High Crimean-Congo hemorrhagic fever incidence linked to greater genetic diversity and differentiation in Hyalomma marginatum populations in Türkiye

BACKGROUND

Ticks are crucial vectors of a wide range of pathogens, posing significant threats to human and animal health globally. Understanding the genetic basis of tick biology and host-parasite interactions is essential for developing effective control programs. This study investigates the fine-scale genetic structure of Hyalomma marginatum Koch, 1844, the primary vector of Crimean-Congo hemorrhagic fever (CCHF) in Türkiye. Despite its significant public health importance, information regarding its population structure and genetic diversity is quite limited.

METHODS

We used restriction site-associated DNA sequencing (RAD-Seq) to obtain genome-wide sequence data from 10 tick populations in Türkiye, collected from regions with low, moderate, and high incidence rates of CCHF. Based on these data, we determined population structure and diversity of populations using principal component analysis (PCA) and admixture analysis. Furthermore, we calculated pairwise FST and utilized discriminant analysis of principal components (DAPC) to understand genetic differentiation between populations.

RESULTS

PCA and admixture analysis indicated minimal genetic structure between populations, but we detected notable genetic differentiation and high genetic diversity from regions with high CCHF rates. Furthermore, our DAPC identified 31 significant single-nucleotide polymorphisms (SNPs) associated with regions with high CCHF incidence, with 25 SNPs located near genes involved in critical biological functions such as nucleic acid binding, transmembrane transport, and proteolysis. These findings suggest that genetic variations in these regions may confer adaptive advantages in environments with high pathogen loads.

CONCLUSIONS

This study provides the first comprehensive analysis of H. marginatum genetic diversity in Türkiye, revealing significant differentiation in populations from CCHF-endemic regions. These results underscore the importance of considering fine-scale genetic diversity to fully understand the drivers of genetic variation in ticks and their implications for vectorial capacity.

A new species of tick, Ixodes (Ixodes) mojavensis (Acari: Ixodidae), from the Amargosa Valley of California

Ixodes (Ixodes) mojavensis, n. sp. (Acari: Ixodidae), is described from all parasitic stages collected from the endangered vole Microtus californicus scirpensis Bailey, 1900 (Rodentia: Cricetidae), Mus musculus L. 1758 (Rodentia: Muridae), and Reithrodontomys megalotis (Baird; 1857) (Rodentia: Cricetidae) in the Amargosa Valley of California. When first collected in 2014, this tick was tentatively identified as Ixodes minor Neumann, 1902 because the nucleotide similarity between its 16S rDNA sequence and a homologous GenBank sequence from an I. minor from the eastern U.S. was 99.51%. Nevertheless, adults of I. mojavensis differ morphologically from I. minor by hypostomal dentition, absence of a spur on palpal segment I, and punctation patterns; nymphs by the shapes of basis capituli, auriculae, cervical grooves and external files of hypostomal denticles; and larvae by the length of idiosomal setae and hypostomal dentition. DNA sequencing of fragments of 4 different genes, 12S rDNA, 16S rDNA, cytochrome c oxidase subunit I (COI), and intergenic transcribed spacer 2 (ITS2) of I. mojavensis and of closely related species of Ixodes shows that the mitochondrial gene sequences of the new tick species are almost identical to the I. minor homologous genes. Phylogenetically, the two species do not cluster in mutually exclusive monophyletic clades. However, ITS2 sequences of I. mojavensis and I. minor diverge deeply (≥ 5.74% maximum likelihood divergence) and are as different as homologous genes from other recognized species. The discrepancy between the two sets of genes is suggestive of past mitochondrial introgression or incomplete mitochondrial lineage sorting.

