Transfusion-acquired, autochthonous human babesiosis in Japan: isolation of Babesia microti-like parasites with hu-RBC-SCID mice

Evolutionary analysis of Babesia vulpes and Babesia microti-like parasites

Background

The Babesia microti-like parasite is an emerging tick-borne piroplasm that has been detected in a range of hosts worldwide. Babesia vulpes, which is found in dogs and foxes, has been reclassified from B. microti-like parasites. The relationships among these B. microti-like parasites and B. vulpes with respect to host range and geographical origin have not been elucidated.

Methods

Blood samples were collected from 27 raccoon dogs in South Korea and used to screen for B. microti-like parasites based on a PCR assay targeting the 18S rRNA gene of Babesia. For comparative purposes, in addition to 18S rRNA sequences from nine raccoon dogs, we also analyzed 18S rRNA sequences from B. microti-like parasites infecting hosts in different geographical regions worldwide obtained from the GenBank database, giving 123 sequences in total. The genetic variation and evolutionary relationships among these sequences were examined based on analyses using DnaSP, MEGA, Arlequine, and BEAST software.

Results

Babesia microti-like parasites were identified in nine raccoon dogs and found to be related to B. vulpes obtained from Spanish dogs. Among the 123 sequences from 14 countries and various hosts, we identified 43 haplotypes with high genetic variance. Based on the genetic variance and phylogenetic analyses, we established that the B. microti-like parasites isolated in different geographical regions and from hosts belonging to five orders showed higher among-population variation than within-population variation. Babesia vulpes parasites infecting carnivore hosts, including raccoon dogs, foxes, skunks and dogs, appear to be genetically distinct from B. microti-like parasites infecting hosts belonging to the other orders.

Conclusions

Our study demonstrated the genetic variation and evolutionary relationships among 18S rRNA sequences obtained from blood samples collected from various hosts and different geographical regions. Babesia vulpes was identified from raccoon dogs in South Korea. In addition, higher genetic variations were observed among populations of different hosts and geographical origins and, in particular, low connectivity was observed among host populations in the order Carnivora and those in other orders. These results suggest the B. vulpes, a piroplasmid species pathogenic in domestic dogs and wild canines, is genetically and evolutionarily different from B. microti-like parasites.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s13071-022-05528-9.

Comparative single-cell transcriptional atlases of Babesia species reveal conserved and species-specific expression profiles

Babesia is a genus of apicomplexan parasites that infect red blood cells in vertebrate hosts. Pathology occurs during rapid replication cycles in the asexual blood stage of infection. Current knowledge of Babesia replication cycle progression and regulation is limited and relies mostly on comparative studies with related parasites. Due to limitations in synchronizing Babesia parasites, fine-scale time-course transcriptomic resources are not readily available. Single-cell transcriptomics provides a powerful unbiased alternative for profiling asynchronous cell populations. Here, we applied single-cell RNA sequencing to 3 Babesia species (B. divergens, B. bovis, and B. bigemina). We used analytical approaches and algorithms to map the replication cycle and construct pseudo-synchronized time-course gene expression profiles. We identify clusters of co-expressed genes showing "just-in-time" expression profiles, with gradually cascading peaks throughout asexual development. Moreover, clustering analysis of reconstructed gene curves reveals coordinated timing of peak expression in epigenetic markers and transcription factors. Using a regularized Gaussian graphical model, we reconstructed co-expression networks and identified conserved and species-specific nodes. Motif analysis of a co-expression interactome of AP2 transcription factors identified specific motifs previously reported to play a role in DNA replication in Plasmodium species. Finally, we present an interactive web application to visualize and interactively explore the datasets.

A Review of Zoonotic Babesiosis as an Emerging Public Health Threat in Asia

Zoonotic babesiosis poses a serious health risk in many parts of the world. Its emergence in Asia is thus a cause for significant concern, demanding that appropriate control measures are implemented to suppress its spread in this region. This study focuses on zoonotic Babesia species reported in Asia, offering an extensive review of those species reported in animals and humans. We reported 11 studies finding zoonotic Babesia species in animals and 16 in humans. In China, the most prevalent species was found to be Babesia microti, reported in both humans (n = 10) and wild and domesticated animals (n = 4). In Korea, only two studies reported human babesiosis, with a further two studies reporting Babesia microti in wild animals. Babesia microti was also reported in wild animal populations in Thailand and Japan, with evidence of human case reports also found in Singapore, Mongolia and India. This is the first review to report zoonotic babesiosis in humans and animals in Asia, highlighting concerns for future public health in this region. Further investigations of zoonotic species of Babesia in animal populations are required to confirm the actual zoonotic threat of babesiosis in Asia, as well as its possible transmission routes.

