Ecology of rabies virus exposure in colonies of Brazilian free-tailed bats (Tadarida brasiliensis) at natural and man-made roosts in Texas

Abstract

Previous studies have investigated rabies virus (RABV) epizootiology in Brazilian free-tailed bats (Tadarida brasiliensis) in natural cave roosts. However, little is known about geographic variation in RABV exposure, or if the use of man-made roosts by this species affects enzootic RABV infection dynamics within colonies. We sampled rabies viral neutralizing antibodies in bats at three bridge and three cave roosts at multiple time points during the reproductive season to investigate temporal and roost variation in RABV exposure. We report seropositive bats in all age and sex classes with minimal geographic variation in RABV seroprevalence among Brazilian free-tailed bat colonies in south-central Texas. While roost type was not a significant predictor of RABV seroprevalence, it was significantly associated with seasonal fluctuations, suggesting patterns of exposure that differ between roosts. Temporal patterns suggest increased RABV seroprevalence after parturition in cave colonies, potentially related to an influx of susceptible young, in contrast to more uniform seroprevalence in bridge colonies. This study highlights the importance of life history and roost ecology in understanding patterns of RABV seroprevalence in colonies of the Brazilian free-tailed bat.

FIG. 1.

The geographic location of all sites sampled in Texas, United States. Cave sites (black circles) include Eckert James River Cave (JRC), Davis Blowout Cave (DBC), and Frio Cave (FC). Bridge sites (gray squares) include Seco Creek Bridge (SCB), East Elm Creek Bridge (EEB), and McNeil Bridge (MB).

FIG. 2.

The reproductive activity of adult female bats measured during four periods: Early, Mid, Late, and Premigratory. Solid lines represent cave roosts, and dashed lines represent bridge roosts. Reproductive status was as follows: not determined (diamond), pregnant (circle), lactating (square), or nonreproductive (triangle).

FIG. 3.

A histogram of the subset of viral neutralizing antibody (VNA) titers that were less than 2 IU/mL (97%; 519 of 534), from (A) female (n = 329) and (B) male (n = 190) bats sampled in Texas during 2005 across adult and juvenile cohorts. The cutoff for positive VNA titers is shown with a dashed vertical line.

FIG. 4.

Mean rabies VNA seroprevalence among colonies of adult female bats, from three cave (black; FC, DBC, and JRC) and three bridge (white; MB, SCB, and EEB) roosts, across time periods (n = 305). Sample sizes are listed parenthetically above histogram bars.

FIG. 5.

Mean rabies VNA seroprevalence among colonies of adult male bats, from three bridges and one cave colony (MB, SCB, EEB, and FC), across time periods (n = 148). Sample sizes are listed parenthetically above the histogram bars, and different letters represent significantly different seroprevalence proportions.

FIG. 6.

Mean (± standard error) body condition indices among adult female bats, from three cave (black; FC, DBC, and JRC) and three bridge (white; MB, SCB, and EEB) roosts, across time periods (n = 351). Different letters above the histogram bars represent significantly different mean body condition indices.