Emerging tick-borne infections: rediscovered and better characterized, or truly ‘new’?

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.

Evaluating spatial and temporal patterns of tick exposure in the United States using community science data submitted through a smartphone application

Research initiatives that engage the public (i.e., community science or citizen science) increasingly provide insights into tick exposures in the United States. However, these data have important caveats, particularly with respect to reported travel history and tick identification. Here, we assessed whether a smartphone application, The Tick App, provides reliable and novel insights into tick exposures across three domains - travel history, broad spatial and temporal patterns of species-specific encounters, and tick identification. During 2019-2021, we received 11,424 tick encounter submissions from across the United States, with nearly all generated in the Midwest and Northeast regions. Encounters were predominantly with human hosts (71%); although one-fourth of ticks were found on animals. Half of the encounters (51%) consisted of self-reported peri‑domestic exposures, while 37% consisted of self-reported recreational exposures. Using phone-based location services, we detected differences in travel history outside of the users' county of residence along an urbanicity gradient. Approximately 75% of users from large metropolitan and rural counties had travel out-of-county in the four days prior to tick detection, whereas an estimated 50-60% of users from smaller metropolitan areas did. Furthermore, we generated tick encounter maps for Dermacentor variabilis and Ixodes scapularis that partially accounted for travel history and overall mirrored previously published species distributions. Finally, we evaluated whether a streamlined three-question sequence (on tick size, feeding status, and color) would inform a simple algorithm to optimize image-based tick identification. Visual aides of tick coloration and size engaged and guided users towards species and life stage classification moderately well, with 56% of one-time submitters correctly selecting photos of D. variabilis adults and 76% of frequent-submitters correctly selecting photos of D. variabilis adults. Together, these results indicate the importance of bolstering the use of smartphone applications to engage community scientists and complement other active and passive tick surveillance systems.

Tick and Tickborne Pathogen Surveillance as a Public Health Tool in the United States

In recent decades, tickborne disease (TBD) cases and established populations of medically important ticks have been reported over expanding geographic areas, and an increasing number of tickborne bacteria, viruses, and protozoans have been recognized as human pathogens, collectively contributing to an increasing burden of TBDs in the United States. The prevention and diagnosis of TBDs depend greatly on an accurate understanding by the public and healthcare providers of when and where persons are at risk for exposure to human-biting ticks and to the pathogens these ticks transmit. However, national maps showing the distributions of medically important ticks and the presence or prevalence of tickborne pathogens are often incomplete, outdated, or lacking entirely. Similar deficiencies exist regarding geographic variability in host-seeking tick abundance. Efforts to accurately depict acarological risk are hampered by lack of systematic and routine surveillance for medically important ticks and their associated human pathogens. In this review, we: 1) outline the public health importance of tick surveillance; 2) identify gaps in knowledge regarding the distributions and abundance of medically important ticks in the United States and the presence and prevalence of their associated pathogens; 3) describe key objectives for tick surveillance and review methods appropriate for addressing those goals; and 4) assess current capacity and barriers to implementation and sustainability of tick surveillance programs.

The Population Structure of Borrelia lusitaniae Is Reflected by a Population Division of Its Ixodes Vector

Populations of vector-borne pathogens are shaped by the distribution and movement of vector and reservoir hosts. To study what impact host and vector association have on tick-borne pathogens, we investigated the population structure of Borrelia lusitaniae using multilocus sequence typing (MLST). Novel sequences were acquired from questing ticks collected in multiple North African and European locations and were supplemented by publicly available sequences at the Borrelia Pubmlst database (accessed on 11 February 2020). Population structure of B. lusitaniae was inferred using clustering and network analyses. Maximum likelihood phylogenies for two molecular tick markers (the mitochondrial 16S rRNA locus and a nuclear locus, Tick-receptor of outer surface protein A, trospA) were used to confirm the morphological species identification of collected ticks. Our results confirmed that B. lusitaniae does indeed form two distinguishable populations: one containing mostly European samples and the other mostly Portuguese and North African samples. Of interest, Portuguese samples clustered largely based on being from north (European) or south (North African) of the river Targus. As two different Ixodes species (i.e., I. ricinus and I. inopinatus) may vector Borrelia in these regions, reference samples were included for I. inopinatus but did not form monophyletic clades in either tree, suggesting some misidentification. Even so, the trospA phylogeny showed a monophyletic clade containing tick samples from Northern Africa and Portugal south of the river Tagus suggesting a population division in Ixodes on this locus. The pattern mirrored the clustering of B. lusitaniae samples, suggesting a potential co-evolution between tick and Borrelia populations that deserve further investigation.