Direct Capture and Early Detection of Lyme Disease Spirochete in Skin with a Microneedle Patch

Borrelia burgdorferi sensu lato family of spirochetes causes Lyme disease (LD) in animals and humans. As geographic territory of ticks expands across the globe, surveillance measures are needed to measure transmission rates and provide early risk testing of suspected bites. The current standard testing of LD uses an indirect two-step serological assay that detects host immune reactivity. Early detection remains a challenge because the host antibody response develops several weeks after infection. A microneedle (MN) device was developed to sample interstitial fluid (ISF) and capture spirochetes directly from skin. After sampling, the MN patch is easily dissolved in water or TE buffer, and the presence of spirochete DNA is detected by PCR. Performance was tested by spiking porcine ear skin with inactivated Borrelia burgdorferi, which had an approximate recovery of 80% of spirochetes. With further development, this simple direct PCR method could be a transformative approach for early detection of the causative agent of Lyme disease and enable rapid treatment to patients when infection is early, and numbers of systemic spirochetes are low.

Differentiation of Laboratory-Obtained Ixodes ricinus × Ixodes persulcatus Hybrid Ticks: Selection of Suitable Genes

Ixodes ricinus and Ixodes persulcatus ticks are the main vectors of tick-borne encephalitis virus and some bacterial pathogens. The regions where these tick species live overlap, forming large sympatric areas. It has previously been shown that these tick species have no morphological barrier, and interspecies crossing is possible with the appearance of sterile hybrids. It has also been shown that hybrid larvae and nymphs can be differentiated using discriminant functions based on a set of morphological features. However, such an approach is laborious and rather ineffective with adult ticks, making a molecular approach necessary. In the current work, we tested the ability of different systems to differentiate laboratory-obtained hybrid ticks. Our data suggest that commonly used primer sets that target rRNA are unsuitable for hybrid tick determination, likely due to the rRNA region being linked with the X chromosome in I. ricinus and I. persulcatus ticks. We tested several primer sets targeting different non rRNA genes to assess their ability to determine hybrids. The best primer set, Toll_R, targeting the putative Toll gene, showed little to no bias when used for DNA amplification from hybrid ticks. Thus, Toll gene can be further used for hybrid detection.

Emergence of Ixodes scapularis (Acari: Ixodidae) in a Small Mammal Population in a Coastal Oak-Pine Forest, Maine, USA

In the United States, surveillance has been key to tracking spatiotemporal emergence of blacklegged ticks [Ixodes scapularis Say (Ixodida:Ixodidae)] and their pathogens such as Borrelia burgdorferi Johnson, Schmid, Hyde, Steigerwalt & Brenner (Spirochaetales: Spirochaetaceae), the agent of Lyme disease. On the Holt Research Forest in midcoastal Maine, collection of feeding ticks from live-trapped small mammal hosts allowed us to track the emergence and establishment of I. scapularis, 1989-2019. From 1989-1995, we collected only I. angustus Neumann (Ixodida: Ixodidae)(vole tick), Dermacentor variabilis Say (Ixodida: Ixodidae) (American dog tick), and I. marxi Banks (Ixodida: Ixodidae) (squirrel tick) from seven species of small mammals. The most abundant tick host was the white-footed mouse [Peromyscus leucopus Rafinesque (Rodentia:Cricetidae)] followed by the red-backed vole (Myodes gapperi Vigors (Rodentia: Cricetidae)). Emergence of I. scapularis was signaled via the appearance of subadult I. scapularis in 1996. Emergence of B. burgdorferi was signaled through its appearance in I. scapularis feeding on mice in 2005. There was a substantial increase in I. scapularis prevalence (proportion of hosts parasitized) and burdens (ticks/host) on white-footed mice and red-backed voles in 2007. The ~11-yr time-to-establishment for I. scapularis was consistent with that seen in other studies. White-footed mice comprised 65.9% of all captures and hosted 94.1% of the total I. scapularis burden. The white-footed mouse population fluctuated interannually, but did not trend up as did I. scapularis prevalence and burdens. There were concurrent declines in I. angustus and D. variabilis. We discuss these results in the broader context of regional I. scapularis range expansion.

