Dispersion and sampling of adult Dermacentor andersoni in rangeland in Western North America

Comparison of the supercooling points of questing Dermacentor variabilis adults in two populations on the Canadian prairies and implications for overwinter survival

A comparison was made of the supercooling points (SCPs) of questing Dermacentor variabilis adults from two populations located ca. 800 km apart on the Canadian prairies. This is also the first study to examine whether there are seasonal fluctuations in the SCP of questing D. variabilis adults. The SCPs of adult ticks from Lizard Lake Community Pasture, a recently established population in west-central Saskatchewan, varied over spring and summer, with the median SCP warming over time. In addition, the SCPs of ticks from Lizard Lake Community Pasture were significantly higher than those of adult ticks collected from Sandy Hook in Manitoba, a population that has been established for decades. The off-host survival of adults from Sandy Hook between summer and spring has been shown previously to be significantly greater than that of adults from Lizard Lake Community Pasture. The findings of the present study suggest that there may be geographical variation in the SCPs of D. variabilis adults which may be associated with differences in overwinter survival. The relatively low SCPs of questing D. variabilis adults, and the ability of some adults to survive off-host during winter, may be factors contributing to the range expansion of this tick species in Canada.

Differences in the reproductive output and larval survival of Rocky Mountain wood ticks (Dermacentor andersoni) and American dog ticks (Dermacentor variabilis) from prairie populations near their northern distributional limits in western Canada

The effects of temperature and relative humidity (RH) on female reproductive output, egg development and larval survival were determined for Rocky Mountain wood ticks (Dermacentor andersoni) from a prairie population (Chin Lakes, Alberta, Canada) near the northern distribution limit of this species. The responses of D. andersoni eggs and unfed larvae to different temperature (25 or 32 °C) and RH (35, 55, 75, 85 or 95%) regimes were compared to our previously published data (Diyes et al. 2021) for a northern prairie population of American dog ticks (Dermacentor variabilis). Oviposition by D. andersoni females took 21-30 days at 25 °C and 95% RH compared to 10-21 days for D. variabilis. The number of eggs laid by female ticks was strongly dependent on their engorgement weight, and D. andersoni females produced more eggs than D. variabilis females of an equivalent body weight. Eggs of D. andersoni took less time to develop at 32 °C than 25 °C with ≥ 85% RH, and hatched faster than those of D. variabilis. Larval survival times declined as temperature increased and RH decreased, but D. andersoni survived longer at 32 °C and ≤ 75% RH than D. variabilis. The interspecific differences in responses to the same temperature and humidity regimes indicate that D. andersoni is xerophilic, whereas D. variabilis is hydrophilic. Hence, 'prairie' populations of the Rocky Mountain wood tick occur in the drier grassland ecoregions but are absent in Aspen Parklands Ecoregion which is located to the north and east of the distributional range of D. andersoni.

Distribution of Dermacentor andersoni (Acari: Ixodidae) in Grassland Regions of Alberta, Canada

The geographic distribution of the Rocky Mountain wood tick, Dermacentor andersoni Stiles, was determined in Alberta, Canada, by drag sampling at 86 and 89 sites during 2011 and 2012, respectively. Tick density and prevalence varied between years, averaging (range) 1.0 (0-26.2) and 5.9 (0-110) ticks/1,000 m2 in 2011 and 2012, respectively. Ticks were detected at 24.4% and 42.7% of the sites sampled in each respective year. Tick density and presence declined in a northerly direction to 51.6°N and in a westerly direction to ca. 113°W, except for a small area of high density at the edge of the Rocky Mountains in the southeastern portion of the province. Ticks were most abundant in the Dry Mixedgrass and Montane natural subregions and in areas with Brown Chernozemic, Regosol, and Solodized Solonetzic great soil groups. A logistic regression model indicated that tick presence was increased in the Dry Mixedgrass natural subregion and in regions with greater temperatures during the previous summer and normal winter precipitation but was reduced in areas with Dark Brown Chernozemic soils. The model will be useful for predicting tick presence and the associated risk of tick-borne diseases in the province.

