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Rabies is almost universally fatal in humans, but are all humans equally susceptible? To find out, investigators studied residents of two remote communities in the Peruvian Amazon — an area with deadly rabies outbreaks linked to vampire bat bites. Vampire bats feed primarily on livestock, but when these animals are unavailable, will feed on other mammals, including humans.
Twenty-three percent of the total community population (73/316) reported exposure to bats. Among 92 persons interviewed (mean age, 25; 55% male), 54% reported previous bat bites. Serum samples were obtained from 63 individuals. Screening with the rapid fluorescent focus inhibition test detected rabies virus neutralizing antibodies in samples from seven people (11%). Six of these seven people reported previous bat bites; one reported receiving postexposure prophylaxis. Rabies virus (RABV) ribonucleoprotein IgG antibodies were found in three samples (including 2 of those with neutralizing antibodies); RABV ribonucleoprotein IgM antibodies were detected in one sample. All nine seropositive individuals had a history of bat exposure — seven of them, bite exposure. Seropositivity status was associated with age: People aged <29 were significantly less likely to be seropositive.
Gilbert AT et al. Evidence of rabies virus exposure among humans in the Peruvian Amazon. Am J Trop Med Hyg 2012 Aug; 87:206.
Willoughby RE Jr. Resistance to rabies. Am J Trop Med Hyg 2012 Aug; 87:205.
Comment
All mammals are susceptible to RABV infection, but susceptibility varies by species. Humans are considered highly susceptible. This study suggests that RABV exposures in humans are not invariably fatal — at least in this population. The authors note the possibility that this isolated population might be genetically and immunologically unique, perhaps with a selective advantage because of enhanced resistance to rabies infection; an editorialist points out the potential insights that can be gained by studying such populations. Nonlethal rabies exposure could also be explained in other ways. For example, abortive early infection or clearance of a small viral inoculum at the periphery could be mechanisms for stimulating immune response. Alternatively, the presence of other flora in the saliva of the bat could potentially contribute to an inflammatory immune response and viral clearance.