Identification of Hard Ticks in the United States: A Practical Guide for Clinicians and Pathologists

ABSTRACT

According to guidelines published by the Infectious Disease Society of America, Lyme disease prophylaxis is possible if a tick can be identified as Ixodes scapularis (nymphal or adult) within 72 hours of tick removal. However, a recent survey of medical practitioners indicates generally poor proficiency in tick identification. In this study, we provide a simple, practical guide to aid medical practitioners in identifying the most commonly encountered human biting ticks of North America.

Mate choice errors may contribute to slow spread of an invasive Eurasian longhorn beetle in North America

Tetropium fuscum (Coleoptera: Cerambycidae) is a Eurasian longhorn beetle and forest pest that first became invasive to Nova Scotia, Canada around 1990. In the time since its introduction, T. fuscum has spread only about 150 km from its point of introduction. In its invasive range, T. fuscum co-exists with its congener Tetropium cinnamopterum. Although they are ecologically similar species, T. fuscum tends to infest healthier trees and has a smaller host range than T. cinnamopterum. If they successfully interbreed, this could lead to hybrid individuals that are more problematic than either parent species. On the other hand, if T. fuscum can make mating errors in the field, but is not producing hybrid offspring, then this waste of mating resources could help explain the slow spread of T. fuscum in North America. We conducted no-choice and choice mating experiments between T. fuscum and T. cinnamopterum males and females and determined that both T. fuscum and T. cinnamopterum males make mate-choice errors with heterospecific females in a laboratory setting. Our results suggest that mating errors may play a role in the slow spread of T. fuscum in North America.

Monitoring Risk: Tick and Borrelia burgdorferi Public Participatory Surveillance in the Canadian Maritimes, 2012-2020

Ticks are vectors of many diseases, including Lyme disease (Ld). Lyme disease is an emerging disease in Canada caused by infection with the Lyme borreliosis (Lb) members of the Borrelia genus of spirochaete bacteria, of which Borrelia burgdorferi is regionally the most prevalent. The primary tick vector in central and eastern Canada, Ixodes scapularis, is increasing in numbers and in the geographical extent of established populations. This study documents the distribution of ticks recovered by passive surveillance, and their B. burgdorferi infection prevalence, in three Canadian Maritime provinces from 2012-2020. These regions represent areas in which tick populations are widely established, establishing, and considered non-established. Using a community science approach by partnering with veterinarians and members of the public, we collected over 7000 ticks from the 3 provinces. The three species found most often on companion animals and humans were I. scapularis (76.9%), Ixodes cookei (10.4%) and Dermacentor variabilis (8.9%). The most common hosts were dogs (60.5%), cats (16.8%) and humans (17.6%). As is typical of passive surveillance tick collections, the majority of ticks recovered were adult females; for I. scapularis 90.2%, 5.3%, 3.9% and 0.6% of the total of 5630 ticks recovered for this species were adult females, adult males, nymphs and larvae, respectively. The majority of B. burgdorferi-infected ticks were I. scapularis, as expected. Borrelia infection prevalence in I scapularis was higher in Nova Scotia (20.9%), the province with the most endemic regions, than New Brunswick (14.1%) and Prince Edward Island (9.1%), provinces thought to have established and non-established tick populations, respectively. The province-wide Borrelia infection prevalence generally increased in these latter tow provinces over the course of the study. The host did not have a significant effect on B. burgdorferi infection prevalence; I. scapularis ticks from dogs, cats, humans was, 13.3% (n = 3622), 15.6% (n = 817), 17.9% (n = 730), respectively. No I. scapularis larvae were found infected (n = 33) but B. burgdorferi was detected in 14.8% of both adults (n = 5140) and nymphs (n = 215). The incidence of B. burgdorferi infection also did not differ by engorgement status 15.0% (n = 367), 15.1% (n = 3101) and 14.4% (n = 1958) of non-engorged, engorged and highly engorged ticks, respectively, were infected. In New Brunswick, at the advancing front of tick population establishment, the province-wide infection percentages generally increased over the nine-year study period and all health district regions showed increased tick recoveries and a trend of increased percentages of Borrelia-infected ticks over the course of the study. Within New Brunswick, tick recoveries but not Borrelia infection prevalence were significantly different from endemic and non-endemic regions, suggesting cryptic endemic regions existed prior to their designation as a risk area. Over the 9 years of the study, tick recoveries increased in New Brunswick, the primary study region, and I. scapularis recoveries spread northwards and along the coast, most but not all new sites of recoveries were predicted by climate-based models, indicating that ongoing tick surveillance is necessary to accurately detect all areas of risk. Comparison of tick recoveries and public health risk areas indicates a lag in identification of risk areas. Accurate and timely information on tick distribution and the incidence of Borrelia and other infections are essential for keeping the public informed of risk and to support disease prevention behaviors.

