10.21 Rabies Prophylaxis
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agk's Library of Common Simple Emergencies

Presentation
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A possibly contagious animal has bitten the 
patient, or the animal's saliva, brain tissue 
or cerebrospinal fluid contaminated an abrasion 
or mucous membrane.

What to do:
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- Clean and debride the wound thoroughly. 
    Irrigate with soap and water or 1% 
    benzalkonium chloride and rinse with normal 
    saline.
- Know the local prevalence of rabies, or ask 
    someone who knows (e.g., local health 
    department).
- If the offending animal was an apparently 
    healthy dog or cat, arrange to have the 
    animal observed for ten days. During that 
    period, an animal affected with rabies will 
    show symptoms and should be sacrificed and 
    examined for rabies using a fluorescent 
    rabies antibody (FRA) technique. If the 
    test is positive, begin prophylaxis with 
    rabies immune globulin and human diploid 
    cell vaccine. If the animal is not 
    available for observation, the decision of 
    whether to provide rabies prophylaxis 
    depends on the local prevalence of rabies 
    in domestic animals, rodents, and 
    lagomorphs.
- If a wild animal (e.g., bat, bobcat, coyote, 
    fox, opossum, raccoon, skunk) capable of 
    transmitting rabies is caught, it should be 
    killed, placed on ice and sent to the local 
    public health department so the brain can 
    be examined with immunofluorescence. If the 
    animal did not appear to be healthy, or if 
    the bite is on the patient's face, the 
    patient should be started on RIG and HDCV 
    in the meantime and stopped only if the 
    test is negative.
- If the offending wild animal was not 
    captured, no matter how normal-appearing, 
    assume it was rabid, and give a full course 
    of RIG and HDCV.
- Provide rapid passive immunity with 20 IU/kg 
    of rabies immune globulin, half im and half 
    infiltrating the area of the bite. This 
    passive protection has a half-life of 21 
    days.
- Begin rapid immunization with human diploid 
    cell vaccine, lml im.
- Make arrangements for repeat doses of HDCV at 
    3, 7, 14, and 28 days post exposure.

What not to do:
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- Do not treat the bites of rodents and 
    lagomorphs (hamsters, rabbits, squirrels, 
    rats, etc.) unless rabies is endemic in 
    your area. As of 1996, rodent and lagomorph 
    bites have not caused human rabies in the 
    United States.
- Do not treat exposures where contact was 
    limited to petting a rabid animal or where 
    these was only contact with the animal's 
    blood, urine, feces or skunk spray.
- Do not omit rabies immune globulin. Treatment 
    failures have resulted from giving HDCV 
    alone.

Discussion
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The older duck embryo vaccine for rabies 
required 21 injections, and produced more side 
effects and less of an antibody response than 
the new human diploid cell vaccine. Sometimes, 
neurological symptoms would arise from DEV 
treatment, raising the agonizing question of 
whether they represented early signs of rabies 
or side effects of the treatment, and thus 
whether treatment should be continued or 
discontinued. It is much easier nowadays to 
initiate immunization with HDCV and follow 
through, because side effects are minimal and 
antibody response excellent. Roughly 25% of 
patients experience redness, tenderness and 
itching around the injection site and another 
20% experience headaches, myalgia or nausea.

Patients with an immunosupressive illness or 
those taking corticosteroids, immunosupressive 
agents or antimalarial drugs may have an 
inadequate immune response to vaccination, and 
should have assays of serum antibodies. 
Pregnancy is not a contraindication to 
postexposure prophylaxis.

The incubation period of rabies varies from 
weeks to months roughly in proportion to the 
length of the axons up which the virus must 
propagate to the brain, which is why 
prophylaxis is especially urgent in facial 
bites.

References:
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- Kauffman FH, Goldmann BJ: Rabies *Am J Emerg 
    Med* 1986;4:525- 531.

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