Epidemiology^1,2

• Substantially more dog bites occur than cat bites.
• It has been estimated that dog bites account for 60-90% of bites, cat bites for 5-18% and human bites for 4-23%.
• Between a third and half of all mammalian bites occur in children (they are often bitten by a household pet).
• One study reported that of an estimated 740 people per 100,000 annually bitten by dogs, only a small proportion seek medical attention. 2.6 in 100,000 require hospital admission. Half of all children had been bitten by dogs at some time, boys more frequently than girls. A telephone surgery of 1,184 families concluded that the annual incidence of bites in children aged under 15 years was 22/1,000.³
• German shepherds, pit bull terriers and Rottweilers are the most likely to bite but all dogs should be considered potentially dangerous.⁴ Knowing the breed of dog is important, as a bite from a larger dog is more prone to damage deeper structures.
• With regard to human bites, a UK study at an Emergency Medicine Department found that, in a four-year period, 421 (13%) human bites were identified out of 3,136 case notes. Most patients were males aged between 16-25.⁵

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 bitten and are most at risk of serious injury.⁶

Assessment^1,2

• Injuries may be more extensive than they appear.
• Dog bites typically produce crushing injuries which damage muscles, tendons and nerves, whereas cat bites are more likely to produce 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.
• All injuries on the dorsal surface of the metacarpophalangeal joint, received during an affray, should be considered bite wounds until proved otherwise: such wounds may be sustained without the patient realising it.
• Consider the circumstances of the injury. Alcohol and domestic violence are two common causes in adults.
• The history should include tetanus immunisation status, the delay from injury to presentation, any disability and any history of immunosuppressive conditions.
• Signs of infection should be noted (redness, tenderness, swelling, heat, discharge), especially if presentation is late.
• Inspection of human bites should include assessment for tendon damage, infection, depth of injury and tissue loss.

Differential diagnosis^1,2

• Consider non-accidental injury if there is an adult human bite inflicted on a child.
• For animal bites inflicted on children, consider poor parenting and supervision.
• Without a clear history, you may have to infer whether a bite has been received from a human, an animal or an insect.
• Non-traumatic infections can given an appearance resembling a bite.

Management^1,2

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 the need for tetanus immunisation and human tetanus immunoglobulin.
• If the patient has sustained a dog bite, however minor, in a country in which rabies is known to occur, contact the Health Protection Agency's Centre for Infection or Health Protection Scotland.^7,8 To assess the need for prophylaxis, staff will enquire about the following:
  • Previous vaccination status.
  • Country where bitten.
  • Site and date of bite.
  • Provoked or unprovoked bite.
  • Domestic or feral dog.
  • Current health of animal - if known.
• Consider referral to A&E 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 six 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 six hours old.
• Cover with a sterile, non-adhesive dressing to protect the wound.

Antibiotic prophylaxis

• Studies suggest that 'low-risk' human bites (i.e. those which do not penetrate the epidermal layer) probably do not need antibiotic prophylaxis as long as they do not involve the hands, feet, joints, or cartilaginous structures. Otherwise, antibiotic prophylaxis should be given. Hand bites of any description are at particular risk of infection and prophylaxis should be given.
  Prophylaxis is generally recommended for animal bites when:
  • People are at high risk from infection, e.g. 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 two 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:
  • Staphylococcus spp.
  • Streptococcus spp.
  • Eikenella spp.
  • Pasteurella spp.
  • Proteus spp.
  • Klebsiella spp.
  • Haemophilus spp.
  • Enterobacter spp.
  • Capnocytophaga canimorsus (formerly known as DF-2).
  • Bacteroides spp.
  One case of Corynebacterium auriscanis has been reported.⁹
• Infected cat bites are usually due to P. multocida. Staphylococcus spp., Streptococcus spp., and anaerobes are also important pathogens.
• Infected human bites usually contain Streptococcus spp., S. aureus, E. corrodens, and anaerobic bacteria.
• Co-amoxiclav is recommended as first-line treatment for mild-to-moderate infections following a dog, cat, or human bite.
• If the person is allergic to penicillin, first-line treatment is doxycycline plus metronidazole.¹⁰
• Oral treatment is usually given unless the infection is severe.