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.

Generation of Novel Human Red Blood Cell-Bearing Humanized Mouse Models Based on C3-Deficient NOG Mice

Despite recent advances in immunodeficient mouse models bearing human red blood cells (hRBCs), the elimination of circulating hRBCs by residual innate immune systems remains a significant challenge. In this study, we evaluated the role of mouse complement C3 in the elimination of circulating hRBCs by developing a novel NOG substrain harboring a truncated version of the murine C3 gene (NOG-C3^ΔMG2-3). Genetic C3 deletion prolonged the survival of transfused hRBCs in the circulation. Chemical depletion and functional impairment of mouse macrophages, using clodronate liposomes (Clo-lip) or gadolinium chloride (GdCl₃), respectively, further extended the survival of hRBCs in NOG-C3^ΔMG2-3 mice. Low GdCl₃ toxicity allowed the establishment of hRBC-bearing mice, in which hRBCs survived for more than 4 weeks with transfusion once a week. In addition, erythropoiesis of human hematopoietic stem cells (hHSCs) was possible in NOG-C3^ΔMG2-3/human GM-CSF-IL-3 transgenic mice with Clo-lip treatment. These findings indicate that mouse models harboring hRBCs can be achieved using NOG-C3^ΔMG2-3 mice, which could facilitate studies of human diseases associated with RBCs.

Recombinase polymerase amplification with lateral flow strip for detecting Babesia microti infections

Babesia microti is one of the most important pathogens causing humans and rodents babesiosis-an emerging tick-borne disease that occurs worldwide. At present, the gold standard for the detection of Babesia is the microscopic examination of blood smears, but this diagnostic test has several limitations. The recombinase polymerase amplification with lateral flow (LF-RPA) assay targeting the mitochondrial cytochrome oxidase subunit I (cox I) gene of B. microti was developed in this study. The LF-RPA can be performed within 10-30 min, at a wide range of temperatures between 25 and 45 °C, which is much faster and easier to perform than conventional PCR. The results showed that the LF-RAP can detect 0.25 parasites/μl blood, which is 40 times more sensitive than the conventional PCR based on the V4 variable region of 18S rRNA. Specificity assay showed no cross-reactions with DNAs of related apicomplexan parasites and their host. The applicability of the LF-RPA method was further evaluated using two clinical human samples and six experimental mice samples, with seven samples were positively detected, while only three of them were defined as positive by conventional PCR. These results present the developed LF-RPA as a new simple, specific, sensitive, rapid and convenient method for diagnosing infection with B. microti. This novel assay was the potential to be used in field applications and large-scale sample screening.

Emerging Tick-Borne Diseases

Increases in tick-borne disease prevalence and transmission are important public health issues. Efforts to control these emerging diseases are frustrated by the struggle to control tick populations and to detect and treat infections caused by the pathogens that they transmit. This review covers tick-borne infectious diseases of nonrickettsial bacterial, parasitic, and viral origins. While tick surveillance and tracking inform our understanding of the importance of the spread and ecology of ticks and help identify areas of risk for disease transmission, the vectors are not the focus of this document. Here, we emphasize the most significant pathogens that infect humans as well as the epidemiology, clinical features, diagnosis, and treatment of diseases that they cause. Although detection via molecular or immunological methods has improved, tick-borne diseases continue to remain underdiagnosed, making the scope of the problem difficult to assess. Our current understanding of the incidence of tick-borne diseases is discussed in this review. An awareness of the diseases that can be transmitted by ticks in specific locations is key to detection and selection of appropriate treatment. As tick-transmitted pathogens are discovered and emerge in new geographic regions, our ability to detect, describe, and understand the growing public health threat must also grow to meet the challenge.

