Genetic diversity, infection prevalence, and possible transmission routes of Bartonella spp. in vampire bats

Abstract

Bartonella spp. are globally distributed bacteria that cause endocarditis in humans and domestic animals. Recent work has suggested bats as zoonotic reservoirs of some human Bartonella infections; however, the ecological and spatiotemporal patterns of infection in bats remain largely unknown. Here we studied the genetic diversity, prevalence of infection across seasons and years, individual risk factors, and possible transmission routes of Bartonella in populations of common vampire bats (Desmodus rotundus) in Peru and Belize, for which high infection prevalence has previously been reported. Phylogenetic analysis of the gltA gene for a subset of PCR-positive blood samples revealed sequences that were related to Bartonella described from vampire bats from Mexico, other Neotropical bat species, and streblid bat flies. Sequences associated with vampire bats clustered significantly by country but commonly spanned Central and South America, implying limited spatial structure. Stable and nonzero Bartonella prevalence between years supported endemic transmission in all sites. The odds of Bartonella infection for individual bats was unrelated to the intensity of bat flies ectoparasitism, but nearly all infected bats were infested, which precluded conclusive assessment of support for vector-borne transmission. While metagenomic sequencing found no strong evidence of Bartonella DNA in pooled bat saliva and fecal samples, we detected PCR positivity in individual saliva and feces, suggesting the potential for bacterial transmission through both direct contact (i.e., biting) and environmental (i.e., fecal) exposures. Further investigating the relative contributions of direct contact, environmental, and vector-borne transmission for bat Bartonella is an important next step to predict infection dynamics within bats and the risks of human and livestock exposures.

Fig 1. Phylogenetic relationships for the gltA gene among the sample of Bartonella genotypes detected in vampire bats from this study and vampire bat Bartonella genotypes from GenBank.

All sequences are displayed with their GenBank accession numbers, and sequences from this study are listed in bold with bat ID numbers. The tips of all sequences are colored by geography, and diamonds depict posterior probabilities of nodes greater than 50%.

Fig 2. Distribution of the 11 paraphyletic genotypes identified from the 35 vampire bat Bartonella spp. gltA sequences.

Belize and Peru are shown in grey with black outlines (A). Insets show the location of sampling sites (white), and pie graphs illustrate the genotype composition of Bartonella spp. per site (B and C) pooled across both study years. Pie charts are scaled by sample size. Shapefiles were obtained from the maps and mapdata packages in R [86].

Fig 3. Phylogenetic relationships for the gltA gene among the sample of Bartonella sequences detected in vampire bats and top BLAST hits from GenBank (S3 Table).

Bartonella sequences from this study are displayed with genotype, bat ID numbers, and accession numbers. Sequences from GenBank are colored by host taxa and provided with accession numbers, species, and sampling location. Diamonds depict posterior probabilities of nodes greater than 50%.

Fig 4

Vampire bat sampling sites in Latin America, with Belize and Peru shown in grey with black outlines (A). Insets show the location of sampling sites (white) and the prevalence of Bartonella per site (B and C) across study years (solid line = 2015, dashed line = 2016), with black denoting the proportion of infected bats. Pie graphs are scaled by sample size. Shapefiles were obtained from the maps and mapdata packages in R [86].

Fig 5. Modeled Bartonella infection prevalence (black line) and 95% confidence intervals (grey) from the GLMM of individual risk factors, displayed in order of effect size: forearm size (χ² = 14.01), bat sex (χ² = 8.48), reproductive status (χ² = 2.79), and age (χ² = 0.76).

Individual data points are jittered and colored by infection status (black = positive, white = negative).

Fig 6. Heatmap of pairwise similarity (%) between the 35 vampire bat–associated Bartonella sequences from this study and the nine Bartonella sequences derived from a subset of positive saliva and fecal samples, calculated with Kimura's 2-parameters distance model.

Sequences with greater than 96% similarity were assumed to be part of the same Bartonella genotype.