Importance of Host Abundance and Microhabitat in Tick Abundance

Evaluating the vector potential of deer keds Lipoptena fortisetosa for selected pathogens in Hokkaido sika deer (Cervus nippon yesoensis)

Deer keds (Lipoptena fortisetosa) are hematophagous insects that parasitize various ungulates, including Hokkaido sika deer (Cervus nippon yesoensis). Although deer keds are potential vectors for several pathogens, their role in disease transmission in Japan remains unclear. This study aimed to evaluate the potential of L. fortisetosa as a vector for selected pathogens in sika deer. Blood samples were collected from 32 sika deer and 149 deer keds (64 from deer and 85 from the environment) from the Rusha area of the Shiretoko Peninsula, Hokkaido, Japan. Nested PCRs and sequencing were performed to detect 18S rRNA gene of Theileria sp. Thrivae, 16S rRNA gene of Anaplasma sp. AP-sd (AP-sd), and flagellin B gene of Borrelia sp. in deer and deer keds. In sika deer, the infection rate was 84 % for Theileria sp. Thrivae, 75 % of AP-sd, and 3 % of Borrelia sp. The prevalence in deer keds collected from deer was 62 % for Theileria sp. Thrivae, 2 % AP-sd, and 1 % Borrelia sp. No pathogens were detected in nonparasitic deer keds captured from the environment. Notably, Theileria sp. Thrivae and AP-sd were detected in deer keds collected from PCR-negative sika deer, suggesting that deer keds acquired pathogens from a previously infested host. The absence of pathogens in non-parasitized deer keds suggests that they do not play as a biological vector for the tested pathogens. This study suggests a potential role for L. fortisetosa as a mechanical vector, emphasizing the need for additional experiments, including infection studies.

Forest Fragmentation and Warmer Climate Increase Tick-Borne Disease Infection

Anthropogenic disturbances degrade ecosystems, elevating the risk of emerging infectious diseases from wildlife. However, the key environmental factors for preventing tick-borne disease infection in relation to host species, landscape components, and climate conditions remain unknown. This study focuses on identifying crucial environmental factors contributing to the outbreak of severe fever with thrombocytopenia syndrome (SFTS), a tick-borne disease, in Miyazaki Prefecture, southern Japan. We collected data on SFTS case numbers, annual temperature and precipitation, species richness of large- and middle-sized mammals, forest perimeter length (indicating the amount of forest boundaries), percentage of agricultural land, human population, and sightseeing place numbers for each 25 km2 grid cell encompassing Miyazaki Prefecture. Through the construction of a model incorporating these factors, we found that longer forest perimeter and higher temperature led to a higher number of SFTS cases. Precipitation, mammal species richness, percentage of agricultural land, human population, and sightseeing point numbers had no effect on SFTS case numbers. In conclusion, climate condition and forest fragmentation, which increase the opportunity for human infection, played a pivotal role in SFTS outbreak.

Detection of host vertebrate DNA in tick species collected from vegetation in Fukuoka, Japan

Ticks are vectors of tick-borne diseases (TBDs) between humans and wild vertebrates. The relationship between ticks, host vertebrates, and their pathogens should be investigated for the effective control of TBDs. Hence, this study aimed to detect vertebrate DNA in ticks by using molecular methods and identify the species of such ticks collected in Fukuoka Prefecture, which is located in the northern Kyushu area of Japan. Ticks from vegetation were collected by flagging from 2017 to 2023. Out of 152 ticks collected by flagging, 65 (42.8%) were found to have vertebrate DNA. By stage, vertebrate DNAs were detected in 26 of 83 nymphs (31.3%) and 39 of 69 adults (56.5%). Among the host vertebrates, Sika deer was the main blood-feeding source of ticks in Fukuoka Prefecture. Owing to the widespread of deer across this prefecture, control of its population and other wildlife populations could be a countermeasure of reducing TBD risk.

Environmental and host factors underlying tick infestation in invasive raccoons (Procyon lotor) in Hokkaido, Japan

