Reservoir competence of wildlife host species for Babesia microti

T(r)icky Environments: Higher Prevalence of Tick-Borne Zoonotic Pathogens in Rodents from Natural Areas Compared with Urban Areas

Background: Urban areas are unique ecosystems with stark differences in species abundance and composition compared with natural ecosystems. These differences can affect pathogen transmission dynamics, thereby altering zoonotic pathogen prevalence and diversity. In this study, we screened small mammals from natural and urban areas in the Netherlands for up to 19 zoonotic pathogens, including viruses, bacteria, and protozoan parasites. Materials and Methods: In total, 578 small mammals were captured, including wood mice (Apodemus sylvaticus), bank voles (Myodes glareolus), yellow-necked mice (Apodemus flavicollis), house mice (Mus musculus), common voles (Microtus arvalis), and greater white-toothed shrews (Crocidura russula). We detected a wide variety of zoonotic pathogens in small mammals from both urban and natural areas. For a subset of these pathogens, in wood mice and bank voles, we then tested whether pathogen prevalence and diversity were associated with habitat type (i.e., natural versus urban), degree of greenness, and various host characteristics. Results: The prevalence of tick-borne zoonotic pathogens (Borrelia spp. and Neoehrlichia mikurensis) was significantly higher in wood mice from natural areas. In contrast, the prevalence of Bartonella spp. was higher in wood mice from urban areas, but this difference was not statistically significant. Pathogen diversity was higher in bank voles from natural habitats and increased with body weight for both rodent species, although this relationship depended on sex for bank voles. In addition, we detected methicillin-resistant Staphylococcus aureus, extended-spectrum beta-lactamase/AmpC-producing Escherichia coli, and lymphocytic choriomeningitis virus for the first time in rodents in the Netherlands. Discussion: The differences between natural and urban areas are likely related to differences in the abundance and diversity of arthropod vectors and vertebrate community composition. With increasing environmental encroachment and changes in urban land use (e.g., urban greening), it is important to better understand transmission dynamics of zoonotic pathogens in urban environments to reduce potential disease risks for public health.

Effects of residential acaricide treatments on patterns of pathogen coinfection in blacklegged ticks

Medically important ixodid ticks often carry multiple pathogens, with individual ticks frequently coinfected and capable of transmitting multiple infections to hosts, including humans. Acquisition of multiple zoonotic pathogens by immature blacklegged ticks (Ixodes scapularis) is facilitated when they feed on small mammals, which are the most competent reservoir hosts for Anaplasma phagocytophilum (which causes anaplasmosis in humans), Babesia microti (babesiosis) and Borrelia burgdorferi (Lyme disease). Here, we used data from a large-scale, long-term experiment to ask whether patterns of single and multiple infections in questing nymphal I. scapularis ticks from residential neighbourhoods differed from those predicted by independent assortment of pathogens, and whether patterns of coinfection were affected by residential application of commercial acaricidal products. Quantitative polymerase chain reaction was used for pathogen detection in multiplex reactions. In control neighbourhoods and those treated with a fungus-based biopesticide deployed against host-seeking ticks (Met52), ticks having only single infections of either B. microti or B. burgdorferi were significantly less common than expected, whereas coinfections with these 2 pathogens were significantly more common. However, use of tick control system bait boxes, which kill ticks attempting to feed on small mammals, eliminated the bias towards coinfection. Although aimed at reducing the abundance of host-seeking ticks, control methods directed at ticks attached to small mammals may influence human exposure to coinfected ticks and the probability of exposure to multiple tick-borne infections.

Coinfection of Babesia and Borrelia in the Tick Ixodes ricinus-A Neglected Public Health Issue in Europe?

Ixodes ricinus nymphs and adults removed from humans, and larvae and nymphs from birds, have been analysed for infection with Babesia species and Borrelia species previously in separately published studies. Here, we use the same data set to explore the coinfection pattern of Babesia and Borrelia species in the ticks. We also provide an overview of the ecology and potential public health importance in Sweden of I. ricinus infected both with zoonotic Babesia and Borrelia species. Among 1952 nymphs and adult ticks removed from humans, 3.1% were PCR-positive for Babesia spp. Of these Babesia-positive ticks, 43% were simultaneously Borrelia-positive. Among 1046 immatures of I. ricinus removed from birds, 2.5% were Babesia-positive, of which 38% were coinfected with Borrelia species. This study shows that in I. ricinus infesting humans or birds in Sweden, potentially zoonotic Babesia protozoa sometimes co-occur with human-pathogenic Borrelia spp. Diagnostic tests for Babesia spp. infection are rarely performed in Europe, and the medical significance of this pathogen in Europe could be underestimated.

Ticks (Acari: Ixodida) on synanthropic small and medium-sized mammals in areas of the northeastern United States infested with the Asian longhorned tick, Haemaphysalis longicornis

The northeastern United States (US) is a hotspot for tick-borne diseases. Adding to an already complex vector landscape, in 2017 large populations of the invasive Haemaphysalis longicornis, the Asian longhorned tick, were detected in New Jersey (NJ) and later found to be widespread from Connecticut to Georgia. In its native range in northeastern Asia, H. longicornis is considered an important vector of deadly pathogens to humans, companion animals, and livestock. To identify the primary hosts of H. longicornis, we surveyed synanthropic small and medium-sized mammals in three different sites in suburban New Brunswick, NJ. Specifically, we collected approximately 9,000 tick specimens belonging to nine species from 11 different species of mammals sampled between May and September 2021. We found that H. longicornis feeds more frequently on rodents than previously thought, and that this invasive tick is likely exposed to important enzootic and zoonotic pathogens. Overall, we obtained detailed information about the seasonal dynamics and feeding patterns of six tick species common in the northeastern US, Haemaphysalis longicornis, Amblyomma americanum, Dermacentor variabilis, Ixodes scapularis, Ixodes texanus and Ixodes cookei. We found that unlike I. scapularis that feeds on mammals of all sizes, H. longicornis feeds on hosts following the general pattern of A. americanum, favoring larger species such as skunks, groundhogs, and raccoons. However, our survey revealed that unlike A. americanum, H. longicornis reaches high densities on Virginia opossum. Overall, the newly invasive H. longicornis was the most numerous tick species, both on multiple host species and in the environment, raising significant questions regarding its role in the epidemiology of tick-borne pathogens, especially those affecting livestock, companion animals and wildlife. In conclusion, our findings provide valuable insights into the tick species composition on mammalian hosts in NJ and the ongoing national expansion of H. longicornis.

Experimental assessment of cross-species transmission in a natural multihost-multivector-multipathogen community

Vector-borne pathogens, many of which cause major suffering worldwide, often circulate in diverse wildlife communities comprising multiple reservoir host and/or vector species. However, the complexities of these systems make it challenging to determine the contributions these different species make to transmission. We experimentally manipulated transmission within a natural multihost-multipathogen-multivector system, by blocking flea-borne pathogen transmission from either of two co-occurring host species (bank voles and wood mice). Through genetic analysis of the resulting infections in the hosts and vectors, we show that both host species likely act together to maintain the overall flea community, but cross-species pathogen transmission is relatively rare-most pathogens were predominantly found in only one host species, and there were few cases where targeted treatment affected pathogens in the other host species. However, we do provide experimental evidence of some reservoir-spillover dynamics whereby reductions of some infections in one host species are achieved by blocking transmission from the other host species. Overall, despite the apparent complexity of such systems, we show there can be 'covert simplicity', whereby pathogen transmission is primarily dominated by single host species, potentially facilitating the targeting of key hosts for control, even in diverse ecological communities.

Detection of a novel Babesia sp. in Amblyomma javanense, an ectoparasite of Sunda pangolins

BACKGROUND

Babesia is a protozoal, tick-borne parasite that can cause life-threatening disease in humans, wildlife and domestic animals worldwide. However, in Southeast Asia, little is known about the prevalence and diversity of Babesia species present in wildlife and the tick vectors responsible for its transmission. Recently, a novel Babesia species was reported in confiscated Sunda pangolins (Manis javanica) in Thailand. To investigate the presence of this parasite in Singapore, we conducted a molecular survey of Babesia spp. in free-roaming Sunda pangolins and their main ectoparasite, the Amblyomma javanense tick.

METHODS

Ticks and tissue samples were opportunistically collected from live and dead Sunda pangolins and screened using a PCR assay targeting the 18S rRNA gene of Babesia spp. DNA barcoding of the cytochrome oxidase subunit I (COI) mitochondrial gene was used to confirm the species of ticks that were Babesia positive.

RESULTS

A total of 296 ticks and 40 tissue samples were obtained from 21 Sunda pangolins throughout the 1-year study period. Babesia DNA was detected in five A. javanense ticks (minimum infection rate = 1.7%) and in nine different pangolins (52.9%) located across the country. Phylogenetic analysis revealed that the Babesia 18S sequences obtained from these samples grouped into a single monophyletic clade together with those derived from Sunda pangolins in Thailand and that this evolutionarily distinct species is basal to the Babesia sensu stricto clade, which encompasses a range of Babesia species that infect both domestic and wildlife vertebrate hosts.