Detection and characterization of an emerging type of Babesia sp. similar to Babesia motasi for the first case of human babesiosis and ticks in Korea

Babesiosis is a tick-transmitted intraerythrocytic zoonosis. In Korea, the first mortalities were reported in 2005 due to Babesia sp. detection in sheep; herein we report epidemiological and genetic characteristics of a second case of babesiosis. Microscopic analysis of patient blood revealed polymorphic merozoites. To detect Babesia spp., PCR was performed using Babesia specific primers for β-tubulin, 18S rDNA, COB, and COX3 gene fragments. 18S rDNA analysis for Babesia sp., showed 98% homology with ovine Babesia sp. and with Babesia infections in Korea in 2005. Moreover, phylogenetic analysis of 18S rDNA, COB, and COX3 revealed close associations with B. motasi. For identifying the infectious agent, Haemaphysalis longicornis (296) and Haemaphysalis flava (301) were collected around the previous residence of the babesiosis patient. Babesia genes were identified in three H. longicornis: one sample was identified as B. microti and two samples were 98% homologous to B. motasi. Our study is the first direct confirmation of the infectious agent for human babesiosis. This case most likely resulted from tick bites from ticks near the patient house of the babesiosis patient. H. longicornis has been implicated as a vector of B. microti and other Babesia sp. infections.

Analysis of antigen-antibody cross-reactivity among lineages and sublineages of Babesia microti parasites using human babesiosis specimens

BACKGROUND

Human babesiosis is caused mainly by Babesia microti and has recently become a public health concern due to an increase in transfusion-transmitted infection. Thus, the development of an antibody detection method with high specificity and sensitivity is a priority. Seroreactivity against B. microti has been reported to be highly specific not only to B. microti lineages but also to sublineages. This study aimed to elucidate the human antibody reactivity against various lineages, including US, Kobe, and Hobetsu, and sublineages (North America and East Asia) in the US lineage.

STUDY DESIGN AND METHODS

Twenty samples obtained from individuals infected with B. microti in the United States were tested for the presence of anti-B. microti antibodies using indirect immunofluorescence assay (IFA) and Western blotting (WB) to indicate antigens of each (sub-)lineage.

RESULTS

By IFA, 20 samples showed reactivity to the North America sublineage (titer range, 64-4096), 16 to the East Asia sublineage (64-512), 10 to the Kobe (64-128), and five to the Hobetsu (64). Antibody titers to the East Asia sublineage, Kobe, and Hobetsu were significantly lower than those to the North America sublineage (p < 0.01). By WB, in parallel with the IFA results, 18 samples showed strong reactions to the North America sublineage, weak reactions to the East Asia sublineage, and near-zero reactions to the Kobe and Hobetsu.

CONCLUSION

Human antibodies induced by B. microti infection are highly specific against B. microti lineages and sublineages with low cross-reactivity. Developing a precise antibody detection method may require specific antigens based on B. microti lineages and sublineages.

Babesia microti Infection Changes Host Spleen Architecture and Is Cleared by a Th1 Immune Response

Babesia microti is a malaria-like parasite, which infects ∼2000 people annually, such that babesiosis is now a notifiable disease in the United States. Immunocompetent individuals often remain asymptomatic and are tested only after they feel ill. Susceptible C3H/HeJ mice show several human-like disease manifestations and are ideal to study pathogenesis of Babesia species. In this study, we examined parasitemia of B. microti at different time points and assessed its impact on hemoglobin levels in blood, on spleen pathology and overall immune response in C3H/HeJ mice. Peak parasitemia of 42.5% was immediately followed by diminished hemoglobin level. Parasitemia at 21 days of infection was barely detectable by microscopy presented 5.7 × 10⁸ to 5.9 × 10⁹B. microti DNA copies confirming the sensitivity of our qPCR. We hypothesize that qPCR detects DNA released from recently lysed parasites or from extracellular B. microti in blood, which are not easily detected in blood smears and might result in under-diagnosis of babesiosis in patients. Splenectomized patients have been reported to show increased babesiosis severity and result in high morbidity and mortality. These results emphasize the importance of splenic immunity in resolution of B. microti infection. Splenomegaly in infected mice associated with destruction of marginal zone with lysed erythrocytes and released B. microti life forms in our experiments support this premise. At conclusion of the experiment at 21 days post-infection, significant splenic B and T cells depletion and increase in macrophages levels were observed in B. microti infected mice suggesting a role of macrophage in disease resolution. Infected mice also showed significantly higher plasmatic concentration of CD4 Th1 cells secreted cytokines such as IL-2 and IFN-γ while cytokines such as IL-4, IL-5, and IL-13 secreted by Th2 cells increase was not always significant. Thus, Th1 cells-mediated immunity appears to be important in clearance of this intracellular pathogen. Significant increase in IL-6 that promotes differentiation of Th17 cells was observed but it resulted in only moderate change in IL-17A, IL-17F, IL-21, and IL-22, all secreted by Th17 cells. A similar immune response to Trypanosoma infection has been reported to influence the clearance of this protozoan, and co-infecting pathogen(s).

