Effect of snow cover on the off-host survival of Dermacentor variabilis (Acari: Ixodidae) larvae.

The geographical range of the American dog tick, Dermacentor variabilis (Say), in Canada continues to expand northwards into areas with colder winter temperatures. Understanding what influences the off-host survival of D. variabilis over winter is important for predicting the northern distributional limit of this species. A field experiment was conducted to determine the effect of snow cover on the off-host survival of unfed D. variabilis larvae from a population situated near the northern distributional limit in Saskatchewan, Canada. Ticks were placed in tubes within 1 of 9 field enclosures (tickaria) in early fall. The 9 tickaria were divided into 3 equal treatment groups: no snow cover, natural snow cover (maximum depth of 25 cm) and extra snow cover (maximum depth of 32 cm). Tick survival was measured in mid-winter and in early spring (i.e., ~17 and ~26 wk after start of experiment). The results showed that snow cover had a significant impact on the relative humidity, but not temperature, in the tickaria. Larvae in tickaria with no snow cover had a higher mortality rate (27%) than larvae in tickaria with natural snow cover (6%) or extra snow cover (4%). Although snow cover enhanced off-host survival, many individuals were able to survive in sub-zero temperatures under leaf litter in the absence of continuous snow cover for a period of 108 days. These findings have implications for the construction of predictive models to determine the northern distributional limits of D. variabilis, a species that is an important vector of several pathogens.

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.

Detection of Ehrlichia minasensis in a female winter tick (Dermacentor albipictus) feeding on a moose (Alces alces) in western Canada.

Ehrlichia minasensis, a pathogen of cattle in Brazil, was detected in genomic DNA of a female Dermacentor albipictus feeding on a moose (Alces alces) in west-central Saskatchewan, Canada. This bacterium has not previously been confirmed in ticks in Canada. It is unknown whether moose are reservoirs for E. minasensis.

Anaplasma bovis-Like Infections in Humans, United States, 2015-2017.

We detected the DNA of an Anaplasma bovis-like bacterium in blood specimens from 4 patients from the United States with suspected tickborne illnesses. Initial molecular characterization of this novel agent reveals identity to A. bovis-like bacteria detected in Dermacentor variabilis ticks collected from multiple US states.

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.

Sentinel surveillance of Lyme disease risk in Canada, 2019: Results from the first year of the Canadian Lyme Sentinel Network (CaLSeN).

BACKGROUND: Lyme disease is an emerging vector-borne zoonotic disease of increasing public health importance in Canada. As part of its mandate, the Canadian Lyme Disease Research Network (CLyDRN) launched a pan-Canadian sentinel surveillance initiative, the Canadian Lyme Sentinel Network (CaLSeN), in 2019. OBJECTIVES: To create a standardized, national sentinel surveillance network providing a real-time portrait of the evolving environmental risk of Lyme disease in each province. METHODS: A multicriteria decision analysis (MCDA) approach was used in the selection of sentinel regions. Within each sentinel region, a systematic drag sampling protocol was performed in selected sampling sites. Ticks collected during these active surveillance visits were identified to species, and Ixodes spp. ticks were tested for infection with Borrelia burgdorferi, Borrelia miyamotoi, Anaplasma phagocytophilum, Babesia microti and Powassan virus. RESULTS: In 2019, a total of 567 Ixodes spp. ticks (I. scapularis [n=550]; I. pacificus [n=10]; and I. angustus [n=7]) were collected in seven provinces: British Columbia, Manitoba, Ontario, Québec, New Brunswick, Nova Scotia and Prince Edward Island. The highest mean tick densities (nymphs/100 m2) were found in sentinel regions of Lunenburg (0.45), Montréal (0.43) and Granby (0.38). Overall, the Borrelia burgdorferi prevalence in ticks was 25.2% (0%-45.0%). One I. angustus nymph from British Columbia was positive for Babesia microti, a first for the province. The deer tick lineage of Powassan virus was detected in one adult I. scapularis in Nova Scotia. CONCLUSION: CaLSeN provides the first coordinated national active surveillance initiative for tick-borne disease in Canada. Through multidisciplinary collaborations between experts in each province, the pilot year was successful in establishing a baseline for Lyme disease risk across the country, allowing future trends to be detected and studied.

