Tick-borne zoonotic flaviviruses and Borrelia infections in wildlife hosts: What have field studies contributed?

Abstract

Tick-borne flaviviruses and Borrelia spp. are globally spread pathogens of zoonotic potential that are maintained by a transmission cycle at the interface between ticks and vertebrate hosts, mainly wild animals. Aside data on pathogen burden in ticks, information on the status of various hosts relative to infection is important to acquire. We reviewed how those infections have been studied in wildlife host species in the field to discuss how collected data provided relevant epidemiological information and to identify needs for further studies. The literature was screened for observational studies on pathogen or antibody detection for tick-borne Borrelia spp. and flaviviruses in wildlife host animals. Overall, Borrelia spp. were more studied (73% of case studies, representing 297 host species) than flaviviruses (27% of case studies, representing 114 host species). Studies on both Borrelia spp. and flaviviruses focused mainly on the same species, namely bank vole and yellow-necked mouse. Most studies were order-specific and cross-sectional, reporting prevalence at various locations, but with little insight into the underlying epidemiological dynamics. Host species with potential to act as reservoir hosts of these pathogens were neglected, notably birds. We highlight the necessity of collecting both demographics and infection data in wildlife studies, and to consider communities of species, to better estimate zoonotic risk potential in the One Health context.

Keywords: Borrelia; Flavivirus; Host; Reservoir; Sentinel; Tick-borne diseases; Wildlife.

Fig. 1

Diagram of inclusion and exclusion in PubMed database screening. See section Results - Literature metrics of Supplementary material 1 for details on literature search and additional searches.

Fig. 2

Sankey diagram pairing case studies by pathogen and taxonomic order. Width of the ribbon is proportional to the number of cases for this taxonomic order-pathogen couple. rf = relapsing fever. Data are available in Supplementary material 2.

Fig. 3

A-D: Investigation efforts for TBP by taxonomic orders, expressed as average percentage of positives and number of individuals tested, by taxonomic Order. Both serological and “active infection” data are presented. Top row shows for Borrelia spp. (A) the average percentage of animals positive to Borrelia by order, (B) the number of tested animals in each order. Bottom row shows for TBFV (C) the percentage of animals positive to TBFV by order, (D) the number of tested animals in each order. Most publications regarding TBFV used an indirect methodology (antibody detection), direct detection was used in only 11% of TBFV cases. (B) and (D) show the number of tested individuals on a log10 scale, and the number of different host species tested in each order is shown at the bottom of each bar. Orders are grouped by class, Mammalia are shown to the left, Aves to the right, and for Borrelia spp., Lepidosauria at the bottom. Data are available in Supplementary material 2.