Mitochondrial Genomes of the American Dog Tick (Dermacentor variabilis) Isolated from Horses in the Midwestern United States.

Here, we report two complete and three partial mitochondrial genome sequences of Dermacentor variabilis specimens collected from horses in the United States. The complete genomes are 14,837 bp long and contain 13 protein-coding genes, 2 rRNA genes, and 22 tRNA genes. The sequences have been deposited under GenBank accession numbers ON052120 to ON052124.

Analysis of the complete mitochondrial genomes of Dermacentor albipictus suggests a species complex.

Dermacentor albipictus is a one-host tick broadly distributed across North America. There are two easily recognizable color variants - ornate and inornate/brown - that have been taxonomically synonymized. Based on mt-cox1 and mt-16S data, there is also evidence for two genetic lineages which do not match the color variants. We present for the first time the complete mitochondrial genomes of the two color variants of D. albipictus including representatives of each lineage. The AT-rich genomes are 14,822 bp - 14,865 bp in length and contain 13 protein coding genes, 2 ribosomal RNA genes and 22 transfer RNA genes, arranged in the conserved type 3 metastriate mitochondrial genome order. The overall differences were 10.66% between the mitochondrial genomes of D. albipictus ornate variant lineage 1 and lineage 2, 10.51% between lineage 1 and inornate/brown variant and 5.87% between lineage 2 and inornate/brown variant. The inornate/brown variant did not form a separate lineage and all inornate isolates were found to belong to lineage 2. Ornate variant isolates occurred in both lineage 1 and 2. The high divergence of the mitochondrial genome suggests that D. albipictus may represent a species complex. Other barcoding genes that may help capture the genetic differences between color and lineage variants include nad1, nad2, nad5, cox1 and atp8 loci. The mtDNA data generated in this study are available in GenBank (Accession numbers: OM678457 - OM678459 and ON032564 - ON032573) for future studies on tick taxonomy, phylogenetics and molecular epidemiology.

Early onset of pre-lethal effects of lotilaner (Credelio®) on Amblyomma americanum ticks on experimentally infested dogs.

BACKGROUND: The speed with which acaricides paralyze and kill ticks is relevant to impeding pathogen transmission. The objective of this study was to assess early-onset lotilaner effects on the motility and weights of Amblyomma americanum ticks collected from treated dogs. METHODS: Twelve healthy dogs were randomized between two groups to receive either lotilaner (Credelio®) on Day 0 or to be sham treated. On Day 7, 25 male and 25 female A. americanum were placed under bandages, two on each flank of each dog. After 30 or 45 min, all unattached ticks were removed and T = 0 was set. At T = 2, 4, 8 and 24 h post attachment, 5 attached ticks removed from each bandage on each dog were weighed, assessed by blinded observers for righting ability and movement recorded. RESULTS: After the infestation period significantly fewer treated than control dogs had 20 ticks attached (50.0% versus 91.7%, P = 0.0015). At 24 h post attachment, mean weights of ticks from treated dogs (males 1.69 mg; females 2.72) were significantly less than ticks from controls (males 2.66 mg; females 4.67) (Pmale = 0.0002; Pfemale < 0.0001). Mean tick weights from the treated group were significantly lower at 24 h than at earlier time points (Pmale < 0.0307; Pfemale = 0.0021). At 4 and 8 h, significantly fewer ticks from treated (14.3%, 0.0%, respectively) than from control dogs could right (73.3%, 70.0%) (P4h < 0.0001; P8h = 0.0024) (at 24 h, all ticks from treated dogs were dead), and distance moved was significantly less at all time points (P2h = 0.0413; P4h, P8h < 0.0001). Mean and maximum velocity of ticks from treated dogs were significantly lower, relative to controls, at 4 and 8 h (P ≤ 0.0001). Within the treated group, collected ticks had significantly lower mean and maximum velocities at 4 and 8 h compared to 2 h (Pmean < 0.0042; Pmax < 0.0194). CONCLUSION: The observed changes indicate that lotilaner may disrupt tick attachment. In ticks that attached, a progressive impairment of neuromuscular processes began within 2 h. Those irreversible changes could substantially reduce the risk of pathogen transmission from tick to host.