Animal Bite-associated Infections

Microbiology and Treatment

Nicole Thomas; Itzhak Brook


Expert Rev Anti Infect Ther. 2011;9(2):215-226. 

In This Article

Human Bites

Although human bites are the third most common bite injury, after those inflicted by dogs and cats, they are clinically very important. These wounds can range in severity, with the mechanism of injury ranging from intentionally inflicted bites to any injury due to contact with the teeth. Examples include closed fist injury during a fight, accidental bite due to collision contact with resultant laceration, or injury to the nail bed with resultant paronychia. Children who sustain a bite injury from an adult (i.e., bite mark with intercanine distance >3 cm) should be evaluated for abuse.[6] Puncture wounds from punching (i.e., clenched fist injury) may lead to fractures of the third metacarpal and/or neck of the fifth metacarpal. If not adequately addressed, osteomyelitis or joint infection may develop and result in loss of function.[7] Injury to the common extensor tendons that cover the joint may separate, allowing bacterial entry into the joint space. When the clenched fist is relaxed, the tendons may carry bacteria deeper into the hand, extending infection to other spaces.[8]

Human bites tend to have a higher complication and infection rate than animal bites, with approximately 10–15% of human bites becoming infected.[9] Infection usually emerges 1–2 days after the bite; however, this may be delayed with deeper infection. Unfortunately, patients often present for care after infection has become well established.

Human saliva can contain up to 109 organisms per ml, and there may be as many as 190 different species of bacteria present.[202] Commonly isolated aerobes include Streptococcus anginosis, Staphlococcus aureus, coagulase-negative Staphylococcus spp., Enterococcus spp. and Corynebacterium spp.[8]S. aureus is often associated with severe infections. Eikenella corrodens, a capnophilic slow-growing Gram-negative rod, is often associated with chronic infection and abscess formation, and has been shown to have synergistic activity with α-Streptococcal species in causing infection. Anaerobes that are often isolated include Gram-negative bacilli including pigmented Prevotella, Porphyromonas and Bacteroides spp., as well as Fusobacterium (especially Fusobacterium nucleatum) and Gram-positive species such as Peptostreptococcus.[10]Candida species have been isolated from occlusional bites.[8]

Viruses associated with human bite wounds include hepatitis B and C, as well as HIV. Hepatitis B antigen has been detected in the saliva of up to 75% of patients with this infection.[11] If the victim has not been vaccinated against hepatitis B, and the assailant's hepatitis B status is unknown, it is recommended that a vaccine series be administered immediately. If the biter is hepatitis B positive, the vaccine series should be completed, and hepatitis B immune globulin should be given as soon as possible, preferably within 24 h after exposure.[12]

Although rare, there have been documented cases of HIV transmission after human bite, usually in association with the presence of bloody saliva.[13] The level of risk of HIV transmission can be determined by the health status of both the assailant and the victim, as well as the severity of the wound. HIV postexposure prophylaxis may need to be considered in high-risk injuries, and consultation with an HIV specialist regarding management is recommended. According to the CDC, if the biter has blood in the mouth, the biter should be tested for HIV, hepatitis B and C, and syphilis.[203] The detection of any associated infection requires referral to an infectious disease specialist. Other infections that have been rarely transmitted via human bite include herpes simplex virus, TB, actinomycosis and tetanus.[8]


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