Prevalence of five human pathogens in host-seeking Ixodes scapularis and Ixodes pacificus by region, state, and county in the contiguous United States generated through national tick surveillance

Trigeminal Neuralgia Unmasked: A Case of Anaplasma Phagocytophilum Infection

BACKGROUND

Anaplasma phagocytophilum is a bacteria transmitted to humans by tick bites, and like other tick-borne illnesses, its incidence has increased over the past several decades. A symptomatic patient infected with A. phagocytophilum typically presents with fever, chills, myalgia, other flu-like symptoms, leukopenia, thrombocytopenia, elevated liver enzymes, and inclusion bodies on a peripheral blood smear.

CASE REPORT

We report a case of a 72-year-old female with an infection of A. phagocytophilum who presented to the emergency department (ED) with intermittent pain that originated behind her right ear and radiated to their jaw and cheek. Laboratory testing revealed leukocytopenia, thrombocytopenia, elevated liver enzymes, inclusion bodies on blood smear, and a rash was identified on their left hip. The patient was treated with doxycycline for the infection and with dexamethasone and ketorolac for the trigeminal neuralgia. WHY SHOULD AN EMERGENCY PHYSICIAN BE AWARE OF THIS?: As the incidence of Human Granulocytic Anaplasmosis (HGA) increases, emergency physicians encounter more patients presenting to the ED. HGA can have life-threatening complications such as respiratory distress, shock, organ dysfunction and death. Emergency physicians must know how to diagnose and treat HGA to avoid complications, which can be difficult when unusual presentations are seen. Our patient did not have the common symptoms of fever, myalgia, and malaise. Instead, they presented with right ear and jaw pain, which was diagnosed as trigeminal neuralgia. The diagnosis of HGA in the ED relied on laboratory findings. These typical findings included inclusion bodies on a peripheral blood smear, leukopenia, thrombocytopenia and elevated liver enzymes. The patient's infection resolved with doxycycline (100 mg oral twice daily).

Emerging babesiosis in the mid-Atlantic: autochthonous human babesiosis cases and Babesia microti (Piroplasmida: Babesiidae) in Ixodes scapularis (Acari: Ixodidae) and Ixodes keiransi (Acari: Ixodidae) ticks from Delaware, Maryland, Virginia, West Virginia, and the District of Columbia, 2009 to 2024

The range of Babesia microti (Franca, 1910)-infected ticks is expanding, resulting in locally acquired human babesiosis cases occurring in new areas: Maryland (2009), the District of Columbia (2013), Virginia (2016), and West Virginia (2017). We collected host-seeking ticks from old fields, ecotones, forested habitats and animal hosts in Delaware, Maryland, and Virginia, 2010 to 2024. Ixodes scapularis Say, the tick vector of babesiosis, was captured in all 3 states. PCR revealed B. microti in 2.7% (36/1310) of I. scapularis, with site prevalence ranging from <1% to 12.5% infected. The first B. microti-positive I. scapularis was collected in Northampton County, Virginia, 2012. Of the B. microti-infected ticks, 50% (18/36) were coinfected with Borrelia burgdorferi and one was triple-infected with B. microti, B. burgdorferi, and Anaplasma phagocytophilum. We collected Ixodes keiransi Beati, Nava, Venzal, and Guglielmone ticks from Delaware and Virginia. We found B. microti and B. burgdorferi in those from Virginia, and B. burgdorferi in ticks from a shrew in Delaware. To our knowledge, this is the first report of B. microti and B. burgdorferi-positive I. keiransi from Virginia, and the first report of B. burgdorferi-positive I. keiransi from Delaware. Ixodes keiransi ticks rarely bite humans but are involved in the maintenance and spread of pathogens when sympatric with I. scapularis. We tested a subset of both tick species for Babesia duncani; none were positive. Jurisdictions in the southern mid-Atlantic region should expect babesiosis cases, and Lyme disease and anaplasmosis coinfections, and healthcare providers should consider these tick-borne infections as part of the differential diagnosis.

