Mammalian bites are a common injury in the United States, accounting for 1% of all emergency department visits annually,¹ with 10 to 20 of these cases resulting in a fatality.² According to the CDC, there are 4.7 million dog bites per year, with an estimated emergency department cost of $53.9 million per year.¹ Approximately half of these injuries are to children.³ The majority of bites are caused by dogs (80%–90%), followed by cats (5%–10%), humans (2%–3%), and the remainder by other domesticated or wild animals.⁴

Domesticated house dogs may exert a force of 200 to 400 pounds per square inch, and police and fighting dogs up to 2000 pounds per square inch,⁵ enough force to penetrate sheet metal.⁶ Most bites are superficial crush injuries that cause ecchymoses and hematomas without skin penetration,⁶ but may also cause lacerations, puncture wounds, severe crush injuries, tissue avulsions, fractures, dislocations, and neurovascular injuries.⁵ The upper and lower extremities are the most common site of injury for older children.⁴ Children less than 5 years old are commonly bitten on the head and neck due to their face-to-face contact with the offending dog.^3,7 Most of the head and neck injuries involve the nose, lips, and cheeks.^4,6 On rare occasions, especially in children less than 2 years of age, the bite may penetrate the cranium and lead to depressed skull fractures, intracranial lesions, and meningitis.^4,6 Infection rates are generally low for dog bites. However, the site of injury plays a major role. Dog bites to the face have a lower risk of infection (1%–5%) than bites to the hands, which have a high infection rate (12%–30%).⁶

Cat bites are common in the upper extremities, mainly presenting with a puncture wound rather than a laceration or contusion.⁴ The feline characteristic long, sharp teeth introduce bacteria into deeper tissues and may involve tendons, bones, or joints.⁶ This causes a wound that may appear small and unremarkable but have an infection rate as high as 80%.⁸ Cat scratch disease due to Bartonella henselae may develop 7 to 12 days after a cat bite or scratch. The syndrome consists of regional lymphadenitis, constitutional symptoms, and infrequently organ involvement such as encephalopathy and atypical pneumonia. The disease is usually self-limiting and resolves in 2 to 5 months without antibiotics, but precautions should be taken for those who are immunocompromised, due to the risk of bacteremia and severe infection. A 7- to 10-day course of trimethoprim–sulfamethoxazole or ciprofloxacin may be used in this high-risk population.⁹ One study suggested azithromycin as a suitable option to reduce lymphadenopathy.¹⁰

Human bites in children are generally caused by other children.⁷ Common sites include the face, trunk, and upper extremities and present as superficial abrasions.⁷ There should be a high index of suspicion for child abuse for bites where the intercanine distance is greater than 3 cm, as this indicates the biter had permanent teeth.⁷ Human bites in older children and adolescents commonly occur during an altercation when an individual strikes another in the mouth with a clenched fist, frequently referred to as a fight bite. This serious injury often occurs over the metacarpal–phalangeal joint and presents with high infection rates, which may range from cellulitis to osteomyelitis.⁴ Upon return of the hand to a relaxed position after the bite, bacteria is carried by the extensor tendon further into a closed environment suitable for growth.¹¹ HIV and hepatitis B transmission through human bites is rare and post-exposure prophylaxis is not routinely indicated.^7,12 However, if the assailant is positive for either virus and the bite is deep with possible blood transfer, post-exposure prophylaxis should be started.¹²

Most animal bites are polymicrobial, but common bacterial isolates include Staphylococcus aureus, Pasteurella multocida, streptococci, coagulase-negative staphylococci, and enteric bacteria.^4,6 Human bites also tend to be polymicrobial with Streptococcus anginosus, Staphylococcus aureus, and Eikenella corrodens being the most common pathogens.¹² Signs and symptoms include erythema, tenderness, swelling, and purulent drainage around the site of the bite⁷ but may also present with systemic symptoms such as fever, chills, swollen lymph nodes, and racing heart. Pasteurella and Bacteroides species predominate within the first 12 hours, but Staphylococci and anaerobes are more common after 24 hours.^13,14 A rare systemic infection caused by Capnocytophaga canimorsus is seen 2 to 3 days after a dog bite and mainly occurs in the immunocompromised. The infection usually manifests as hypotension, disseminated intravascular coagulation, and renal failure. Mortality is as high as 30%, with a majority being those who are immunocompromised. A 5-day course of amoxicillin/clavulanate will suffice for prophylaxis in those who sustained a dog bite and are immunocompromised.⁵