Vector competence of human-biting ticks Ixodes scapularis, Amblyomma americanum and Dermacentor variabilis for Powassan virus

Background

Powassan virus (POWV; genus Flavivirus) is the sole North American member of the tick-borne encephalitis sero-complex and an increasing public health threat in the USA. Maintained in nature by Ixodes spp. ticks, POWV has also been isolated from species of other hard tick genera, yet it is unclear if these species can serve as vectors. Dermacentor variabilis and Amblyomma americanum share geographic and ecologic overlap with Ixodes spp. ticks and POWV transmission foci, raising the possibility that POWV could become established in these tick species and leading to range expansion and increased human risk. Therefore, we assessed the competency of Ixodes scapularis, D. variabilis and A. americanum for POWV lineage II (POWV II).

Methods

Larvae from all three species were co-infested on POWV-infected Balb/c mice. The engorged larvae were allowed to molt to nymphs and screened for the presence of POWV II RNA by reverse transcription-qPCR. Eight infected nymphs from each species were allowed to individually feed on a naïve mouse. Mice were screened for the presence of POWV II RNA to determine infection status.

Results

The results demonstrated that larvae from all three tick species were able to efficiently acquire POWV II via feeding on viremic mice, maintain infection through molting and successively transmit POWV to naïve mice at the nymphal stage at comparable rates across all three species.

Conclusions

Our findings reveal that non-Ixodes tick species can serve as competent vectors for POWV and highlight the potential role of these species in the ecology and epidemiology of POWV. Future studies examining the possible implications of these findings on POWV epidemiology and the adaptability of POWV in these new vectors are warranted.

Graphical abstract

Morphology of Pholeoixodes species associated with carnivores in the western Palearctic: Pictorial key based on molecularly identified Ixodes (Ph.) canisuga, I. (Ph.) hexagonus and I. (Ph.) kaiseri males, nymphs and larvae

Three Palearctic members of the subgenus Pholeoixodes, i.e., Ixodes canisuga, Ixodes hexagonus and Ixodes kaiseri are frequently collected from dogs, cats, red foxes, badgers and other carnivorous/insectivorous hosts in Europe. While a pictorial identification key has been reported for female Pholeoixodes ticks, a similar work has not been done on their male, nymphal and larval specimens. This study was initiated in order to clarify and re-examine those morphological characters of these three tick species, which can be used relatively easily to identify/distinguish them. In the case of larvae the aims included finding alternatives to chaetotaxy, which is difficult to observe and its usefulness is also affected by uncertainties in literature data. For this, 609 Pholeoixodes ticks (males, nymphs and larvae) were collected from carnivores, hedgehogs and their environment in six European countries (representing Western, Central and Southeastern Europe), followed by detailed morphological examination and/or molecular analyses to confirm the identity of their species. Based on the morphology of 84 molecularly analyzed specimens and a new identification key compiled accordingly, altogether 116 I. canisuga, 277 I. hexagonus and 216 I. kaiseri males, nymphs and larvae were identified. Ixodes kaiseri was not found in Western Europe, where I. canisuga predominated. In Central Europe, all three Pholeoixodes species were collected, the largest number of specimens represented by I. hexagonus. On the other hand, in Southeastern Europe I. kaiseri had the highest abundance. In conclusion, the morphology of internal spur on the first coxae (as the traditionally used character to distinguish I. hexagonus from other Pholeoixodes species) is trustworthy to recognize males but is less informative in the case of nymphs and larvae. The latter can be identified more properly by observing the morphology of basis capituli. In particular, nymphs and larvae of I. canisuga have anteriorly flattened basis capituli, forming a plateau that surrounds the base of the hypostome. On the other hand, nymphs and larvae of I. hexagonus and I. kaiseri lack a similar plateau, but (unlike I. canisuga) have cornuae, which are either posterolaterally or caudally directed, respectively.