Perspectives from federal and state public health departments on their participation in and the utility of Ixodes scapularis (Acari: Ixodidae) and Ixodes pacificus tick and tick-borne pathogen surveillance in the United States

In response to notable increases in tick-associated illnesses in the United States, recent public health policies encouraged multi-sector collaborative approaches to preventing vector-borne diseases. Primary prevention strategies focus on educating the public about risks for tick-borne diseases and encouraging adoption of personal protection strategies. Accurate descriptions of when and where people are at risk for tick-borne diseases aid in the optimization of prevention messaging. Tick and tick-borne pathogen data can be used to fill gaps in epidemiological surveillance. However, the utility of acarological data is limited by their completeness. National maps showing the distribution of medically important tick species and the pathogens they carry are often incomplete or non-existent. Recent policies encourage accelerated efforts to monitor changes in the distribution and abundance of medically important ticks and the presence and prevalence of human pathogens that they carry, and to provide actionable, evidence-based information to the public, health care providers and public health policy makers. In 2018, the Centers for Disease Control and Prevention initiated a national tick surveillance program focused on Ixodes ticks. The national program coordinated and expanded upon existing efforts led by public health departments and academic institutions. Here, we describe experiences of state public health departments engaged in Ixodes tick surveillance, including information on why they initiated Ixodes surveillance programs, programmatic objectives, and strategies for maintaining tick surveillance programs. We share experiences and challenges in interpreting or communicating tick surveillance data to stakeholders and explore how the acarological data are used to complement epidemiological data.

Responses of juvenile blacklegged ticks (Acari: Ixodidae) to hosts of varying quality

Blacklegged ticks (Ixodes scapularis) are the most medically and economically important vectors in North America. Each of their 3 life stages requires a blood meal from one of many potential host species, during which they can acquire or transmit pathogens. Host species, however, vary tremendously in their quality for ticks, as measured by differences in feeding and molting success. There should be clear fitness benefits for ticks that preferentially feed upon high-quality hosts (e.g., white-footed mice, Peromyscus leucopus), or at least avoid feeding on very low-quality hosts (e.g., Virginia opossums, Didelphis virginiana). Indeed, laboratory experiments have found some evidence of host preferences in I. scapularis; but these involve presenting ticks with hosts simultaneously and measuring movement towards hosts on a horizontal plane. In nature, however, host-seeking ticks encounter hosts sequentially and their movements are principally in a vertical plane. Here, we present the results of a study in which we measured the vertical movements of host-seeking juvenile blacklegged ticks before and after a host (P. leucopus, Tamias striatus, Sciurus carolinensis, or D. virginiana) was present, and whether the strength of their responses varies with host quality. We found ticks did not measurably alter the speed of their vertical movement in the presence of any hosts, regardless of host quality. Both larvae and nymphs quested slightly higher in the presence of hosts, but this did not vary by host species. These results call into question the existence of active host preferences, at least in this stage of the host-seeking process.

Seasonal activity patterns of Ixodes scapularis and Ixodes pacificus in the United States

Knowledge of seasonal activity patterns of human-biting life stages of tick species serving as vectors of human disease agents provides basic information on when during the year humans are most at risk for tick bites and tick-borne diseases. Although there is a wealth of published information on seasonal activity patterns of Ixodes scapularis and Ixodes pacificus in the United States, a critical review of the literature for these important tick vectors is lacking. The aims of this paper were to: (i) review what is known about the seasonal activity patterns of I. scapularis and I. pacificus in different parts of their geographic ranges in the US, (ii) provide a synthesis of the main findings, and (iii) outline key knowledge gaps and methodological pitfalls that limit our understanding of variability in seasonal activity patterns. Based on ticks collected while questing or from wild animals, the seasonal activity patterns were found to be similar for I. pacificus in the Far West and I. scapularis in the Southeast, with synchronous activity of larvae and nymphs, peaking in spring (April to June) in the Far West and from spring to early summer (April to July) in the Southeast, and continuous activity of adults from fall through winter and spring with peak activity from fall through winter (November/December to March). In the colder climates of the Upper Midwest and Northeast, I. scapularis adults have a bimodal seasonal pattern, with activity peaks in fall (October to November) and spring (April to May). The seasonal activity patterns for immatures differ between the Upper Midwest, synchronous for larvae and nymphs with peak activity in spring and summer (May to August), and the Northeast, where the peak activity of nymphs in spring and early summer (May to July) precedes that of larvae in summer (July to September). Seasonality of human tick encounters also is influenced by changes over the year in the level of outdoor activities in tick habitat. Studies on the seasonality of ticks infesting humans have primarily focused on the coastal Northeast and the Pacific Coast states, with fewer studies in the Southeast, inland parts of the Northeast, and the Upper Midwest. Discrepancies between seasonal patterns for peak tick questing activity and peak human infestation appear to occur primarily for the adult stages of I. scapularis and I. pacificus. Study design and data presentation limitations of the published literature are discussed. Scarcity of data for seasonal activity patterns of I. pacificus outside of California and for I. scapularis from parts of the Southeast, Northeast, and Upper Midwest is a key knowledge gap. In addition to informing the public of when during the year the risk for tick bites is greatest, high-quality studies describing current seasonal activity patterns also will generate the data needed for robust model-based projections of future climate-driven change in the seasonal activity patterns and provide the baseline needed to empirically determine in the future if the projections were accurate.

