10.21 Rabies Prophylaxis

agk’s Library of Common Simple Emergencies

Presentation

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:

• 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:

• 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

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:

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

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