CONCLUSIONS

This is the first report documenting the detection of a Babesia species in A. javanense ticks, the main ectoparasite of Sunda pangolins. While our results showed that A. javanense can carry this novel Babesia sp., additional confirmatory studies are required to demonstrate vector competency. Further studies are also necessary to investigate the role of other transmission pathways given the low infection rate of ticks in relation to the high infection rate of Sunda pangolins. Although it appears that this novel Babesia sp. is of little to no pathogenicity to Sunda pangolins, its potential to cause disease in other animals or humans cannot be ruled out.

Transfusion-transmitted Babesia spp.: a changing landscape of epidemiology, regulation, and risk mitigation

Babesia spp. are tick-borne parasites with a global distribution and diversity of vertebrate hosts. Over the next several decades, climate change is expected to impact humans, vectors, and vertebrate hosts and change the epidemiology of Babesia. Although humans are dead-end hosts for tick-transmitted Babesia, human-to-human transmission of Babesia spp. from transfusion of red blood cells and whole blood-derived platelet concentrates has been reported. In most patients, transfusion-transmitted Babesia (TTB) results in a moderate-to-severe illness. Currently, in North America, most cases of TTB have been described in the United States. TTB cases outside North America are rare, but case numbers may change over time with increased recognition of babesiosis and as the epidemiology of Babesia is impacted by climate change. Therefore, TTB is a concern of microbiologists working in blood operator settings, as well as in clinical settings where transfusion occurs. Microbiologists play an important role in deploying blood donor screening assays in Babesia endemic regions, identifying changing risks for Babesia in non-endemic areas, investigating recipients of blood products for TTB, and drafting TTB policies and guidelines. In this review, we provide an overview of the clinical presentation and epidemiology of TTB. We identify approaches and technologies to reduce the risk of collecting blood products from Babesia-infected donors and describe how investigations of TTB are undertaken. We also describe how microbiologists in Babesia non-endemic regions can assess for changing risks of TTB and decide when to focus on laboratory-test-based approaches or pathogen reduction to reduce TTB risk.

Alternative and Complementary Approaches to Consider for Effective Babesia Vaccine Development

The Babesia genus encompasses several species of apicomplexan hemoprotozoan parasites [...].

Molecular Screening of Blood Donors for Babesia in Tyrol, Austria

Introduction

Babesia is a tick-borne intraerythrocytic parasite that is globally ubiquitous, yet understudied. Several species of Babesia have been shown to be transfusion-transmissible. Babesia has been reported in blood donors, animals, and ticks in the Tyrol (Western Austria), and regional cases of human babesiosis have been described. We sought to characterize the risk of Babesia to the local blood supply.

Methods

Prospective molecular testing was performed on blood donors who presented to regional, mobile blood collection drives in the Tyrol, Austria (27 May to October 4, 2021). Testing was conducted using the cobas® Babesia assay (Roche Molecular Systems, Inc.), a commercial PCR assay approved for blood donor screening that is capable of detecting the 4 primary species causing human babesiosis (i.e., B. microti, B. divergens, B. duncani, and B. venatorum). A confirmatory algorithm to manage initial PCR-reactive samples was developed, as were procedures for donor and product management.

Results

A total of 7,972 donors were enrolled and screened; 4,311 (54.1%) were male, with a median age of 47 years (IQR = 34-55). No positive cases of Babesia were detected, corresponding with an overall prevalence of 0.00% (95% CI: 0.00%, 0.05%).

Discussion

The findings suggest that the prevalence of Babesia is low in Austrian blood donors residing in the Tyrol, even during months of peak tick exposure. Although one cannot conclude the absence of Babesia in this population given the limited sample size, the findings suggest that the regional risk of transfusion-transmitted babesiosis is low.

Tick Densities and Infection Prevalence on Coastal Islands in Massachusetts, USA: Establishing a Baseline

Tick-borne diseases and a tick-induced red meat allergy have become increasingly common in the northeastern USA and elsewhere. At the scale of local communities, few studies have documented tick densities or infection levels to characterize current conditions and provide a baseline for further monitoring. Using the town of Nantucket, MA, as a case study, we recorded tick densities by drag sampling along hiking trails in nature preserves on two islands. Nymphal blacklegged ticks (Ixodes scapularis Say) were most abundant at shadier sites and least common in grasslands and scrub oak thickets (Quercus ilicifolia). Lone star ticks (Amblyomma americanum L.) were common on Tuckernuck Island and rare on Nantucket Island, while both tick species were more numerous in 2021 compared to 2020 and 2022. We tested for pathogens in blacklegged nymphs at five sites over two years. In 2020 and 2021, infection levels among the four Nantucket Island sites averaged 10% vs. 19% for Borrelia burgdorferi, 11% vs. 15% for Babesia microti, and 17% (both years) for Anaplasma phagocytophilum, while corresponding levels were significantly greater on Tuckernuck in 2021. Our site-specific, quantitative approach represents a practical example of how potential exposure to tick-borne diseases can be monitored on a local scale.

Expanding the universe of Piroplasmids: morphological detection and phylogenetic positioning of putative novel piroplasmids in black-eared opossums (Didelphis aurita) from southeastern Brazil, with description of "South American Marsupialia Group" of Piroplasmida

The growing proximity of wildlife to large urban niches arouses greater interest in understanding wild reservoirs in the epidemiology of diseases of importance to animal and human health. The aim of the present study was to investigate the presence of piroplasmids in opossums rescued from the metropolitan region of Rio de Janeiro state, Brazil. Blood and bone marrow samples were collected from 15 Didelphis aurita and subjected to DNA extraction and PCR using primers for the 18S rRNA, cox1, cox3, and hsp70 genes of piroplasmids. Clinical and hematological evaluation of the animals was also performed. Five (33.3%) of the 15 opossums tested positive for piroplasms in the nested PCR based on the 18S rRNA, and in two animals, it was possible to observe intra-erythrocytic structures compatible with merozoites. One of the positive animals showed clinical signs of infection such as jaundice, fever, and apathy. Anemia, low level of plasma protein, leukocytosis, and regenerative erythrocyte signs were observed in positive animals. Phylogenetic analysis based on both 18S rRNA and cox-3 genes demonstrated that the piroplasmids detected in D. aurita formed a unique sub-clade, albeit related to piroplasmids previously detected in Didelphis albiventris and associated ticks from Brazil. This study proposes the novel Piroplasmida Clade, namely "South American Marsupialia Group," and reinforces the need for new clinical-epidemiological surveys to understand the dynamics of these infections in didelphids in Brazil.

Identifying suitable habitat for Ixodes scapularis (Acari: Ixodidae) infected with Anaplasma phagocytophilum (Rickettsiales: Anaplasmataceae), Babesia microti (Piroplasmida: Babesiidae), and Borrelia miyamotoi (Spirochaetales: Spirochaetaceae) to guide surveillance efforts in the eastern United States

Understanding the distribution of infected ticks is informative for the estimation of risk for tickborne diseases. The blacklegged tick, Ixodes scapularis (Acari: Ixodidae), is the primary vector for 7 medically significant pathogens in United States. However, knowledge of the ranges of these pathogens in host-seeking ticks is incomplete, particularly for those occurring at low prevalence. To aid in prioritizing costly field sampling efforts, we estimated ranges of suitable habitat for Anaplasma phagocytophilum, Babesia microti, and Borrelia miyamotoi in the eastern United States based on existing county-level surveillance records. The resulting suitability maps were compared against those developed previously for Bo. burgdorferi s.s., which shares similar ecology but has been detected in a greater number of counties. The overall accuracy of the habitat suitability models was high (AUC ≥ 0.92) for all 4 pathogens. The most important predictors were related to temperature and moisture. The upper midwestern and northeastern states were predicted to be highly suitable for all 4 pathogens. Based on our models, we prioritized sampling in 431, 275, and 539 counties currently lacking pathogen records that our models classified as suitable for A. phagocytophilum, Ba. microti, and Bo. miyamotoi, respectively. As a second-tier priority, we identified 311 (A. phagocytophilum), 590 (Ba. microti), and 252 (Bo. miyamotoi) counties, based on high suitability scores for Bo. burgdorferi. Our models can be used to improve cost-effectiveness of field sampling efforts aimed at improving accuracy and completeness of pathogen distribution maps.