Comparison of Habitat Suitability Models for Haemaphysalis longicornis Neumann in North America to Determine Its Potential Geographic Range.

Haemaphysalis longicornis Neumann, 1901 is a vector of many pathogens of public and veterinary health importance in its native range in East Asia and introduced range in Oceania. In North America, this tick was first detected in New Jersey in 2017. Currently, this tick has been reported from 15 states of the United States. In this study, we modeled the habitat suitability of H. longicornis using the MaxEnt modeling approach. We separated occurrence records from the published literature from four different geographical regions in the world and developed MaxEnt models using relevant environmental variables to describe the potential habitat suitability of this tick in North America. The predictive accuracy of the models was assessed using the U.S. county locations where this tick species has been reported. Our best model predicted that the most suitable North American areas for geographic expansion of H. longicornis are from Arkansas-South Carolina to the south of Quebec-Nova Scotia in the east, and from California to the coast of British Columbia in the west. Enhanced surveillance and further investigation are required to gain a better understanding of the role that this tick might play in the transmission of diseases to humans and animals in North America.

American Dog Ticks (Dermacentor variabilis) as Biological Indicators of an Association between the Enteric Bacterium Moellerella wisconsensis and Striped Skunks (Mephitis mephitis) in Southwestern Manitoba, Canada.

Total genomic (g)DNA from 100 American dog ticks (Dermacentor variabilis) collected from humans, dogs, raccoons, and skunks near Minnedosa (Manitoba, Canada) in 2005 was tested for the presence of Moellerella wisconsensis (Gammaproteobacteria: Enterobacteriales) using PCR. Although two gDNA samples derived from ticks attached to two striped skunks (Mephitis mephitis) contained M. wisconsensis DNA, it is unlikely that D. variabilis is a vector of this bacterium. Genomic DNA prepared from the washes of the external surfaces of these two ticks (i.e., before DNA extraction from the whole tick) and another two ticks attached to same skunks were also PCR positive for M. wisconsensis. This suggests that ticks acquired the bacterium by physical contact with contaminated or infected skunks. However, it does not exclude the possibility that the ticks may have also imbibed the bacterium from their host blood and lymph. Nonetheless, the results of this molecular study suggest that the four adult D. variabilis represent biological indicators of the presence of M. wisconsensis in association with their vertebrate hosts (i.e., striped skunks). Additional work is needed to determine if M. wisconsensis is present in the blood and lymph of striped skunks in southwestern Manitoba and if there are potential health risks for persons coming into contact with infected animals.

Molecular Characterization of Haemaphysalis Species and a Molecular Genetic Key for the Identification of Haemaphysalis of North America.

Haemaphysalis longicornis (Acari: Ixodidae), the Asian longhorned tick, is native to East Asia, but has become established in Australia and New Zealand, and more recently in the United States. In North America, there are other native Haemaphysalis species that share similar morphological characteristics and can be difficult to identify if the specimen is damaged. The goal of this study was to develop a cost-effective and rapid molecular diagnostic assay to differentiate between exotic and native Haemaphysalis species to aid in ongoing surveillance of H. longicornis within the United States and help prevent misidentification. We demonstrated that restriction fragment length polymorphisms (RFLPs) targeting the 16S ribosomal RNA and the cytochrome c oxidase subunit I (COI) can be used to differentiate H. longicornis from the other Haemaphysalis species found in North America. Furthermore, we show that this RFLP assay can be applied to Haemaphysalis species endemic to other regions of the world for the rapid identification of damaged specimens. The work presented in this study can serve as the foundation for region specific PCR-RFLP keys for Haemaphysalis and other tick species and can be further applied to other morphometrically challenging taxa.

Identification of bacteria in the Rocky Mountain wood tick, Dermacentor andersoni, using single-strand conformation polymorphism (SSCP) and DNA sequencing.

