Microbiology · Year 2 · from Microbiology
Case 2: Rabies Exposure
Presentation
A 35-year-old hiker presents to the emergency department after being bitten on the hand by a bat while camping in a cave. The bite occurred 6 hours ago when he tried to remove a bat that had landed on his backpack. He has a small puncture wound on his right index finger with minimal bleeding. He is otherwise healthy with no symptoms. His tetanus vaccination is current. The bat was not captured.
Clinical Image
Diagram illustrating the components of rabies post-exposure prophylaxis: wound care, human rabies immune globulin (HRIG) infiltration at the wound site, and rabies vaccine series.
Image Source: Lecture image - rabies prevention
Questions
- Why is this considered a high-risk exposure requiring post-exposure prophylaxis?
- What are the components of rabies post-exposure prophylaxis (PEP)?
- What is the rationale for the different components of PEP?
- What is the prognosis if rabies infection develops?
Answers
- High-risk exposure rationale: This is a high-risk rabies exposure for several critical reasons:
- Bats are major rabies reservoirs in the United States (causing most human rabies cases)
- The bat was not captured for testing, so rabies status is unknown
- Bat bites can be very small or unrecognized, and any direct contact with a bat (even without obvious bite) may warrant PEP
- Bat rabies variants are particularly adapted for transmission to humans
- Rabies is nearly 100% fatal once clinical symptoms develop
For bat exposures, PEP is recommended when a bite, scratch, or mucous membrane exposure occurs, OR when a bat is found in a room with a sleeping person, unattended child, or cognitively impaired individual who cannot reliably report exposure.
- Components of rabies PEP (for previously unvaccinated individuals):
- Immediate wound care: Thorough washing with soap and water for at least 15 minutes
- Human rabies immune globulin (HRIG): 20 IU/kg, infiltrated around the wound site
- Rabies vaccine: Four doses on days 0, 3, 7, and 14
- Rationale for PEP components:
- Wound care: Physically removes and dilutes viral inoculum; soap has virucidal activity against the lipid envelope
- HRIG: Provides passive immunity by immediately neutralizing virus at the wound site before it can enter peripheral nerves; must be given at the wound site to be effective
- Rabies vaccine: Stimulates active immunity with antibody production; the vaccine is highly immunogenic and provides long-lasting protection
- Together, HRIG provides immediate protection while the vaccine generates durable immunity
- Prognosis if rabies develops: Once clinical symptoms of rabies appear, the disease is virtually 100% fatal. There are only a handful of documented survivors (typically with severe neurologic sequelae), despite aggressive intensive care. This is why PEP is so critical - it is highly effective if given before symptoms develop but useless after. The incubation period (typically 1-3 months, but can be weeks to years) provides a window for PEP to work.