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.¹¹
• 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.
• The risk of HIV transmission from human bites is extremely low, due to the presence of salivary inhibitors with antiviral properties.¹²
• 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 exposure prophylaxis for hepatitis B with immunoglobulin is considered necessary, it should be started preferably within 12 hours and not later than one 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.

Complications^1,2

• 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.¹³
• 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.
• The three human bites most likely to cause infection are a chomping bite to the finger, a tooth injury to the head and a closed-fist striking the opponent's tooth.
• Less frequent complications include tetanus, rabies, septicaemia, septic arthritis, tenosynovitis, tendonitis, fractures, osteomyelitis, peritonitis, endocarditis, endophthalmitis, meningitis and disfiguring wounds from severe mauling.
• Necrotising fasciitis has been reported in a diabetic after an animal bite and can occur after a minor injury in immunocompromised patients.¹⁴
• Psychological:
  • Increased anxiety.
  • Children may have nightmares and flashbacks.
  • Children who have suffered severe and multiple dog bites are at risk of developing post-traumatic stress disorder.
  • Permanent scarring and disfigurement may lead to depression and decreased self-esteem.
• Cat-scratch disease is caused by Bartonella henselae and can follow a bite or scratch from a cat or dog.
• C. 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.¹⁵

Prevention¹⁶

Dog owners can be prosecuted by the police under the Dangerous Dogs Act 1991, which makes ownership of certain breeds illegal. An amendment in 1997 removed the mandatory destruction order provisions of the 1991 Act by giving the courts discretion on sentencing and re-opened the Index of Exempted Dogs for those prohibited dogs which the courts consider would not pose a risk to the public. A civil claim can also be made against the owners for damages under the Animal Act 1991.

Document references

1. Perkins Garth A et al; Animal Bites in Emergency Medicine, Medscape, Dec 2010
2. Barrett J et al; Human Bites in Emergency Medicine, Medscape, Apr 2010
3. Morgan M, Palmer J; Dog bites. BMJ. 2007 Feb 24;334(7590):413-7.
4. Shewell PC, Nancarrow JD; Dogs that bite. BMJ. 1991 Dec 14;303(6816):1512-3. [abstract]
5. Harrison M; A 4-year review of human bite injuries presenting to emergency medicine and Injury. 2009 Aug;40(8):826-30. Epub 2009 Feb 1. [abstract]
6. Daniels DM, Ritzi RB, O'Neil J, et al; Analysis of nonfatal dog bites in children. J Trauma. 2009 Mar;66(3 Suppl):S17-22. [abstract]
7. Health Protection Agency
8. Health Protection Scotland
9. Bygott JM, Malnick H, Shah JJ, et al; First clinical case of Corynebacterium auriscanis isolated from localized dog bite infection. J Med Microbiol. 2008 Jul;57(Pt 7):899-900. [abstract]
10. British National Formulary
11. Medeiros I, Saconato H; Antibiotic prophylaxis for mammalian bites. Cochrane Database Syst Rev. 2001;(2):CD001738. [abstract]
12. McLeod K et al; Human Bites, Medscape, May 2008
13. Brook I; Microbiology and management of human and animal bite wound infections. Prim Care. 2003 Mar;30(1):25-39, v. [abstract]
14. Lee S, Roh KH, Kim CK, et al; A case of necrotizing fasciitis due to Streptococcus agalactiae, Arcanobacterium Korean J Lab Med. 2008 Jun;28(3):191-5. [abstract]
15. O'Rourke GA, Rothwell R; Capnocytophaga canimorsis a cause of septicaemia following a dog bite: A case Aust Crit Care. 2011 May;24(2):93-9. Epub 2011 Jan 15. [abstract]
16. Dogs that are banned in the UK, Directgov

Internet and further reading

• Revis DR; Human Bite Infections, Medscape, Aug 2009
• Dendle C, Looke D; Management of mammalian bites. Aust Fam Physician. 2009 Nov;38(11):868-74. [abstract]