Wise Use of Antibiotics: Animal and Human Bites … How Do You Manage?

Column Author & Editor: Rana El Feghaly, MD, MSCI | Director, Clinical Services | Director, Outpatient Antibiotic Stewardship Program | Associate Professor of Pediatrics, UMKC School of Medicine

Now that the weather is nicer and kids are getting out more, you may start seeing more animal bites. In fact, an estimated 5 million human and animal bite wounds occur in the U.S. each year, accounting for about 1% of emergency department visits.¹ What infections should you consider? When should you provide prophylaxis? Which antibiotic should you use? At what dose? For how long? When should you worry about rabies? This article has you covered!

Bites from different animals may need to be managed differently.

When we think of animal bites, we often automatically think of dogs. Although dog bites account for 90% of bites, there are many other animals that may bite us, and the types of infections that may result may be different.

• The rate of infection depends on several factors:
  • The animal: the rate of infection is much higher in cat bites (~50%) compared to human and dog bites (5%-20%).
  • The mechanism: crush and puncture injuries carry a much higher risk of infection.
  • The location of the bite: bites to the hands and feet have high rate of infection.

This is why antibiotics are not necessary to prevent an infection following all bites.¹

• In addition to rabies considerations, certain infections should be considered based on the animal.² Below are few examples:
  • Herpes B infection, an infrequent viral infection that can lead to brain damage or death, may occur after bites from certain monkeys, particularly macaque monkeys. Antivirals may be recommended to prevent this infection.³
  • Rodent bites may lead to rat-bite fever, an infection caused by Streptobacillus moniliformisor Spirillum minus, that is associated with rash, fever, migratory polyarthritis and multiple complications.⁴
  • Marine animal bites may be associated with infections commonly encountered in water, such as Vibrio spp. (salt water or brackish water) and Aeromonas, Plesiomonas, and Pseudomonas (fresh water).⁵
  • Reptile and amphibian bites can transmit Salmonella.

These infections need to be treated with different antimicrobials as opposed to common animal bites. When in doubt, call your infectious diseases colleagues!

When are antibiotics needed? And what is the best antibiotic to use?

The most important step to prevent a bite wound infection is thorough cleansing/irrigation (typically with water and saline; 1% povidone–iodine or 1% benzalkonium chloride can be used for particularly soiled wounds). Debridement and removal of foreign material are also helpful.¹

Post-exposure antibiotic prophylaxis is typically recommended in patients with:

• Immunocompromising conditions, advanced liver disease, or diabetes
• Moderate-to-severe injuries such as crush injuries, need for surgical repair or debridement
• Deep puncture wounds (e.g., cat bites)
• Injuries to areas with preexisting cellulitis or venous/lymphatic compromise
• Injuries that penetrate the periosteum or joint capsule
• Wounds in which cleansing and closure has been delayed by more than eight hours
• Wounds to hand, face or genitals^6,7

When prophylaxis is warranted, amoxicillin-clavulanate is an excellent antibiotic to treat and prevent infection from animal and human bites because its coverage includes skin flora such as streptococci and oxacillin-susceptible Staphylococcus aureus, oral flora (e.g., Haemophilus spp., Neisseria spp.) in addition to specific bacteria found in specific animals’ saliva (Pasteurella spp. and Capnocytophaga spp. in dogs, cats and mammals; Eikenella spp. in humans; and enteric gram negatives in reptile bites).^1,8 A three-day course is sufficient to prevent infection, while treating an infection typically requires a longer course of five to seven days.⁶ Remember that you do not need to prescribe high-dose amoxicillin-clavulanate for a dog bite; we recommend using 22.5 mg/kg/dose twice a day with a maximum dose of 875 mg amoxicillin. The Children’s Mercy Outpatient Antibiotic Handbook has an excellent table on page 28 that helps you choose the right formulation. A rule of thumb is if you’re using standard dosing, you should choose the formulation with higher clavulanate concentration. If the patient has a true allergy to amoxicillin, then you will need to use a combination of antibiotics, typically clindamycin PLUS either doxycycline or trimethoprim/sulfamethoxazole.