Geographic variation in the distribution of Anaplasma phagocytophilum variants in host-seeking Ixodes scapularis nymphs and adults in the eastern United States elucidated using next generation sequencing

Human anaplasmosis cases, caused by Anaplasma phagocytophilum, are increasing in the United States. This trend is explained, in part, by expansion in the geographic range of the primary vector, Ixodes scapularis. Multiple variants of A. phagocytophilum have been identified in field collected ticks, but only a single variant (human active, or "Ap-ha," variant) has been shown to be pathogenic in humans. Until recently, laboratory methods used to differentiate variants were cumbersome and seldomly used in large scale assessments of the pathogen's geographic distribution. As a result, many surveys reported A. phagocytophilum without segregating variants. Lack of discrimination among A. phagocytophilum variants could lead to overestimation of anaplasmosis risk to humans. Next Generation Sequencing (NGS) assays were recently developed to efficiently detect multiple Ixodes scapularis-borne human pathogens including Ap-ha. In this study, we utilized NGS to detect and differentiate A. phagocytophilum variants (Ap-ha vs. non ha) in host-seeking I. scapularis nymphs and adults collected across 23 states in the eastern United States from 2012 to 2023 as part of national tick surveillance efforts and research studies. Many of the included ticks were tested previously using a TaqMan PCR assay that could detect A. phagocytophilum but could not differentiate variants. We retested A. phagocytophilum infected ticks with NGS to differentiate variants. Anaplasma phagocytophilum (any variant) was identified in 165 (35 %) of 471 counties from which ticks were tested, whereas Ap-ha was detected in 70 (15 %) of 469 counties where variants were differentiated. Both variants were identified in 32 % (n = 40) of 126 counties with either variant detected. Among states where A. phagocytophilum (any variant) was detected, prevalence ranged from 2 % to 19 % in unfed adults and from 0.2 % to 7.8 % in unfed nymphs; prevalence of Ap-ha variant ranged from 0.0 % to 16 % in adults, and 0.0 % to 4.6 % in nymphs.

Comparative genome-wide identification and characterization of SET domain-containing and JmjC domain-containing proteins in piroplasms

BACKGROUND

SET domain-containing histone lysine methyltransferases (HKMTs) and JmjC domain-containing histone demethylases (JHDMs) are essential for maintaining dynamic changes in histone methylation across parasite development and infection. However, information on the HKMTs and JHDMs in human pathogenic piroplasms, such as Babesia duncani and Babesia microti, and in veterinary important pathogens, including Babesia bigemina, Babesia bovis, Theileria annulata and Theileria parva, is limited.

RESULTS

A total of 38 putative KMTs and eight JHDMs were identified using a comparative genomics approach. Phylogenetic analysis revealed that the putative KMTs can be divided into eight subgroups, while the JHDMs belong to the JARID subfamily, except for BdJmjC1 (BdWA1_000016) and TpJmjC1 (Tp Muguga_02g00471) which cluster with JmjC domain only subfamily members. The motifs of SET and JmjC domains are highly conserved among piroplasm species. Interspecies collinearity analysis provided insight into the evolutionary duplication events of some SET domain and JmjC domain gene families. Moreover, relative gene expression analysis by RT‒qPCR demonstrated that the putative KMT and JHDM gene families were differentially expressed in different intraerythrocytic developmental stages of B. duncani, suggesting their role in Apicomplexa parasite development.

CONCLUSIONS

Our study provides a theoretical foundation and guidance for understanding the basic characteristics of several important piroplasm KMT and JHDM families and their biological roles in parasite differentiation.

Willingness and capacity of publicly-funded vector control programs in the USA to engage in tick management

BACKGROUND

The vast majority of vector-borne diseases in the USA are associated with mosquitoes or ticks. Mosquito control is often conducted as part of community programs run by publicly-funded entities. By contrast, tick control focuses primarily on individual residential properties and is implemented predominantly by homeowners and the private pest control firms they contract. We surveyed publicly-funded vector control programs (VCPs), presumed to focus mainly on mosquitoes, to determine what tick-related services they currently offer, and their interest in and capacity to expand existing services or provide new ones.

METHODS

We distributed a survey to VCPs in the Northeast, Upper Midwest and Pacific Coast states of the USA, where humans are at risk for bites by tick vectors (Ixodes scapularis or Ixodes pacificus) of agents causing Lyme disease and other tick-borne diseases. The data we report are based on responses from 118 VCPs engaged in vector control and with at least some activities focused on ticks.