Deployment of a Reservoir-Targeted Vaccine Against Borrelia burgdorferi Reduces the Prevalence of Babesia microti Coinfection in Ixodes scapularis Ticks

In the Northeast and upper Midwest of the United States, Babesia microti and Borrelia burgdorferi use Ixodes scapularis ticks as vector and Peromyscus leucopus mice as major reservoir host. We previously established, in a 5-year field trial, that a reservoir-targeted outer surface protein A vaccine reduces the prevalence of B. burgdorferi-infected ticks. We accessed ticks and mouse blood samples collected during the trial, extracted total DNA, and amplified the B. microti 18S rRNA gene. Vaccine deployment reduced the prevalence of ticks coinfected with B. microti and that of mice infected with B. microti. Breaking the enzootic cycle of B. burgdorferi may reduce the incidence of babesiosis.

Bird Louse Flies Ornithomya spp. (Diptera: Hippoboscidae) as Potential Vectors of Mammalian Babesia and Other Pathogens

Background: Birds and mammals share various ectoparasites, which are responsible for the transmission of a wide range of pathogens. The louse flies (family Hippoboscidae) are ectoparasitic dipterans feeding strictly on the blood of mammals and birds. Both sexes of the louse flies are obligatory hematophagous and are known to act as the vectors of infectious agents. Materials and Methods: A total of 20 specimens of Ornithomya sp. were collected by hand on birds caught in nets or by hand from humans in two localities in Eastern Slovakia in 2021. The DNA samples were individually screened by species-specific PCRs for the presence of selected vector-borne pathogens. Results: Taxonomic identification folowed by molecular analyses revealed two louse fly species of Ornithomya spp. (O. avicularia and O. biloba). The molecular screening provided negative PCR results for Anaplasma phagocytophilum, Borrelia burgdorferi s.l., Rickettsia spp., Bartonella spp., and Hepatozoon canis. In contrast, positive PCR results were obtained for Babesia spp., Wolbachia spp., and Trypanosoma corvi. Conclusions: Of epidemiological importance is that the louse flies can presumably spread Babesia and other pathogens by host switching which facilitates the transmission and spread of numerous pathogens.

Molecular detection of Babesia spp. and Rickettsia spp. in coatis (Nasua nasua) and associated ticks from midwestern Brazil

Procyonids are reservoirs of many zoonotic infectious diseases, including tick-borne pathogens. The role of coatis (Nasua nasua) in the epidemiology of piroplasmids and Rickettsia has not been fully addressed in Brazil. To molecularly study these agents in coatis and associated ticks, animals were sampled in two urban areas in Midwestern Brazil. Blood (n = 163) and tick (n = 248) DNA samples were screened by PCR assays targeting the 18S rRNA and gltA genes of piroplasmids and Rickettsia spp., respectively. Positive samples were further molecularly tested targeting cox-1, cox-3, β-tubulin, cytB, and hsp70 (piroplasmid) and ompA, ompB, and htrA 17-kDa (Rickettsia spp.) genes, sequenced and phylogenetically analyzed. All coatis' blood samples were negative for piroplasmids, whereas five pools of ticks (2%) were positive for two different sequences of Babesia spp.. The first from Amblyomma sculptum nymphs was close (i.e., ≥ 99% nucleotide identity) to a Babesia sp. previously found in capybaras (Hydrochoerus hydrochaeris); the second from Amblyomma dubitatum nymphs and Amblyomma spp. larvae was identical (100% nucleotide identity) to a Babesia sp. detected in opossums (Didelphis albiventris) and associated ticks. Four samples (0.8%) were positive by PCR to two different Rickettsia spp. sequences, being the first from Amblyomma sp. larva identical to Rickettsia belli and the second from A. dubitatum nymph identical to Rickettsia species from Spotted Fever Group (SFG). The detection of piroplasmids and SFG Rickettsia sp. highlights the importance of Amblyomma spp. in the maintenance of tick-borne agents in urban parks where humans and wild and domestic animals are living in sympatry.

Advances in Babesia Vaccine Development: An Overview

Babesiosis is a tick-borne zoonotic disease, which is caused by various species of intracellular Babesia parasite. It is a problem not only for the livestock industry but also for global health. Significant global economic losses, in particular in cattle production, have been observed. Since the current preventive measures against babesiosis are insufficient, there is increasing pressure to develop a vaccine. In this review, we survey the achievements and recent advances in the creation of antibabesiosis vaccine. The scope of this review includes the development of a vaccine against B. microti, B. bovis, B. bigemina, B. orientalis and B. divergens. Here, we present different strategies in their progress and evaluation. Scientists worldwide are still trying to find new targets for a vaccine that would not only reduce symptoms among animals but also prevent the further spread of the disease. Molecular candidates for the production of a vaccine against various Babesia spp. are presented. Our study also describes the current prospects of vaccine evolution for successful Babesia parasites elimination.

Effects of Neighborhood-Scale Acaricidal Treatments on Infection Prevalence of Blacklegged Ticks (Ixodes scapularis) with Three Zoonotic Pathogens

Acaricides are hypothesized to reduce human risk of exposure to tick-borne pathogens by decreasing the abundance and/or infection prevalence of the ticks that serve as vectors for the pathogens. Acaricides targeted at reservoir hosts such as small mammals are expected to reduce infection prevalence in ticks by preventing their acquisition of zoonotic pathogens. By reducing tick abundance, reservoir-targeted or broadcast acaricides could reduce tick infection prevalence by interrupting transmission cycles between ticks and their hosts. Using an acaricide targeted at small-mammal hosts (TCS bait boxes) and one sprayed on low vegetation (Met52 fungal biocide), we tested the hypotheses that infection prevalence of blacklegged ticks with zoonotic pathogens would be more strongly diminished by TCS bait boxes, and that any effects of both acaricidal treatments would increase during the four years of deployment. We used a masked, placebo-controlled design in 24 residential neighborhoods in Dutchess County, New York. Analyzing prevalence of infection with Borrelia burgdorferi, Anaplasma phagocytophilum, and Babesia microti in 5380 nymphal Ixodes scapularis ticks, we found little support for either hypothesis. TCS bait boxes did not reduce infection prevalence with any of the three pathogens compared to placebo controls. Met52 was associated with lower infection prevalence with B. burgdorferi compared to placebo controls but had no effect on prevalence of infection with the other two pathogens. Although significant effects of year on infection prevalence of all three pathogens were detected, hypothesized cumulative reductions in prevalence were observed only for B. burgdorferi. We conclude that reservoir-targeted and broadcast acaricides might not generally disrupt pathogen transmission between reservoir hosts and tick vectors or reduce human risk of exposure to tick-borne pathogens.

Patterns and Ecological Mechanisms of Tick-Borne Disease Exposure Risk in Acadia National Park, Mount Desert Island, Maine, United States

National parks are unique and significant vector-borne pathogen transmission settings, engaging over 300 million people in outdoor recreation per year. In this study, we integrated vector surveys and ecological habitat feature data in spatial models to characterize tick-borne disease exposure risk in Acadia National Park (ANP), Maine. To determine the broad-scale patterns of blacklegged tick Ixodes scapularis Say (Acari: Ixodidae) densities in ANP, we conducted host-seeking tick collections at 114 sites across the park over two years. Using these tick survey data and geospatial landscape feature data (i.e., land cover, elevation, forest patch size, and aspect) we developed a random forest model of nymphal tick density. We found that host-seeking tick density varies significantly across the park and is particularly high in areas characterized by deciduous forest cover and relatively low elevation. To explore potential fine-scale ecological drivers of tick density spatial patterns, we quantified microclimate conditions, host activity, and vegetation characteristics at a subset of 19 sites. We identified significant differences in microclimate conditions but not host activity or vegetation metrics across broad-scale landscape feature classes. Mean temperature and mean humidity were correlated to nymphal densities and therefore may provide a mechanistic link between landscape features and blacklegged tick densities. Finally, we detected multiple tick-borne pathogens in both ticks and small mammals sampled in ANP, including Borrelia burgdorferi, Babesia microti, and Anaplasma phagocytophilum. Our findings demonstrate the value of using ecological metrics to estimate vector-borne disease exposure risk and provide insight into habitat characteristics that may drive tick-borne disease exposure risk.

Transmission Cycle of Tick-Borne Infections and Co-Infections, Animal Models and Diseases

Tick-borne pathogens such as species of Borrelia, Babesia, Anaplasma, Rickettsia, and Ehrlichia are widespread in the United States and Europe among wildlife, in passerines as well as in domestic and farm animals. Transmission of these pathogens occurs by infected ticks during their blood meal, carnivorism, and through animal bites in wildlife, whereas humans can become infected either by an infected tick bite, through blood transfusion and in some cases, congenitally. The reservoir hosts play an important role in maintaining pathogens in nature and facilitate transmission of individual pathogens or of multiple pathogens simultaneously to humans through ticks. Tick-borne co-infections were first reported in the 1980s in white-footed mice, the most prominent reservoir host for causative organisms in the United States, and they are becoming a major concern for public health now. Various animal infection models have been used extensively to better understand pathogenesis of tick-borne pathogens and to reveal the interaction among pathogens co-existing in the same host. In this review, we focus on the prevalence of these pathogens in different reservoir hosts, animal models used to investigate their pathogenesis and host responses they trigger to understand diseases in humans. We also documented the prevalence of these pathogens as correlating with the infected ticks’ surveillance studies. The association of tick-borne co-infections with other topics such as pathogens virulence factors, host immune responses as they relate to diseases severity, identification of vaccine candidates, and disease economic impact are also briefly addressed here.

