How should I manage a 34-year-old man with a dirty right-hand dog scratch from an unvaccinated dog, no prior rabies vaccination, and tetanus immunization over four years ago?

Management of Dog Scratch with Rabies and Tetanus Risk

This patient requires immediate rabies post-exposure prophylaxis (PEP) consisting of thorough wound cleansing, human rabies immune globulin (HRIG) 20 IU/kg infiltrated into the wound, and a 4-dose rabies vaccine series (days 0,3,7,14), plus tetanus toxoid booster. 1, 2

Immediate Wound Management

• Thoroughly wash the scratch wound with soap and water for 15 minutes immediately—this single intervention markedly reduces rabies transmission risk even without other prophylaxis. 3, 4
• Apply povidone-iodine solution or other virucidal agent after washing to further reduce viral load. 3, 2
• The wound was appropriately induced to bleed with alcohol application, which helps flush out potential viral particles. 5

Rabies Post-Exposure Prophylaxis Protocol

Human Rabies Immune Globulin (HRIG)

• Administer HRIG at exactly 20 IU/kg body weight on day 0 (today), ideally simultaneously with the first vaccine dose. 1, 2, 6
• Infiltrate the full calculated dose thoroughly into and around the 1.5 cm scratch wound—inadequate wound infiltration has been associated with rare prophylaxis failures. 3, 4
• Any remaining volume after wound infiltration should be injected intramuscularly at a site distant from vaccine administration (e.g., opposite arm). 1, 2
• Never administer HRIG in the same syringe or at the same anatomical site as the vaccine, as this interferes with vaccine efficacy. 1, 2
• Do not exceed 20 IU/kg—higher doses suppress active antibody production from the vaccine. 3, 1, 2
• If HRIG cannot be given today, it can still be administered up to and including day 7, but not after day 7 as vaccine-induced antibodies are presumed present by then. 1, 2

Rabies Vaccine Series

• Administer 4 doses of HDCV (human diploid cell vaccine) or PCECV (purified chick embryo cell vaccine), 1.0 mL intramuscularly on days 0,3,7, and 14. 1, 2
• Inject in the deltoid muscle for this adult patient—never use the gluteal area as this produces inadequate antibody response and has been associated with vaccine failures. 3, 1, 2
• Day 0 is defined as today (the day the first dose is given), not necessarily the day of exposure. 1, 2
• This regimen is nearly 100% effective when administered promptly and appropriately. 1, 2

Rationale for Full PEP in This Case

Why This Scratch Requires PEP

• Scratches contaminated with saliva or neural tissue from a potentially rabid animal constitute a nonbite exposure requiring PEP evaluation. 3, 6
• The dog is unvaccinated and has an unknown rabies status—any dog that is stray, unwanted, or unavailable for observation should be considered potentially rabid. 3, 6
• The dog was brought to a veterinary clinic for a scrotal mass, suggesting it may be ill, which increases concern for rabies. 3
• In the United States, more cats than dogs were reported rabid during most of the 1990s, but dogs remain a significant risk, especially unvaccinated dogs. 3

Animal Observation vs. Immediate Treatment

• If the dog can be confined and observed for 10 days, PEP can be delayed while monitoring for signs of rabies. 3, 6
• However, if the dog is unavailable, escaped, or cannot be reliably observed, begin immediate prophylaxis. 3, 4, 6
• Given that this is a pet dog brought to a vet, attempt to contact the owner/veterinary clinic to arrange 10-day observation. 3, 6
• If observation is arranged, hold PEP but begin immediately at the first sign of illness in the dog. 6
• If the dog cannot be observed or escapes, initiate full PEP today without delay. 3, 4

Tetanus Prophylaxis

• Administer tetanus toxoid booster immediately—the patient's last tetanus vaccine was more than 4 years ago, and any wound requires a booster if the last dose was >5 years ago for clean wounds or >10 years for dirty wounds. 3, 5
• A dog scratch is considered a dirty wound, so tetanus prophylaxis is clearly indicated. 3
• Tetanus toxoid can be safely mixed with rabies vaccine or given separately without affecting immunogenicity of either vaccine. 7

Antibiotic Prophylaxis Consideration

• Consider antibiotic prophylaxis for this scratch wound—dog bites and scratches commonly harbor Pasteurella multocida, Staphylococcus aureus, Streptococcus viridans, and anaerobes. 8
• Oral amoxicillin-clavulanate provides coverage for typical dog bite pathogens. 5, 8
• The decision depends on wound depth, contamination, and patient risk factors, but prophylaxis is reasonable for this 1.5 cm scratch. 5

Critical Timing Considerations

• Rabies PEP is a medical urgency—initiate as soon as possible after exposure, ideally within 24 hours. 1, 2
• However, treatment can be initiated even if weeks or months have elapsed, as rabies incubation periods can exceed one year and the disease is uniformly fatal once symptoms appear. 3, 1, 2
• There is no absolute cutoff for initiating PEP as long as clinical rabies signs are absent. 3, 2

Common Pitfalls to Avoid

• Do not delay PEP while attempting to locate the dog if it is unavailable—begin treatment immediately and discontinue only if the animal is later proven negative by laboratory testing. 2, 4
• Do not rely on the dog's apparently healthy appearance—rabid animals may appear normal early in infection. 4
• Do not fail to infiltrate HRIG directly into the wound—this is associated with prophylaxis failures. 3, 4
• Do not give HRIG to previously vaccinated persons (not applicable here, but important to note for future cases). 1, 2
• Do not suture the wound unless absolutely necessary for cosmetic or functional reasons, as this may trap virus in deeper tissues. 3, 4

Follow-Up Plan

• If the dog is available for observation: Monitor for 10 days; if the dog remains healthy, discontinue the vaccine series after confirming with public health officials. 3, 6
• If the dog develops signs of rabies or dies: Euthanize immediately and submit brain tissue for rabies testing; continue full PEP regardless of results. 3, 6
• If the dog is unavailable: Complete the full 4-dose vaccine series on schedule. 1, 2
• Ensure the patient returns for vaccine doses on days 3,7, and 14—delays of a few days are acceptable, but substantial delays require serologic testing. 1