Case report of the patient source of the Babesia microti R1 reference strain and implications for travelers

BACKGROUND

In 2002, a previously healthy 69-year-old man travelled to France from the United States and presented to our hospital with a febrile illness that subsequently was determined to be babesiosis. The blood isolated from this patient served as a source for propagation of the Babesia microti R1 strain with subsequent sequencing and annotation of the parasite genome.

METHODS

Upon admission, we obtained a medical history, performed a physical examination, and examined his blood for the presence of a blood borne pathogen by microscopy, PCR and indirect immunofluorescence antibody testing. Once the diagnosis of babesiosis was made, we reviewed the literature to assess the distribution of B. microti-associated babesiosis cases in immunocompetent patients from outside the USA.

RESULTS

The patient recalled a tick bite during the previous month on Cape Cod, Massachusetts. The diagnosis was confirmed by identification of Babesia-infected red blood cells on blood smears, amplification of B. microti DNA in blood by PCR and the presence of B. microti antibody in the serum. This strain was the first isolate of B. microti to be fully sequenced and its annotated genome serves as a reference for molecular and cell biology studies aimed at understanding B. microti pathophysiology and developing diagnostic tests and therapies. A review of babesiosis cases demonstrates a worldwide distribution of B. microti and identifies potential emerging endemic areas where travelers may be at risk of contracting B. microti infection.

CONCLUSION

This case provides clinical information about the patient infected with the R1 isolate and a review of travel risk, diagnosis and treatment of babesiosis in endemic and non-endemic areas.

Inactivation of Babesia microti in red blood cells and platelet concentrates

BACKGROUND

With an increasing number of recognized transfusion-transmitted (TT) babesiosis cases, Babesia microti is the most frequently TT parasite in the United States. We evaluated the inactivation of B. microti in red blood cells (RBCs) prepared in Optisol (AS-5) using amustaline and glutathione (GSH) and in platelet components (PCs) in 100% plasma using amotosalen and low-energy ultraviolet A (UVA) light.

STUDY DESIGN AND METHODS

Individual RBCs and apheresis PCs were spiked with B. microti-infected hamster RBCs (iRBCs) to a final concentration of 10⁶ iRBCs/mL and treated with the respective inactivation systems according to the manufacturer's instruction. Samples were collected before (control) and after (test) each treatment. Dilutions of the control samples to 10^-6 were inoculated into hamsters, while the test samples were inoculated neat or at 10^-1 dilution. At 3 and 5 weeks postinoculation, hamsters were evaluated for B. microti infection by microscopic observation of blood smears and 50% infectivity titers (ID₅₀ ) were determined. Log reduction was calculated as control log ID₅₀ minus test log ID₅₀ .

RESULTS

Parasitemia was detected in hamsters injected with as low as 100,000-fold diluted control samples, while no parasites were detectable in the blood smears of any hamsters receiving neat test samples. Mean log reduction was more than 5 log/mL by amustaline/GSH for RBCs and more than 4.5 log/mL by amotosalen/UVA for PCs.

CONCLUSION

B. microti was inactivated to the limit of detection in RBCs and PCs after the respective inactivation treatment. Complete inactivation of B. microti was achieved in this animal infectivity model, and pathogen reduction treatment inhibited transmission of infection.

Detection of Kobe-type and Otsu-typeBabesia microtiin wild rodents in China's Yunnan province

Babesiosis is an emerging tick-transmitted zoonosis prevalent in large parts of the world. This study was designed to determine the rates ofBabesia microtiinfection among small rodents in Yunnan province, where human cases of babesiosis have been reported. Currently, distribution ofBabesiain its endemic regions is largely unknown. In this study, we cataloged 1672 small wild rodents, comprising 4 orders, from nine areas in western Yunnan province between 2009 and 2011.Babesia microtiDNA was detected by polymerase chain reaction in 4·3% (72/1672) of the rodents analyzed. The most frequently infected rodent species includedApodemus chevrieriandNiviventer fulvescens. Rodents from forests and shrublands had significantly higherBabesiainfection rates. Genetic comparisons revealed thatBabesiawas most similar to the Kobe- and Otsu-type strains identified in Japan. A variety of rodent species might be involved in the enzootic maintenance and transmission ofB. microti, supporting the need for further serological investigations in humans.

