The major innate immune pathways in Asian longhorned ticks, Haemaphysalis longicornis, include Toll, IMD, and JAK/STAT. In the field, H. longicornis can be infected with various pathogens including Severe Fever with Thrombocytopenia Syndrome Virus (SFTS virus), Rickettsia, Babesia and Anaplasma species. One approach to identify whether ticks are infected with pathogens is by examining the expression levels of immune response genes. To evaluate whether upregulation of immune genes from H. longicornis can serve as an indicator for pathogen infection in ticks, we first designed primer sets for Dorsal, STAT, and Relish from the H. longicornis genome. We then conducted quantitative reverse transcription PCR(qRT-PCR) on cDNA of field-collected H. longicornis and identified individuals with high expression levels in immune response genes. Subsequently, we performed digital PCR assays to determine whether selected ticks were infected with SFTS virus. Using this approach, we evaluated correlation between pathogen infection and upregulation of immune response genes in ticks. Although more experiments are needed to draw conclusions, this study suggests immune response gene-based screening methods for pathogen infected ticks from the field.

We monitored the population of Haemaphysalis longicornis, in Andong, Gyungbuk from April to November, 2018. Among total 2,994 ticks collected for 8 months, H. longicornis 1,677(56%), H. spp Larva 1,074(35.9%), H. flava 213(7.1%), Ixodes nipponensis 30(1.0%) were identified. In addition, considering the environment, 1,727(57.7%), 907(30.3%), 192(6.4%) and 168(5.6%) ticks were collected in the grassland, graves, copse, mountain path, respectively. In the pathogen diagnosis with PCR using SFTS virus specific primers, positive viruses were detected in H. longicornis, H. flava and H. spp from June to October. The minimum field infection rate of June, July, August, September and October were 0.4%, 0.8%, 1.2%, 0.8% and 2.3%. respectively.

Heamaphysalis longicornis is a major vector for Severe Fever with Thrombocytopenia Syndrome (SFTS) virus and the density of the vector has been increasing because of the climate change. The incidence of fatalities due to SFTS is increasing every year. In this study, to evaluate the SFTS transmission by ticks, the density of ticks mediating SFTS was monitored. Tick was collected every month from four different sites (Grass land, Mountain path, Grave, Copse) in Andong with the traps containing dry ice as CO2 attractants. Among 2,572 ticks of 3 species; H. longicornis, H. flava, and Ixodes nipponensis were most abundantly collected from April to August. H. longicornis is the richest species (92.8%), whereas Ixodes nipponensis was the least species (0.8%). The 54.5% of the sample were nymph stage and female/male ratio was 64.3%. According to the pathogene analysis, SFTS virus was detected from H. longicornis adult and larvae stages collected in July and August. In July samples, SFTS virus was detected only from grassland site, but the virus was observed in the sample from all four sites in August. For effective prevention of SFTS, the tick density should be continuously monitored based on the onset time of SFTS with the consideration of habitate, habit & life history of ticks.