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.

Enhancement of Risk for Lyme Disease by Landscape Connectivity, New York, New York, USA

Most tickborne disease studies in the United States are conducted in low-intensity residential development and forested areas, leaving much unknown about urban infection risks. To understand Lyme disease risk in New York, New York, USA, we conducted tick surveys in 24 parks throughout all 5 boroughs and assessed how park connectivity and landscape composition contribute to Ixodes scapularis tick nymphal densities and Borrelia burgdorferi infection. We used circuit theory models to determine how parks differentially maintain landscape connectivity for white-tailed deer, the reproductive host for I. scapularis ticks. We found forested parks with vegetated buffers and increased connectivity had higher nymph densities, and the degree of park connectivity strongly determined B. burgdorferi nymphal infection prevalence. Our study challenges the perspective that tickborne disease risk is restricted to suburban and natural settings and emphasizes the need to understand how green space design affects vector and host communities in areas of emerging urban tickborne disease.

Amblyomma scalpturatum Neumann, 1906 (Acari: Ixodidae): confirmation in Acre State, Brazil, and description of parasitism in a human

Abstract Amblyomma scalpturatum is a tick species that is unique to South America. It is commonly associated with the Amazon biome and has been reported in some Brazilian states. This tick species exhibits host specificity: it parasitizes tapirs and suidae. Its role in transmitting pathogens to humans is still unknown. Amblyomma scalpturatum is known to be a human-biting tick; however, there is only one report showing that humans make suitable hosts for this species. The knowledge of tick fauna is lacking in the Acre State. This study collected free-living ticks with the aim of finding new records in Acre State. Collections were carried out in Amazon forest fragments in Rio Branco municipality. An A. scalpturatum specimen was identified and submitted sequencing of the ITS-2 gene. This study presents the first molecular confirmation of A. scalpturatum collected in situ in Acre State, North Region, Brazil. This study also presents the first record of a successfully completed feeding by an A. scalpturatum nymph on a human host in the North region of Brazil. Further investigation is needed to ascertain the complete life cycle of this tick species, its seasonality in the environment, and its relationship to pathogens and competence to transmit them.

Risk of encountering ticks and tick-borne pathogens in a rapidly growing metropolitan area in the U.S. Great Plains

The prevalence of tick-borne diseases has increased dramatically in many urban areas of the U.S., yet little is known about the ecology of ticks and tick-borne pathogens in relation to characteristics of North American urban and suburban landscapes. This study aimed to begin identification of the risk of encountering ticks and tick-borne pathogens within a rapidly expanding metropolitan area in the U.S. Great Plains region. Ten sites across Oklahoma City, Oklahoma were selected for tick sampling based on presence of tick habitat and level of urbanization intensity. Sampling was conducted using CO₂ traps and flagging in June, July and October 2015. A total of 552 ticks were collected from eight of the ten sampled greenspaces. The majority of ticks collected in summer were Amblyomma americanum (N=534 (97.8%)), followed by Dermacentor variabilis (N=10 (1.8%)) and Amblyomma maculatum (N=2 (0.3%)). Ixodes scapularis adult females (N=4) and nymphal A. americanum (N=2) were also collected in October 2015. Tick species diversity was highest in sites with >15% of the surrounding landscape composed of undeveloped land. Rickettsia sp. (including R. amblyommii and 'Candidatus R. andeanae'), Ehrlichia chaffeensis and/or E. ewingii were detected in tick pools from all eight sites where ticks were found. Our data suggest that the risk of encountering ticks and tick-borne pathogens exists throughout the Oklahoma City metropolitan area and that tick populations are likely influenced by urbanization intensity. Continued research is needed to clarify the full range of abiotic and biotic features of urban landscapes that influence the risk of encountering ticks and transmitting tick-borne diseases.

