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.

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.

Iron Reduction in Dermacentor andersoni Tick Cells Inhibits Anaplasma marginale Replication.

Anaplasma spp. are obligate intracellular, tick-borne, bacterial pathogens that cause bovine and human anaplasmosis. We lack tools to prevent these diseases in part due to major knowledge gaps in our fundamental understanding of the tick-pathogen interface, including the requirement for and molecules involved in iron transport during tick colonization. We determine that iron is required for the pathogen Anaplasma marginale, which causes bovine anaplasmosis, to replicate in Dermacentor andersoni tick cells. Using bioinformatics and protein modeling, we identified three orthologs of the Gram-negative siderophore-independent iron uptake system, FbpABC. Am069, the A. marginale ortholog of FbpA, lacks predicted iron-binding residues according to the NCBI conserved domain database. However, according to protein modeling, the best structural orthologs of Am069 are iron transport proteins from Cyanobacteria and Campylobacterjejuni. We then determined that all three A. marginale genes are modestly differentially expressed in response to altered host cell iron levels, despite the lack of a Ferric uptake regulator or operon structure. This work is foundational for building a mechanistic understanding of iron uptake, which could lead to interventions to prevent bovine and human anaplasmosis.

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.

Mutation scanning-based identification of larval and nymphal ticks (Acari: Ixodidae) from Richardson's ground squirrels (Spermophilus richardsonii).

The objective of this study was to identify the tick species parasitizing Richardson's ground squirrels (Spermophilus richardsonii) in southern Saskatchewan (Canada). Morphological examination of the adult ticks revealed the presence of three tick species, Ixodes sculptus, Ixodes kingi and Dermacentor andersoni. However, given the difficulties in identifying some of the larval and nymphal (immature) ticks using this approach, PCR-based single-strand conformation polymorphism (SSCP) and DNA sequence analyses of a portion of the mitochondrial (mt) 16S rRNA gene were used to determine their species identity. The results showed that each tick species had a unique set of SSCP profiles and DNA sequences using this mt marker. The species identity of larval and nymphal ticks was determined based on a comparison of these profiles and sequences with those of morphologically-identified adults. The detection of three tick species, which are known vectors of disease-causing agents, on the same host has important implications for understanding the ecology of vector-borne diseases, and provides an opportunity to examine fundamental questions regarding the structure and composition of the bacterial communities (i.e., both endosymbiotic and pathogenic species) in these ticks. This study shows the utility and benefits of using the present molecular method for the accurate identification of ticks at any stage of development.

The Effect of Rickettsia bellii on Anaplasma marginale Infection in Dermacentor andersoni Cell Culture.

Anaplasma marginale is a tick-borne pathogen that causes bovine anaplasmosis, which affects cattle around the world. Despite its broad prevalence and severe economic impacts, limited treatments exist for this disease. Our lab previously reported that a high proportion of Rickettsia bellii, a tick endosymbiont, in the microbiome of a population of Dermacentor andersoni ticks negatively impacts the ticks' ability to acquire A. marginale. To better understand this correlation, we used mixed infection of A. marginale and R. bellii in D. andersoni cell culture. We assessed the impacts of different amounts of R. bellii in coinfections, as well as established R. bellii infection, on the ability of A. marginale to establish an infection and grow in D. andersoni cells. From these experiments, we conclude that A. marginale is less able to establish an infection in the presence of R. bellii and that an established R. bellii infection inhibits A. marginale replication. This interaction highlights the importance of the microbiome in preventing tick vector competence and may lead to the development of a biological or mechanistic control for A. marginale transmission by the tick.

Colorado tick fever virus: a review of historical literature and research emphasis for a modern era.

Colorado tick fever virus is an understudied tick-borne virus of medical importance that is primarily transmitted in the western United States and southwestern Canada. The virus is the type species of the genus Coltivirus (Spinareoviridae) and consists of 12 segments that remain largely uncharacterized. Patterns of viral distribution are driven by the presence of the primary vector, the Rocky Mountain wood tick, Dermacentor andersoni. Infection prevalence in D. andersoni can range from 3% to 58% across the geographic distribution of the tick. Infection in humans can be severe and often presents with fever relapses but is rarely fatal. Here, we review the literature from primary characterizations in the early 20th century to current virus/vector research being conducted and identify vacancies in current research.