Reproductive output and larval survival of American dog ticks (Dermacentor variabilis) from a population at the northern distributional limit

Female reproductive output and larval survival were determined for American dog ticks, Dermacentor variabilis (Say), from a recently established population near the northern distributional limit in Saskatchewan (Canada). Oviposition took 10-21 days at 25 °C and 95% relative humidity (RH). Temperature and relative humidity had a marked effect on egg development time and larval survival. Unfed larvae survived more than 100 days at 32 °C (with 95% RH) and 25 and 5 °C (with ≥ 85% RH). However, survival times declined markedly at lower relative humidities. In addition, 95% of the larvae placed in field enclosures survived for 140 days over winter during which they were exposed to sub-zero temperatures and 95-100% RH, while covered with snow. The median survival times (LT₅₀) of unfed larvae submerged underwater was 68 days. These results show that D. variabilis larvae in populations near the periphery of the northern distributional limit are adapted to cope with sub-zero temperatures in winter, and can survive in the temporary pools of water created by the spring snow melt.

Behavioral characteristics and endosymbionts of two potential tularemia and Rocky Mountain spotted fever tick vectors

Due to climate change-induced alterations of temperature and humidity, the distribution of pathogen-carrying organisms such as ticks may shift. Tick survival is often limited by environmental factors such as dryness, but a predicted hotter and wetter world may allow the expansion of tick ranges. Dermacentor andersoni and D. variabilis ticks are morphologically similar, co-occur throughout the Inland Northwest of Washington State, U.S.A., and both can be injected with pathogenic Rickettsia and Francisella bacteria. Differences in behavior and the potential role of endosymbiotic Rickettsia and Francisella in these ticks are poorly studied. We wanted to measure behavioral and ecological differences between the two species and determine which, if any, Rickettsia and Francisella bacteria - pathogenic or endosymbiotic - they carried. Additionally, we wanted to determine if either tick species may be selected for if the climate in eastern Washington becomes wetter or dryer. We found that D. andersoni is more resistant to desiccation, but both species share similar questing behaviors such as climbing and attraction to bright light. Both also avoid the odor of eucalyptus and DEET but not permethrin. Although both tick species are capable of transmitting pathogenic species of Francisella and Rickettsia, which cause tularemia and Rocky Mountain Spotted Fever, respectively, we found primarily non-pathogenic endosymbiotic strains of Francisella and Rickettsia, and only one tick infected with F. tularensis subspecies holarctica.

Natural insensitivity and the effects of concentration on the repellency and survival of American dog ticks (Dermacentor variabilis) by DEET

N,N-Diethyl-m-toluamide (DEET) is by far the most used repellent worldwide. When applied topically to the skin, the active ingredient has been shown to provide protection from a variety of hematophagous insects, including mosquitoes and flies. DEET's effectiveness against ticks is influenced by a variety of factors (e.g., duration and concentration of application, drying time, route of exposure, tick species and developmental stage), and may differ from insects due to their unique chemosensory system that primarily involves the Haller's organ. We therefore used several approaches to investigate DEET's efficacy to repel Dermacentor variabilis at different concentrations (5, 30 or 75%), as well as explore its toxicological properties and natural variability in DEET insensitivity across populations from Manitoba, Canada. Climbing bioassays indicated that higher concentrations of DEET were more effective at repelling D. variabilis, and that ticks from some sampling localities were more sensitive to lower concentrations than others. Petri dish arena assays revealed ticks exposed to high concentrations of the repellent lose their ability to discriminate lower concentrations, perhaps due to overstimulation or habituation. Finally, our tactile assays demonstrated reduced tick survival after contact with high DEET concentrations, with mortality occurring more rapidly with increased concentration. Dermacentor variabilis from these tactile assays displayed a multitude of physiological and neurological symptoms, such as 'hot foot' and various bodily secretions. Overall, our study shows a strong association between repellency, concentration and the acaricidal effects of DEET on D. variabilis.