Revealing interactions between ticks and wild animals is vital for gaining insights into the dynamics of tick-borne pathogens in the natural environment. We aimed to elucidate the factors that determine tick infestation in wild animals by investigating ticks on invasive raccoons (Procyon lotor) in Hokkaido, Japan. We first examined the composition, intensity, and seasonal variation of ticks infesting raccoons in six study areas in Hokkaido from March 2022 to August 2023. In one study area, ticks infesting tanukis (raccoon dog, Nyctereutes procyonoides albus) were collected in May to July in both 2022 and 2023, and questing ticks were collected from the vegetation by flagging every other week in the same period. Next, we screened 17 environmental and host variables to determine factors that affect the number of ticks infesting raccoons using generalized linear (mixed) models. From 245 raccoons, we identified a total of 3,917 ticks belonging to eight species of two genera: the most prominent species were Ixodes ovatus (52.9 %), followed by Haemaphysalis megaspinosa (14.4 %), Ixodes tanuki (10.6 %), and Ixodes persulcatus (9.5 %). Ixodes ovatus was also predominant among questing ticks and ticks infesting tanukis. Although I. tanuki was frequently collected from raccoons and tanukis, it was rarely collected in the field. The variables that significantly affected the infestation on raccoons differed by genus, species and developmental stage of the tick. For instance, the infestation of adult I. ovatus was significantly affected by four variables: night-time temperature during nine days before capturing the raccoon, the size of forest area around the capture site, sex of the raccoon, and sampling season. The first two variables were also responsible for the infestation on raccoons of almost all species and stages of ticks. Our study revealed that the number and composition of ticks infesting raccoons can be affected not only by landscape of their habitats but also by weather conditions in several days before capturing.

Abundance Trends of Immature Stages of Ticks at Different Distances from Hiking Trails from a Natural Park in North-Western Italy

Hiking trails may act as hotspots at the wildlife-human interface, posing an acarological risk for people and their pets. Ticks that are maintained in the environment by wild animals may quest on people walking along the trails. Assessing the risk of tick bites for people involved in outdoor activities is a further step in mitigating the risk of tick-borne diseases. This work describes the variation of tick abundance along a gradient of distances from hiking trails, where wildlife passage is favored by higher accessibility. Hiking trails with dense vegetation on the sides were sampled for ticks along a 100 m dragging transect, located in a natural park in North-Western Italy. Additional transects were replicated at 1, 2 and 4 m away from the trail on both sides. After morphological identification, descriptive statistics and modeling were applied to determine the abundance patterns across distances. Larvae were most abundant near the trail, peaking at 1 m and dropping sharply at further distances. Nymphs showed a more gradual and consistent decrease at progressing distance from the trail. Few adults were collected, preventing the identification of a clear trend. With higher tick abundance, the immediate vicinity of hiking trails may represent a source of acarological risk for humans and pets.

Seasonal infestation patterns of ticks on Hokkaido sika deer (Cervus nippon yesoensis)

Ticks prefer specific feeding sites on a host that are influenced by host–tick and tick–tick interactions. This study focused on the spatiotemporal distribution of ticks in Hokkaido sika deer, an important tick host in Hokkaido, Japan. Tick sampling was performed on the sika deer in the Shiretoko National Park between June and October 2022. Ticks were collected from 9 different body parts of the deer to compare their attachment site preferences. Interspecific and intraspecific relationships among ticks were examined using co-occurrence analysis. The collected ticks were nymphal and adult stages of 4 species: Ixodes ovatus, Ixodes persulcatus, Haemaphysalis japonica and Haemaphysalis megaspinosa. Seasonal variations in tick burden were observed, with I. persulcatus and I. ovatus peaking in June and declining towards October; H. japonica showing low numbers in July and August and increasing from September; and H. megaspinosa appearing from September onwards with little variation. Attachment site preferences varied among species, with a significant preference for the pinna in I. ovatus and I. persulcatus. Haemaphysalis japonica was mainly found on the body and legs between June and August, and shifted to the pinna from September. Haemaphysalis megaspinosa showed a general preference for areas other than the legs. Co-occurrence analysis revealed positive, negative and random co-occurrence patterns among the tick species. Ticks of the same genus and species exhibited positive co-occurrence patterns; I. ovatus showed negative co-occurrence patterns with Haemaphysalis spp. This study revealed the unique attachment site preferences and distinct seasonal distributions of tick species in the Hokkaido sika deer.

An Integrated Approach to an Emerging Problem: Implementing a Whole Year of Camera Trap Survey in Evaluating the Impact of Wildlife on Tick Abundance

Tick-borne zoonoses are an emerging health issue. The expansion of ticks is mainly driven by climatic changes but also by new approaches to the management of the natural environment, increasing the abundance of vertebrate host species and thus the potential exposure to tick bites for both humans and companion animals. In this context, a holistic approach to studying ticks' ecology is required. In the present work, we shed light on the link between environmental tick abundance (global and specific of Ixodes ricinus nymphs, as the highest zoonotic threat) and the temporal occupancy of wildlife host species retrieved from camera traps (namely, wild ruminants, mesocarnivores and wild boar). We modelled this relationship by integrating abiotic factors relevant to tick survival, such as the vegetation cover and saturation deficit, and estimated the accuracy of prediction. To collect these data, we deployed camera traps in a peri-urban Natural Park in Northwest Italy to monitor wildlife for 1 whole year while collecting ticks in front of camera traps by dragging transects every 2 weeks. Overall, wildlife temporal occupancy showed an additive impact on tick abundance for species that are preferential hosts (deer and mesocarnivores) and a detractive impact for wild boar, which also presented a lower tick burden, particularly with regard to the tick species collected in the environment (mainly I. ricinus and Haemaphysalis punctata). Accuracy of prediction was higher for I. ricinus nymphs rather than the global model. Temporal fluctuations in the tick population were also highlighted. Wildlife temporal occupancy was not constant and varied between seasons according to feeding habits. In conclusion, we highlighted the utility of camera trap data to investigate tick ecology and acarological risk. This information is crucial in informing monitoring and prevention strategies to decrease the risk of tick bites in humans and thus zoonotic risk of tick-borne diseases.