Invasion of two tick-borne diseases across New England: harnessing human surveillance data to capture underlying ecological invasion processes

Modelling the spatial spread of vector-borne zoonotic pathogens maintained in enzootic transmission cycles remains a major challenge. The best available spatio-temporal data on pathogen spread often take the form of human disease surveillance data. By applying a classic ecological approach-occupancy modelling-to an epidemiological question of disease spread, we used surveillance data to examine the latent ecological invasion of tick-borne pathogens. Over the last half-century, previously undescribed tick-borne pathogens including the agents of Lyme disease and human babesiosis have rapidly spread across the northeast United States. Despite their epidemiological importance, the mechanisms of tick-borne pathogen invasion and drivers underlying the distinct invasion trajectories of the co-vectored pathogens remain unresolved. Our approach allowed us to estimate the unobserved ecological processes underlying pathogen spread while accounting for imperfect detection of human cases. Our model predicts that tick-borne diseases spread in a diffusion-like manner with occasional long-distance dispersal and that babesiosis spread exhibits strong dependence on Lyme disease.

Rhipicephalus sanguineus (ACARI: IXODIDAE) BITING A HUMAN BEING IN PORTO ALEGRE CITY, RIO GRANDE DO SUL, BRAZIL

We report the finding of a female brown dog tick, Rhipicephalus sanguineus (Acari: Ixodidae) on the scalp of a male patient inPorto Alegre, Rio Grande do Sul, Brazil. Human parasitism by this tick is rare and has seldomly been reported in the literature, despite its recognized importance since it can act as a vector of Rickettsia rickettsii, the agent of spotted fever.

Human babesiosis, an emerging tick-borne disease in the People's Republic of China

Babesiosis is a typical zoonotic, emerging disease caused by a tick-borne intraerythrocytic protozoan of Babesia spp. that also can be transmitted by blood transfusion. Babesiosis imposes an increasing public-health threat. We reviewed and mapped epidemiological studies on Babesia in vectors and/or rodents in the People’s Republic of China (P.R. China) and found that B. microti was the predominant species detected in the investigated regions such as Heilongjiang, Zhejiang, Fujian provinces and Taiwan island. We reviewed a series of sporadic human babesiosis cases collected from 1940’s to 2013, in Yunnan, Inner Mongolia, Taiwan and Zhejiang and other regions including a main endemic area of malaria on the China-Myanmar border areas in P.R. China. Clinical manifestations of human babesiosis were also reviewed. Human babesiosis may have previously been overlooked in P.R. China due to a lack of medical awareness and the limitation of clinical diagnostic methods.

Pathogenic Landscape of Transboundary Zoonotic Diseases in the Mexico-US Border Along the Rio Grande

Transboundary zoonotic diseases, several of which are vector borne, can maintain a dynamic focus and have pathogens circulating in geographic regions encircling multiple geopolitical boundaries. Global change is intensifying transboundary problems, including the spatial variation of the risk and incidence of zoonotic diseases. The complexity of these challenges can be greater in areas where rivers delineate international boundaries and encompass transitions between ecozones. The Rio Grande serves as a natural border between the US State of Texas and the Mexican States of Chihuahua, Coahuila, Nuevo León, and Tamaulipas. Not only do millions of people live in this transboundary region, but also a substantial amount of goods and people pass through it everyday. Moreover, it occurs over a region that functions as a corridor for animal migrations, and thus links the Neotropic and Nearctic biogeographic zones, with the latter being a known foci of zoonotic diseases. However, the pathogenic landscape of important zoonotic diseases in the south Texas-Mexico transboundary region remains to be fully understood. An international perspective on the interplay between disease systems, ecosystem processes, land use, and human behaviors is applied here to analyze landscape and spatial features of Venezuelan equine encephalitis, Hantavirus disease, Lyme Borreliosis, Leptospirosis, Bartonellosis, Chagas disease, human Babesiosis, and Leishmaniasis. Surveillance systems following the One Health approach with a regional perspective will help identifying opportunities to mitigate the health burden of those diseases on human and animal populations. It is proposed that the Mexico-US border along the Rio Grande region be viewed as a continuum landscape where zoonotic pathogens circulate regardless of national borders.

Bioinformatic analyses of male and female Amblyomma americanum tick expressed serine protease inhibitors (serpins)

