Date Published: August 01, 2012
Publisher: The American Society of Tropical Medicine and Hygiene
Author(s): Amy T. Gilbert, Brett W. Petersen, Sergio Recuenco, Michael Niezgoda, Jorge Gómez, V. Alberto Laguna-Torres, Charles Rupprecht.
In May of 2010, two communities (Truenococha and Santa Marta) reported to be at risk of vampire bat depredation were surveyed in the Province Datem del Marañón in the Loreto Department of Perú. Risk factors for bat exposure included age less than or equal to 25 years and owning animals that had been bitten by bats. Rabies virus neutralizing antibodies (rVNAs) were detected in 11% (7 of 63) of human sera tested. Rabies virus ribonucleoprotein (RNP) immunoglobulin G (IgG) antibodies were detected in the sera of three individuals, two of whom were also seropositive for rVNA. Rabies virus RNP IgM antibodies were detected in one respondent with no evidence of rVNA or RNP IgG antibodies. Because one respondent with positive rVNA results reported prior vaccination and 86% (six of seven) of rVNA-positive respondents reported being bitten by bats, these data suggest nonfatal exposure of persons to rabies virus, which is likely associated with vampire bat depredation.
Rabies is caused by single-stranded negative-sense RNA viruses in the genus Lyssavirus. Rabies virus (RABV; genotype I) is the most prolific of the 12 viral species classified within the genus, and it is responsible for greater than 55,000 human deaths annually.1 Typically, RABV is transmitted in the saliva after the bite of an infected mammal. In the Americas, bats and carnivores are the major reservoirs of RABV.2 Multiple insectivorous bat species play a role in RABV transmission to humans in the United States.3 In Latin America, RABV is transmitted principally by the common vampire bat (Desmodus rotundus), although several other Neotropical bat species play a role in RABV circulation.4–8 Rabies is the most recognized human health risk from bats in Latin America, with dual impacts for public health and agriculture.9 Wide circulation of RABV among vampire bats throughout their geographic range is shown by extensive reports of vampire bat-associated RABV infections in bats, humans, and cattle throughout Latin America.8,10–12
A total of 92 persons were interviewed from 51 households and represented a total community population of 316 persons (Table 1). The mean age of all respondents was 25 years (range = 2–67 years), and 55% (51 of 92) of respondents were male. Among respondents, 82% (62 of 76) of persons interviewed reported completing a primary education or less. Among households, 86% (44 of 51) owned pets or livestock, and 61% (27 of 44) of households owning pets or livestock reported that their animals were bitten by bats. Among the total community population, 23% (73 of 316) of persons had exposure to bats. Although a biased sample, among persons interviewed, 54% (50 of 92) reported being bitten by bats previously.
Despite a wealth of studies documenting natural seroprevalence among wildlife reservoirs, few prior studies have reported natural human seroprevalence to RABV. One study showed rVNA among 7% (2 of 30) of sera from raccoon hunters in Florida, although at low titers (∼0.1 IU mL−1).42 Another study, among Canadian Inuit hunters having animal contact but no vaccination history for RABV, also detected rVNA in 29% (9 of 31) of individuals.43 However, titers in that study were also uniformly low (< 0.1 IU mL−1). A later study among fox trappers in Alaska reported rVNA among 12% (3 of 26) of individuals.44 Two of three seropositive trappers had a previous vaccination history. The single seropositive Alaska fox trapper who had not received rabies vaccine previously had a high rVNA titer (2.3 IU mL−1), perhaps associated with a 47-year history of trapping and skinning foxes (without personal protective equipment) and a cumulative harvest of over 3,000 foxes. During a human rabies outbreak investigation in the Department of Amazonas in Perú in 1990, 17% (8 of 48) of persons in two affected communities were seropositive for rVNA, one of whom later died.14 In the study by Lopez and others,14 the median rVNA titer among the seven surviving persons was 0.18 IU mL−1 (range = 0.14–0.66 IU mL−1), whereas the person who died had a titer of 7.6 IU mL−1 at the time of sampling. Because the study by Lopez and others14 did not detect a statistical relationship relating to age of the individuals or exposure to bats with antibody concentration, all of the positive rVNA titers among the seven survivors were considered to be nonspecific. Despite potential for low-titer, false-positive neutralizing antibody titers resulting from nonspecific inhibition of virus growth, a recent review did not suggest evidence of nonspecific inhibition of virus growth at serum dilutions of 1:25 or greater in serological neutralization assays, although they were based on observations among non-indigenous persons.45 In the current study, a 50% reduction of fluorescing fields at a 1:25 serum dilution would have resulted in a titer of 0.2 IU mL−1, and given that six of seven rVNA titers were greater than 0.2 IU mL−1, these data do not suggest a high potential for nonspecific inhibition. The single respondent with an rVNA titer below 0.2 IU mL−1 (and RNP IgG titer of 1:8) in this study also reported a history of vaccination (Table 1), which is a more parsimonious explanation for her seropositive status. It is also noteworthy that none of the respondents in either community (seropositive or otherwise) reported the preparation or consumption of bats as a food source. Source: http://doi.org/10.4269/ajtmh.2012.11-0689