Rabies: Evolving Epidemiology, Changes in Prophylaxis Practice

Source: Centers for Disease Control and Prevention. Human rabies-Texas and New Jersey, 1997. JAMA 1998;279:421-423.

Two more case fatalities of bat-associated human rabies have appeared, raising the total of bat-associated rabies cases in the United States to 21 since 1980; this corresponds to 58% of the 36 cases of human rabies that have been reported during that time period, making the bat the number one animal vector of fatal human rabies in the United States. Why is this happening?

Both cases involved males presenting with non-specific symptoms that progressed to the point of devastating meningoencephalitis and death; diagnoses were made by DFA and confirmed by PCR. As in previous cases,1 histories taken from close family contacts did not reveal a history of a bat bite. The case in Texas featured a suspicious exposure. Two months earlier, the patient had awakened to find a bat on his shoulder. Immediate examination by the patient's wife had revealed no bite, and no medical attention was sought. In the New Jersey case, the wife recalled her husband having caught and removed, by hand, two bats from their home approximately three months before the onset of symptoms; neither the patient nor his wife recalled a bite.

Comment by Richard A. Harrigan, MD, FACEP

Prior to these two cases being reported, a definite history of a bite exposure could be documented in only one of the 19 bat-related cases of human rabies reported in the United States since 1980; physical contact without a known bite or risky exposure was reported in eight instances, and, in the remaining 10 cases, a history of bat contact could not be confirmed or definitively denied.1 This disturbing trend has led to a more aggressive approach after bat exposures with regard to post-exposure prophylaxis practices.

As with all potentially rabid animals, a person with a bite, scratch, or mucous membrane exposure from a source animal that is not available for testing should receive post-exposure prophylaxis. The CDC now recommends post-exposure prophylaxis in cases where there has been exposure to a bat, and, although there is no evidence of a bite or scratch, there is "reasonable probability that such contact occurred." Examples include such instances as a bat found in the room of a sleeping person, a previously unattended child, a mentally ill individual, or an intoxicated person.1 This recommendation has nation-wide implications, in that bat rabies is enzootic in the 49 continental United States.2

Post-exposure prophylaxis for individuals not previously immunized against rabies includes wound cleansing with a virucidal agent such as soap, administration of human rabies immune globulin (HRIG), and initiation of the vaccine series-usually with human diploid cell vaccine (HDCV).3 The vaccine should be administered (at a dose of 1 cc) intramuscularly (deltoid in adults, anterolateral thigh in young children) on days 0, 3, 7, 14, and 28. HDCV is most commonly used, but rabies vaccine adsorbed (RVA) and the newer purified chick embryo cell culture vaccine (RabAvert®) are two other FDA-licensed vaccines that are available.4

Also reported in this paper was a change in the Advisory Committee for Immunization Practices administration guidelines for HRIG. Previously, the recommendation was to administer 50% of the calculated HRIG dose (total dose = 20 IU/kg) in the bite/exposure site (if anatomically possible), with the remaining 50% being injected in the gluteal area. The current recommendation is to administer as much as possible of the full dose of HRIG into and around the wound(s), with the remainder being administered intramuscularly at a site distant from the vaccine administration site.

References

    1. Centers for Disease Control and Prevention. Human rabies-Montana and Washington, 1997. MMWR Morb Mortal Wkly Rep 1997;46:770-774.

    2. Krebs JW, et al. Rabies surveillance in the United States during 1996. J Am Vet Med Assoc 1997;211:1525-1539.

    3. Fishbein DB, Robinson LE. Rabies. N Engl J Med 1993; 329:1632-1638.

    4. Centers for Disease Control and Prevention. Availability of new rabies vaccine for human use. MMWR Morb Mortal Wkly Rep 1998;47:12-19.