Population genetics of the Ixodes affinis (Ixodida: Ixodidae) complex in America: new findings and a host-parasite review.

Ticks are hematophagous ectoparasites associated with a wide range of vertebrate hosts. Within this group, the Ixodidae family stands out, in which the Ixodes genus contains at least 245 species worldwide, from which 55 species are present in the Neotropical region. Ixodes affinis, a tick described in 1899, has a wide distribution from the Southern Cone of America to the United States. However, since its description, morphological variability has been reported among its populations. Furthermore, attempts have been made to clarify its status as a species complex using mitochondrial markers, but mainly in restricted populations of South and Central America. Thus, information related to populations of the transition region between the Neotropical and Nearctic zones is lacking. For these reasons, the objectives of the study were to evaluate the genetic diversity and structure of I. affinis across the Americas and to compile all the published records of I. affinis in America, to elucidate the host-parasite relationships and to identify their geographical distribution. For this, a phylogeny, and AMOVA analyses were performed to assess the genetic structure of samples obtained by field work in South Carolina, USA and Yucatán, Mexico. A total of 86 sequences were retrieved from a fragment of the 16S region. Phylogeny and genetic structure analysis showed four groups that were geographically and genetically related with high branch support and Fst values, all of them statistically significant. The results obtained support the hypothesis that I. affinis it corresponds to a complex of four species, which must be validated through future morphological comparisons.

Identification of the G184C, C190A and T2134A mutations in the para-sodium channel gene of the southern cattle tick Rhipicephalus (Boophilus) microplus associated with resistance to cypermethrin in northern Veracruz, Mexico.

The southern cattle tick (Rhipicephalus microplus) represents one of the ectoparasites with the greatest distribution worldwide. Infestations by this arthropod can cause a decrease in the production of meat and milk, as well as anaemia and the transmission of bacterial and parasitic agents. For this reason, several active molecules have been developed to control these arthropods. A widely used group of ixodicides are pyrethroids, especially cypermethrin, which have knockdown effects on ticks. Resistance to cypermethrin has been reported in ticks since the 2000s; it was registered for the first time in Mexico in 2009. Even though multiple studies have evaluated resistance with conventional tests, there are few studies in Mexico that have identified the presence of single nucleotide polymorphisms (SNPs) associated with resistance. Hence, the aim of this work was to monitor three mutations associated with resistance in the sodium/chlorine channel in eight populations of ticks from northern Veracruz. Engorged adult females were collected from which genomic DNA was extracted. Subsequently, three mutations in domains II and III of para­sodium channel gene were detected by conventional PCR and sequencing. Global alignments were done with the reference sequences deposited in GenBank. A total of 116 engorged females were analysed, of which 10 tested positive for G184C and C190A of domain II of the para­sodium channel gene. T2134A was present in domain III in a single production unit. This is the first work where molecular monitoring of cypermethrin resistance has been carried out in the northern zone of the state of Veracruz.