Complete mitochondrial genome of Asian longhorned tick, Haemaphysalis longicornis, Neumann, 1901 (Acari: Ixodida: Ixodidae) identified in the United States

The complete mitochondrial genome analysis of Haemaphysalis hystricis Supino, 1897 (Ixodida: Ixodidae) and its phylogenetic implications

In order to study the sequence characteristics, gene order, and codon usage of the mitochondrial genome of Haemaphysalis hystricis, and to explore its phylogenetic relationship, a total of 36 H. hystricis isolated from dogs were used as sample in this study. The mitochondrial genome of a H. hystricis was amplified with several pairs of specific primers by PCR, and was sequenced by first generation sequencing. The mitochondrial genome of H. hystricis was 14,719 bp in size, and it contained 37 genes including 13 protein coding genes (PCGs), 22 transfer RNA genes (tRNAs), 2 ribosomal RNA genes (rRNAs), and AT-rich region. Each PCG sequence had different lengths, the sequence longest and shortest gene were nad5 (1,652 bp) and atp8 (155 bp), respectively, among the 13 PCGs. All PCGs used ATN as their initiation codon, 10 of 13 PCGs used TAN as their termination codon, and 3 of which had incomplete termination codon (TA/T). Most of the 22 tRNAs with different sizes could form the classical cloverleaf structures expect for tRNA-Ala, tRNA-Ser1, tRNA-Ser2, and tRNA-Glu, and there were base mismatch (U-U and U-G) in all the 22 tRNAs sequences. Two rRNAs, namely rrnL and rrnS, had different lengths, rrnL located between tRNA-Leu1 and tRNA-Val, and rrnS located between tRNA-Val and tRNA-Ile, respectively. Two AT (D-loop) control areas with different lengths were in the mitochondrial genome, the NCRL was located between tRNA-Leu2 and tRNA-Cys, and the NCRS was located between rrnS and tRNA-Ile. The complete mitochondrial genome sequence of H. hystricis was AT preferences, and the gene order is the same as that of other Haemaphysalis family ticks. However, phylogenetic analysis showed that H. hystricis was most closely related to Haemaphysalis longicornis among the selected ticks. The mitochondrial genome not only enriches the genome database, provides more novel genetic markers for identifying tick species, and studying its molecular epidemiology, population genetics, systematics, but also have implications for the diagnosis, prevention, and control of ticks and tick-borne diseases in animals and humans.

First Report of Haemaphysalis longicornis (Neumann) in Oklahoma, USA

Haemaphysalis longicornis (Neumann), the Asian longhorned tick, is a species native to East Asia, but invasive to Australia, New Zealand, and most recently, the United States. It has spread rapidly across the eastern United States after being established in New Jersey in 2017. Aiding this rapid expansion is the ability of this tick to reproduce parthenogenically and feed on diverse host species. In cattle, this tick can cause heavy burdens and act as a vector for the pathogenic hemoprotozoan parasite Theileria orientalis, genotype Ikeda, creating economic losses that impact the cattle industry. Here, we report Asian longhorned ticks, collected from cattle, a dog, and pastures and morphologically identified at the Oklahoma Animal Disease Diagnostic Laboratory as H. longicornis before molecular confirmation through PCR amplification of the cox1 gene. Blood samples from infested cattle were collected and assessed molecularly for the presence of T. orientalis, with no pathogenic DNA detected. This report describes the first record of H. longicornis in Oklahoma and the farthest westward detection of this tick in the United States to date.

Sustained efficacy of collars containing 10% w/w imidacloprid and 4.5% w/w flumethrin (Seresto®) in dogs against laboratory challenge with Haemaphysalis longicornis (Neumann, 1901) ticks

Background

Haemaphysalis longicornis ticks are reported on dogs from an increasing geographic range. This study aimed to determine the sustained efficacy of Seresto^® collars (imidacloprid/flumethrin) against experimental infestations of H. longicornis in dogs.

Methods

Twenty-four Beagle dogs previously assessed for their suitability to harbor ticks were included in the study and randomized into three groups of eight dogs each. Two of the groups were treated with collars at different time points: at the first tick infestation, dogs in group 1 had already worn collars for 92 days, while dogs in group 2 had received collars only on the previous day, thus allowing evaluation of two different treatment durations at the same point in time. Infestation of the treated groups was conducted at 1, 7, 28, and 56 days (group 2) and 92, 119, 147, 168, 196, 227, and 238 days (group 1) after collar placement. Group 3 served as untreated control and was infested whenever the dogs of the other two groups were infested. Infestations were conducted using 50 viable, adult, unfed female ticks of a US isolate of H. longicornis per dog. Ticks were removed and counted 48 h after each infestation. Health and body weight of the dogs were monitored throughout the study. The efficacy against ticks was calculated for groups 1 and 2 based on arithmetic mean values at each assessment day according to Abbott’s formula. The mean post-treatment H. longicornis tick counts were compared statistically between treatments, using an analysis of variance with a treatment effect untransformed tick count.

Results

Dogs in the control group were adequately infested at all tick counts. Efficacy was 88.2% on day 3, however well above 90% (i.e., 98.3 to 100%) at all other time points up to day 240. Statistical analysis confirmed significantly different live tick counts (P < 0.001) between the treated groups and the control group at all time points.

Conclusions

The 8-month sustained acaricidal efficacy demonstrated by the Seresto^® collar (imidacloprid/flumethrin) provides a reliable strategy against H. longicornis infestations in dogs.

Graphical Abstract