Serine protease inhibitors (serpins) are a diverse family of proteins that is conserved across taxa. The diversity of Amblyomma americanum serpins (AAS) is far more complex than previously thought as revealed by discovery of 57 and 33 AAS transcripts that are respectively expressed in male and female A. americanum ticks, with 30 found in both. While distinct reproductively, both male and female metastriate ticks, such as A. americanum, require a blood meal. Thus, 30 AAS sequences found in both male and female ticks could play important role(s) in regulating tick feeding and thus represent attractive candidates for anti-tick vaccine development. Of significant interest, 19 AAS sequences expressed in male and female ticks are also part of the 48 AAS sequences expressed in fed female tick salivary glands or midguts; two organs through which the tick interacts with host blood and immune response factors. Considered the most important domain for serpin function, the reactive center loop (RCL) is further characterized by a single 'P1' site amino acid residue, which is central to determining the protease regulated by the serpin. In this study, a diversity of 17 different P1 site amino acid residues were predicted, suggesting that A. americanum serpins potentially regulate a large number of proteolytic pathways. Our data also indicate that some serpins in this study could regulate target protease common to all tick species, in that more than 40% of AAS show 58-97% inter-species amino acid conservation. Of significance, 24% of AAS showed 62-100% inter-species conservation within the functional RCL domain, with 10 RCLs showing ≥90-100% conservation. In vertebrates, serpins with basic residues at the P1 site regulate key host defense pathways, which the tick must evade to feed successfully. Interestingly, we found that AAS sequences with basic or polar uncharged residues at the putative P1 site are more likely to be conserved across tick species. Another notable observation from our data is that AAS sequences found only in female ticks and those found in both males and females, but not those found only in male ticks, were highly conserved in other tick species. While descriptive, this study provides the basis for more in-depth studies exploring the roles of serpins in tick feeding physiology.

Tick-borne pathogen - reversed and conventional discovery of disease

Molecular methods have increased the number of known microorganisms associated with ticks significantly. Some of these newly identified microorganisms are readily linked to human disease while others are yet unknown to cause human disease. The face of tick-borne disease discovery has changed with more diseases now being discovered in a “reversed way,” detecting disease cases only years after the tick-borne microorganism was first discovered. Compared to the conventional discovery of infectious diseases, reverse order discovery presents researchers with new challenges. Estimating public health risks of such agents is especially challenging, as case definitions and diagnostic procedures may initially be missing. We discuss the advantages and shortcomings of molecular methods, serology, and epidemiological studies that might be used to study some fundamental questions regarding newly identified tick-borne diseases. With increased tick-exposure and improved detection methods, more tick-borne microorganisms will be added to the list of pathogens causing disease in humans in the future.

Risk assessment of transfusion-associated babesiosis in Tyrol: appraisal by seroepidemiology and polymerase chain reaction

BACKGROUND

After malaria, babesiosis is the second most common transfusion-transmitted parasitic disease in the United States. In Europe, one reported transfusion case, concerning Babesia microti, occurred in Germany.

STUDY DESIGN AND METHODS

Due to the fact that Babesia spp. are present in Tyrolean ticks, the aim of this study is to assess the occurrence of immunoglobulin (Ig)G antibodies against the Babesia divergens complex, including B. divergens and Babesia venatorum (EU1), as well as B. microti by screening a representative collective of 988 blood donors from North and East Tyrol (Austria) with indirect immunofluorescence antibody test. Additionally, we investigated 206 local ixodid ticks for the presence of babesial DNA by polymerase chain reaction.

RESULTS

Seroprevalence data resulted in rates of 2.1% for IgG antibodies against the B. divergens complex and 0.6% against B. microti in Tyrolean blood donors. All sera could be confirmed by independent retesting. Our data indicate that cross-reactivity is high between B. divergens and B. venatorum and lower than 19.8% between B. divergens and B. microti.

CONCLUSIONS

This study shows that Babesia spp. are present in the Tyrols, which blood donors come into serologic contact with, and that we have to consider how to sustain blood product safety concerning this new challenge. Additionally, it is the first description of B. venatorum in the Tyrols, found in one Ixodes ricinus at the Italian border.

Non-pet dogs as sentinels and potential synanthropic reservoirs of tick-borne and zoonotic bacteria

Blood samples were collected from 100 shepherd dogs, 12 hunting dogs and 14 stray dogs (apparently healthy) in southern Hungary to screen for the presence of emerging tick-borne pathogens. Based on real-time PCR results, 14 dogs (11%) had single or dual haemoplasma infection, and a same number of samples were positive for Anaplasma phagocytophilum. In one sample Coxiella burnetii was molecularly identified, and 20.3% of dogs seroconverted to the Q fever agent. Rickettsaemia (sensu stricto) was also detected in one animal. This is the first molecular evidence of autochthonous infection of dogs with the above pathogens in Hungary. The relatively high prevalence of haemoplasma and anaplasma infection among non-pet dogs is suggestive of a prolonged carrier status and bacteraemia of these animals rendering them epidemiologically significant as potential reservoirs and sentinels for tick-borne infections.

