The Case
A 37-year-old man with no past medical history presented after he was bit by a bat on the index finger of the right hand. He stated he reached into a box to remove what he thought was a rag. In fact, it was a bat that had its wing trapped by a paint can (Figure 1). He was concerned about rabies and presented to the ED for further care.
Figure 1. The bat in question
Why it Matters?
Rabies, a neurotropic lyssavirus in the family rhabdoviridae, presents as a progressive encephalopathy known to have the highest case fatality rate of all known infectious diseases. As a sobering reminder, the appearance of the clinical signs and symptoms of rabies herald an almost certain death. The incubation period from infection to disease is approximately 15-90 days, and incubation is notably shorter if exposure occurs in well-innervated areas such as the face. Prodromal symptoms are non-specific and may include fever, chills, malaise, and weakness that progress to pharyngeal spasms, hydrophobia, paralysis, and ultimately coma and death.
The decision to administer rabies post exposure prophylaxis (PEP) depends on whether significant exposure has occurred, the type of animal, and the ability to observe the animal. The first and most important branch point is the exposure. Exposure is defined as a bite (or saliva contaminated scratch) or saliva exposure to an open wound or mucus membrane. Exposure of intact skin to saliva or other body fluids does not constitute a significant exposure and patients do not require PEP regardless of type of animal or ability to observe the animal.
While all mammals can contract rabies, bats, followed by raccoons, skunks and foxes, remain the four primary animal reservoirs in the United States and are considered high risk. A significant exposure to a high risk animal requires the initiation of PEP, while the same exposure to a low risk animal (eg, rabbit, rat, squirrel, or chipmunk) does not require PEP. Waking up with a bat in one’s room without signs of a bite or scratch is an indication for PEP according to some guidelines because determining whether there was a mucus membrane exposure or a small undetected bite would be difficult. Lastly, if the animal is healthy and can be observed for a ten-day period (eg, a domestic cat or dog) after a significant exposure, PEP administration can be deferred, and if the animal remains well it can be avoided completely.
If PEP is deemed necessary based on the factors above, the clinician should do the following:
1. Wash all wounds with soap and water and if available, povidine-iodine solution
2. Individuals without previous rabies vaccine exposure should receive a dose of human rabies immune globulin (HRIG) immediately, with administration into the area around and into the wound, with the remaining fluid injected IM (Figure 2).
Figure 2. Rabies PEP regimen provided to our patient. Dosing of immunoglobin is 20 U/kg. At 300 U/mL, the volume in a larger adult can be significant. Because he was bit on the right hand, he was given 2 mL in the right deltoid (max IM dose to the deltoid) and the remainder administered into the gluteal region.
3. Human diploid cell (HDC) or Purified Chick Embryo Cell (PCEC) rabies vaccine 1.0 mL IM should be administered on the day of the rabies exposure (at a different site than HRIG administration) with repeat dosing again on days 3, 7, and 14 post-exposure.
Uncertainties with regards to PEP initiation can be discussed with public health authorities: state contact information can be found at https://www.cdc.gov/rabies/resources/contacts.html?fbclid=IwAR2IwuyZB9Dp0QQ7lNieg9Vvhh3OJyk1sTtvF_zlCOt00fljxrQiKVlnSMo
Created By:
Sherin Mahrat, MD.
Emergency Medicine Resident | PGY1
Cook County Emergency Medicine
Reviewed By:
Scott Sherman, M.D.
Associate Program Director | Cook County Emergency Medicine
Joanne C. Routsolias, PharmD, RN, BCPS
Clinical PharmD Specialist - Emergency Medicine/Toxicology
Cook County Health
References:
Centers for Disease Control and Prevention. Human Rabies Prevention – United States, 2008. MMWR Early Release 2008;57
Tarantola A, Tejiokem MC, Briggs DJ. Evaluating new rabies post-exposure prophylaxis (PEP) regimens or vaccines. Vaccine. 2019 Oct 3;37 Suppl 1:A88-A93. doi: 10.1016/j.vaccine.2018.10.103. Epub 2018 Nov 22. PMID: 30471958.
World Health Organization. (2018). WHO expert consultation on rabies: third report. World Health Organization. https://apps.who.int/iris/handle/10665/272364. License: CC BY-NC-SA 3.0 IGO