First detection and molecular identification of Babesia microti in Rattus losea captured from the offshore Kinmen Island of Taiwan

Babesia microti was firstly detected and identified in brown country rats (Rattus losea, Swinhoe) captured from the offshore Kinmen Island of Taiwan. The prevalence of Babesia infection in 283 rodents was screened by polymerase chain reaction (PCR) assay using a piroplasma-conserved primer set (Piro A/B) and the thirty-seven PCR-positive rodents were further examined by PCR using a species-specific primer set (Bab 1/4) targeting the gene encoding the nuclear small-subunit ribosomal RNA (18S rRNA) of Babesia species. B. microti was detected only in Rattus losea with a total infection rate of 9.9% (28/283). Positivity examined by species-specific PCR (9.9%) is higher than examined by blood smear (4.6%). Sequence and phylogenetic analyses revealed that Babesia species detected in Taiwan were genetically affiliated to the genotypes of B. microti, and can be easily distinguished from other genotypes of Babesia parasites by neighbour-joining and maximum-parsimony methods. Intra- and inter-species analysis also indicate that all these Taiwan species have a lower level of genetic divergence (genetic distance values <0.084) within the genotypes of B. microti, and were genetically more distant to other genotypes (>0.218) of Babesia parasites. This study provides the first evidence of B. microti identified in R. losea in Taiwan, and the high prevalence of Babesia infection in R. losea may imply its possible role served as reservoir host for maintaining an enzoonotic cycle of Babesia transmission in Kinmen Island. The possible vector tick responsible for the transmission of Babesia infection need to be further identified.

Ixodes persulcatus Ticks as Vectors for the Babesia microti U.S. Lineage in Japan

The U.S. lineage, one of the major clades in the Babesia microti group, is known as a causal agent of human babesiosis mostly in the northeastern and upper midwestern United States. This lineage, however, also is distributed throughout the temperate zone of Eurasia with several reported human cases, although convincing evidence of the identity of the specific vector(s) in this area is lacking. Here, the goal was to demonstrate the presence of infectious parasites directly in salivary glands of Ixodes persulcatus, from which U.S. lineage genetic sequences have been detected in Asia, and to molecularly characterize the isolates. Five PCR-positive specimens were individually inoculated into hamsters, resulting in infections in four; consequently, four strains were newly established. Molecular characterization, including 18S rRNA, β-tubulin, and CCT7 gene sequences, as well as Western blot analysis and indirect fluorescent antibody assay, revealed that all four strains were identical to each other and to the U.S. lineage strains isolated from rodents captured in Japan. The 18S rRNA gene sequence from the isolates was identical to those from I. persulcatus in Russia and China, but the genetic and antigenic profiles of the Japanese parasites differ from those in the United States and Europe. Together with previous epidemiological and transmission studies, we conclude that I. persulcatus is likely the principal vector for the B. microti U.S. lineage in Japan and presumably in northeastern Eurasia.

IMPORTANCE

The major cause of human babesiosis, the tick-borne blood parasite Babesia microti, U.S. lineage, is widely distributed in the temperate Northern Hemisphere. However, the specific tick vector(s) remains unidentified in Eurasia, where there are people with antibodies to the B. microti U.S. lineage and cases of human babesiosis. In this study, the first isolation of B. microti U.S. lineage from Ixodes persulcatus ticks, a principal vector for many tick-borne diseases, is described in Japan. Limited antigenic cross-reaction was found between the Japan and United States isolates. Thus, current serological tests based on U.S. isolates may underestimate B. microti occurrence outside the United States. This study and previous studies indicate that I. persulcatus is part of the B. microti U.S. lineage life cycle in Japan and, presumably, northeastern Eurasia. This report will be important for public health, especially since infection may occur through transfusion, and also to researchers in the field of parasitology.

