Knowledge of Bat Rabies and Human Exposure Among United States Cavers

Robert V. Gibbons, Robert C. Holman, Stephen R. Mosberg, and Charles E. Rupprecht

Disclosures

Emerging Infectious Diseases. 2002;8(5) 

In This Article

Abstract and Introduction

We surveyed cavers who attended the National Speleological Society convention in June 2000. Fifteen percent of respondents did not consider a bat bite a risk for acquiring rabies; only 20% had received preexposure prophylaxis against the disease. An under-appreciation of the risk for rabies from bat bites may explain the preponderance of human rabies viruses caused by variant strains associated with bats in the United States.

Over the past century, human rabies has become exceedingly rare in the United States. The decreasing incidence of human rabies has followed the decline of rabies in domestic dogs. From 1946 to 1965, 236 human Rabies virus (RABV) infections were reported in the United States. From 1946 through 1949, the number of human RABV infections averaged 24/year, declining to 1.5/year from 1962 through 1965. Ninety percent of RABV infections were caused by dog bites from 1946 through 1949, decreasing to 67% from 1962 through 1965[1]. As canine rabies declined, the relative importance of other reservoirs in the United States increased. From 1970 to 1989, human infections averaged 3.3/year. Of these infections, 45% were caused by canine RABV variants (all but one was acquired outside the United States), 30% were caused by bat RABV variants, and one was caused by a corneal transplant from an unsuspected rabies patient[2,3]. From 1990 through 2000, bat RABV variants have emerged as the predominant cause of human rabies in the United States[4]. In the past 11 years, total human rabies deaths have averaged 2.9/year, and 24 (75%) of 32 deaths were due to bat RABV variants. If the six cases caused by foreign canine RABV variants are excluded, then 24 (92%) of the 26 human rabies deaths acquired domestically were caused by bat RABV variants. The other two cases were due to a dog/coyote RABV variant found in Texas[4].

Confusion remains about potential exposures to rabies from bats. Only 2 (8%) of the 24 patients with human rabies caused by bat RABV variants had a definitive history of a bat bite. Nine patients (38%) had a history of direct physical contact with bats, 5 (21%) had a history of a bat inside the living area, and 8 (33%) had no history of proximity to bats[4]. Because of the paucity of bat (or other animal) bite histories, could these human rabies cases have been acquired through aerosol transmission? The diagnosis of rabies in two people who had no known history of a bite, but who worked extensively in caves inhabited by bats, received considerable attention in 1953[1,2]. Although the aerosol route is considered a possible mechanism of RABV acquisition, few data support such transmission under typical field conditions. A more plausible hypothesis is that many people may not be aware that a bat bite is a risk for rabies transmission and fail to report it.

Because of the potential contact with bats, cavers are considered at a higher risk for rabies exposure than the general population. Since the 1960s, the recommendation has been that the cavers receive rabies preexposure prophylaxis (PreEP)[5]. The objectives of this study were to learn about cavers' knowledge of the risks for bat-to-human rabies transmission and to quantify cavers' use of rabies PreEP prophylaxis and postexposure prophylaxis (PostEP).

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