PCR-based single-strand conformation polymorphism (SSCP) analyses combined with DNA sequencing of the prokaryotic 16S ribosomal (r) RNA gene encompassing the hypervariable V4 region was used to determine the bacterial composition of Rocky Mountain wood ticks (Dermacentor andersoni) attached to Richardson's ground squirrels (Urocitellus richardsonii) and questing on vegetation in southern Saskatchewan, Canada. The bacteria present in questing adult ticks from Saskatchewan Landing Provincial Park included Rickettsia peacockii, a Francisella-like endosymbiont (FLE) and an Arsenophonus-like endosymbiont. Bacteria in the adult and nymphal ticks attached to U. richardsonii collected from Beechy included R. peacockii, a FLE, and several other genera (e.g., Ralstonia, Sphingobium, Comamonas and Pseudomonas). The bacteria detected in D. andersoni in the present study are consistent with the findings of other studies that have characterized the microbiome of this tick species in the USA using next generation sequencing. This result demonstrates that the SSCP-based approach used in this study is cost- and time-effective for examining bacterial composition in ticks.

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.

Prevalence of Anaplasma bovis in Canadian populations of the Rocky Mountain wood tick, Dermacentor andersoni.

PCR and DNA sequencing were used to determine the prevalence of Anaplasma bovis in Rocky Mountain wood ticks (Dermacentor andersoni) collected in Alberta and Saskatchewan, Canada. These analyses revealed that A. bovis DNA was present in 35 (2.1%) of 1679 ticks collected at 12 of the 24 localities. The discovery of A. bovis in host-seeking female and male D. andersoni from multiple locations in southern Canada may have important implications for diagnosis of anaplasmosis in Canada.

Range expansion of Dermacentor variabilis and Dermacentor andersoni (Acari: Ixodidae) near their northern distributional limits.

Distributional ranges of the ticks Dermacentor andersoni Stiles and Dermacentor variabilis (Say) in the Canadian Prairies were determined by passive surveillance and active collection. These findings were compared with historical records of both species, particularly in the province of Saskatchewan, where the northern distributional limits of both tick species occur. Before the 1960s, D. variabilis and D. andersoni were allopatric in Saskatchewan; however, since then, the distribution of D. variabilis has expanded westward and northward. Although the range of D. andersoni has remained relatively stable, range expansion of D. variabilis has resulted in a zone of sympatry at least 200 km wide. Twenty-nine species of mammals and three species of birds were identified as hosts for different life stages of these ticks.

Association of different genetic types of Francisella-like organisms with the rocky mountain wood tick (Dermacentor andersoni) and the American dog tick (Dermacentor variabilis) in localities near their northern distributional limits.

Dermacentor andersoni and Dermacentor variabilis from allopatric and sympatric populations near their northern distributional limits were examined for the presence of Francisella species using molecular techniques that targeted 373 bp of the 16S rRNA gene. Although there was no evidence for the presence of Francisella tularensis in any tick, Francisella-like endosymbionts (FLEs) were common in D. andersoni and D. variabilis adults and immatures. A significantly greater proportion of female ticks contained FLEs compared to male ticks. In addition, significantly more D. variabilis adult individuals contained multiple FLE sequence types than did D. andersoni adults. Ten different types of FLEs were identified based on the sequence data, which has implications for diagnostic tests and epidemiological studies of F. tularensis in tick populations in Canada. The three most prevalent types of FLEs have been detected previously in D. andersoni or D. variabilis from other parts of their distributional ranges, whereas the other seven FLE types have not been reported previously. A comparison of the FLEs from both allopatric and sympatric populations of these two tick species provided insight into the relative host-specificity and the modes of transmission of these tick-borne bacteria. In general, each FLE type was specific for one tick species, suggesting vertical transmission of each bacterium. However, there were a few instances of potential cross-transfer of two FLE types to the other tick species at locations where D. andersoni and D. variabilis occurred in sympatry, suggesting that there may be occasional horizontal transmission of some FLEs.

Novel genotypes of Anaplasma bovis, "Candidatus Midichloria" sp. and Ignatzschineria sp. in the Rocky Mountain wood tick, Dermacentor andersoni.