Continuous in vivo culture and indirect fluorescent antibody test for zoonotic protozoa of Babesia microti

Babesiosis has attracted attention as a zoonotic disease. The disease is caused in immunocompetent individuals almost solely by Babesia microti, a rodent babesia. Most cases of human babesiosis by B. microti have been reported in the endemic foci of the Northeastern coastal areas and upper Midwest regions of the United States, while some sporadic cases have recently been reported in several Asian countries including Japan. Our previous surveys identified that four small subunit ribosomal RNA gene (SSUrDNA) types of B. microti parasitize Japanese rodents. Indirect fluorescent antibody test (IFAT) is often performed for the diagnosis of babesiosis together with microscopical examination of thin blood smears and PCR. We established IFAT against four SSUrDNA-types of B. microti using erythrocytes of SCID mice or Syrian hamsters infected with each SSUrDNA-type B. microti. The results of IFAT for sera of ICR mice or Syrian hamsters infected with each SSUrDNA-type B. microti demonstrated that the four SSUrDNA-types of B. microti have different serotypes. Here, we report technical or practical procedures of IFAT, which gains sufficiently stable results, including procedures of continuous in vivo culture of B. microti.

Diagnosis and management of human babesiosis

Babesiosis is a protozoan parasitic infection affecting humans and animals. These infections are commonly transmitted by various species of Ixodes ticks depending upon the geographical location. They can also be transmitted by packed cell transfusion and transplacental route from mother to child. Various species have been reported to cause human infections, of which Babesia microti is the most common species reported globally. Usually, Babesia infections are asymptomatic or mild, but can be severe/life-threatening in immunosuppressed or splenectomized individuals. A high index of clinical suspicion in residents of endemic areas or individuals who had a recent travel history to such areas, with laboratory confirmation can guide an early institution of appropriate antimicrobial therapy, thereby preventing complications and death.

Identification of parasitic communities within European ticks using next-generation sequencing

Background

Risk assessment of tick-borne and zoonotic disease emergence necessitates sound knowledge of the particular microorganisms circulating within the communities of these major vectors. Assessment of pathogens carried by wild ticks must be performed without a priori, to allow for the detection of new or unexpected agents.

Methodology/Principal Findings

We evaluated the potential of Next-Generation Sequencing techniques (NGS) to produce an inventory of parasites carried by questing ticks. Sequences corresponding to parasites from two distinct genera were recovered in Ixodes ricinus ticks collected in Eastern France: Babesia spp. and Theileria spp. Four Babesia species were identified, three of which were zoonotic: B. divergens, Babesia sp. EU1 and B. microti; and one which infects cattle, B. major. This is the first time that these last two species have been identified in France. This approach also identified new sequences corresponding to as-yet unknown organisms similar to tropical Theileria species.

Conclusions/Significance

Our findings demonstrate the capability of NGS to produce an inventory of live tick-borne parasites, which could potentially be transmitted by the ticks, and uncovers unexpected parasites in Western Europe.

Diseases transmitted by ticks have diverse etiology (viral, bacterial, parasitic) and are responsible for high morbidity and mortality rates around the world, both in humans and animals. The emergence or re-emergence of tick-borne diseases is increasingly becoming a problem as the geographical distribution of several tick species is expanding, as well as the numbers of potential or known tick-borne pathogens are constantly evolving. It is thus necessary to know which microorganisms circulate within communities of this major vector to ensure adequate epidemiological surveillance. In this study, we evaluated the potential of Next-Generation Sequencing techniques (NGS) to produce, without a priori, an inventory of both predicted and non-expected parasites carried by Ixodes ricinus, the most prevalent human biting tick in France. Our findings suggest that NGS strategies could be used to produce an inventory of live parasites residing in ticks from a selected area, thereby expanding our knowledge base of tick-associated parasites.

Natural history of Zoonotic Babesia: Role of wildlife reservoirs

Babesiosis is an emerging zoonotic disease on all inhabited continents and various wildlife species are the principal reservoir hosts for zoonotic Babesia species. The primary vectors of Babesia are Ixodid ticks, with the majority of zoonotic species being transmitted by species in the genus Ixodes. Species of Babesia vary in their infectivity, virulence and pathogenicity for people. Various factors (e.g., increased interactions between people and the environment, increased immunosuppression, changes in landscape and climate, and shifts in host and vector species abundance and community structures) have led to an increase in tick-borne diseases in people, including babesiosis. Furthermore, because babesiosis is now a reportable disease in several states in the United States, and it is the most common blood transfusion-associated parasite, recognized infections are expected to increase. Because of the zoonotic nature of these parasites, it is essential that we understand the natural history (especially reservoirs and vectors) so that appropriate control and prevention measures can be implemented. Considerable work has been conducted on the ecology of Babesia microti and Babesia divergens, the two most common causes of babesiosis in the United States and Europe, respectively. However, unfortunately, for many of the zoonotic Babesia species, the reservoir(s) and/or tick vector(s) are unknown. We review the current knowledge regarding the ecology of Babesia among their reservoir and tick hosts with an emphasis of the role on wildlife as reservoirs. We hope to encourage the molecular characterization of Babesia from potential reservoirs and vectors as well from people. These data are necessary so that informed decisions can be made regarding potential vectors and the potential role of wildlife in the ecology of a novel Babesia when it is detected in a human patient.