Longistatin is an unconventional serine protease and induces protective immunity against tick infestation

Classical serine proteases use the conserved Ser/His/Asp catalytic triad to hydrolyze substrates. Here, we show that longistatin, a salivary gland protein with two EF-hand domains from the vector tick Haemaphysalis longicornis, does not have the conserved catalytic triad, but still functions as a serine protease. Longistatin was synthesized in and secreted from the salivary glands of ticks, and is injected into host tissues during the acquisition of blood-meals. Longistatin hydrolyzed fibrinogen, an essential plasma protein in the coagulation cascade, and activated plasminogen, into its active form plasmin, a serine protease that dissolves fibrin clots. Longistatin efficiently hydrolyzed several serine protease-specific substrates showing its specificity to the amide bond of Arg. Longistatin did not hydrolyze synthetic substrates specific for other groups of proteases. The enzyme was active at a wide range of temperatures and pHs, with the optimum at 37°C and pH 7. Its activity was efficiently inhibited by various serine protease inhibitors such as phenylmethanesulfonyl fluoride (PMSF), aprotinin, antipain, and leupeptin with the estimated IC(50) of 278.57 μM, 0.35 μM, 41.56 μM and 198.86 μM, respectively. In addition, longistatin was also potently inhibited by Zinc (Zn(2+)) in a concentration-dependent manner with an IC(50) value of 275 μM, and the inhibitory effect of Zn(2+) was revived by ethylenediaminetetra acetic acid (EDTA). Immunization studies revealed that longistatin sharply induced high levels of protective IgG antibodies against ticks. Immunization with longistatin reduced repletion of ticks by about 54%, post engorgement body weight by >11% and molting of nymphs by approximately 34%; thus, the vaccination trial was approximately 73% effective against tick infestation. Taken together, our results suggest that longistatin is a new potent atypical serine protease, and may be an interesting candidate for the development of anti-tick vaccines.

Detection and characterization of Babesia species in Ixodes ticks in Estonia

The presence of Babesia spp. was studied in 2603 Ixodes ricinus and Ixodes persulcatus ticks collected at seven sites in Estonia. By reverse line blot screening, Babesia spp. was detected in 36 (1.4%) ticks, among them 18 (0.7%) were further recognized by a Babesia microti probe, 3 (0.1%) by a Babesia divergens probe, and the other 15 (0.6%) were recognized only by the universal Babesia spp. "catch all" probe. Sequence analyses of 6 of these 15 samples revealed that all of them belonged to Babesia sp. EU1. B. microti was detected in both tick species I. ricinus and I. persulcatus at the seven sites, whereas B. divergens-like and Babesia sp. EU1 were found only in I. persulcatus and I. ricinus, respectively. Genetic characterization based on partial 18S rRNA showed that the Estonian sequences of B. microti, B. divergens-like, and Babesia sp. EU1 share a high rate of similarity and are closely related to sequences from other European countries, Siberia, and United States. The present study demonstrated for the first time the existence and distribution of Babesia spp. in I. persulcatus and I. ricinus ticks in Estonia.

Longistatin, a plasminogen activator, is key to the availability of blood-meals for ixodid ticks

Ixodid ticks are notorious blood-sucking ectoparasites and are completely dependent on blood-meals from hosts. In addition to the direct severe effects on health and productivity, ixodid ticks transmit various deadly diseases to humans and animals. Unlike rapidly feeding vessel-feeder hematophagous insects, the hard ticks feed on hosts for a long time (5-10 days or more), making a large blood pool beneath the skin. Tick's salivary glands produce a vast array of bio-molecules that modulate their complex and persistent feeding processes. However, the specific molecule that functions in the development and maintenance of a blood pool is yet to be identified. Recently, we have reported on longistatin, a 17.8-kDa protein with two functional EF-hand Ca(++)-binding domains, from the salivary glands of the disease vector, Haemaphysalis longicornis, that has been shown to be linked to blood-feeding processes. Here, we show that longistatin plays vital roles in the formation of a blood pool and in the acquisition of blood-meals. Data clearly revealed that post-transcriptional silencing of the longistatin-specific gene disrupted ticks' unique ability to create a blood pool, and they consequently failed to feed and replete on blood-meals from hosts. Longistatin completely hydrolyzed α, β and γ chains of fibrinogen and delayed fibrin clot formation. Longistatin was able to bind with fibrin meshwork, and activated fibrin clot-bound plasminogen into its active form plasmin, as comparable to that of tissue-type plasminogen activator (t-PA), and induced lysis of fibrin clot and platelet-rich thrombi. Plasminogen activation potentiality of longistatin was increased up to 4 times by soluble fibrin. Taken together, our results suggest that longistatin may exert potent functions both as a plasminogen activator and as an anticoagulant in the complex scenario of blood pool formation; the latter is critical to the feeding success and survival of ixodid ticks.

