Ecological and anthropogenic drivers of rabies exposure in vampire bats: implications for transmission and control

Abstract

Despite extensive culling of common vampire bats in Latin America, lethal human rabies outbreaks transmitted by this species are increasingly recognized, and livestock rabies occurs with striking frequency. To identify the individual and population-level factors driving rabies virus (RV) transmission in vampire bats, we conducted a longitudinal capture-recapture study in 20 vampire bat colonies spanning four regions of Peru. Serology demonstrated the circulation of RV in vampire bats from all regions in all years. Seroprevalence ranged from 3 to 28 per cent and was highest in juvenile and sub-adult bats. RV exposure was independent of bat colony size, consistent with an absence of population density thresholds for viral invasion and extinction. Culling campaigns implemented during our study failed to reduce seroprevalence and were perhaps counterproductive for disease control owing to the targeted removal of adults, but potentially greater importance of juvenile and sub-adult bats for transmission. These findings provide new insights into the mechanisms of RV maintenance in vampire bats and highlight the need for ecologically informed approaches to rabies prevention in Latin America.

Figure 1.

Map of study sites in Peru with spatio-temporal patterns of rabies virus (RV) exposure. White points show sampling locations. Coloured regions indicate the governmental departments that were sampled (red, Apurimac; green, Madre de Dios; blue, Lima; orange, Cajamarca). Pie charts show the proportion of seropositive (white) vampire bats in each site in each year, with pie diameter proportional to sample size (range = 6–102). Colonies with less than or equal to five samples in a single year were classified as seropositive (open diamond) or seronegative (filled diamond). Dashed lines connect sites across years and orbits around Peru group sites by year.

Figure 2.

Effects of (a) age and (b) culling history on RV exposure in vampire bats. Error bars are 95% confidence intervals. Letters indicate statistically significant differences among groups (p < 0.05) in generalized linear mixed models. Sample sizes for groups are indicated below bar labels.

Figure 3.

The relationship between vampire bat colony size and seroprevalence. Colours indicate the departmental region as in figure 1. A logistic regression found no significant association between colony size and seroprevalence (z₁ = 0.71, p = 0.479). When the two sites with unusually high seroprevalence were removed (see top left portion of figure), this relationship became weakly, but significantly positive (z₁ = 2.138, p = 0.031). However, the y-intercept remained significantly greater than zero, suggesting the absence of a strict population threshold for viral invasion. The dotted and dashed lines show model predictions of prevalence for the full and partial datasets, respectively. Squares, 2008; circles, 2009; triangles, 2010.