Unexpected diversity in the host-generalist oribatid mite Paraleius leontonychus (Oribatida, Scheloribatidae) phoretic on Palearctic bark beetles

Bark beetles are feared as pests in forestry but they also support a large number of other taxa that exploit the beetles and their galleries. Among arthropods, mites are the largest taxon associated with bark beetles. Many of these mites are phoretic and often involved in complex interactions with the beetles and other organisms. Within the oribatid mite family Scheloribatidae, only two of the three nominal species of Paraleius have been frequently found in galleries of bark beetles and on the beetles themselves. One of the species, P. leontonychus, has a wide distribution range spanning over three ecozones of the world and is believed to be a host generalist, reported from numerous bark beetle and tree species. In the present study, phylogenetic analyses of one mitochondrial and two nuclear genes identified six well supported, fairly divergent clades within P. leontonychus which we consider to represent distinct species based on molecular species delimitation methods and largely congruent clustering in mitochondrial and nuclear gene trees. These species do not tend to be strictly host specific and might occur syntopically. Moreover, mito-nuclear discordance indicates a case of past hybridization/introgression among distinct Paraleius species, the first case of interspecific hybridization reported in mites other than ticks.

Inadequate treatment of taxonomic information prevents replicability of most zoological research

We evaluated the quality of information about taxonomic identifications in 710 papers published in seven zoological journals in 2017. We found that only 10.7% of papers cited identification methods, 29.2% made available specimen-level material for later verification, and 6.9% indicated taxon concepts applied to studied animals. Only 4.0% provided details about all three practices, while almost two-thirds provided none. Invertebrate papers were more likely than vertebrate papers to provide identification methods and deposit vouchers, but taxon concepts were rarely provided, and none of the three practices were common in any category. In short, our data suggest that most zoological research is irreplicable. To address this problem, journals should require submitted manuscripts to meet the following guidelines: (1) methods used to identify studied taxa must be stated; (2) literature supporting these identifications must be cited; (3) taxon concept(s) applied to species-level taxa must be indicated; (4) specimen-level material should be available for later examination. We argue that research which falls short of these guidelines is not replicable. We provide recommendations for how authors can better document how studied animals are identified and permit others to verify their identifications, which is necessary for transparent, replicable, and ultimately scientific zoological research.

Ixodes persulcatus/pavlovskyi natural hybrids in Siberia: Occurrence in sympatric areas and infection by a wide range of tick-transmitted agents

Ixodes persulcatus and Ixodes pavlovskyi ticks, two closely related species of the I. ricinus - I. persulcatus group, are widely distributed in the southern part of Western Siberia. Recently, the existence of natural hybrids of I. persulcatus and I. pavlovskyi ticks has been demonstrated. The aim of this study was to evaluate the abundance of I. persulcatus/pavlovskyi hybrids in several locations with different ratios of parental tick species and to investigate the prevalence and genetic variability of a wide range of infectious agents in these hybrids compared to the parental tick species. Natural hybrids of I. persulcatus and I. pavlovskyi ticks were identified in all examined locations in Altai and Novosibirsk, Western Siberia, Russia. The abundance of hybrids varied from 7% to 40% in different locations and was maximal in a location with similar proportions of I. persulcatus and I. pavlovskyi ticks. For the first time, it was shown that hybrids can be infected with the same agents as their parental tick species: tick-borne encephalitis and Kemerovo viruses, Borrelia afzelii, Borrelia bavariensis, Borrelia garinii, Borrelia miyamotoi, Rickettsia helvetica, Rickettsia raoultii, Rickettsia sibirica, "Candidatus Rickettsia tarasevichiae", Anaplasma phagocytophilum, Ehrlichia muris, "Candidatus Neoehrlichia mikurensis", and Babesia microti. The prevalence of most bacterial agents in hybrids was intermediate compared to their parental tick species. Most genetic variants of the identified agents have been previously found in the parental tick species. Wide distribution of I. persulcatus/pavlovskyi natural hybrids implies that I. persulcatus, I. pavlovskyi and their hybrids coexist in all I. persulcatus - I. pavlovskyi sympatric areas.