Global Climate Changes and International Trade and Travel: Effects on Human Health Outcomes

There is now near-unanimous scientific agreement that greenhouse gas emissions generated by human activities have increased global temperatures and changed the earth's climate. There is, however, no universal agreement on how rapidly, regionally, or asymmetrically the earth will warm; or on the true impact of global warming on infectious disease outbreaks and natural disasters and their inevitable public health outcomes. In addition, many other factors influence the emergence and reemergence of infectious diseases in a changing environment including international trade and travel, exotic eating habits, lifestyle and residential choices, host susceptibility, and microbial adaptation. The ultimate effects of climate changes and the increased distribution of pathogens by international trade and travel will not be limited to infectious disease outbreaks in immunologically naïve populations but will also impact world food production and quality, air quality, drinking water availability and quality, immigration, urban relocation, and civil unrest. Despite the uncertainties in outcomes and their magnitudes, the active responses to climate changes in a global economy must include combinations of environmental, political, regulatory, socioeconomic, and public health measures.

Dermatologic changes induced by repeated Ixodes scapularis bites and implications for prevention of tick-borne infection

Previous studies in rodents and people have demonstrated that repeated tick exposure is associated with reduced Borrelia burgdorferi transmission but the mechanism of prevention remains unclear. We examined the acute histopathologic reactions to initial and repeated Ixodes scapularis bites in BALB/c mice and in people. Skin biopsies of BALB/c mice infested for the first time by I. scapularis nymphs revealed vascular dilatation and an accumulation of inflammatory cells adjacent to the bite site but absent at the site of tick attachment. Such changes would enhance tick-borne pathogen transmission. Mice reexposed to I. scapularis nymphs experienced a decrease in vascular dilatation and a marked increase in inflammatory cells at the site of tick attachment. Skin biopsies of people with attached I. scapularis nymphs revealed similar histologic patterns. These results indicate that cellular changes at the tick-dermal interface following I. scapularis attachment are likely to allow for successful transmission of tick-borne pathogens in non-tick-immune hosts and to inhibit tick-borne pathogen transmission in hosts that have developed tick immunity.

Burden of tick-borne infections on American companion animals

This review examines the biology of ticks and tick-borne infections in the United States. The most common tick-borne diseases in dogs and cats are discussed. We demonstrate that there is much interest in tick-borne infections at the level of the lay public (pet owners), describe trends in the distribution and prevalence of tick-borne infections in the United States, summarize some issues in understanding the degree of ill health due to tick-borne infections, and suggest some avenues for research that would clarify these issues.

Transovarial transmission of Francisella-like endosymbionts and Anaplasma phagocytophilum variants in Dermacentor albipictus (Acari: Ixodidae)

Dermacentor albipictus (Packard) is a North American tick that feeds on cervids and livestock. It is a suspected vector of anaplasmosis in cattle, but its microbial flora and vector potential remain underevaluated. We screened D. albipictus ticks collected from Minnesota white-tailed deer (Odocoileus virginianus) for bacteria of the genera Anaplasma, Ehrlichia, Francisella, and Rickettsia using polymerase chain reaction (PCR) gene amplification and sequence analyses. We detected Anaplasma phagocytophilum and Francisella-like endosymbionts (FLEs) in nymphal and adult ticks of both sexes at 45 and 94% prevalences, respectively. The A. phagocytophilum and FLEs were transovarially transmitted to F1 larvae by individual ticks at efficiencies of 10-40 and 95-100%, respectively. The FLEs were transovarially transmitted to F2 larvae obtained as progeny of adults from F1 larval ticks reared to maturity on a calf, but A. phagocytophilum were not. Based on PCR and tissue culture inoculation assays, A. phagocytophilum and FLEs were not transmitted to the calf. The amplified FLE 16S rRNA gene sequences were identical to that of an FLE detected in a D. albipictus from Texas, whereas those of the A. phagocytophilum were nearly identical to those of probable human-nonpathogenic A. phagocytophilum WI-1 and WI-2 variants detected in white-tailed deer from central Wisconsin. However, the D. albipictus A. phagocytophilum sequences differed from that of the nonpathogenic A. phagocytophilum variant-1 associated with Ixodes scapularis ticks and white-tailed deer as well as that of the human-pathogenic A. phagocytophilum ha variant associated with I. scapularis and the white-footed mouse, Peromyscus leucopus. The transovarial transmission of A. phagocytophilum variants in Dermacentor ticks suggests that maintenance of A. phagocytophilum in nature may not be solely dependent on horizontal transmission.

