Bites - Human and Animal

Bite wounds are mainly caused by humans, dogs, or cats. About 1 in 5 people bitten by a dog seek medical attention and 1% of those seeking attention require admission to hospital.¹

• It has been estimated that dog bites account for 60-90% of bites; cat bites for 5-18%, and human bites for 4-23%.²
• Between a third and half of all mammalian bites occur in children (often bitten by a household pet).

Risk Factors

• In over 70% of cases, people are bitten by their own pets or by an animal known to them. Children under 5 years old were significantly more likely than older children to provoke animals before being bitten² and are most at risk of serious injury.³ The majority of animal bites occur in warm weather.⁴

• Injuries may be more extensive than they appear, due to the high incidence of puncture wounds.
• If pain is out of proportion to the apparent extent of the wound, especially with a cat bite on the hand, it is possible that a joint or tendon may have been damaged.
• Signs of infection should be noted (redness, tenderness, swelling, heat, discharge), especially if presentation is late.

• Consider non-accidental injury if adult human bite inflicted on a child.
• For animal bites inflicted on children, consider poor parenting and supervision.

Initial management

• Apply pressure to control bleeding.
• Irrigate the wound thoroughly with normal saline to remove dirt and bacteria. Drinkable tap water has equal or lower wound infection rates when used for simple lacerations. However a 1% povidone solution has been shown to be superior to saline for contaminated wounds or bites (because the 10% povidone has been diluted to 1%, it is germicidal but not toxic to tissues).
• Consider need for tetanus immunisation.
• Consider the risk of rabies in anyone who has sustained a bite or scratch from a dog or cat whilst abroad.
• Consider referral to accident and emergency or plastic surgery for:
  • Bites involving arteries, nerves, muscles, tendons, or bones.
  • Penetrating bites to the hands or feet.
  • Facial wounds (excluding very minor wounds).
  • Bites where there is the possibility of a foreign body in the wound.
  • Devitalised wounds where extensive debridement is required.
  • Bites where the severity of the injury is difficult to assess.
  • People with infected wounds who are systemically unwell.

Wound closure

• Primary closure with sutures is not generally recommended for non-facial bite wounds, especially deep punctures, bites to the hand, and clinically infected wounds. Delayed closure is usually more appropriate and should also be considered for wounds more than 6 hours old.
• Facial wounds and larger lacerations may require sutures (or steristrips) to prevent scarring and improve cosmetic outcome. There is uncertainty about the risks of this, but in most cases it is safe providing the person has presented early and the wound has been adequately cleaned.
• Delayed primary closure (after 3-5 days) is advisable for bites to the hand, bites with extensive crush injury, wounds needing a considerable amount of debridement, and wounds more than 6 hours old.
• Cover with a sterile, non-adhesive dressing to protect the wound.

Antibiotic prophylaxis

• The effects of antibiotics in preventing complications of mammalian bites remain unclear, except some evidence that there is a benefit in reducing the infection rate following bites to the hand and in people with human bites.⁵ Prophylaxis is generally recommended for:
  • Human bites where there has been clear penetration of the skin.
  • People with high-risk animal bite wounds, i.e. hand, foot, and facial injuries; puncture wounds (particularly likely with cat bites); wounds requiring surgical debridement; wounds involving joints, tendons, ligaments, or suspected fractures.
  • Wounds that have undergone primary closure.
  • People who are at risk of serious wound infection complications, e.g. those who are diabetic, cirrhotic, asplenic, or immunosuppressed.
  • People with a prosthetic valve or who have suffered a bite proximal to prosthetic joints.
• Antibiotics are not generally needed if the wound is more than 2 days old and there is no sign of local or systemic infection.
• The choice of antibiotic is the same as for treatment of established infection.

Treatment of established infection

• Most infections resulting from bites are polymicrobial, often including anaerobes.
• Infected dog bites often contain multiple species of bacteria, including Pasteurella canis, Pasteurella multocida, Staphylococcus aureus, other staphylococci, streptococci, and anaerobic bacteria.
• Infected cat bites are usually due to P.multocida. Staphylococcus sp. Streptococcus sp. and anaerobes are also important pathogens.
• Infected human bites usually contain Streptococcus sp., S.aureus, Eikenella corrodens, and anaerobic bacteria.
• Co-amoxiclav is recommended as first-line treatment for mild to moderate infections following a dog, cat, or human bite.⁶
• If the person is allergic to penicillin, first-line treatment is doxycycline plus metronidazole.⁶

Hepatitis B, hepatitis C, and HIV

• Blood-borne viruses are potentially transmissible by a human bite if the skin is broken.
• The risk from a bite is thought to be considerably less than for needle-stick injury.⁵
• There are some cases reported where hepatitis C has been transmitted through bites. Although there is no prophylaxis available, serological testing and follow up should be arranged in accordance with local guidelines.
• Several studies have followed up people bitten by HIV-infected individuals and no-one in these studies has seroconverted. Only four cases have been published in which HIV transmission through bites may have occurred.⁷
• If there is any suggestion of risk or genuine uncertainty then local guidelines should be followed for post-exposure prophylaxis with hepatitis B immunoglobulin and hepatitis B vaccine, and/or the use of antiretroviral drugs following exposure to HIV infection.
• If post-exposure prophylaxis for hepatitis B with immunoglobulin is considered necessary it should be started preferably within 12 hours, and not later than 1 week after exposure.
• If post-exposure prophylaxis for HIV is considered necessary it should be started as soon as possible, i.e. within hours. In humans the time interval after which it is not effective is not known and treatment may be started after 36 hours.

• In children, dog bites frequently involve the face, potentially resulting in severe lacerations and scarring.
• Wound infection: occurs in 2-30% of dog bites, 15-50% of cat bites, and 9-50% of human bites.⁸
• Risk of infection is particularly high in: puncture wounds, hand injuries, full-thickness wounds, wounds requiring surgical debridement, and wounds involving joints, tendons, ligaments, or fractures.
• Less frequent complications include tetanus, rabies, septicaemia, septic arthritis, tenosynovitis, tendonitis, fractures, osteomyelitis, peritonitis, endocarditis, endophthalmitis, meningitis, and disfiguring wounds from severe mauling.⁷
• Cat-scratch disease is caused by Bartonella henselae and can follow a bite or scratch from a cat or dog.
• Capnocytophaga canimorsus (part of the normal canine oral flora) has been associated with severe infections in immunocompromised patients, which may result in meningitis, endocarditis, renal failure, and septicaemia.⁹