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 mm2 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.
Highlights
Understanding the geographical origin of ticks is essential for evaluating the risk of tick-bornedisease introduction to new territories
As in previous studies (Kaufman and Flynn, 2018; de la Fuente et al, 2020), the results of the analysis of tick exoskeleton elementome showed the presence with high relative abundance (>10 atomic %) of C, O, and N in tick samples (Supplementary Data S1, S2)
Despite the limited number of samples included in the analysis, matched-pair analyses showed some differences in the exoskeleton composition of some chemical elements between tick developmental stages (C, Cl, and K in I. ricinus larvae and nymphs; p < 0.05, Supplementary Data S1 reference 1 vs. 2)
Summary
Understanding the geographical origin of ticks is essential for evaluating the risk of tick-bornedisease introduction to new territories. The non-parasitic tick stages do not move too much, and the main territorial spread of ticks is by hosts (Ogden et al, 2013). For long distance migrators, such as birds, dispersal can be significant, and the origin of ticks can be very distant. When collecting engorged ticks from a host, it is virtually impossible to identify the geographical location where this tick was acquired by the host and suppositions were made based on expected migration routes of birds or by modeling. Birds carry mainly the immature stages of such ticks, some of them are spending a significant time feeding, which in case of two hosts ticks such as Hy. marginatum and Hy. rufipes can reach up to 26 days (Hoogstraal, 1979) and allow theoretically even long distance spreading
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