Passive and Active Surveillance for Ixodes scapularis (Acari: Ixodidae) in Saskatchewan, Canada

Passive and active surveillance for the blacklegged tick, Ixodes scapularis Say, in the Canadian province of Saskatchewan was conducted over a 9-yr period (2009-2017). More than 26,000 ixodid ticks, representing 10 species, were submitted through passive surveillance. Most (97%) of these were the American dog tick, Dermacentor variabilis (Say). Of the 65 I. scapularis adults submitted, 75% were collected from dogs. Infection rates of Borrelia burgdorferi, Anaplasma phagocytophilum, and Babesia microti in I. scapularis were 12%, 8%, and 0%, respectively. Although the I. scapularis submitted by passive surveillance were collected from five of seven ecoregions in central and southern Saskatchewan, they were most frequent in the Moist Mixed Grassland and Aspen Parklands. In contrast, no I. scapularis were collected from the extensive field sampling conducted at multiple sites in different ecoregions across the province. Hence, there is no evidence of I. scapularis having established a breeding population in Saskatchewan. Nonetheless, continued surveillance for blacklegged ticks is warranted given their important role as a vector of medically and veterinary important pathogens, and because they have recently become established across much of the southern portions of the neighboring province of Manitoba.

Bacterial microbiomes of Ixodes scapularis ticks collected from Massachusetts and Texas, USA

Background

The blacklegged tick, Ixodes scapularis, is the primary vector of the Lyme disease spirochete Borrelia burgdorferi in North America. Though the tick is found across the eastern United States, Lyme disease is endemic to the northeast and upper midwest and rare or absent in the southern portion of the vector’s range. In an effort to better understand the tick microbiome from diverse geographic and climatic regions, we analysed the bacterial community of 115 I. scapularis adults collected from vegetation in Texas and Massachusetts, representing extreme ends of the vector’s range, by massively parallel sequencing of the 16S V4 rRNA gene. In addition, 7 female I. scapularis collected from dogs in Texas were included in the study.

Results

Male I. scapularis ticks had a more diverse bacterial microbiome in comparison to the female ticks. Rickettsia spp. dominated the microbiomes of field-collected female I. scapularis from both regions, as well as half of the males from Texas. In addition, the male and female ticks captured from Massachusetts contained high proportions of the pathogens Anaplasma and Borrelia, as well as the arthropod endosymbiont Wolbachia. None of these were found in libraries generated from ticks collected in Texas. Pseudomonas, Acinetobacter and Mycobacterium were significantly differently abundant (p < 0.05) between the male ticks from Massachusetts and Texas. Anaplasma and Borrelia were found in 15 and 63% of the 62 Massachusetts ticks, respectively, with a co-infection rate of 11%. Female ticks collected from Texas dogs were particularly diverse, and contained several genera including Rickettsia, Pseudomonas, Bradyrhizobium, Sediminibacterium, and Ralstonia.

Conclusions

Our results indicate that the bacterial microbiomes of I. scapularis ticks vary by sex and geography, with significantly more diversity in male microbiomes compared to females. We found that sex plays a larger role than geography in shaping the composition/diversity of the I. scapularis microbiome, but that geography affects what additional taxa are represented (beyond Rickettsia) and whether pathogens are found. Furthermore, recent feeding may have a role in shaping the tick microbiome, as evident from a more complex bacterial community in female ticks from dogs compared to the wild-caught questing females. These findings may provide further insight into the differences in the ability of the ticks to acquire, maintain and transmit pathogens. Future studies on possible causes and consequences of these differences will shed additional light on tick microbiome biology and vector competence.

Electronic supplementary material

The online version of this article (10.1186/s12866-019-1514-7) contains supplementary material, which is available to authorized users.