Bovine anaplasmosis, caused by Anaplasma marginale, is a vector-borne disease that is enzootic in many parts of the USA. Although Dermacentor andersoni, a major vector of A. marginale, occurs in Canada, the Canadian cattle herds are currently considered free of bovine anaplasmosis. There have been two outbreaks of the disease in the province of Saskatchewan, but these have been linked to the importation of infected animals. However, the distribution of bovine anaplasmosis may alter with range expansion of the vectors. The aim of the present study was to use molecular techniques to determine if Anaplasma were present in D. andersoni at a locality near its northeastern distributional limit in Saskatchewan. Nested PCR analyses of the bacterial 16S rRNA gene were conducted on the total genomic DNA of 105 individual ticks. Single strand conformation polymorphism analysis and DNA sequencing of the 11 PCR-positive amplicons revealed the presence of three species of bacteria, none of which have been previously reported in D. andersoni. Although no ticks were infected with A. marginale, a novel genotype of A. bovis was detected in eight individuals. This discovery represents the first report of A. bovis in Canada. The potential implications of this finding with respect to animal health and anaplasmosis surveillance in Canada are discussed. The other two bacterial species detected were genetically similar to "Candidatus Midichloria mitochondrii" and Ignatzschineria larvae, the latter of which has been associated with human disease in Europe. Further investigations are needed to determine the prevalence, reservoir hosts, and pathogenicity of the Canadian genotype of A. bovis.

Genetic variation in the mitochondrial 16S rRNA gene of the American dog tick, Dermacentor variabilis (Acari: Ixodidae).

Genetic variation in the mitochondrial (mt) 16S ribosomal RNA (rRNA) gene was examined for the American dog tick, Dermacentor variabilis (Say, 1821). Nine different haplotypes were detected among 369 adult D. variabilis collected from four localities in Canada. There were eight variable nucleotide positions in the 404 bp sequence alignment. Individuals of haplotype 1 occurred at frequency of >75% at all localities. Five haplotypes were detected at only one of the four localities. High haplotype diversity and low nucleotide diversity, combined with significantly negative Fs values for ticks at three localities, suggest a recent population expansion. Genetic differences were found between populations at different localities, but a Mantel regression analysis revealed no association between genetic differences and geographical distances. There was also no association between tick haplotype and the prevalence of the bacterium, Rickettsia montanensis Weiss and Moulder, 1984, in D. variabilis among localities or on opposite sides of Blackstrap Lake (Saskatchewan). The 16S rDNA haplotypes from Canadian populations of D. variabilis formed a clade with those from the eastern and central U.S.A., to the exclusion of D. variabilis from geographically isolated populations in the western U.S.A. Although sample sizes for D. variabilis in the eastern U.S.A. are small, there may be genetic divergence between populations in Canada and those in the eastern U.S.A., which may have implications for studies on the pathogenic agents transmitted by D. variabilis to its hosts.

Detection of a new Arsenophonus-type bacterium in Canadian populations of the Rocky Mountain wood tick, Dermacentor andersoni.

Ticks of the genus Dermacentor are important vectors of human and animal pathogens in North America. They also carry a variety of endosymbiotic (i.e. non-pathogenic) bacteria. The American dog tick, D. variabilis, is known to be infected with gammaproteobacteria of the genus Arsenophonus. However, there have been no previous reports of Arsenophonus-type bacteria in the Rocky Mountain wood tick, D. andersoni, a species that is sympatric with D. variabilis in the western parts of its distributional range. In this study, the presence of Arsenophonus-type bacteria was determined by PCR and DNA sequencing for 338 D. andersoni and 448 D. variabilis adults from western Canada. Fifty-one (15%) of the D. andersoni were found to be infected with Arsenophonus, whereas only a single D. variabilis was infected. The prevalence of Arsenophonus in D. andersoni varied among localities (0-27%). The 16S rDNA sequences of Arsenophonus in Canadian D. andersoni and D. variabilis were identical to one another, but the results of a phylogenetic analysis showed that they were genetically distinct from, and may represent a different species to, the Arsenophonus in D. variabilis and Amblyomma americanum in eastern USA.