Large-Scale Sequencing of Borreliaceae for the Construction of Pan-Genomic-Based Diagnostics

The acceleration of climate change has been associated with an alarming increase in the prevalence and geographic range of tick-borne diseases (TBD), many of which have severe and long-lasting effects-particularly when treatment is delayed principally due to inadequate diagnostics and lack of physician suspicion. Moreover, there is a paucity of treatment options for many TBDs that are complicated by diagnostic limitations for correctly identifying the offending pathogens. This review will focus on the biology, disease pathology, and detection methodologies used for the Borreliaceae family which includes the Lyme disease agent Borreliella burgdorferi. Previous work revealed that Borreliaceae genomes differ from most bacteria in that they are composed of large numbers of replicons, both linear and circular, with the main chromosome being the linear with telomeric-like termini. While these findings are novel, additional gene-specific analyses of each class of these multiple replicons are needed to better understand their respective roles in metabolism and pathogenesis of these enigmatic spirochetes. Historically, such studies were challenging due to a dearth of both analytic tools and a sufficient number of high-fidelity genomes among the various taxa within this family as a whole to provide for discriminative and functional genomic studies. Recent advances in long-read whole-genome sequencing, comparative genomics, and machine-learning have provided the tools to better understand the fundamental biology and phylogeny of these genomically-complex pathogens while also providing the data for the development of improved diagnostics and therapeutics.

Reported County-Level Distribution of Seven Human Pathogens Detected in Host-Seeking Ixodes scapularis and Ixodes pacificus (Acari: Ixodidae) in the Contiguous United States

Tickborne disease cases account for over 75% of reported vector-borne disease cases in the United States each year. In addition to transmitting the agents of Lyme disease (Borrelia burgdorferi sensu strict [Spirochaetales: Spirochaetaceae] and Borrelia mayonii [Spirochaetales: Spirochaetaceae]), the blacklegged tick, Ixodes scapularis, and the western blacklegged tick, Ixodes pacificus collectively transmit five additional human pathogens. By mapping the distributions of tickborne pathogens in host-seeking ticks, we can understand where humans are at risk of contracting tickborne diseases and devise targeted strategies to prevent them. Using publicly available tickborne pathogen surveillance databases, internal CDC pathogen testing databases, and SCOPUS search records published since 2000, we mapped the county-level distribution of Borrelia miyamotoi (Spirochaetales: Spirochaetaceae), Anaplasma phagocytophilum (Rickettsiales: Anaplasmataceae), Ehrlichia muris eauclairensis (Rickettsiales: Ehrlichiaceae), Babesia microti (Piroplasmida: Babesiidae), and Powassan virus (Flaviviridae) reported in host-seeking I. scapularis or I. pacificus in the contiguous United States. We also updated recently published maps of the distributions of Borrelia burgdorferi sensu stricto and Borrelia mayonii. All seven pathogen distributions were more limited than the distributions of vector ticks, with at least one of the seven pathogens detected in 30 states out of 41 total states (73.2% of states) where vector ticks are considered to be established. Prevention and diagnosis of tickborne diseases rely on an accurate understanding by the public and health care providers of where people are at risk for exposure to infected ticks. Our county-level pathogen distribution maps expand on previous efforts showing the distribution of Lyme disease spirochetes and highlight counties where further investigation may be warranted.

Relevance of Spatial and Temporal Trends in Nymphal Tick Density and Infection Prevalence for Public Health and Surveillance Practice in Long-Term Endemic Areas: A Case Study in Monmouth County, NJ

Tick-borne diseases are a growing public health problem in the United States, and the US northeast has reported consistently high case rates for decades. Monmouth County, New Jersey, was one of the earliest jurisdictions to report Lyme disease cases in 1979 and reports several hundred cases per year nearly 40 yr later. In the time since, however, tick-borne health risks have expanded far beyond Lyme disease to include a variety of other bacterial pathogens and viruses, and additional vectors, necessitating a continually evolving approach to tick surveillance. In 2017, Monmouth County initiated an active surveillance program targeting sites across three ecological regions for collection of Ixodes scapularis Say (Acari: Ixodidae) and Amblyomma americanum L. (Acari: Ixodidae) as well as testing via qPCR for associated bacterial pathogens. During the first five years of this program (2017-2021), we report high levels of spatiotemporal variability in nymphal density and infection prevalence in both species, limiting the granularity with which human risk can be predicted from acarological data. Nonetheless, broader patterns emerged, including an ongoing trend of A. americanum dominance, risks posed by Borrelia miyamotoi, and the frequency of coinfected ticks. We present some of the first county-level, systematic surveillance of nymphal A. americanum density and infection prevalence in the northeastern US. We also documented a temporary decline in Borrelia burgdorferi that could relate to unmeasured trends in reservoir host populations. We discuss the implications of our findings for tick-borne disease ecology, public health communication, and tick surveillance strategies in endemic areas.

Multi-scale analysis of habitat fragmentation on small-mammal abundance and tick-borne pathogen infection prevalence in Essex County, MA

Habitat fragmentation and heterogeneity transform otherwise contiguous tracks of forest into smaller patches in the northeastern U.S. and likely impact abundances, movement patterns, and disease transmission pathways for small-mammal communities at multiple scales. We sought to determine the structure of a small-mammal community in terms of mammal abundance and infection prevalence of Borrelia burgdorferi sensu stricto (s.s.), Anaplasma phagocytophilum, and Babesia microti within a fragmented landscape in Essex County, Massachusetts, USA. We studied communities at multiple spatial scales, including vegetation, edge type, and landscape (including 200-m, 500-m, and 1000-m radii) scales. A total of 16 study sites were chosen to represent four edge types: interior forest, pasture edge, natural edge, and residential edge. At each site, we trapped small mammals and conducted vegetation surveys and GIS analysis. Upon capture, a tissue sample was collected to analyze for presence of pathogens. Northern short-tailed shrew (Blarina brevicauda) abundance did not differ based on edge type, whereas abundance of the white-footed mouse (Peromyscus leucopus) was greatest at pasture edges, although the relationship was relatively weak. White-footed mouse abundance was negatively associated with amount of forested area within a 500-m radius, whereas northern short-tailed shrew abundance demonstrated a positive relationship with fragmentation indices at the 200-m radius. White-footed mice captured at interior-forest habitat were more likely be infected with B. burgdorferi (s.s.) than individuals from edge habitat. Greater prevalence of B. burgdorferi infection of white-footed mice in forest interiors compared to edge habitats counters previous studies. Reasons for this and implications are discussed.

Sympatric occurrence of Ixodes ricinus with Dermacentor reticulatus and Haemaphysalis concinna and the associated tick-borne pathogens near the German Baltic coast

Background

Ixodid ticks from the Northern Hemisphere have registered a northward expansion in recent years, and Dermacentor reticulatus is such an example in Europe, its expansion being considered a result of climate change alongside other factors. The aim of this study was to identify the composition of questing tick species and the associated pathogens at different sites near the German Baltic coast.

Methods

Questing ticks were collected monthly at four sites (May–November, 2020), mainly grasslands, and in October and November 2020 at a fifth site. Molecular screening of ticks for pathogens included RT-qPCR for the tick-borne encephalitis virus (TBEV), qPCR for Anaplasma phagocytophilum, PCR for Babesia species and Rickettsia species, and nested PCR for Borrelia species.

Results

Altogether 1174 questing ticks were collected: 760 Ixodes ricinus, 326 D. reticulatus and 88 Haemaphysalis concinna. The highest activity peak of I. ricinus and D. reticulatus was in May, in June for H. concinna while a second peak was observed only for I. ricinus and D. reticulatus in September and October, respectively. All samples tested negative for TBEV. For A. phagocytophilum, 1.5% of I. ricinus adults tested positive while the minimum infection rate (MIR) in nymphs was 1.3%. This pathogen was found in 0.6% of D. reticulatus. Babesia spp. were detected in I. ricinus (18.2% adults, 2.1% MIR in nymphs) and H. concinna (13.3% adults, 9.7% MIR in nymphs). Borrelia spp. were present only in I. ricinus (49.1% adults, 11.9% MIR in nymphs), while Rickettsia spp. were detected in I. ricinus (14% adults, 8.9% MIR in nymphs) and D. reticulatus (82%). Co-detection of pathogens was observed in 26.6% and 54.8% of positive I. ricinus adults and nymph pools, respectively, while one D. reticulatus tested positive for A. phagocytophilum and Rickettsia spp. The most common co-infection in I. ricinus adults was Babesia microti and Borrelia afzelii (12.3% of positive ticks).