Exposure and preventive behaviours toward ticks and Lyme disease in Canada: Results from a first national survey

Lyme disease (LD) risk is increasing in Canada. In 2014, the government of Canada launched a national communication campaign to raise awareness and promote the adoption of individual preventive behaviours toward ticks and LD. The objectives of this study were to evaluate and compare the adoption of LD preventive behaviours and the exposure to tick bites of Canadians in the five main targeted regions (British Columbia, Prairie provinces, Ontario, Quebec and the Atlantic provinces). A national survey was conducted in December 2014 (n=2876) to collect data on LD awareness, behaviours and risk factors. Overall, the proportion of respondents reporting tick exposure was high (20%). The results suggest that even though LD awareness was found to be high (with only 12% of the respondents reporting that they never heard about LD), less than half of the Canadians who heard about it have adopted specific preventive behaviours toward tick bites, such as regular tick checks (reported by 52%), protective clothing (50%), using tick repellent (41%) or shower or bath (41%) after visiting a wooded area in a LD risk area. Moreover, significant differences were found between regions, gender, age groups and dog ownership status, regarding preventive behaviours and factors of exposure. A high level of knowledge of Lyme disease, living in the Prairie region, as well as having found a tick on oneself or a relative, were found to be associated with the adoption of preventive behaviours. This study underlines the importance to take into account specific regional characteristics of risk and to maintain public health communication efforts through time in order to increase the adoption of preventive behaviours of Canadians.

The bacterial microbiome of Dermacentor andersoni ticks influences pathogen susceptibility

Ticks are of medical importance owing to their ability to transmit pathogens to humans and animals. The Rocky Mountain wood tick, Dermacentor andersoni, is a vector of a number of pathogens, including Anaplasma marginale, which is the most widespread tick-borne pathogen of livestock. Although ticks host pathogenic bacteria, they also harbor bacterial endosymbionts that have a role in tick physiology, survival, as well as pathogen acquisition and transmission. The goal of this study was to characterize the bacterial microbiome and examine the impact of microbiome disruption on pathogen susceptibility. The bacterial microbiome of two populations of D. andersoni with historically different susceptibilities to A. marginale was characterized. In this study, the microbiome was disrupted and then ticks were exposed to A. marginale or Francisella novicida to determine whether the microbiome correlated with pathogen susceptibility. Our study showed that an increase in proportion and quantity of Rickettsia bellii in the microbiome was negatively correlated to A. marginale levels in ticks. Furthermore, a decrease in Francisella endosymbionts was associated with lower F. novicida infection levels, demonstrating a positive pathogen-endosymbiont relationship. We demonstrate that endosymbionts and pathogens have varying interactions, and suggest that microbiome manipulation may provide a possible method for biocontrol by decreasing pathogen susceptibility of ticks.

Can Subclinical Infestation by Paralyzing Dermacentor andersoni (Acari: Ixodidae) Induce Immunity to Tick Paralysis in Sheep?

Cattle and sheep can develop immunity to paralysis caused by Dermacentor andersoni Stiles; however, this has been reported only in animals that were initially challenged with a high dose of ticks and exhibited clear symptoms of paralysis. Paralysis in sheep occurs in a dose-dependent fashion, with no paralysis occurring in sheep exposed to <0.2 ticks per kilogram sheep weight, and 100% paralysis in sheep exposed to >0.8 ticks per kilogram. This experiment was conducted to determine if sheep exposed to a low dose of ticks would also develop immunity to paralysis. Sheep were exposed to either a low (0.2 ticks per kilogram) or high dose of ticks (0.8 ticks per kilogram), then re-exposed to a second challenge of a paralyzing dose of ticks. All naïve sheep (eight of the eight) were paralyzed, while paralysis occurred in only four of the eight sheep previously exposed to a low dose, and one of the eight sheep previously exposed to a high dose. Results indicate that immunity can develop when sheep are exposed to a subclinical dose of paralyzing ticks, but in a smaller percentage of animals than those exposed to a high dose of ticks. Vaccine development perhaps remains the best option for nonacaricidal control of tick paralysis.