ABSTRACT: Ticks are among the most economically important arthropod parasites due to the heavy infestations they provoke, affecting human and animal health and food production. Ticks are also important vectors of pathogens, mediating the dispersion of livestock and zoonotic diseases. Some examples of livestock diseases vectored by ticks include bovine babesiosis, anaplasmosis, theileriosis, and/or heartwater disease, all of which are enlisted by the World Organization for Animals as possible threats to animals and public health. The family Ixodidae (hard ticks) is of veterinary relevance, and many ixodid tick species within the genera Ixodes, Dermacentor, Amblyomma, Haemophysalis, Hyalomma, and Rhipicephalus, among others, impact farming production worldwide. However, there is no doubt that most pernicious tick species is Rhipicephalus microplus, commonly known as the southern cattle fever tick. This specie is not only the major economically important tick parasite for livestock production, but it is also the vector of Babesia bovis and B. bigemina, the causal agents of babesiosis, a severe disease that affects cattle from tropical and subtropical regions. Currently, global economic losses of the cattle industry attributable to R. microplus are estimated at around $18.7 US billion dollars per year. The economic impact is the leading reason to develop different strategies to constrains R. microplus and its vector-borne pathogens, including chemical, mechanical or environmental treatments, biological control, and/or genetic methods. Chemical, among other methods, are the most frequently applied, but the intense use worldwide, has led to the selection of acaricidal-resistant ticks populations. The molecular adaptations of ticks to overcome the effects of acaricides (e.g., deltamethrin, cypermethrin, amitraz, ivermectin) includes metabolic detoxification mechanisms and/or the selection of mutated molecular targets. Recently, a couple of systematic reviews pointed out a significant increment in the number of studies intended to understand the acaricidal resistance in ticks. These reports highlighted the acaricide resistance observed in R. microplus and the wide geographical dispersion of this problem. Whereas many acaricide-resistant R. microplus populations have been reported in Brazil, India, and Mexico, the lack of strict regulatory policies on tick control, leaving the application of acaricides at discretion of farmers. Therefore, the correct implementation of existing strategies together with novel sustainable control methods may be crucial to safeguard livestock production in the context of growing population and global warming. However, until the implementation of such sanitary measures becomes the rule, the main control strategy will still rely on the use of chemical acaricides, such as ivermectin (IVM). Ivermectin is an antiparasitic macrocyclic lactone used to control the populations of R. microplus and other ticks in livestock farming. As occurs in other countries, in Mexico ivermectin is the primary synthetic antiparasitic drug, and its abuse during the last three decades represents an important selection pressure that boosted the development of ivermectin-resistant populations of R. microplus. Therefore, the understanding of the molecular basis of the R. microplus resistance to ivermectin, especially in those cases occurring in tropical and subtropical areas of developing countries, can help to underpin the development of novel strategies to tackle this problem. In this context, omics tools can provide helpful information for the discovery of the molecular mechanisms behind the ivermectin resistance in R. microplus and other related tick species. Previous studies identified the main proteomic components of ovaries of R. microplus, including proteins involved in protein synthesis, post-translational modification, nuclear regulation, cytoskeleton, proteasome, transcriptional regulation, energetic metabolism, detoxification metabolism, or energy storage. Recently, the vitellogenin receptor (VgR) was suggested as a target for tick control because of its essential role in egg formation and maturation. However, molecular information on tick ovaries currently available limits explores the feasibility of VgR or other reproduction-related molecules as promissory targets for tick control.
Miguel Elizalde 
