What is the treatment for a rat bite, including the use of Equine Rabies Immune Globulin (ERIG)?

Rat Bite Treatment with ERIG

Immediate Wound Management

For rat bites, immediately wash the wound thoroughly with soap and water for 15 minutes, followed by irrigation with povidone-iodine solution if available, as this alone markedly reduces infection risk. 1, 2

• Wound cleansing is the single most critical first step and has been shown in animal studies to significantly reduce the likelihood of rabies transmission even without other prophylaxis 1
• Avoid suturing when possible, as this can drive pathogens deeper into tissues 1, 2
• Administer tetanus prophylaxis as indicated 1

Rabies Risk Assessment for Rat Bites

Rabies post-exposure prophylaxis (including ERIG or HRIG) is generally NOT indicated for rat bites in the United States and most developed countries, as small rodents including rats are not considered rabies vectors. 1

• The CDC guidelines do not list rats among animals requiring rabies prophylaxis 1
• Rabies has not been documented to be transmitted from rats to humans in modern medical literature
• However, if you are in a region where rabies risk from rats exists or the epidemiological situation is uncertain, proceed with full rabies post-exposure prophylaxis

Rabies Post-Exposure Prophylaxis Protocol (If Indicated)

For Previously Unvaccinated Patients:

Administer both rabies immunoglobulin and vaccine together on day 0. 3, 4

Immunoglobulin Administration:

• Human Rabies Immunoglobulin (HRIG) is preferred at 20 IU/kg body weight 1, 3, 4
• Equine Rabies Immunoglobulin (ERIG) can be used as an alternative when HRIG is unavailable or cost-prohibitive, particularly in resource-limited settings 5
• Infiltrate the full dose around and into the wound(s) if anatomically feasible 1, 3
• Inject any remaining volume intramuscularly at a site distant from vaccine administration 1, 3
• Administer only once, at the beginning of prophylaxis 1, 3
• Can be given up to day 7 if not administered initially, but NOT beyond day 7 1, 3
• Never administer in the same syringe or anatomical site as the vaccine 1, 3

ERIG-Specific Considerations:

• Modern purified and pepsin-digested ERIG products have very low rates of anaphylaxis 5
• Skin testing before ERIG administration has limited predictive value for anaphylaxis and does not predict serum sickness 5
• A positive skin test should only be considered if a wheal >10 mm develops (with or without flare), or a wheal of 5-10 mm with flare >20 mm 5

Vaccine Schedule:

• Administer 4 doses of rabies vaccine (HDCV or PCECV) on days 0,3,7, and 14 3, 4
• For immunocompromised patients, use the 5-dose schedule: days 0,3,7,14, and 28 3, 4
• Inject intramuscularly in the deltoid area for adults and older children 1, 3
• Use anterolateral thigh for younger children 1, 3
• Never use the gluteal area, as this results in lower antibody titers 1, 3, 2

For Previously Vaccinated Patients:

• Administer only 2 doses of vaccine on days 0 and 3 3, 4
• No immunoglobulin (HRIG or ERIG) is needed 3, 4

Bacterial Infection Management

Rat bites carry significant risk of polymicrobial bacterial infection, with Staphylococcus aureus being the most common pathogen, but 72.5% of infections are polymicrobial. 6

• Consider prophylactic broad-spectrum antibiotics covering both aerobic and anaerobic Gram-positive and Gram-negative bacteria, given the deep puncturing nature of rodent bites 6
• Monitor for signs of infection including inflammation, ulceration, or abscess formation 7
• Most superficial scratches (Type I wounds) require only conservative wound care 7
• Deeper bites with infection (Type II wounds) may require drainage and debridement 7
• Full-thickness wounds with tissue loss (Type III wounds) may require skin grafting 7

Common Pitfalls to Avoid

• Failing to adequately wash the wound for the full 15 minutes 2, 8
• Administering vaccine in the gluteal area 1, 3, 2
• Not infiltrating the full immunoglobulin dose around the wound when anatomically feasible 1, 3
• Administering immunoglobulin and vaccine in the same anatomical site 1, 3
• Giving immunoglobulin beyond day 7 of the vaccine series 1, 3