Conclusions

The results of this study confirm the northern expansion of D. reticulatus and H. concinna in Germany. The detailed data of the infection levels at each location could be useful in assessing the risk of pathogen acquisition following a tick bite.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s13071-022-05173-2.

Host contributions to the force of Borrelia burgdorferi and Babesia microti transmission differ at edges of and within a small habitat patch

In the northeastern United States, the emergence of Lyme disease has been associated, in part, with the increase of small forest patches. Such disturbed habitat is exploited by generalist species, such as white-footed mice, which are considered the host with the greatest reservoir capacity for the agents of Lyme disease (Borrelia burgdorferi sensu stricto) and human babesiosis (Babesia microti). Spatial risk analyses have identified edge habitat as particularly risky. Using a retrotransposon-based quantitative PCR assay for host bloodmeal remnant identification, we directly measured whether the hosts upon which vector ticks fed differed at the edge or within the contiguous small habitat patch. Questing nymphal deer ticks, Ixodes dammini, the northern clade of Ixodes scapularis, were collected from either the edge or within a thicket on Nantucket Island over 3 transmission seasons and tested for evidence of infection as well as bloodmeal hosts. Tick bloodmeal hosts significantly differed by site as well as by year. Mice and deer were identified most often (49.9%), but shrews, rabbits and birds were also common. Ticks from the edge fed on a greater diversity of hosts than those from the thicket. Surprisingly, mice were not strongly associated with either infection at either sampling site (OR<2 for all). Although shrews were not the most common host utilized by ticks, they were highly associated with both infections at both sites (OR= 4.5 and 7.9 B. burgdorferi and 7.9 and 19.0 B. microti, edge and thicket). We conclude that reservoir hosts may differ in their contributions to infecting ticks between edge and contiguous vegetated patches. Importance Habitat fragmentation is thought to be a main factor in the emergence of Lyme disease and other of the deer tick-transmitted infections. The patchwork of forest and edges promotes altered biodiversity, favoring the abundance of generalist rodents such as white footed mice, heretofore considered a key tick and reservoir host in the northeastern U.S. We used tick bloodmeal analyses to directly identify the hosts from which nymphal deer ticks became infected. We demonstrate that there is considerable microfocality in host contributions to the cohort of infected ticks and that shrews, although they fed fewer ticks than mice, disproportionately influenced the force of pathogen transmission in our site. The venue of transmission of certain deer tick-transmitted agents may comprise a habitat scale of 10 meters or fewer and depend on alternative small mammal hosts such as shrews.

Potential Role of Avian Populations in the Epidemiology of Rickettsia spp. and Babesia spp

Birds often are carriers of hard and/or soft ticks harboring pathogens of humans and veterinary concern. Migratory avian species, which cover long distance by their flight, may deeply influence the ticks’ distribution worldwide; in particular, they can introduce in a given geographic area new tick species and related tick-borne pathogens. Studies about the detection of tick-borne agents in birds are not numerous, whereas more attention has been turned to the presence of these microorganisms in ticks carried by birds. The present review focused on the role of avian populations in the epidemiology of rickettsioses and babesioses, which represent two severe problems for the health of humans and other mammals.

High Prevalence of Borrelia mayonii (Spirochaetales: Spirochaetaceae) in Field-Caught Tamias striatus (Rodentia: Sciuridae) From Northern Wisconsin

Borrelia mayonii is a recently discovered bacterial spirochete that causes Lyme disease and is transmitted by the blacklegged tick, Ixodes scapularis Say (Acari: Ixodidae). To date, B. mayonii has been isolated from two vertebrate host species in Minnesota: field-caught white-footed mice (Peromyscus leucopus Rafinesque; Rodentia: Cricetidae) and American red squirrel (Tamiasciurus hudsonicus Erxleben). Here, we describe the first detection of B. mayonii in field-caught eastern chipmunks (Tamias striatus L. (Rodentia: Cricetidae)) from northern Wisconsin. During our study, we captured 530 unique small mammals and found an infection prevalence of 23.50% in field-caught eastern chipmunks (4/17) and 1.19% in Peromyscus spp. (5/420). Mean larval and nymphal burdens were determined for captured Blarina brevicauda (0, 0), Glaucomys volans (0.29, 0.14), Myodes gapperi (0.27, 0), Napaeozapus insignis (0, 0.25), Peromyscus spp. (1.88, 0.11), T. striatus (1.06, 0.65), and Sorex cinereus (0.09, 0). The high B. mayonii infection prevalence in eastern chipmunks suggests that the species may be an important reservoir for B. mayonii in the Upper Midwest.

A Comparative Spatial and Climate Analysis of Human Granulocytic Anaplasmosis and Human Babesiosis in New York State (2013-2018)

Human granulocytic anaplasmosis (HGA) and human babesiosis are tick-borne diseases spread by the blacklegged tick (Ixodes scapularis Say, Acari: Ixodidae) and are the result of infection with Anaplasma phagocytophilum and Babesia microti, respectively. In New York State (NYS), incidence rates of these diseases increased concordantly until around 2013, when rates of HGA began to increase more rapidly than human babesiosis, and the spatial extent of the diseases diverged. Surveillance data of tick-borne pathogens (2007 to 2018) and reported human cases of HGA (n = 4,297) and human babesiosis (n = 2,986) (2013-2018) from the New York State Department of Health (NYSDOH) showed a positive association between the presence/temporal emergence of each pathogen and rates of disease in surrounding areas. Incidence rates of HGA were higher than human babesiosis among White and non-Hispanic/non-Latino individuals, as well as all age and sex groups. Human babesiosis exhibited higher rates among non-White individuals. Climate, weather, and landscape data were used to build a spatially weighted zero-inflated negative binomial (ZINB) model to examine and compare associations between the environment and rates of HGA and human babesiosis. HGA and human babesiosis ZINB models indicated similar associations with forest cover, forest land cover change, and winter minimum temperature; and differing associations with elevation, urban land cover change, and winter precipitation. These results indicate that tick-borne disease ecology varies between pathogens spread by I. scapularis.

The Global Emergence of Human Babesiosis

Babesiosis is an emerging tick-borne disease caused by intraerythrocytic protozoa that are primarily transmitted by hard-bodied (ixodid) ticks and rarely through blood transfusion, perinatally, and organ transplantation. More than 100 Babesia species infect a wide spectrum of wild and domestic animals worldwide and six have been identified as human pathogens. Babesia microti is the predominant species that infects humans, is found throughout the world, and causes endemic disease in the United States and China. Babesia venatorum and Babesia crassa-like agent also cause endemic disease in China. Babesia divergens is the predominant species in Europe where fulminant cases have been reported sporadically. The number of B. microti infections has been increasing globally in recent decades. In the United States, more than 2000 cases are reported each year, although the actual number is thought to be much higher. In this review of the epidemiology of human babesiosis, we discuss epidemiologic tools used to monitor disease location and frequency; demographics and modes of transmission; the location of human babesiosis; the causative Babesia species in the Americas, Europe, Asia, Africa, and Australia; the primary clinical characteristics associated with each of these infections; and the increasing global health burden of this disease.

Ticks, Human Babesiosis and Climate Change

The effects of current and future global warming on the distribution and activity of the primary ixodid vectors of human babesiosis (caused by Babesia divergens, B. venatorum and B. microti) are discussed. There is clear evidence that the distributions of both Ixodes ricinus, the vector in Europe, and I. scapularis in North America have been impacted by the changing climate, with increasing temperatures resulting in the northwards expansion of tick populations and the occurrence of I. ricinus at higher altitudes. Ixodes persulcatus, which replaces I. ricinus in Eurasia and temperate Asia, is presumed to be the babesiosis vector in China and Japan, but this tick species has not yet been confirmed as the vector of either human or animal babesiosis. There is no definite evidence, as yet, of global warming having an effect on the occurrence of human babesiosis, but models suggest that it is only a matter of time before cases occur further north than they do at present.

Dilution effects in disease ecology

For decades, people have reduced the transmission of pathogens by adding low‐quality hosts to managed environments like agricultural fields. More recently, there has been interest in whether similar ‘dilution effects’ occur in natural disease systems, and whether these effects are eroded as diversity declines. For some pathogens of plants, humans and other animals, the highest‐quality hosts persist when diversity is lost, so that high‐quality hosts dominate low‐diversity communities, resulting in greater pathogen transmission. Meta‐analyses reveal that these natural dilution effects are common. However, studying them remains challenging due to limitations on the ability of researchers to manipulate many disease systems experimentally, difficulties of acquiring data on host quality and confusion about what should and should not be considered a dilution effect. Because dilution effects are widely used in managed disease systems and have been documented in a variety of natural disease systems, their existence should not be considered controversial. Important questions remain about how frequently they occur and under what conditions to expect them. There is also ongoing confusion about their relationships to both pathogen spillover and general biogeographical correlations between diversity and disease, which has resulted in an inconsistent and confusing literature. Progress will require rigorous and creative research.