Detection of a novel Francisella in Dermacentor reticulatus: a need for careful evaluation of PCR-based identification of Francisella tularensis in Eurasian ticks

Francisella tularensis, the causative agent of tularemia, has been detected in ixodid ticks in some regions of North America, Europe, and Asia. In the present study, 245 Dermacentor reticulatus, 211 Ixodes ricinus, and 194 Haemaphysalis concinna adults from Hungary were tested for the presence of F. tularensis by polymerase chain reaction (PCR) assays based on 16S ribosomal RNA (16S rDNA) and T-cell epitope of a Francisella membrane protein (TUL4). No Francisella-specific amplification products were detected in I. ricinus and H. concinna ticks. Francisella DNA was identified using PCR assays based on 16S rDNA and TUL4 gene in D. reticulatus with similar prevalence (minimum 1.2%) as demonstrated in earlier European and Asian studies detecting F. tularensis in D. reticulatus. However, the 16S rDNA and TUL4 gene sequences of the Francisella-like agent occurring in D. reticulatus differed from the homologous sequences of Francisella spp. deposited in GenBank. Phylogenetic reconstructions showed that the new genotype detected in D. reticulatus was closely related to Francisella-like endosymbionts of North American Dermacentor ticks. Although further studies are needed on the relationship of this bacterium with ticks, the results highlight the need for careful evaluation of PCR-based identification in European and Asian laboratories that screen ixodid ticks for F. tularensis.

Babesia species occurring in Austrian Ixodes ricinus ticks

Babesiosis is a tick-transmitted disease of veterinary and medical importance. The first Austrian case of human babesiosis was recently recorded. In the current study, ticks at all life cycle stages (instars), including 853 Ixodes ricinus and 11 Haemaphysalis concinna ticks, from sampling sites throughout Austria were examined for the presence of Babesia spp. by using 18S rRNA gene PCR and sequencing, and the overall mean infection rate was 51.04%. The infection rates for sampling sites were highly variable, ranging from 0% to almost 100%. Different instars and different sexes were infected almost equally. Babesia isolates occurring in Austrian ticks were identified as Babesia divergens, Babesia divergens-like, and Babesia sp. strain DD by sequencing a fragment of the heat shock protein 70 gene and internal transcribed spacer regions 1 and 2. To our knowledge, this is the first investigation of Babesia spp. in Austrian ticks.

A cysteine protease is critical for Babesia spp. transmission in Haemaphysalis ticks

Vector ticks possess a unique system that enables them to digest large amounts of host blood and to transmit various animal and human pathogens, suggesting the existence of evolutionally acquired proteolytic mechanisms. We report here the molecular and reverse genetic characterization of a multifunctional cysteine protease, longipain, from the babesial parasite vector tick Haemaphysalis longicornis. Longipain shares structural similarity with papain-family cysteine proteases obtained from invertebrates and vertebrates. Endogenous longipain was mainly expressed in the midgut epithelium and was specifically localized at lysosomal vacuoles and possibly released into the lumen. Its expression was up-regulated by host blood feeding. Enzymatic functional assays using in vitro and in vivo substrates revealed that longipain hydrolysis occurs over a broad range of pH and temperature. Haemoparasiticidal assays showed that longipain dose-dependently killed tick-borne Babesia parasites, and its babesiacidal effect occurred via specific adherence to the parasite membranes. Disruption of endogenous longipain by RNA interference revealed that longipain is involved in the digestion of the host blood meal. In addition, the knockdown ticks contained an increased number of parasites, suggesting that longipain exerts a killing effect against the midgut-stage Babesia parasites in ticks. Our results suggest that longipain is essential for tick survival, and may have a role in controlling the transmission of tick-transmittable Babesia parasites.

