What are the categories of animal bites in terms of rabies exposure risk?

Categories of Animal Bites Based on Rabies Exposure Risk

Animal bites are categorized into two primary exposure types (bite and nonbite) for rabies risk assessment, with the World Health Organization further stratifying these into three categories (I, II, and III) that determine whether post-exposure prophylaxis is required. 1

Primary Exposure Categories

Bite Exposures

• Any penetration of the skin by teeth constitutes a bite exposure, regardless of body location or severity of visible trauma. 2
• All bites represent potential rabies transmission risk, even when the wound appears minor (particularly with bats, which can inflict barely detectable injuries). 2
• The risk varies based on the biting animal species, anatomic site, and wound severity, but these factors should not delay the decision to initiate treatment. 2

Nonbite Exposures

• Scratches, abrasions, open wounds, or mucous membranes contaminated with saliva or other potentially infectious material (such as neural tissue) from a rabid animal. 2
• Nonbite exposures from terrestrial animals rarely cause rabies, but occasional transmission has been documented. 2
• The highest-risk nonbite exposures include: aerosolized rabies virus exposure in laboratories or bat caves, organ/corneal transplants from rabies-infected donors, and scratches by rabid animals. 2
• If the material containing virus is dry, it can be considered noninfectious (rabies virus is inactivated by desiccation and ultraviolet irradiation). 2

Non-Exposures (No Prophylaxis Needed)

• Petting or handling an animal, contact with blood, urine, or feces (including guano), and contact of saliva with intact skin do NOT constitute exposures. 2
• Indirect contact alone is not an indication for prophylaxis. 2

WHO Three-Category Classification System

Category I (No Prophylaxis Required)

• Touching or feeding animals on intact skin. 1
• Licks on intact skin. 1
• No post-exposure prophylaxis needed. 1

Category II (Vaccine Only, No Immunoglobulin)

• Nibbling of uncovered skin without bleeding. 1
• Minor scratches or abrasions without bleeding. 1
• Licks on broken skin. 1
• Requires rabies vaccine series only (5 doses for unvaccinated persons on days 0,3,7,14,28; or 2 doses for previously vaccinated persons on days 0 and 3). 1
• Thorough wound washing with soap and water for 15 minutes is essential. 1

Category III (Vaccine + Immunoglobulin Required)

• Any penetration of skin by teeth (bite exposure). 1
• Contamination of mucous membranes with saliva. 1
• Contamination of open wounds with saliva or potentially infectious material. 1
• Bat contact when a bite cannot be excluded. 1
• Requires immediate thorough wound washing, Human Rabies Immune Globulin (HRIG) at 20 IU/kg infiltrated around wounds, and complete vaccine series. 1, 3
• Previously vaccinated persons require only 2 vaccine doses (days 0 and 3) without immunoglobulin. 1

Animal Species Risk Stratification

High-Risk Animals (Immediate PEP Unless Proven Negative)

• Wild terrestrial carnivores: raccoons, skunks, foxes, coyotes, and bobcats must be considered rabid unless proven otherwise. 2, 3
• Bats: All 49 continental U.S. states have documented rabid bats; any bat contact requires PEP when bite/scratch cannot be excluded. 2, 3
• Wild animal hybrids: Should never be kept as pets and require immediate PEP for any bite. 2

Conditional Risk Animals (10-Day Observation Possible)

• Healthy domestic dogs, cats, and ferrets: Can be confined and observed for 10 days rather than immediately starting PEP. 2
• If the animal remains healthy for 10 days after biting, it would not have been shedding rabies virus at the time of the bite. 2
• If signs suggestive of rabies develop during observation, immediately initiate PEP and euthanize the animal for testing. 2
• In developing countries where dogs are major rabies vectors, exposures represent significantly increased risk. 2

Minimal Risk Animals (Almost Never Require PEP)

• Small rodents and lagomorphs: Squirrels, hamsters, guinea pigs, gerbils, chipmunks, rats, mice, rabbits, and hares are almost never infected with rabies. 2, 3
• These animals have not been known to transmit rabies to humans in the United States. 2, 3
• Consult state or local health department before deciding on prophylaxis for rodent bites. 2

Critical Pitfalls to Avoid

• Never delay wound washing while arranging for PEP; immediate thorough washing with soap and water for 15 minutes is the most important first step. 1
• Do not fail to recognize bat exposures when a bite cannot be definitively ruled out, especially in sleeping persons, young children, or intoxicated individuals. 1
• Do not confuse management of small rodent bites with bat or wild carnivore bites, as the latter almost always require PEP. 1
• Delaying post-exposure prophylaxis for severe wounds to the face and head is particularly dangerous given the shorter incubation period with proximity to the central nervous system. 1, 3
• Never administer vaccine in the gluteal area; the deltoid is the only acceptable site in adults and older children. 1