JapaneseBabesia microtiCytologically Detected in Salivary Glands of Naturally Infected TickIxodes ovatus

Babesia microti protozoa were detected by light and electron microscopy in the salivary glands of field-collected Ixodes ovatus ticks; 6 of 85 adult ticks were demonstrated to be positive for B. microti DNA by polymerase chain reaction assays. In the salivary glands of unfed ticks, B. microti existed in the sporoblast stage in the granular acinus cells, and developed into the sporozoite stage during feeding on the host for 2 days. The present results indicated for the first time that I. ovatus can indeed carry B. microti and is not infected mechanically with the parasites by blood-sucking. This frequent infection of I. ovatus with B. microti demonstrates the significance of such a vector-pathogen relationship in Japan, and strongly suggests that I. ovatus is involved in the maintenance of B. microti in the fauna of Japanese rodents.

Survey ofBabesia microtiInfection in Field Rodents in Japan: Records of the Kobe-Type in New Foci and Findings of a New Type Related to the Otsu-Type

Of 247 rodents comprising 5 genera and 7 species collected at 17 sites throughout Japan from 2003 to 2005, Babesia microti was detected microscopically and by polymerase chain reaction (PCR) in 36 rodents comprising 2 genera and 3 species from 12 sites. Based on the analysis of small subunit ribosomal RNA gene (SSUrDNA) sequences, the Kobe-type, the etiological type of the first Japanese case of human infection was found in Apodemus speciosus and Apodemus argenteus in Aomori, the northernmost prefecture of the Japanese mainland, while the U.S.-type was found on Hokkaido Island and the Otsu-type was widely distributed. In addition, a new Otsu-related type was detected exclusively in Eothenomys andersoni in Nagano, a prefecture in central Japan. The sequences of internal transcribed spacer 1 to 2 (ITS1/2) of the present Kobe- and Otsu-types were almost identical to those of the same types previously identified. The ITS1/2 sequence of the U.S.-type identified in Hokkaido in this survey was somewhat different from that of the U.S.-type strain originating from the U.S.A., with approximately 95% identity. This value was similar to the 94% identity found between the ITS1/2 sequences of the Otsu-type and the new Otsu-related type. The new Otsu-related type of B. microti was isolated as the Nagano strain, which was serologically differentiated from the other type strains of B. microti. The divergence and distribution of genotypes are important factors in investigating the epidemiology of human B. microti infection in Japan.

Human babesiosis in Europe: what clinicians need to know

Although best known as an animal disease, human babesiosis is attracting increasing attention as a worldwide emerging zoonosis. Humans are commonly infected by the bite of ixodid ticks. Rare ways of transmission are transplacental, perinatal and transfusion-associated. Infection of the human host can cause a very severe host-mediated pathology including fever, and hemolysis leading to anemia, hyperbilirubinuria, hemoglobinuria and possible organ failure. In recent years, apparently owing to increased medical awareness and better diagnostic methods, the number of reported cases in humans is rising steadily worldwide. Hitherto unknown zoonotic Babesia spp. are now being reported from geographic areas where babesiosis was not previously known to occur and the growing numbers of travelers and immunocompromised individuals suggest that the frequency of cases in Europe will also continue to rise. Our review is intended to provide clinicians with practical information on the clinical management of this rare, but potentially life-threatening zoonotic disease. It covers epidemiology, phylogeny, diagnostics and treatment of human babesiosis and the potential risk of transfusion-transmitted disease with a special focus on the European situation.

Co-infections with Babesia microti and Plasmodium parasites along the China-Myanmar border

Background

Babesiosis is an emerging health risk in several parts of the world. However, little is known about the prevalence of Babesia in malaria-endemic countries. The area along the China-Myanmar border in Yunnan is a main endemic area of malaria in P.R. China, however, human infection with Babesia microti (B. microti) is not recognized in this region, and its profile of co-infection is not yet clear.