Ticks are important ectoparasites among the blood-feeding arthropods and serve as vectors of many deadly diseases of humans and animals. Of tick-transmitted pathogens, Babesia, an intracellular haemoprotozoan parasite causing a malaria-like disease, called babesiosis, gain increasing interest due to its zoonotic significance. When vector ticks acquire the protozoa via blood-meals, they invade midgut and undergo several developmental stages prior to exit through salivary glands. It has long been conceived that midguts of these ticks evolve diverse innate immune mechanisms and perform blood digestion critical for tick survival. A cysteine proteinase, longipain, was identified from the three-host tick Haemaphysalis longicornis, which shows potent parasiticidal activity. Longipain is localized in midgut epithelium and its expression is induced by blood feeding. This protein is passively secreted into midgut lumen where it exerts enzymatic degradation of blood-meals. A series of experiments unveil that longipain-knockdown ticks when fed on Babesia-infected dog, exhibited a significantly increased numbers of parasites compared with controls. Longipain has shown to interact on the surface of Babesia parasites in vitro and in vivo, and is thought to mediate direct killing of the parasites, suggesting that longipain may be a potential chemotherapeutic target against babesiosis and ticks themselves.

Feeding by the tick, Ixodes scapularis, causes CD4+T cells responding to cognate antigen to develop the capacity to express IL-4

Effects of tick feeding on an early antigen-specific T cell response were studied by monitoring a clonotypic population of adoptively transferred T cell receptor (TCR) transgenic CD4 cells responding to a tick-associated antigen. When recipient mice were infested with pathogen-free Ixodes scapularis nymphs several days prior to T cell transfer and intradermal injection of soluble cognate antigen at the feeding site, the clonotypic CD4 cells gained the ability to express the Th2 effector cytokine IL-4. Notably, this effect was not only observed in BALB/c mice predisposed towards developing Th2 responses but also in B10.D2 mice predisposed towards Th1 responsiveness. Furthermore, tick feeding was able to superimpose IL-4 expression potential onto a strong Th1 response (indicated by robust IFN-gamma expression potential) elicited by immunization with a vaccinia virus expressing the cognate antigen. The magnitude to which tick feeding was able to programme IL-4 expression potential in CD4 cells was partially reduced in mice that had been previously exposed to pathogen-free tick nymphs 6 weeks earlier, as well as when the nymphs were infected with Borrelia burgdorferi. Intradermal injection of salivary gland extract programmed IL-4 expression potential similar to that of tick infestation, suggesting that IL-4 programming activity is contained within tick saliva.

Transcriptome analysis of the salivary glands of Dermacentor andersoni Stiles (Acari: Ixodidae)

Amongst blood-feeding arthropods, ticks of the family Ixodidae (hard ticks) are vectors and reservoirs of a greater variety of infectious agents than any other ectoparasite. Salivary glands of ixodid ticks secrete a large number of pharmacologically active molecules that not only facilitate feeding but also promote establishment of infectious agents. Genomic, proteomic and immunologic characterization of bioactive salivary gland molecules are, therefore, important as they offer new insights into molecular events occurring at the tick-host interface and they have implications for development of novel control strategies. The present work uses complementary DNA (cDNA) sequence analysis to identify salivary gland transcripts expressed by the Rocky Mountain wood tick, Dermacentor andersoni, a vector of the human pathogens causing Rocky Mountain spotted fever, Colorado tick fever, tularemia, and Powassan encephalitis as well as the veterinary pathogen Anaplasma marginale. Dermacentor andersoni is also capable of inducing tick paralysis. Automated single-pass DNA sequencing was conducted on 1440 randomly selected cDNA clones from the salivary glands of adult female D. andersoni collected during the early stages of feeding (18-24h). Analysis of the expressed sequence tags (ESTs) resulted in 544 singletons and 218 clusters with more than one quality read and attempts were made to assign putative functions to tick genes based on amino acid identity to published protein databases. Approximately 25.6% (195) of the sequences showed limited or no homology to previously identified gene products. A number of novel sequences were identified which presented significant sequence similarity to mammalian genes normally associated with extracellular matrix (ECM), regulation of immune responses, tumor suppression, and wound healing. Several coding sequences possessed various degrees of homology to previously described proteins from other tick species. Preliminary nucleotide variation analysis of these and other tick sequences suggests extensive nucleotide diversity, which has implications for evolution of tick feeding. Intra-species diversity studies can be a promising tool for identifying sequence variations potentially associated with phenotypic traits affecting vector-host-pathogen interactions.