Spatial risk of Haemaphysalis longicornis borne Dabieshan tick virus (DBTV) in China

The uncertainty and unknowability of emerging infectious diseases have caused many major public health and security incidents in recent years. As a new tick-borne disease, Dabieshan tick virus (DBTV) necessitate systematic epidemiological and spatial distribution analysis. In this study, tick samples from Liaoning Province were collected and used to evaluate distribution of DBTV in ticks. Outbreak points of DBTV and the records of the vector Haemaphysalis longicornis in China were collected and used to establish a prediction model using niche model combined with environmental factors. We found that H. longicornis and DBTV were widely distributed in Liaoning Province. The risk analysis results showed that the DBTV in the eastern provinces of China has a high risk, and the risk is greatly influenced by elevation, land cover, and meteorological factors. The risk geographical area predicted by the model is significantly larger than the detected positive areas, indicating that the etiological survey is seriously insufficient. This study provided molecular and important epidemiological evidence for etiological ecology of DBTV. The predicted high-risk areas indicated the insufficient monitoring and risk evaluation and the necessity of future monitoring and control work.

Detection and Phylogenetic Analysis of a Novel Tick-Borne Virus in Yunnan and Guizhou Provinces, Southwestern China

Dabieshan tick virus (DTV) is a novel tick-borne virus with the potential to infect both animals and humans. It has been confirmed that DTV is widely distributed in Shandong and Zhejiang Provinces. In this study, a total of 389 ticks were sampled from Honghe city of Yunnan Province and Bijie city of Guizhou Province, and then divided into 148 pools according to the location and species. QRT-PCR and nested PCR were performed to confirm the presence of DTV. The results showed a minimum infection rate of 2.43% (5/206) in Yunnan Province and 3.28% (6/183) in Guizhou Province, respectively. Interestingly, DTV was identified in Rhipicephalusmicroplus for the first time besides Haemaphysalis longicornis. Phylogenetic analysis showed that DTV from Yunnan and Guizhou Provinces shared over 94% identity with isolates derived from Hubei and Shandong Provinces, and DTV was relatively conservative in evolutionary dynamics. These findings provide molecular evidence of Dabieshan tick virus in different species of ticks from unrecognized endemic regions and suggest that DTV may be widely prevalent in southwestern China.

A Novel miRNA-hlo-miR-2-Serves as a Regulatory Factor That Controls Molting Events by Targeting CPR1 in Haemaphysalis longicornis Nymphs

Successful completion of the molting process requires new epidermal growth and ecdysis of the old cuticle in Haemaphysalis longicornis (H. longicornis). MicroRNAs (miRNAs) participate in the development of organisms by inhibiting the expression of their target mRNAs. In this study, a novel tick-specific miRNA was identified and denoted hlo-miR-2 that serves as a novel regulator of molting events in H. longicornis nymphs by targeting a cuticular protein. The full length of this cuticular protein was first obtained and named it CPR1. A qRT-PCR analysis showed that hlo-miR-2 and CPR1 exhibit significant tissue and temporal specificity and that their transcription levels are negatively correlated during the molting process. CPR1, as a direct target of hlo-miR-2, was identified by a luciferase reporter assay in vitro. Agomir treatment indicated that the overexpression of hlo-miR-2 significantly reduced the protein expression level of CPR1, decreased the molting rate and delayed the molting time point in H. longicornis nymphs. RNA interference (RNAi) experiments demonstrated that CPR1 was significantly associated with the molting process in H. longicornis nymphs. Phenotypic rescue experiments convincingly showed that hlo-miR-2 participated in molting events by targeting CPR1 in H. longicornis nymphs. In summary, we present evidence demonstrating that miRNAs constitute a novel important regulator of molting events in addition to hormones. The described functional evidence implicating CPR1 in molting events contributes to an improved understanding of the distinct functions of the CPR family in ticks and will aid the development of a promising application of cuticular protein RNAi in tick control.

The efficacy of propylene glycol alginate (PGA), a food additive, in controlling Haemaphysalis longicornis ticks

Ticks and tick-borne pathogens threaten the health of both domestic animals and humans, and are associated with a high economic burden in many countries. Tick control can be achieved with chemical acaricides, but issues remain regarding their safety as well as emerging tick resistance. Propylene glycol alginate (PGA) is a food additive commonly used in China. It has been used to kill whiteflies in agriculture as an environmentally friendly insecticide. The aims of this study were to (i) explore the efficacy of PGA to kill Haemaphysalis longicornis ticks and (ii) assess the potential to develop a new tick control acaricide containing PGA and a reduced amount of synthetic pyrethroid. Beta-cypermethrin was chosen as the reference pyrethroid in this study. PGA, beta-cypermethrin and mixes (PGA and beta-cypermethrin formulated in proportions of A = 2:1, B = 1:1, and C = 1:2) were compared for efficacy to kill larval and adult H. longicornis ticks. Overall, we found no statistically significant differences in the killing efficacy of PGA as compared to beta-cypermethrin across examined time-points post-tick exposure. At 24 h post-tick exposure, similar killing efficacy for H. longicornis larvae was recorded for beta-cypermethrin alone, PGA alone, and mixed formulations B and C. Mixed formulation C had the strongest killing effect when compared to PGA alone or mixed formulation B. Similar outcomes were observed in experiments with adult H. longicornis ticks. Based on these findings, we propose that PGA can be useful as a tick control acaricide, either as a single active ingredient or formulated together with a pyrethroid.