Animal Bite-associated Infections

Microbiology and Treatment

Nicole Thomas; Itzhak Brook


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

In This Article

Ungulate Bites

Of the ungulates in the USA, pigs are the most likely to bite, whereas horses, cows, sheep and deer are more likely to injure via kicking or crushing. Pig bites are often severe with a high incidence of infection that is often polymicrobial with organisms including Staphylococcus and Streptococcus spp. (including Streptococcus suis), Haemophilus influenzae, Pasteurella, Actinobacillus and Flavobacterium species.[56–58]

In 2005 there were an estimated 9.2 million horses in the USA.[207] Of all horse-related injuries, only approximately 4% are related to bites.[59] As with other animal bites, injury may range from superficial trauma (nips), to amputation of digits. The oral flora of horses has been shown to contain up to 270 bacterial isolates, 98 of which are anaerobes.[60] Of the organisms associated with human infection, the Gram-negative coccobacilli Actinobacilli (especially Actinobacillus lignieresii) are common culprits. As mentioned previously, these are also part of the normal flora of pigs. Clinically, the majority of cases present with an abscess around the bite wound.

Other organisms associated with horse bite infections include S. aureus, Steptococcus equi (as well as other Viridans Streptococci), Neisseria spp. and Pasteurella spp. including P. multocida.[61] Anaerobes, as with other mammal bites include Fusobacterium spp., including the recently identified Fusobacterium equinum,[62,63] as well as Bacteroides and Prevotella spp.[64] Of note, horses may become infected with rabies, although there have been no cases of rabies transmission from horse to human.[65]

As with most mammalian bites, amoxicillin/clavulanic acid (augmentin) is a reasonable empiric antibiotic in an individual bitten by an ungulate. Doxycycline may be used in individuals greater than 8 years of age, or metronidazole/clindamycin plus ciprofloxacin, or trimethoprim/sulfamethoxazole may be used in PCN-allergic patients.


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