Colorado Tick Fever Virus in the Far West: Forgotten, but Not Gone.

In the past few decades, reported human cases of Colorado tick fever in the western United States have decreased dramatically. The goal of this study was to conduct surveillance for Colorado tick fever virus (CTFV) in Dermacentor ticks in recreational sites in Colorado, Wyoming, and California to determine whether the virus is still present in Dermacentor ticks from these states. Surveillance focused on regions where surveys had been conducted in the 1950s, 1960s, and 1970s. Adult Rocky Mountain wood ticks (Dermacentor andersoni), Pacific Coast ticks (Dermacentor occidentalis), and winter ticks (Dermacentor albipictus) were tested by PCR. A subset of PCR-positive D. andersoni ticks (n = 7) were cultured in Vero cells. CTFV-positive Rocky Mountain wood ticks were found in all states: Colorado (58% prevalence), Wyoming (21%), and California (4%). Although no winter ticks tested positive, Pacific Coast ticks tested positive in one county (Siskiyou County, 15% prevalence) and were positive only in a location that also maintained Rocky Mountain wood ticks and golden mantled ground squirrels, a known CTFV host. In summary, CTFV is prevalent in D. andersoni and D. occidentalis in regions where they are sympatric in California and in D. andersoni in Colorado and Wyoming. Although the number of human CTFV cases has declined dramatically, this decrease in reported disease does not appear to be due to the disappearance or even the decline in prevalence of this virus in ticks in historically endemic regions of the country.

Anaplasma marginale Infection of Dermacentor andersoni Primary Midgut Cell Culture Is Dependent on Fucosylated Glycans.

Tick midgut is the primary infection site required by tick-borne pathogens to initiate their development for transmission. Despite the biological significance of this organ, cell cultures derived exclusively from tick midgut tissues are unavailable and protocols for generating primary midgut cell cultures have not been described. To study the mechanism of Anaplasma marginale-tick cell interactions, we successfully developed an in vitro Dermacentor andersoni primary midgut cell culture system. Midgut cells were maintained for up to 120 days. We demonstrated the infection of in vitro midgut cells by using an A. marginale omp10::himar1 mutant with continued replication for up to 10 days post-infection. Anaplasma marginale infection of midgut cells regulated the differential expression of tick α-(1,3)-fucosyltransferases A1 and A2. Silencing of α-(1,3)-fucosyltransferase A2 in uninfected midgut cells reduced the display of fucosylated glycans and significantly lowered the susceptibility of midgut cells to A. marginale infection, suggesting that the pathogen utilized core α-(1,3)-fucose of N-glycans to infect tick midgut cells. This is the first report using in vitro primary D. andersoni midgut cells to study A. marginale-tick cell interactions at the molecular level. The primary midgut cell culture system will further facilitate the investigation of tick-pathogen interactions, leading to the development of novel intervention strategies for tick-borne diseases.

Rickettsia and Anaplasma species in Dermacentor andersoni ticks from Washington.

Dermacentor andersoni, the Rocky Mountain wood tick, occurs predominantly in the northwestern United States and southwestern Canada. There are relatively few contemporary data to evaluate the occurrence of Rickettsia and Anaplasma species in D. andersoni in western North America, and even less information about these associations in the state of Washington, where this tick species is widely distributed and often bites humans. We used PCR assays to detect DNA of Rickettsia and Anaplasmataceae bacteria in 203 adult D. andersoni ticks collected from 17 sites in 9 counties of Washington between May 2012 and May 2015. Of these, 56 (27.6 %) were infected with a Rickettsia species and 3 (5.4 %) with a member of the Anaplasmataceae family. Rickettsia peacockii, R. bellii and R. rhipicephali were found in 17.7 %, 4.9 %, and 4.4 % of the Rickettsia positive ticks, respectively. Coinfections of R. bellii with R. peacockii or R. rhipicephali were identified in 6 ticks. Of the Anaplasmataceae-positive ticks, one was identified as being infected with Anaplasma phagocytophilum AP-Variant 1. No ticks were infected with a recognized human or animal pathogen, including R. rickettsii, A. phagocytophilum-ha, A. bovis, or A. marginale.

What Is Going on With the Genus Dermacentor? Hybridizations, Introgressions, Oh My!