Rabies considerations depend on the animal.⁹

In the U.S., most cases of rabies occur after a bat bite; dog and cat bites rarely account for any cases. Although all mammals are susceptible, bats, raccoons, skunks, foxes, coyotes and mongooses are reservoir species most likely to be infected. If a child was bitten by any of these animals, and the animal cannot be recovered to evaluate for rabies, then the child should receive post-exposure prophylaxis with rabies immune globulin (20 IU/Kg to infiltrate around the wound on day 0), and human rabies vaccine (1 mL IM on day 0, 3, 7 and 14). Bites of small rodents (e.g., chipmunks, squirrels, hamsters, guinea pigs, gerbils, mice, rats) and lagomorphs (rabbits, pikas, hares) typically do not require prophylaxis. Dog and cat bites should be evaluated based on risks (e.g., was the attack unprovoked? Is the animal unimmunized? Is the animal showing rabid behavior?). Post-exposure prophylaxis is not an absolute emergency; if the animal can be observed for 10 days, and tested if it exhibits rabid behavior, that is safe to do in most circumstances.

Finally, remember to evaluate tetanus vaccinations, and provide if indicated:

• DTaP or Tdap + tetanus immune globulin if child is unvaccinated or has received fewer than three tetanus-containing vaccines.
• DTaP or Tdap if child has received three or more vaccinations, but last vaccine was over five years ago.

In summary, when facing an animal or dog bite, thoroughly irrigate the bite wound and consider the animal for special infectious risks. Only bites at high risk of infection need prophylaxis with a three-day course of standard-dose amoxicillin-clavulanate. Consider rabies post-exposure prophylaxis particularly in carnivore wildlife and bats. Always evaluate tetanus vaccinations. Call your infectious diseases colleagues if you need help!

References

1. Bite wounds. In: Kimberlin DW, Barnett ED, Lynfield R, Sawyer MH, eds. Redbook 2021-2024 Report of the Committee on Infectious Diseases. American Academy of Pediatrics; 2021:169-175.
2. Brook I. Management of human and animal bite wound infection: an overview. Curr Infect Dis Rep. 2009;11(5):389-95. doi:10.1007/s11908-009-0055-x
3. Cohen JI, Davenport DS, Stewart JA, et al. Recommendations for prevention of and therapy for exposure to B virus (cercopithecine herpesvirus 1). Clin Infect Dis. 2002;35(10):1191-1203. doi:10.1086/344754
4. Rat-bite fever. In: Kimberlin DW, Barnett ED, Lynfield R, Sawyer MH, eds. Redbook 2021-2024 Report of the Committee on Infectious Diseases. American Academy of Pediatrics; 2021:627-628.
5. Prentice KC, Himstead AS, Briggs AL, Algaze-Gonzalez IM. Emergency management strategies and antimicrobial considerations for nonmammalian marine vertebrate penetrating trauma in North America, the Caribbean, and Hawaii: a review article. Wilderness Environ Med. 2023;34(1):106-112. doi:10.1016/j.wem.2022.09.008
6. Stevens DL, Bisno AL, Chambers HF, et al. Practice guidelines for the diagnosis and management of skin and soft tissue infections: 2014 update by the Infectious Diseases Society of America. Clin Infect Dis. 2014;59(2):e10-52. doi:10.1093/cid/ciu444
7. Cummings P. Antibiotics to prevent infection in patients with dog bite wounds: a meta-analysis of randomized trials. Ann Emerg Med. 1994;23(3):535-540. doi:10.1016/s0196-0644(94)70073-7
8. Savu AN, Schoenbrunner AR, Politi R, Janis JE. Practical review of the management of animal bites. Plast Reconstr Surg Glob Open. 2021;9(9):e3778. doi:10.1097/GOX.0000000000003778
9. Rabies. In: Kimberlin DW, Barnett ED, Lynfield R, Sawyer MH, eds. Redbook 2021-2024 Report of the Committee on Infectious Diseases. American Academy of Pediatrics; 2021:619-627.