Targeting the Exoskeleton Elementome to Track Tick Geographic Origins

Abstract

Understanding the origin of ticks is essential for evaluating the risk of tick-borne disease introduction into new territories. However, when collecting engorged ticks from a host, it is virtually impossible to identify the geographical location where this tick was acquired. Recently, the elementome of tick exoskeleton was characterized by using scanning electron microscopy (SEM) and energy dispersive spectroscopy analysis (EDS). The objective of our preliminary proof-of-concept study was to evaluate the use of SEM-EDS for the analysis of tick exoskeleton elementome to gain insight into the tick geographic and host origin. For this preliminary analysis we used 10 samples of engorged ticks (larvae and nymphs of six species from three genera) collected from various resident hosts and locations. The elementome of the tick exoskeleton was characterized in dorsal and ventral parts with three scans on each part using an EDS 80 mm 2 detector at 15 kV in a field emission scanning electron microscope. We used principal component analysis (PCA) (varimax rotation) to reduce the redundancy of data under the premise of losing information as little as possible. The PCA was used to test whether the different variables (tick species, stages, hosts, or geographic locations) differ in the composition of exoskeleton elementome (C, O, P, Cl, and Na). Analyses were carried out using SPSS. The PCA analysis explained a high percentage of variance using the first two factors, C and O (86.13%). The first PC (PC-1; 63.12%) was positively related to P, Cl, and Na, and negatively related to C. The second principal component (23.01%) was mainly positively related to C. In the space defined by the two extracted PC (PC-1 and PC-2), the elementome of tick samples was clearly associated with tick species, but not with developmental stages, hosts or geographic locations. A differentiated elementome pattern was observed within Romanian regions (CJ and TL) for the same tick species. The use of the SEM-EDS methodological approach provided additional information about the tick exoskeleton elementome with possible applications to the identification of tick origin host and location.

Comparative analysis of Rhipicephalus tick salivary gland and cement elementome

“…This study advanced previous studies in R. microplus and other tick species ( Villar et al., 2020 ; de la Fuente et al., 2020 ; Pacheco et al., 2020 ) using the same SEM-EDS experimental approach and provided the first characterization of the tick SG and/or cement elementome in R. sanguineus and R. bursa . A limitation of this study which is particularly relevant for the analysis of tick SG elementome is the fact that the EDS method is limited or strongly biased toward the elements on the surface layer.…”

“…However, in our study trace elements such as Se, Cu, Mn, Zn and Co present in mammalian cover hair ( BioCheck, 2014 ) were not identified in the tick SG and cement or in dog hair, thus suggesting that these elements are rare and with a low contribution to tick elementome. Some of the chemical elements identified here in the elementome of SG and cement and in dog hair were recently reported in tick exoskeleton using a similar experimental approach ( de la Fuente et al., 2020 ; Pacheco et al., 2020 ).…”

“…Differences in the elementome composition were also observed between R. bursa cement and SG (Figures 4 A and 4B), which probably reflects the fact that only a fraction of the molecules present in the SG are secreted into the cement ( Bullard et al., 2016 , 2019 ; Suppan et al., 2018 ; Hollmann et al., 2018 ; Villar et al., 2020 ). As shown for exoskeleton elementome, other factors such as pathogen infection ( de la Fuente et al., 2020 ) and geographic origin ( Pacheco et al., 2020 ) of ticks may affect cement chemical composition.…”

“…The elementome was characterized using SEM-EDS as previously described ( de la Fuente et al., 2020 ; Villar et al., 2020 ; Pacheco et al., 2020 ). Rhipicephalus bursa SG and cement samples were dehydrated in an incubator at 37 °C for 24 h prior to analysis with SEM-EDS.…”