphadenopathy, or fever).
- Facial bites: perform an intraoral examination to exclude cheek lacerations with an intraoral communication.
- Although rare, suspect child maltreatment if there is a report or appearance of a human bite mark that is thought unlikely to have been caused by a young child. Also consider safeguarding issues if a vulnerable adult receives a bite injury.
- Assess the person's risk of tetanus, rabies and blood-borne virus infection.
Antibiotic Prophylaxis Guidelines
| Type of bite | Bite has not broken the skin | Bite has broken the skin but not drawn blood | Bite has broken the skin and drawn blood |
|---|---|---|---|
| Human bite | Do not offer antibiotics | Consider antibiotics if in high-risk area or person at high risk | Offer antibiotics |
| Cat bite | Do not offer antibiotics | Consider antibiotics if the wound could be deep | Offer antibiotics |
| Dog or other traditional pet bite | Do not offer antibiotics | Do not offer antibiotics |
Offer antibiotics if:
|
First-line Antibiotic Regimen
- Co-amoxiclav for 3 days
- For penicillin-allergic adults: Metronidazole + Doxycycline for 3 days
- For infected wounds: Extend treatment to 5 days
High-Risk Considerations
- High-risk people: Diabetes, immunosuppression, asplenia or decompensated liver disease
- High-risk areas: Hands, feet, face, genitals, skin overlying cartilaginous structures or areas of poor circulation
Adder Bites
Vipera berus - European common adder
Image: Vipera berus (European common adder)
Grey or reddish-brown with dark zig-zag stripe down back
Envenoming from snake bite is uncommon in the UK. Many exotic snakes are kept, some illegally, but the only indigenous venomous snake is the European common adder/viper (Vipera berus). Two other types of snake are found in the wild in the UK (grass snakes and smooth snakes) but these are non-venomous. Adders are grey or reddish-brown, with a dark zig-zag shaped stripe down their back. The majority of adder bites occur between April and September, with a marked peak in July-August. This pattern probably reflects the outdoor activity of people, combined with the seasonal behaviour patterns of adders.
Most adder bites occur to the hand or arm, with slightly lower numbers to the foot, and much lower numbers to other parts of the body. The bites are extremely painful, but very rarely life threatening. In around 70% of cases there is no or very little envenomation result in a negligible reaction or only local effects. The first symptoms may take from a few minutes to hours to become evident. Fatal envenoming is rare but the potential for severe envenoming must not be underestimated. It is estimated that in around one third of all adder bites, the snake does not actually inject any venom (a "dry bite").
Clinical Features
The bite may cause local and systemic effects:
- Local effects include pain, swelling, bruising, and tender enlargement of regional lymph nodes.
- Systemic effects include early anaphylactic symptoms (transient hypotension with syncope, angioedema, urticaria, abdominal colic, diarrhoea, and vomiting), with later persistent or recurrent hypotension, ECG abnormalities, spontaneous systemic bleeding, coagulopathy, adult respiratory distress syndrome, and acute renal failure.
Management
- Initial management is to reassure, give paracetamol to control pain, and immobilise the whole patient (especially the bitten limb with a splint or sling) during urgent transport to hospital.
- Early anaphylactic symptoms should be treated with intramuscular adrenaline/epinephrine.
- Any interference with the wound should be avoided. Tourniquets, ligatures, and compression bandages should not be used.
- In hospital, rapid clinical assessment of the degree of envenoming and resuscitation may be needed, followed by careful monitoring of the blood pressure and evolution of envenoming over at least 24 hours. The most important decision is whether antivenom should be given.
- Indications for european viper snake venom antiserum are:
- Hypotension with or without signs of shock
- Other signs of systemic envenoming, electrocardiographic abnormalities, peripheral neutrophil leucocytosis, elevated serum creatine kinase, or metabolic acidosis
- Local swelling that is either extensive (involving more than half the bitten limb within 48 hours of the bite) or rapidly spreading (beyond the wrist after bites on the hand or beyond the ankle after bites on the foot within about four hours of the bite)
- For those patients who present with clinical features of severe envenoming (e.g. shock, ECG abnormalities, or local swelling that has advanced from the foot to above the knee or from the hand to above the elbow within 2 hours of the bite), a higher initial dose of the european viper snake venom antiserum is recommended; if symptoms of systemic envenoming persist contact the National Poisons Information Service.
- Adrenaline injection must be immediately to hand for treatment of anaphylactic reactions to the european viper snake venom antiserum.
Other Stings/Bites
Antivenom is available for bites by certain foreign snakes and spiders, stings by scorpions and fish. For information on identification, management, and for supply in an emergency, telephone the National Poisons Information Service. Whenever possible the TOXBASE entry should be read, and relevant information collected, before telephoning the National Poisons Information Service.