Animal reservoirs of zoonotic Babesia species: A global systematic review and meta-analysis of their prevalence, distribution and species diversity

Zoonotic babesiosis caused by Babesia divergens, B. microti and B. venatorum is a vector-borne protozoan zoonosis of increasing public health importance worldwide. A complex system of animal reservoirs including a wide range of mammals and a limited number of birds play a central role in maintaining the infection. Governed by the PRISMA guidelines, we conducted a systematic review and meta-analysis to determine the global prevalence, distribution and the diversity of zoonotic Babesia species in animal reservoirs. We pooled data using the random-effects model and determined quality of individual studies, heterogeneity and across study bias using the Joanna Briggs Institute critical appraisal instrument for prevalence studies, Cochran's Q-test and Egger's regression test respectively. Seventy nine studies from 29 countries reported a total 9311 positive cases of zoonotic Babesia infections from 46,649 animal reservoirs, yielding an overall estimated prevalence of 12.45% (95% CI: 10.09-15.27). Continental prevalence ranged between 8.55 (95% CI: 1.90-31.11) in Africa and 27.81% (95% CI: 21.25-35.48) in North America. Estimated prevalence in relation to country income levels, methods of diagnosis, study periods, sample sizes and reservoir categories ranged between 4.97 (95% CI: 1.80-13.00) and 30.12% (95% CI: 22.49-39.04). B. divergens was the most prevalent (12.50%, 95% CI: 8.30-18.39) of the 3 species of zoonotic Babesia reported in animal reservoirs. Zoonotic Babesia infections are prevalent in animal reservoirs across the world with the highest prevalence in North America and domestic animals. B. microti had the widest geographic distribution. We recommend tick control as well as strategic and prophylactic treatment against these parasites in animal reservoirs to curtail the economic losses associated with zoonotic Babesia species and possible transmission to humans.

The Contribution of Wildlife Hosts to the Rise of Ticks and Tick-Borne Diseases in North America

Wildlife vertebrate hosts are integral to enzootic cycles of tick-borne pathogens, and in some cases have played key roles in the recent rise of ticks and tick-borne diseases in North America. In this forum article, we highlight roles that wildlife hosts play in the maintenance and transmission of zoonotic, companion animal, livestock, and wildlife tick-borne pathogens. We begin by illustrating how wildlife contribute directly and indirectly to the increase and geographic expansion of ticks and their associated pathogens. Wildlife provide blood meals for tick growth and reproduction; serve as pathogen reservoirs; and can disperse ticks and pathogens-either through natural movement (e.g., avian migration) or through human-facilitated movement (e.g., wildlife translocations and trade). We then discuss opportunities to manage tick-borne disease through actions directed at wildlife hosts. To conclude, we highlight key gaps in our understanding of the ecology of tick-host interactions, emphasizing that wildlife host communities are themselves a very dynamic component of tick-pathogen-host systems and therefore complicate management of tick-borne diseases, and should be taken into account when considering host-targeted approaches. Effective management of wildlife to reduce tick-borne disease risk further requires consideration of the 'human dimensions' of wildlife management. This includes understanding the public's diverse views and values about wildlife and wildlife impacts-including the perceived role of wildlife in fostering tick-borne diseases. Public health agencies should capitalize on the expertise of wildlife agencies when developing strategies to reduce tick-borne disease risks.

The dilution effect behind the scenes: testing the underlying assumptions of its mechanisms through quantifying the long-term dynamics and effects of a pathogen in multiple host species

Disentangling the mechanisms that mediate the relationships between species diversity and disease risk has both theoretical and applied implications. We employed a model system of rodents and their Mycoplasma pathogens, in which an extreme negative diversity-disease relationship was demonstrated, to test the assumptions underlying three mechanisms that may explain this field pattern. Through quantifying the long-term dynamics and effects of the pathogen in its three host species, we estimated the between-host differences in pathogen spreading and transmission potentials, and host recovery potential and vulnerability to infection. The results suggest that one of the hosts is a pathogen amplifier and the other two hosts function as diluters. Considering the similarity in infection success and intensity among hosts, and the failure to detect any pathogen-induced damage, we could not validate the assumption underlying the hypotheses that diluters reduce the overall transmission or increase the mortality of infected hosts in the system. Instead, the results demonstrate that diluters clear the infection faster than amplifiers, supporting the possibility that the addition of diluters to the community may reduce the overall number of infected hosts through this mechanism. This study highlights the contribution of experimental studies that simultaneously explore different aspects of host-pathogen interactions in multiple hosts, in diversity-disease research.

Three Babesia species in Ixodes ricinus ticks from migratory birds in Sweden

Background

Migratory birds can cross geographical and environmental barriers and are thereby able to facilitate transmission of tick-borne pathogens both as carriers of infected ticks and as reservoirs of pathogenic microorganisms. Ixodes ricinus is one of the most abundant tick species in the Northern Hemisphere and a main vector of several Babesia species, some which pose a potential threat to human and animal health. At present only two cases of overt babesiosis in humans have so far been reported in Sweden. To better understand the potential role of birds as disseminators of zoonotic Babesia protozoan parasites, we investigated the presence of Babesia species in ticks removed from migratory birds.

Methods

Ticks were collected from birds captured at Ottenby Bird Observatory, south-eastern Sweden, from March to November 2009. Ticks were molecularly identified to species, and morphologically to developmental stage, and the presence of Babesia protozoan parasites was determined by real-time PCR.

Results

In total, 4601 migratory birds of 65 species were examined for tick infestation. Ticks removed from these birds have previously been investigated for the presence of Borrelia bacteria and the tick-borne encephalitis virus. In the present study, a total of 1102 ticks were available for molecular analysis of Babesia protozoan parasites. We found that 2.4% of the ticks examined, all I. ricinus, were positive for mammal-associated Babesia species. Out of all Babesia-positive samples, Babesia venatorum was the most prevalent (58%) species, followed by Babesia microti (38%) and Babesia capreoli (4.0%). B. venatorum and B. capreoli were detected in I. ricinus larvae, whereas B. microti was only present in I. ricinus nymphs. This supports the view that the two first-mentioned species are vertically (transovarially) transmitted in the tick population, in contrast to B. microti. The largest number of Babesia-infected ticks was removed from the common redstart (Phoenicurus phoenicurus) and European robin (Erithacus rubecula).

Conclusions

This study reveals that Babesia protozoan parasites are present in ticks infesting migratory birds in south-eastern Sweden, which could potentially lead to the dissemination of these tick-borne microorganisms into new areas, thus posing a threat to humans and other mammals.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13071-021-04684-8.

Using Data Surveillance to Understand the Rising Incidence of Babesiosis in the United States, 2011-2018

Babesiosis is a tick-borne disease that is caused by intraerythrocytic protozoan parasites of the genus Babesia. Common symptoms of babesiosis are generally characterized as nonspecific flu-like symptoms, such as fever or chills. Human infections are reported to the Centers for Disease Control and Prevention (CDC) through the National Notifiable Diseases Surveillance System (NNDSS). This study summarizes data of Babesia infections reported to the CDC by the NNDSS from 2011 to 2018. In total, there were 14,159 reported cases of babesiosis, and the incidence rate was 5.55 cases per million persons per year, displaying an increasing trend during the study period. The demographic group most affected was middle-aged and elderly white males. Infections were most abundant in the New England and the Mid-Atlantic regions of the United States. Our study provides useful results for a basic understanding of incidence, spatial and temporal distribution, and severity of babesiosis.

Clofazimine, a Promising Drug for the Treatment of Babesia microti Infection in Severely Immunocompromised Hosts

BACKGROUND

Persistent and relapsing babesiosis caused by Babesia microti often occurs in immunocompromised patients, and has been associated with resistance to antimicrobial agents such as atovaquone. Given the rising incidence of babesiosis in the United States, novel drugs are urgently needed. In the current study, we tested whether clofazimine (CFZ), an antibiotic used to treat leprosy and drug-resistant tuberculosis, is effective against B. microti.

METHODS

Mice with severe combined immunodeficiency were infected with 107B. microti-infected erythrocytes. Parasites were detected by means of microscopic examination of Giemsa-stained blood smears or nested polymerase chain reaction. CFZ was administered orally.

RESULTS

Uninterrupted monotherapy with CFZ curtailed the rise of parasitemia and achieved radical cure. B. microti parasites and B. microti DNA were cleared by days 10 and 50 of therapy, respectively. A 7-day administration of CFZ delayed the rise of parasitemia by 22 days. This rise was caused by B. microti isolates that did not carry mutations in the cytochrome b gene. Accordingly, a 14-day administration of CFZ was sufficient to resolve high-grade parasitemia caused by atovaquone-resistant B. microti parasites.

CONCLUSIONS

Clofazimine is effective against B. microti infection in the immunocompromised host. Additional preclinical studies are required to identify the minimal dose and dosage of CFZ for babesiosis.

