Rabies in BC: A prophylaxis guidelines update

Rabies is an almost invariably fatal zoonotic infection, and globally claims an average of 55 000 lives annually, mostly in Asia and Africa.[1] Rabies is transmitted by the saliva of an infected animal, usually through a bite or scratch. Symptoms include fever, headache, malaise, dysphagia, and finally paralysis and death due to respiratory failure 2 to 6 days after the onset of symptoms. Diagnosis is made by fluorescent antibody (FA) staining or cell culture of brain tissue. Presumptive diagnosis is made by FA staining of skin tissue from the hairline at the back of the head. The incubation period is 3 to 8 weeks, or as long as several years depending on such factors as the severity of the wound, richness of innervation at the wound site, its distance from the brain, and the strain of virus.[2] Immediate wound washing and a course of rabies postexposure prophylaxis (RPEP) as soon as possible following rabies exposure are critical to prevent this disease.

In 1995 the Centers for Disease Control and Prevention first suggested that, in addition to direct contact exposures, RPEP should also be offered to people awakening to find a bat in their bedroom, even if there was no evidence of a bite or scratch.[3] This was based partly on the recognition that bat bites/scratches may be so minute as to go undetected and because human cases of bat rabies had been reported without recognized contact. In the following years, all North Amer­ican jurisdictions revised their policies to recommend that a potential rabies exposure should be considered where a bat is physically present in a room and the individual cannot provide a history that excludes any possible bite, scratch, or mucous membrane exposure (e.g., child in a room with a bat, person sleeping in a room/tent with a bat). From 2003 through 2007, 364 recommendations for RPEP for this type of exposure were made in BC, representing a nearly sixfold increase in the use of RPEP in BC between 1997 and 2007 (unpublished data).

A recent Quebec survey found that ~0.1% of the population annually may qualify for RPEP under the revised recommendation as exposed while sleeping to a bat in the bedroom. However, only a small minority (~ < 5%) of such exposed and RPEP-eligible individuals sought medical advice and received RPEP.[4] Nevertheless, the in­cidence of rabies in the US and Canada remains exceedingly rare; only 56 nontransplant bat-variant cases were reported between 1950 and 2007 (six in Canada, including one indigenously acquired case in BC); only two of these cases of bat-variant rabies had unrecognized physical contact in the bedroom.[5] The incidence of rabies preventable by providing RPEP to people with unrecognized exposure in the bedroom is thus estimated at 1 per 2.7 billion person-years. The number needed to vaccinate to prevent a single case of rabies in that context is 2.7 million at a cost of $2.1 billion in biologicals alone, per case prevented.[4]

On the basis of this re-analysis of the rare risk of rabies associated with bedroom exposure alone (without recognized bat contact), the 2009 BC Rabies Guideline has been revised to recommend that RPEP should be offered only if direct physical contact with a bat has occurred. A few other Canadian provinces have already made this policy change and the rest are expected to follow. RPEP should still be considered after bites, scratches, or mucous membrane contact with any other animal with suspected or confirmed rabies as indicated in the Table.[6]

In the event that rabies is not prevented, recognition of symptoms is critical. Transplanting of organs from individuals who have died from undiagnosed rabies has been implicated in five cases of ra­bies transmission from two donors.[5]

Fortunately, rabies remains a rare disease. Therefore, guidelines for administering RPEP in relation to bats have been revised to more reasonably reflect that risk assessment. Prevention by limiting op­portunities for physical contact with bats as well as postexposure prophylaxis constitute the cornerstone of protection.

References

1. World Health Organization. Rabies vaccines WHO position paper. Weekly epidemiological record. 7 Dec 2007;49/50:425-435.
2. Heymann, DL. Control of Commun­icable Diseases in Man. 18th ed. Washington, DC: American Public Health Association; 2004.
3. Paves A, Gill P, Mckenzie J, et al. Human rabies: Washington 1995. MMWR 1 Sep 1995;44(34):625-627.
4. De Serres G, Skowronski D, Mimault P, et al. Bats in the bedroom, bats in the belfry: Re-analysis of the rationale for rabies post-exposure prophylaxis. Clin Infect Dis 2009. In press.
5. De Serres G, Dallaire F, Cote M, et al. Bat rabies in the United States and Canada from 1950 through 2007: Human cases with and without bat contact. Clin Infect Dis 2008;46:1329-1337.
6. BC Centre for Disease Control. Communicable Disease Control—Chapter 1—Management of Specific Diseases: Rabies [updated 28 Feb 2009]. http://bccdc.org/content.php?item=192.

hidden

Mr Cooper is senior environmental health specialist at the BC Centre for Disease Control. Drs Galanis and Skowronski are both physician epidemiologists at the BCCDC.