Identification of Borrelia bissettii in Ixodes scapularis ticks from New Brunswick, Canada

Lyme disease is a tick-borne disease that is emerging in Canada. The disease is caused by spirochetes of the Lyme borreliosis group, which is expanding as new species are discovered. In Canada, Lyme disease risk has so far been assessed primarily by detection of Borrelia burgdorferi sensu stricto. Of Ixodes scapularis ticks collected between 2014 and 2016 in New Brunswick, Canada, 7 were shown to be infected with Borrelia bissettii by nested PCR and sequencing of 5 B. bissettii genes. Since different Borrelia species are associated with different clinical manifestations and are not detected with the same diagnostic tests, the identification of a previously undocumented or underreported pathogenic Borrelia species has important implications for public and veterinary medicine.

Citizen Science and Community Engagement in Tick Surveillance-A Canadian Case Study

Lyme disease is the most common tick-borne disease in North America and Europe, and on-going surveillance is required to monitor the spread of the tick vectors as their populations expand under the influence of climate change. Active surveillance involves teams of researchers collecting ticks from field locations with the potential to be sites of establishing tick populations. This process is labor- and time-intensive, limiting the number of sites monitored and the frequency of monitoring. Citizen science initiatives are ideally suited to address this logistical problem and generate high-density and complex data from sites of community importance. In 2014, the same region was monitored by academic researchers, public health workers, and citizen scientists, allowing a comparison of the strengths and weaknesses of each type of surveillance effort. Four community members persisted with tick collections over several years, collectively recovering several hundred ticks. Although deviations from standard surveillance protocols and the choice of tick surveillance sites makes the incorporation of community-generated data into conventional surveillance analyses more complex, this citizen science data remains useful in providing high-density longitudinal tick surveillance of a small area in which detailed ecological observations can be made. Most importantly, partnership between community members and researchers has proven a powerful tool in educating communities about of the risk of tick-vectored diseases and in encouraging tick bite prevention.

Combining public participatory surveillance and occupancy modelling to predict the distributional response of Ixodes scapularis to climate change

Ixodes scapularis, a known vector of Borrelia burgdorferi sensu stricto (Bbss), is undergoing range expansion in many parts of Canada. The province of New Brunswick, which borders jurisdictions with established populations of I. scapularis, constitutes a range expansion zone for this species. To better understand the current and potential future distribution of this tick under climate change projections, this study applied occupancy modelling to distributional records of adult ticks that successfully overwintered, obtained through passive surveillance. This study indicates that I. scapularis occurs throughout the southern-most portion of the province, in close proximity to coastlines and major waterways. Milder winter conditions, as indicated by the number of degree days <0 °C, was determined to be a strong predictor of tick occurrence, as was, to a lesser degree, rising levels of annual precipitation, leading to a final model with a predictive accuracy of 0.845 (range: 0.828-0.893). Both RCP 4.5 and RCP 8.5 climate projections predict that a significant proportion of the province (roughly a quarter to a third) will be highly suitable for I. scapularis by the 2080s. Comparison with cases of canine infection show good spatial agreement with baseline model predictions, but the presence of canine Borrelia infections beyond the climate envelope, defined by the highest probabilities of tick occurrence, suggest the presence of Bbss-carrying ticks distributed by long-range dispersal events. This research demonstrates that predictive statistical modelling of multi-year surveillance information is an efficient way to identify areas where I. scapularis is most likely to occur, and can be used to guide subsequent active sampling efforts in order to better understand fine scale species distributional patterns.