Association of the invasive Haemaphysalis longicornis tick with vertebrate hosts, other native tick vectors, and tick-borne pathogens in New York City, USA

Haemaphysalis longicornis, the Asian longhorned tick, is an invasive ixodid tick that has rapidly spread across the northeastern and southeastern regions of the United States since first reported in 2017. The emergence of H. longicornis presents a potential threat for livestock, wildlife, and human health as the host associations and vector potential of this invasive pest in the United States are poorly understood. Previous field data from the United States has shown that H. longicornis was not associated with natural populations of small mammals or birds, but they show a preference for medium sized mammals in laboratory experiments. Therefore, medium and large sized mammals were sampled on Staten Island, New York, United States, to determine H. longicornis host associations and vector potential for a range of human and veterinary pathogens. A total of 97 hosts were sampled and five species of tick (Amblyomma americanum, Dermacentor variabilis, H. longicornis, Ixodes scapularis, Ixodes cookei) were found feeding concurrently on these hosts. Haemaphysalis longicornis was found in the highest proportions compared with other native tick species on raccoons (55.4%), Virginia opossums (28.9%), and white-tailed deer (11.5%). Tissue, blood, and engorged larvae were tested for 17 different pathogens using a nanoscale PCR platform. Infection with five pathogens (Borrelia burgdorferi, Anaplasma phagocytophilum, Rickettsia spp., Mycoplasma haemocanis, and Bartonella spp.) was detected in host samples, but no pathogens were found in any larval samples. These results suggest that although large and medium sized mammals feed large numbers of H. longicornis ticks in the environment, there is presently a low potential for H. longicornis to acquire pathogens from these wildlife hosts.

Spatial and temporal patterns of the emerging tick-borne pathogen Borrelia miyamotoi in blacklegged ticks (Ixodes scapularis) in New York

Borrelia miyamotoi, a bacterium that causes relapsing fever, is found in ixodid ticks throughout the northern hemisphere. The first cases of human infection with B. miyamotoi were identified in 2011. In the eastern USA, blacklegged ticks (Ixodes scapularis) become infected by feeding on an infected vertebrate host, or through transovarial transmission. We surveyed B. miyamotoi prevalence in ticks within forested habitats in Dutchess County, New York, and identified possible reservoir hosts. To assess spatial variation in infection, we collected questing nymphal ticks at > 150 sites. To assess temporal variation in infection, we collected questing nymphs for 8 years at a single study site. We collected questing larval ticks from nine plots to estimate the amount of transovarial transmission. To evaluate potential reservoir hosts, we captured 14 species of mammal and bird hosts naturally infested with larval blacklegged ticks and held these hosts in the laboratory until ticks fed to repletion and molted to nymphs. We determined infection for all ticks using quantitative polymerase chain reaction. The overall infection prevalence of questing nymphal ticks across all sites was ~ 1%, but prevalence at individual sites was as high as 9.1%. We detected no significant increase in infection through time. Only 0.4% of questing larval ticks were infected. Ticks having fed as larvae from short-tailed shrews, red squirrels, and opossums tended to have higher infection prevalence than did ticks having fed on other hosts. Further studies of the role of hosts in transmission are warranted. The locally high prevalence of B. miyamotoi in the New York/New England landscape suggests the importance of vigilance by health practitioners and the public.

Retrotransposon-Based Blood Meal Analysis of Nymphal Deer Ticks Demonstrates Spatiotemporal Diversity of Borrelia burgdorferi and Babesia microti Reservoirs

Deer tick-transmitted Borrelia burgdorferi sensu stricto (Lyme disease) and Babesia microti (babesiosis) increasingly burden public health across eastern North America. The white-footed mouse is considered the primary host for subadult deer ticks and the most important reservoir host for these and other disease agents. Local transmission is thought to be modulated by less reservoir-competent hosts, such as deer, diverting ticks from feeding on mice. We measured the proportion of mouse-fed or deer-fed host-seeking nymphs from 4 sites during 2 transmission seasons by blood meal remnant analysis using a new retrotransposon-based quantitative PCR (qPCR) assay. We then determined the host that was associated with the infection status of the tick. During the first year, the proportion of mouse-fed ticks ranged from 17% on mainland sites to 100% on an island, while deer-fed ticks ranged from 4% to 24%. The proportion of ticks feeding on mice and deer was greater from island sites than mainland sites (on average, 92% versus 43%). Mouse-fed ticks decreased significantly during year 2 in 3 of 4 sites (most were <20%), while deer-fed ticks increased for all sites (75% at one site). Overall, ticks were more likely to be infected when they had fed on mice (odds ratio [OR] of 2.4 and 1.6 for Borrelia and Babesia, respectively) and were less likely to be infected if they had fed on deer (OR, 0.8 and 0.4). We conclude that host utilization by deer ticks is characterized by significant spatiotemporal diversity, which may confound efficacy tests of interventions targeting reservoir hosts.IMPORTANCE White-footed mice are thought to be the most important reservoir host for the deer tick-transmitted pathogens that cause Lyme disease and human babesiosis because they are the primary host for immature ticks. Transmission would be reduced, however, if ticks feed on deer, which are not capable of infecting ticks with either pathogen. By directly measuring whether ticks had fed on either mice or deer using a new quantitative PCR (qPCR) assay to detect remnants of host DNA leftover from the larval blood meal, we demonstrate that host utilization by ticks varies significantly over time and space and that mice often feed fewer ticks than expected. This finding has implications for our understanding of the ecology of these diseases and for the efficacy of control measures.

Human babesiosis: recent advances and future challenges

PURPOSE OF REVIEW

As human babesiosis caused by apicomplexan parasites of the Babesia genus is associated with transfusion-transmitted illness and relapsing disease in immunosuppressed populations, it is important to report novel findings relating to parasite biology that may be responsible for such pathology. Blood screening tools recently licensed by the FDA are also described to allow understanding of their impact on keeping the blood supply well tolerated.

RECENT FINDINGS

Reports of tick-borne cases within new geographical regions such as the Pacific Northwest of the USA, through Eastern Europe and into China are also on the rise. Novel features of the parasite lifecycle that underlie the basis of parasite persistence have recently been characterized. These merit consideration in deployment of both detection, treatment and mitigation tools such as pathogen inactivation technology. The impact of new blood donor screening tests in reducing transfusion transmitted babesiosis is discussed.

SUMMARY

New Babesia species have been identified globally, suggesting that the epidemiology of this disease is rapidly changing, making it clear that human babesiosis is a serious public health concern that requires close monitoring and effective intervention measures. Unlike other erythrocytic parasites, Babesia exploits unconventional lifecycle strategies that permit host cycles of different lengths to ensure survival in hostile environments. With the licensure of new blood screening tests, incidence of transfusion transmission babesiosis has decreased.

Field evaluation of a novel oral reservoir-targeted vaccine against Borrelia burgdorferi utilizing an inactivated whole-cell bacterial antigen expression vehicle

Blacklegged ticks (Ixodes scapularis) are the principal vector for Borrelia burgdorferi, among other infectious agents, in the northeastern, mid-Atlantic, and upper midwestern USA. White-footed mice (Peromyscus leucopus) are the primary and most competent reservoir host of B. burgdorferi in the Northeast. Live reservoir-targeted vaccines (RTVs) to limit enzootic transmission of B. burgdorferi were previously developed and successfully evaluated in laboratory and controlled field trials. A novel, inactivated RTV was developed to minimize regulatory and market challenges facing previous RTVs based on live bacterial or viral vehicles. Thirty-two residential properties in Redding, Connecticut, participated in a field trial of an orally delivered, inactivated RTV efficacy study (2015-2016). During the two-year vaccination period, a significant decrease in the percentage of B. burgdorferi-infected I. scapularis larvae parasitizing P. leucopus was observed, as was a significant reduction in the percentage of infected P. leucopus on RTV-treated properties when compared to control properties. This novel inactivated RTV was effective in reducing numbers of B. burgdorferi-infected I. scapularis and B. burgdorferi-infected P. leucopus on properties where it was distributed.

