Abstract
The tick Amblyomma mixtum is an ectoparasite of veterinary and public health importance because of its role as a vector of zoonotic pathogens. However, little is known about A. mixtum intraspecific variability and if morphological differentiation exists between populations across its geographic range. This study aimed to determine by electron microscopy the morphological variability of A. mixtum populations in the state of Veracruz, which has a large livestock population among states in Mexico. Forty male and 40 female A. mixtum collected from the 10 natural regions of Veracruz state were analyzed microscopically to accomplish main component analysis for each sex. Clusters were calculated with the out-tree method and a dendrogram produced to group the specimens according to their morphometric characteristics. Using 10 main components, 77% of the morphological variation of the ticks was explained. This is a reflection of scarce intraspecific variation between females. The dendogram for females grouped six clusters of specimens with similar characteristics. Morphometric variability in males was described using eight main components. Limited intraspecific variation was also observed between males. In males, the dendogram yielded six groups with similar morphometric characteristics. Morphometric analyses confirmed that the only species from the Amblyomma cajennense complex that are parasites to livestock in Veracruz state is A. mixtum. The eryxenous nature of A. mixtum combined with the frequent movement of livestock hosts may contribute to the apparent homogeneous phenotype of this tick species in Mexico.
Highlights
Ticks are economically important ectoparasites of livestock [1]
Based on the results of the descriptive statistics of the morphological characters evaluated, it is observed that the males surpassed the females in terms of the dimensions of the CB, TL, LSII, HL, HW and Tal characters, in the remaining morphometric characters, both males and females did not show evident morphological differentiation (Table 1)
Two individuals (35 and 40 individual) did not show similarities in the morphometric characteristics of the group made up of the rest (n = 38 individuals), which were grouped by the similarity of its morphometric features (Figure 2)
Summary
Ticks are economically important ectoparasites of livestock [1]. Their economic importance derives from the obligate blood feeding habit and role as vectors of pathogens causing significant morbidity and mortality in host populations [2]. Its impact on livestock health is amplified by the role of A. mixtum as a mechanical vector of Anasplasma that causes bovine anaplasmosis, which can result in significant mortality among cattle herds, it parasitizes horses, being an important vector of various species of rickettsiae [9]. The public health importance of A. mixtum stems from its host range that includes humans, and ability to vector zoonotic pathogens [10]. As it is the case with other Amblyomma species in Mexico [11], there are biological aspects of A. mixtum that remain to be defined
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