In the 1930s, R. A. Cooley noted that Dermacentor occidentalis (Acarina: Ixodidae) and Dermacentor andersoni were closely related and could hybridize. Decades later, James Oliver discovered that crosses of Dermacentor variabilis, D. andersoni, and D. occidentalis could, on occasion, produce hybrids. A recent molecular analysis (both mtDNA and nDNA) in our laboratory revealed that certain specimens of Dermacentor andersoni nested with Dermacentor parumapertus. Does this close relationship, along with the mito-nuclear discordance we have observed, mean D. andersoni and D. parumapertus are a single species? By contemporary taxonomic criteria, this seems improbable based on their distinctly different morphologies, host associations, and ecologies. This paper explores ideas related to mito-nuclear discordance, hybridization, and introgression (primarily) not only in these two species but also other members of the genus Dermacentor. Both D. andersoni and D. parumapertus can be found on the same hosts and have sympatric distributions, so introgression of genetic material by occasional cross-mating between these two species is possible. Further, the difficulty in applying specific species concepts in ticks has been recently pointed out and a unified agreement on an integrative species concepts could clearly be useful in this situation. With the discovery of D. parumapertus as a potential vector of Rickettsia parkeri and the historically recognized role of D. andersoni in transmission of Rickettsia rickettsii, understanding the specific status of each lineage of these species (and others in the genus) is extremely important from a public health perspective.

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.

A Retrospective Cohort Study of Tick Paralysis in British Columbia.

BACKGROUND: Tick paralysis is a frequently overlooked severe disease characterized by bilateral ascending flaccid paralysis caused by a neurotoxin produced by feeding ticks. We aimed to characterize suspected tick paralysis cases documented at the BC Centre for Disease Control (BCCDC) in British Columbia (BC) from 1993 to 2016 and reviewed prevention, diagnosis, and treatment considerations. METHODS: Demographic, geographic, and clinical data from test requisition forms for ticks submitted to the BCCDC Public Health Laboratory (PHL) from patients across BC between 1993 and 2016 for suspected human and animal tick paralysis were reviewed. Descriptive statistics were generated to characterize tick paralysis cases in BC, including tick species implicated, seasonality of disease, and regional differences. RESULTS: From 1993 to 2016, there were 56 cases of suspected tick paralysis with at least one tick specimen submitted for testing at the BCCDC PHL. Humans and animals were involved in 43% and 57% of cases, respectively. The majority of cases involved a Dermacentor andersoni tick (48 cases or 86%) and occurred between the months of April and June (49 cases or 88%). Among known locations of tick acquisition, the Interior region of BC was disproportionately affected, with 25 cases (69%) of tick bites occurring in that area. CONCLUSIONS: Tick paralysis is a rare condition in BC. The region of highest risk is the Interior, particularly during the spring and summer months. Increasing awareness of tick paralysis among healthcare workers and the general public is paramount to preventing morbidity and mortality from this rare disease.

Infection with Colorado tick fever virus among humans and ticks in a national park and forest, Wyoming, 2010.

BACKGROUND: Colorado tick fever (CTF) is an underreported tick-borne viral disease occurring in the western United States. CTF illness includes fever, headache, and severe myalgia lasting for weeks. Wyoming has one of the highest CTF incidence rates with approximately 30% of infected persons reporting tick exposure in a Wyoming National Park or Forest before symptom onset. We assessed CTF virus infections among humans and Dermacentor andersoni ticks in Grand Teton National Park (GRTE) and Bridger-Teton National Forest (BTNF). METHODS: In June of 2010, 526 eligible employees were approached to participate in a baseline and 3-month follow-up serosurvey and risk behavior survey. Seropositivity was defined as antibody titers against CTF virus ≥10, as measured by the plaque reduction neutralization test. Ticks were collected at 27 sites within GRTE/BTNF and tested by RT-PCR for the CTF virus. RESULTS: A total of 126 (24%) employees participated in the baseline and follow-up study visits. Three (2%) employees were seropositive for CTF virus infection at baseline. During the study, 47 (37%) participants found unattached ticks on themselves, and 12 (10%) found attached ticks; however, no participants seroconverted against CTF virus. Walking through sagebrush (p=0.04) and spending time at ≥7000 feet elevation (p<0.01) were significantly associated with tick exposure. Ninety-nine percent (174/176) of ticks were D. andersoni, and all were found at ≥7000 feet elevation in sagebrush areas; 37 (21%) ticks tested positive for CTF virus and were found at 10 (38%) of 26 sites sampled. CONCLUSIONS: Although no GRTE or BTNF employees were infected with CTF virus during the study period, high rates of infected ticks were identified in areas with sagebrush at ≥7000 feet. CTF education and personal protection measures against tick exposure should be targeted to visitors and employees traveling to the high-risk environs identified in this study.