Relating Wildlife Camera Trap Data to Tick Abundance: Testing the Relationship in Different Habitats

The increase in acarological risk of tick bites is significantly driven by profound changes in landscape, which alter the density and distribution of wildlife that support tick populations. As a result of habitat shifts and land abandonment, which create environments conducive to tick proliferation, the risk of disease transmission to humans and animals is increasing. In this context, it is important to explore tick ecology by applying a comprehensive methodology. In this study, we examined the relationship between wildlife temporal occupancy and tick abundance in two distinct regions: an alpine hunting district and a natural park in the Apennines. For each sampling point, we calculated wildlife temporal occupancy from camera trap pictures and estimated ticks' abundance from dragging transects in the area immediately surrounding camera traps. In modelling the relationship between those two variables, we included abiotic factors such as saturation deficit, normalized difference vegetation index, and altitude. Results show the importance of altitude and wildlife temporal occupancy (itself related to different habitat and land management characteristics) on the ecology of questing ticks. If employed in management decisions for natural environments, such information is useful to modulate the acarological risk and thus the risk of tick-borne pathogens' transmission.

Quantifying the direct and indirect effects of sika deer (Cervus nippon) on the prevalence of infection with Rickettsia in questing Haemaphysalis megaspinosa: A field experimental study

Sika deer (Cervus nippon) are important hosts for all life stages of Haemaphysalis megaspinosa, a suspected Rickettsia vector. Because some Rickettsia are unlikely to be amplified by deer in Japan, the presence of deer may decrease the prevalence of Rickettsia infection in questing H. megaspinosa. As sika deer decrease vegetation cover and height and thereby indirectly cause changes in the abundance of other hosts, including reservoirs of Rickettsia, the prevalence of Rickettsia infection in questing ticks can also change. We investigated these possible effects of deer on the prevalence of infection with Rickettsia in questing ticks in a field experiment in which deer density was manipulated at three fenced sites: a deer enclosure (Deer-enclosed site); a deer enclosure where deer had been present until 2015 and only indirect effects remained (Indirect effect site); and a deer exclosure in place since 2004 (Deer-exclosed site). Density of questing nymphs and the prevalence of infection with Rickettsia sp. 1 in questing nymphs at each site were compared from 2018 to 2020. The nymph density at the Deer-exclosed site did not significantly differ from that at the Indirect effect site, suggesting that the deer herbivory did not affect the nymph density by reducing vegetation and increasing the abundance of other host mammals. However, the prevalence of infection with Rickettsia sp. 1 in questing nymphs was higher at the Deer-exclosed site than at the Deer-enclosed site, possibly because ticks utilized alternative hosts when deer were absent. The difference in Rickettsia sp. 1 prevalence between the Indirect effect and Deer-exclosed sites was comparable to that between the Indirect effect and Deer-enclosed sites, indicating that the indirect effects of deer were as strong as the direct effects. Examining the indirect effects of ecosystem engineers in the study of tick-borne diseases may be more important than previously recognized.

Prediction of the visit and occupy of the sika deer (Cervus nippon) during the summer season using a virtual ecological approach

Prediction of the spaces used by animals is an important component of wildlife management, but requires detailed information such as animal visit and occupy in a short span of the target species. Computational simulation is often employed as an effective and economical approach. In this study, the visit and occupy of sika deer (Cervus nippon) during the plant growing season were predicted using a virtual ecological approach. A virtual ecological model was established to predict the visit and occupy of sika deer based on the indices of their food resources. The simulation results were validated against data collected from a camera trapping system. The study was conducted from May to November in 2018 in the northern Kanto region of Japan. The predictive performance of the model using the kernel normalized difference vegetation index (kNDVI) was relatively high in the earlier season, whereas that of the model using landscape structure was relatively low. The predictive performance of the model using combination of the kNDVI and landscape structure was relatively high in the later season. Unfortunately, visit and occupy of sika deer could not predict in November. The use of both models, depending on the month, achieved the best performance to predict the movements of sika deer.