Ticks feeding on northern pocket gophers (Thomomys talpoides) in central Saskatchewan and the unexpected detection of Ixodes scapularis larvae

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.

The Battle Against Flystrike - Past Research and New Prospects Through Genomics

Flystrike, or cutaneous myiasis, is caused by blow fly larvae of the genus Lucilia. This disease is a major problem in countries with large sheep populations. In Australia, Lucilia cuprina (Wiedemann, 1830) is the principal fly involved in flystrike. While much research has been conducted on L. cuprina, including physical, chemical, immunological, genetic and biological investigations, the molecular biology of this fly is still poorly understood. The recent sequencing, assembly and annotation of the draft genome and analyses of selected transcriptomes of L. cuprina have given a first global glimpse of its molecular biology and insights into host-fly interactions, insecticide resistance genes and intervention targets. The present article introduces L. cuprina, flystrike and associated issues, details past control efforts and research foci, reviews salient aspects of the L. cuprina genome project and discusses how the new genomic and transcriptomic resources for this fly might accelerate fundamental molecular research of L. cuprina towards developing new methods for the treatment and control of flystrike.

Genetic variation in the mitochondrial 16S ribosomal RNA gene of Ixodes scapularis (Acari: Ixodidae)

BACKGROUND

Ixodes scapularis is a vector of several human pathogens in the United States, and there is geographical variation in the relative number of persons infected with these pathogens. Geographically isolated populations of I. scapularis have established or are in the process of establishing in southern Canada. Knowledge of the genetic variation within and among these populations may provide insight into their geographical origins in the United States and the potential risk of exposure of Canadians to the different pathogens carried by I. scapularis.

METHODS

Part of the mitochondrial (mt) 16S ribosomal (r) RNA gene was amplified by PCR from 582 ticks collected from southern Canada, and Minnesota and Rhode Island in the United States. Sequence variation was examined in relation to the predicted secondary structure of the gene. Genetic diversity among populations was also determined.

RESULTS

DNA sequence analyses revealed 52 haplotypes. Most mutational alterations in DNA sequence occurred at unpaired sites or represented partial compensatory base pair changes that maintained the stability of the secondary structure. Significant genetic variation was detected within and among populations in different geographical regions. A greater proportion of the haplotypes of I. scapularis from the Canadian Prairie Provinces were found in the Midwest of the United States than in other regions, whereas more of the haplotypes of I. scapularis from the Canadian Central and Atlantic Provinces occurred in the Northeast of the United States. Nonetheless, 58% of I. scapularis were of a haplotype that occurs in the Midwest and Northeast of the United States; thus, their geographical origins could not be determined.

CONCLUSIONS

There is considerable genetic variation in the mt 16S rRNA gene of I. scapularis. There is some evidence to support the hypothesis that some lineages of I. scapularis in the Atlantic and Central Provinces of Canada may be derived from colonizing individuals originating in the Northeast of the United States, whereas those in the Prairie Provinces may be derived from individuals originating in the Midwest of the United States. However, additional genetic markers are needed to test hypotheses concerning the geographical origins of I. scapularis in Canada.

Comparison of the DNA sequences and secondary structure of the mitochondrial 16S rRNA gene of Ixodes kingi, Ixodes sculptus and Ixodes angustus

The DNA sequences and predicted secondary structure of domains IV and V of the mitochondrial (mt) 16S rRNA gene were compared for three species of Ixodes: Ixodes kingi, Ixodes sculptus and Ixodes angustus. Each species had a unique set of DNA sequences for the 16S gene. Many of the differences in DNA sequence within and among species occurred in a "hypervariable" region of domain V, and either represented partial or full compensatory base pair changes that maintained the helices within the secondary structure, or nucleotide alterations at unpaired positions that had no effect on the secondary structure. The results of the phylogenetic analyses revealed that I. kingi, I. sculptus and I. angustus were placed in a clade with some other species of the subgenera Pholeoixodes and Ixodiopsis. In addition, individuals of I. sculptus from Saskatchewan (Canada) and Colorado (USA) did not form a monophyletic clade, suggesting the possible existence of cryptic species.