Salivary gland degeneration and ovary development in the Rocky Mountain wood tick, Dermacentor andersoni Stiles (Acari: Ixodidae). II. Determination of the 'critical weight'.

The feeding cycle of female ixodid ticks is divided into preparatory, slow, and rapid feeding phases. When a female Amblyomma hebraeum is removed from the host after achieving a minimum size of about 10-13× the unfed weight, various physiological and behavioural changes occur: (a) haemolymph ecdysteroid concentration rises dramatically, (b) the tick does not reattach to the host when given the opportunity, (c) its salivary glands degenerate within about 4 days (if mated) or 8 days (if virgin), and (d) oocyte maturation and oviposition occur (Kaufman and Lomas, 1996; Invert. Repr. Devel. 30: 191-198). None of these changes occur if the tick is removed from the host at smaller sizes. This transition, which occurs when the tick enters the rapid phase of engorgement, has been named the 'critical weight'. To date, the critical weight has been determined for A. hebraeum only. The present study established that, in both mated and virgin D. andersoni, the critical weight is similar to that of A. hebraeum. Although a small percentage of virgin A. hebraeum do exceed the critical weight, achieving perhaps 20× the unfed weight, virgin D. andersoni regularly fed well beyond their CW (>50× the unfed weight) and occasionally engorged completely (100× the unfed weight), although they did not detach spontaneously from the host within 21 days of attachment.

Salivary gland degeneration and ovarian development in the Rocky Mountain wood tick, Dermacentor andersoni Stiles (Acari: Ixodidae). I. Post-engorgement events.

It is well known that female ixodid ticks undergo salivary gland degeneration and the greater part of ovarian development following engorgement. The process has been particularly well studied in Amblyomma hebraeum, including the hormonal control of these processes. The purpose of this study, and the second one in this series, is to compare the processes in Dermacentor andersoni with those of A. hebraeum. A major difference between the two species is that virgin female D. andersoni feed to a much higher fed-to-unfed weight ratio than do virgin female A. hebraeum, the former achieving an average of 67× the unfed weight in this study, the latter normally achieving an average of only about 10-15× the unfed weight. We show here that although engorged virgins (defined here as those that exceed a fed-unfed weight ratio of 50, even though they do not detach from the host spontaneously) degenerate their salivary glands and develop their ovaries, these processes proceed more slowly in virgins that they do in mated females, as is the case for A. hebraeum.

Hybridization in natural sympatric populations of Dermacentor ticks in northwestern North America.

Hybridization in ticks has been described in a handful of species and mostly as a result of laboratory experiments. We used 148 AFLP loci to describe putative hybridization events between D. andersoni and D. variabilis in sympatric populations from northwestern North America. Recently, D. variabilis has expanded its range westward into the natural range of D. andersoni. Using a sample of 235 D. andersoni and 62 D. variabilis, we identified 31 individuals as putative hybrids: four F2 individuals and 27 backcrosses to D. andersoni (as defined by NewHybrids). We found no evidence of hybrids backcrossing into D. variabilis. Furthermore, all hybrids presented 16S mtDNA signatures characteristic of D. andersoni, which indicates the directionality of the hybrid crosses: female D. andersoni × male D. variabilis. We also discovered 13 species-specific AFLP fragments for D. andersoni. These loci were found to have a decreased occurrence in the putative hybrids and were absent altogether in D. variabilis samples. AFLP profiles were also used to determine the levels of genetic population structure and gene flow among nine populations of D. andersoni and three of D. variabilis. Genetic structure exists in both species (D. andersoni, ΦST = 0.110; D. variabilis, ΦST = 0.304) as well as significant estimates of isolation by distance (D. andersoni, ρ = 0.066, P = 0.001; D. variabilis, ρ = 0.729, P = 0.001).