Identifying the Naphthalene-Based Compound 3,5-Dihydroxy 2-Napthoic Acid as a Novel Lead Compound for Designing Lactate Dehydrogenase-Specific Antibabesial Drug

Human babesiosis is caused by apicomplexan Babesia parasites, including Babesia microti, Babesia crassa, Babesia sp. MOI, Babesia divergens, Babesia duncani, and Babesia venatorum. Among them, B. microti is the most common cause of human and rodent babesiosis. Currently, no vaccine is available, and drugs for the treatment have high failure rates and side effects. Due to lack of a traditional tricarboxylic acid cycle (TCA cycle) and its dominant dependence on anaerobic metabolism to produce ATP, B. microti lactate dehydrogenase (BmLDH) was assumed to play a critical role in B. microti ATP supply. Our previous study demonstrated that BmLDH is a potential drug target and Arg99 is a crucial site. Herein, a molecular docking was performed based on the crystal structure of BmLDH from a series of gossypol derivatives or structural analogs to find the potent inhibitors interacting with the residue Arg99, and three naphthalene-based compounds 2,6-naphthalenedicarboxylic acid (NDCA), 1,6-dibromo-2-hydroxynapthalene 3-carboxylic acid (DBHCA), and 3,5-dihydroxy 2-napthoic acid (DHNA) were selected for further tests. Enzyme activity inhibitory experiments show that DBHCA and DHNA inhibit recombinant BmLDH (rBmLDH) catalysis with ~109-fold and ~5,000-fold selectivity over human LDH, respectively. Surface plasmon resonance (SPR) assays demonstrate that DHNA has a lower K _D value to BmLDH (3.766 x 10^-5 M), in contrast to a higher value for DBHCA (3.988 x 10^-8 M). A comparison of the kinetic parameters [association constant (k _a) and dissociation constant (k _d) values] reveals that DBHCA can bind the target faster than DHNA, while the complex of DHNA with the target dissociates slower than that of DBHCA. Both DBHCA and DHNA can inhibit the growth of B. microti in vitro with half-maximal inhibitory concentration (IC₅₀) values of 84.83 and 85.65 μM, respectively. Cytotoxicity tests in vitro further indicate that DBHCA and DHNA have selectivity indexes (SI) of 2.6 and 22.1 between B. microti and Vero cells, respectively. Although the two naphthalene-based compounds only display modest inhibitory activity against both rBmLDH and the growth of B. microti, the compound DHNA features high selectivity and could serve as a novel lead compound for designing LDH-specific antibabesial drug.

Effect of rodent density on tick and tick-borne pathogen populations: consequences for infectious disease risk

BACKGROUND

Rodents are considered to contribute strongly to the risk of tick-borne diseases by feeding Ixodes ricinus larvae and by acting as amplifying hosts for pathogens. Here, we tested to what extent these two processes depend on rodent density, and for which pathogen species rodents synergistically contribute to the local disease risk, i.e. the density of infected nymphs (DIN).

METHODS

In a natural woodland, we manipulated rodent densities in plots of 2500 m² by either supplementing a critical food source (acorns) or by removing rodents during two years. Untreated plots were used as controls. Collected nymphs and rodent ear biopsies were tested for the presence of seven tick-borne microorganisms. Linear models were used to capture associations between rodents, nymphs, and pathogens.

RESULTS

Investigation of data from all plots, irrespective of the treatment, revealed a strong positive association between rodent density and nymphal density, nymphal infection prevalence (NIP) with Borrelia afzelii and Neoehrlichia mikurensis, and hence DIN's of these pathogens in the following year. The NIP, but not the DIN, of the bird-associated Borrelia garinii, decreased with increasing rodent density. The NIPs of Borrelia miyamotoi and Rickettsia helvetica were independent of rodent density, and increasing rodent density moderately increased the DINs. In addition, NIPs of Babesia microti and Spiroplasma ixodetis decreased with increasing rodent density, which had a non-linear association with DINs of these microorganisms.

CONCLUSIONS

A positive density dependence for all rodent- and tick-associated tick-borne pathogens was found, despite the observation that some of them decreased in prevalence. The effects on the DINs were variable among microorganisms, more than likely due to contrasts in their biology (including transmission modes, host specificity and transmission efficiency). The strongest associations were found in rodent-associated pathogens that most heavily rely on horizontal transmission. Our results draw attention to the importance of considering transmission mode of a pathogen while developing preventative measures to successfully reduce the burden of disease.

Influence of Forest Disturbance on La Crosse Virus Risk in Southwestern Virginia

Forest disturbance effects on La Crosse virus (LACV) are currently unknown. We determined the abundance of three LACV accessory vectors (Aedes albopictus, Ae. canadensis, and Ae. vexans) and the primary amplifying host (Eastern chipmunk; Tamias striatus), and tested for LACV prevalence in both vectors and chipmunks, across a gradient of experimental forest disturbance treatments in southwest Virginia. Forest disturbance significantly affected the abundance of LACV accessory vectors, with a higher abundance on disturbed sites for Ae. canadensis and Ae.vexans. However, there was no significant disturbance effect on chipmunk abundance. Forest disturbance significantly affected LACV prevalence in mosquito vectors, with most (80%) detections on unlogged control sites, which past work showed harbor the highest abundance of the two most common LACV vectors (the primary vector Aedes triseriatus, and Ae. japonicus). Interestingly, LACV nucleic acid was only detected in Ae. japonicus and Culex pipiens/restuans, with no detections in the primary vector, Ae. triseriatus. In contrast to the vector results, antibodies were only found in chipmunks on logged sites, but this result was not statistically significant. Overall, our results suggest that human LACV risk should generally decline with logging, and reveal the potential importance of accessory vectors in LACV maintenance in Appalachian forests.

[Human babesiosis: clinical cases in the european part of the Russian Federation]

The article describes four clinical observations of patients with babesiosis detected in the European part of the Russian Federation, two of whom were under the direct supervision of the authors. The analysis of epidemiological data, clinical picture, results of laboratory studies in the dynamics of the disease. Differential diagnosis and treatment are discussed.

Ticks as Soil-Dwelling Arthropods: An Intersection Between Disease and Soil Ecology

Ticks are widespread vectors for many important medical and veterinary infections, and a better understanding of the factors that regulate their population dynamics is needed to reduce risk for humans, wildlife, and domestic animals. Most ticks, and all non-nidicolous tick species, spend only a small fraction of their lives associated with vertebrate hosts, with the remainder spent in or on soils and other substrates. Ecological studies of tick-borne disease dynamics have emphasized tick-host interactions, including host associations, burdens, and efficiencies of pathogen transmission, while under emphasizing tick biology during off-host periods. Our ability to predict spatiotemporal trends in tick-borne diseases requires more knowledge of soil ecosystems and their effect on host and tick populations. In this review, we focus on tick species of medical and veterinary concern and describe: 1) the relationships between soil factors and tick densities; 2) biotic and abiotic factors within the soil ecosystem that directly affect tick survival; 3) potential indirect effects on ticks mediated by soil ecosystem influences on their vertebrate hosts; 4) the potential for tick-mediated effects on vertebrate host populations to affect ecosystems; and 5) possible nontarget impacts of tick management on the soil ecosystem. Soils are complex ecosystem components with enormous potential to affect the survival and behavior of ticks during their off-host periods. Hence, tick-borne disease systems present an excellent opportunity for soil ecologists and public health researchers to collaborate and improve understanding of these medically important and ecologically complex disease cycles.

Splenic infarction in babesiosis: A rare presentation

Babesiosis is a protozoan parasitic infection transmitted by the Ixodes tick. Splenic infarction is a rare, but potentially life-threatening complication of babesiosis; it is therefore vital that this complication is recognized.

Prevalence, distribution, and diversity of cryptic piroplasm infections in raccoons from selected areas of the United States and Canada

The order Piroplasmida contains a diverse group of intracellular parasites, many of which can cause significant disease in humans, domestic animals, and wildlife. Two piroplasm species have been reported from raccoons (Procyon lotor), Babesia lotori (Babesia sensu stricto clade) and a species related to Babesia microti (called B. microti-like sp.). The goal of this study was to investigate prevalence, distribution, and diversity of Babesia in raccoons. We tested raccoons from selected regions in the United States and Canada for the presence of Babesia sensu stricto and Babesia microti-like sp. piroplasms. Infections of Babesia microti-like sp. were found in nearly all locations sampled, often with high prevalence, while Babesia sensu stricto infections had higher prevalence in the Southeastern United States (20–45% prevalence). Co-infections with both Babesia sp. were common. Sequencing of the partial 18S rRNA and cytochrome oxidase subunit 1 (cox1) genes led to the discovery of two new Babesia species, both found in several locations in the eastern and western United States. One novel Babesia sensu stricto sp. was most similar to Babesia gibsoni while the other Babesia species was present in the ‘western piroplasm’ group and was related to Babesia conradae. Phylogenetic analysis of the cox1 sequences indicated possible eastern and western genetic variants for the three Babesia sensu stricto species. Additional analyses are needed to characterize these novel species; however, this study indicates there are now at least four species of piroplasms infecting raccoons in the United States and Canada (Babesia microti-like sp., Babesia lotori, a novel Babesia sensu stricto sp., a novel western Babesia sp.) and a possible fifth species (Babesia sensu stricto) in raccoons in Japan.

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Raccoons in all locations tested were infected with piroplasms.

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Babesia microti-like sp. was commonly found in raccoons throughout North America.

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Babesia sensu stricto spp. were less common throughout North America.

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Four, possibly five, distinct species of piroplasms in raccoons.

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Possible spatial genetic variation within the two raccoon piroplasm species.