Discovery of novel Rickettsiella spp. in ixodid ticks from Western Canada

The genomic DNA from four species of ixodid ticks in western Canada was tested for the presence of Rickettsiella by PCR analyses targeting the 16S rRNA gene. Eighty-eight percent of the Ixodes angustus (n = 270), 43% of the I. sculptus (n = 61), and 4% of the I. kingi (n = 93) individuals examined were PCR positive for Rickettsiella, whereas there was no evidence for the presence of Rickettsiella in Dermacentor andersoni (n = 45). Three different single-strand conformation polymorphism profiles of the 16S rRNA gene were detected among amplicons derived from Rickettsiella-positive ticks, each corresponding to a different sequence type. Furthermore, each sequence type was associated with a different tick species. Phylogenetic analyses of sequence data of the 16S rRNA gene and three other genes (rpsA, gidA, and sucB) revealed that all three sequence types were placed in a clade that contained species and pathotypes of the genus Rickettsiella. The bacterium in I. kingi represented the sister taxon to the Rickettsiella in I. sculptus, and both formed a clade with Rickettsiella grylli from crickets (Gryllus bimaculatus) and "R. ixodidis" from I. woodi. In contrast, the Rickettsiella in I. angustus was not a member of this clade but was placed external to the clade comprising the pathotypes of R. popilliae. The results indicate the existence of at least two new species of Rickettsiella: one in I. angustus and another in I. kingi and I. sculptus. However, the Rickettsiella strains in I. kingi and I. sculptus may also represent different species because each had unique sequences for all four genes.

A novel Rickettsia species detected in Vole Ticks (Ixodes angustus) from Western Canada

The genomic DNA of ixodid ticks from western Canada was tested by PCR for the presence of Rickettsia. No rickettsiae were detected in Ixodes sculptus, whereas 18% of the I. angustus and 42% of the Dermacentor andersoni organisms examined were PCR positive for Rickettsia. The rickettsiae from each tick species were characterized genetically using multiple genes. Rickettsiae within the D. andersoni organisms had sequences at four genes that matched those of R. peacockii. In contrast, the Rickettsia present within the larvae, nymphs, and adults of I. angustus had novel DNA sequences at four of the genes characterized compared to the sequences available from GenBank for all recognized species of Rickettsia and all other putative species within the genus. Phylogenetic analyses of the sequence data revealed that the rickettsiae in I. angustus do not belong to the spotted fever, transitional, or typhus groups of rickettsiae but are most closely related to "Candidatus Rickettsia kingi" and belong to a clade that also includes R. canadensis, "Candidatus Rickettsia tarasevichiae," and "Candidatus Rickettsia monteiroi."

Babesia odocoilei infection in a Saskatchewan elk (Cervus elaphus canadensis) herd

An 8-year-old female elk (Cervus elaphus canadensis) cow, presented for chronic severe weight loss and unthriftiness, was diagnosed with Babesia odocoilei infection based on blood smear evaluation, polymerase chain reaction (PCR), and DNA sequence analysis. Subsequently, velvet antler from a male that died acutely on the same farm was also PCR positive for Babesia spp. Both animals originated from a game ranch of Saskatchewan-bred and -raised animals with no known history of tick exposure, but with a history of numerous sudden deaths of unknown etiology. The presence of B. odocoilei in Canada might be a result of a recent introduction that could have deleterious effects on local wild ungulates or may represent discovery of a previously unrecognized endemic disease in local wildlife.

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.

Detection of a novel Rickettsia (Alphaproteobacteria: Rickettsiales) in rotund ticks (Ixodes kingi) from Saskatchewan, Canada

A novel Rickettsia was detected in the rotund tick, Ixodes kingi Bishopp, 1911, based on comparative DNA sequence analyses of 4 genes; the rickettsial-specific 17-kDa antigen gene, citrate synthase gene (gltA), the outer surface membrane protein A gene (ompA), and the 16S rRNA gene. The rickettsiae in I. kingi differed in nucleotide sequence from those of other Rickettsia species by 5.8-18.3% for the 17-kDa gene, 0.9-13.9% for gltA, 5.5-22.8% for ompA, and 0.9-1.6% for the 16S rRNA gene. Phylogenetic analyses of the sequence data revealed that this putative new species of Rickettsia, provisionally named Candidatus Rickettsia kingi, does not belong to the spotted fever group or typhus group of rickettsiae, but represents a sister taxon to R. canadensis and Candidatus Rickettsia tarasevichiae. This novel Rickettsia was found in 60 of the 87 (69%) ticks examined, which included all feeding life cycle stages of I. kingi. Although adult I. kingi occasionally parasitize dogs and humans, it remains to be determined if this Rickettsia is pathogenic to these host species.