RESULTS

Despite our survey targeting geographic regions where ticks and tick-borne diseases are persistent and increasing public health concerns, only 11% (12/114) of VCPs reported they took direct action to suppress ticks questing in the environment. The most common tick-related activities conducted by the VCPs were tick bite prevention education for the public (70%; 75/107 VCPs) and tick surveillance (48%; 56/116). When asked which services they would most likely include as part of a comprehensive tick management program, tick bite prevention education (90%; 96/107), tick surveillance (89%; 95/107) and tick suppression guidance for the public (74%; 79/107) were the most common services selected. Most VCPs were also willing to consider engaging in activities to suppress ticks on public lands (68%; 73/107), but few were willing to consider suppressing ticks on privately owned land such as residential properties (15%; 16/107). Across all potential tick-related services, funding was reported as the biggest obstacle to program expansion or development, followed by personnel.

CONCLUSIONS

Considering the hesitancy of VCPs to provide tick suppression services on private properties and the high risk for tick bites in peridomestic settings, suppression of ticks on residential properties by private pest control operators will likely play an important role in the tick suppression landscape in the USA for the foreseeable future. Nevertheless, VCPs can assist in this effort by providing locally relevant guidelines to homeowners and private pest control firms regarding best practices for residential tick suppression efforts and associated efficacy evaluations. Publicly-funded VCPs are also well positioned to educate the public on personal tick bite prevention measures and to collect tick surveillance data that provide information on the risk of human encounters with ticks within their jurisdictions.

Density of host-seeking Ixodes scapularis nymphs by region, state, and county in the contiguous United States generated through national tick surveillance

The majority of vector-borne disease cases reported annually in the United States are caused by pathogens spread by the blacklegged tick, Ixodes scapularis. The number and geographic distribution of cases have increased as the geographic range and abundance of the tick have expanded in recent decades. A large proportion of Lyme disease and other I. scapularis-borne diseases are associated with nymphal tick bites; likelihood of such bites generally increases with increasing nymphal densities. National tick surveillance was initiated in 2018 to track changes in the distribution and abundance of medically important ticks at the county spatial scale throughout the United States. Tick surveillance records, including historical data collected prior to the initiation of the national program, are collated in the ArboNET Tick Module database. Through exploration of ArboNET Tick Module data, we found that efforts to quantify the density of host-seeking I. scapularis nymphs (DON) were unevenly distributed among geographic regions with the greatest proportion of counties sampled in the Northeast and Upper Midwest. Submissions covering tick collections from 2004 through 2022 revealed extensive variation in DON estimates at collection site, county, state, and regional spatial scales. Throughout the entire study period, county DON estimates ranged from 0.0 to 488.5 nymphs/1,000 m2 . Although substantial variation was recorded within regions, DON estimates were greatest in the Northeast, Upper Midwest, and northern states within the Southeast regions (Virginia and North Carolina); densities were intermediate in the Ohio Valley and very low in the South and Northern Rockies and Plains regions. The proportion of counties classified as moderate or high DON was lower in the Northeast, Ohio Valley, and Southeast regions during the 2004 through 2017 time period (prior to initiation of the national tick surveillance program) compared to 2018 through 2022; DON estimates remained similarly low between these time periods in the South and the Northern Rockies and Plains regions. Despite the limitations described herein, the ArboNET Tick Module provides useful data for tracking changes in acarological risk across multiple geographic scales and long periods of time.

Estimating the Incidence and Economic Cost of Lyme Disease Cases in Canada in the 21st Century with Projected Climate Change

BACKGROUND

Lyme disease (LD) is emerging in Canada owing to the range expansion of the tick vector Ixodes scapularis (I. scapularis).

OBJECTIVES

Our objective was to estimate future LD incidence in Canada, and economic costs, for the 21st century with projected climate change.

METHODS

Future regions of climatic suitability for I. scapularis were projected from temperature output of the North American Coordinated Regional Climate Downscaling Experiment regional climate model ensemble using greenhouse gas Representative Concentration Pathways (RCPs) 4.5 and 8.5. Once regions became climatically suitable for ticks, an algorithm derived from tick and LD case surveillance data projected subsequent increasing LD incidence. Three scenarios (optimistic, intermediate, and pessimistic) for maximum incidence at endemicity were selected based on LD surveillance, and underreporting estimates, from the United States. Health care and productivity cost estimates of LD cases were obtained from the literature.

RESULTS

Projected annual LD cases for Canada ranged from 120,000 to > 500,000 by 2050. Variation in incidence was mostly due to the maximum incidence at endemicity selected, with minor contributions from variations among climate models and RCPs. Projected annual costs were substantial, ranging from CA $ 0.5  billion to $ 2.0  billion a year by 2050. There was little difference in projected incidence and economic cost between RCPs, and from 2050 to 2100, because projected climate up to 2050 is similar for RCP4.5 and RCP8.5 (mitigation of greenhouse gas emissions captured in RCP4.5 does not impact climate before the 2050s) and by 2050 the most densely populated areas of the study region are projected to be climatically suitable for ticks.

CONCLUSIONS

Future incidence and economic costs of LD in Canada are likely to be substantial, but uncertainties remain. Because densely populated areas of Canada are projected to become endemic under conservative climate change scenarios, mitigation of greenhouse gas emissions is unlikely to provide substantial health co-benefits for LD. https://doi.org/10.1289/EHP13759.

Detection of Borrelia burgdorferi sensu lato species in host-seeking Ixodes species ticks in the United States

Lyme disease is the most commonly reported vector-borne disease in the United States and is transmitted by Ixodes scapularis in the eastern US and I. pacificus in the west. The causative agents, Borrelia burgdorferi sensu stricto (Bbss) and B. mayonii belong to the B. burgdorferi sensu lato (Bbsl) species complex. An additional eight species of Bbsl have been identified in Ixodes species ticks in the US, but their geographic distribution, vector associations, human encounter rates and pathogenicity in humans are poorly defined. To better understand the geographic distribution and vector associations of Bbsl spirochetes in frequent and infrequent human-biting Ixodes species ticks in the US, we previously screened 29,517 host-seeking I. scapularis or I. pacificus ticks and 692 ticks belonging to eight other Ixodes species for Borrelia spirochetes using a previously described tick testing algorithm that utilizes a combination of real-time PCR and Sanger sequencing for Borrelia species identification. The assay was designed to detect known human pathogens spread by Ixodes species ticks, but it was not optimized to detect Bbsl co-infections. To determine if such co-infections were overlooked particularly in ticks infected with Bbss, we retested and analyzed a subsample of 845 Borrelia infected ticks using a next generation sequencing multiplex PCR amplicon sequencing (MPAS) assay that can identify Borrelia species and Bbsl co-infections. The assay also includes targets that can molecularly confirm identifications of Ixodes species ticks to better inform pathogen-vector associations. We show that Bbss is the most prevalent species in I. scapularis and I. pacificus; other Bbsl species were rarely detected in I. scapularis and the only Bbsl co-infections identified in I. scapularis were with Bbss and B. mayonii. We detected B. andersonii in I. dentatus in the Mid-Atlantic and Upper Midwest regions, B. kurtenbachii in I. scapularis in the Upper Midwest, B. bissettiae in I. pacificus and I. spinipalpis in the Northwest, and B. carolinensis in I. affinis in the Mid-Atlantic and Southeast, and B. lanei in I. spinipalpis in the Northwest. Twelve of 62 (19.4%) Borrelia-infected I. affinis from the Mid-Atlantic region were co-infected with Bbss and B. carolinensis. Our data support the notion that Bbsl species are maintained in largely independent enzootic cycles, with occasional spill-over resulting in multiple Bbsl species detected in Ixodes species ticks.

Tick-Borne Co-Infections: Challenges in Molecular and Serologic Diagnoses

Co-infections are a poorly understood aspect of tick-borne diseases. In the United States alone, nineteen different tick-borne pathogens have been identified. The majority of these agents are transmitted by only two tick species, Ixodes scapularis and Amblyomma americanum. Surveillance studies have demonstrated the presence of multiple pathogens in individual ticks suggesting a risk of polymicrobial transmission to humans. However, relatively few studies have explored this relationship and its impact on human disease. One of the key factors for this deficiency are the intrinsic limitations associated with molecular and serologic assays employed for the diagnosis of tick-borne diseases. Limitations in the sensitivity, specificity and most importantly, the capacity for inclusion of multiple agents within a single assay represent the primary challenges for the accurate detection of polymicrobial tick-borne infections. This review will focus on outlining these limitations and discuss potential solutions for the enhanced diagnosis of tick-borne co-infections.

Perception of Ticks and Tick-Borne Diseases Worldwide

In this comprehensive review study, we addressed the challenge posed by ticks and tick-borne diseases (TBDs) with growing incidence affecting human and animal health worldwide. Data and perspectives were collected from different countries and regions worldwide, including America, Europe, Africa, Asia, and Oceania. The results updated the current situation with ticks and TBD and how it is perceived by society with information bias and gaps. The study reinforces the importance of multidisciplinary and international collaborations to advance in the surveillance, communication and proposed future directions to address these challenges.