Methods

To understand its profile of co-infections with B. microti, our investigation was undertaken in the malaria-endemic area along the China-Myanmar border in Yunnan between April 2012 and June 2013. Four parasite species, including B. microti, Plasmodium falciparum (P. falciparum), P. vivax, and P. malariae, were identified among 449 suspected febrile persons detected by nested polymerase chain reaction (PCR) assay based on small subunit ribosomal ribonucleic acid (RNA) genes of B. microti and Plasmodium spp.

Results

Of all the collected samples from febrile patients, mono-infection with B. microti, P. vivax, P. falciparum, and P. malariae accounted for 1.8% (8/449), 9.8% (44/449), 2.9% (13/449), and 0.2% (1/449), respectively. The rate of mixed infections of B. microti with P. falciparum or P. vivax are both 0.2% (1/449), and mixed infections of P. falciparum and P. vivax accounted for 1.1% (5/449).

Conclusions

This report supports the hypothesis that babesiosis caused by B. microti is emerging along the China-Myanmar border in the Yunnan province, P.R. China, but it was ignored because of low parasitemia or mixed infection with Plasmodium spp. More sensitive and specific diagnosis methods are needed to find the rapid response mechanism of emergency for babesiosis and malaria co-prevalence areas.

Detection of two zoonotic Babesia microti lineages, the Hobetsu and U.S. lineages, in two sympatric tick species, ixodes ovatus and Ixodes persulcatus, respectively, in Japan

The species Babesia microti, commonly found in rodents, demonstrates a high degree of genetic diversity. Three lineages, U.S., Kobe, and Hobetsu, are known to have zoonotic potential, but their tick vector(s) in Japan remains to be elucidated. We conducted a field investigation at Nemuro on Hokkaido Island and at Sumoto on Awaji Island, where up to two of the three lineages occur with similar frequencies in reservoirs. By flagging vegetation at these spots and surrounding areas, 4,010 ticks, comprising six species, were collected. A nested PCR that detects the 18S rRNA gene of Babesia species revealed that Ixodes ovatus and I. persulcatus alone were positive. Lineage-specific PCR for rRNA-positive samples demonstrated that I. ovatus and I. persulcatus carried, respectively, the Hobetsu and U.S. parasites. No Kobe-specific DNA was detected. Infected I. ovatus ticks were found at multiple sites, including Nemuro and Sumoto, with minimum infection rates (MIR) of ∼12.3%. However, all I. persulcatus ticks collected within the same regions, a total of 535, were negative for the Hobetsu lineage, indicating that I. ovatus, but not I. persulcatus, was the vector for the lineage. At Nemuro, U.S. lineage was detected in 2 of 139 adult I. persulcatus ticks (MIR, 1.4%), for the first time, while 48 of I. ovatus ticks were negative for that lineage. Laboratory experiments confirmed the transmission of Hobetsu and U.S. parasites to hamsters via I. ovatus and I. persulcatus, respectively. Differences in vector capacity shown by MIRs at Nemuro, where the two species were equally likely to acquire either lineage of parasite, may explain the difference in distribution of Hobetsu throughout Japan and U.S. taxa in Nemuro. These findings are of importance in the assessment of the regional risk for babesiosis in humans.

A double antibody sandwich enzyme-linked immunosorbent assay for detection of secreted antigen 1 of Babesia microti using hamster model

A double antibody sandwich enzyme-linked immunosorbent assay (DAS-ELISA) targeting secreted antigen 1 of Babesia microti (BmSA1) was developed for detection of B. microti infection. The optimized DAS-ELISA was sensitive enough to detect circulating BmSA1 by day 2 post-infection, in sequential sera of a hamster infected with B. microti. This detection was 4 days earlier than antibody detection by indirect ELISA. The kinetics of circulating BmSA1 coincided with the profile of parasitemia. The specificity of this assay was evaluated using sera from animals experimentally infected with different species of Babesia. The DAS-ELISA had a higher sensitivity than the microscopic examination of Giemsa-stained blood smears for detection of the infection in hamsters. Taken together, these results indicated that BmSA1 could be a potential marker for surveillance of human babesiosis.

Development of real-time PCR assay for differential detection and quantification for multiple Babesia microti-genotypes

We have developed a real-time PCR assay that can rapidly and differentially detect and quantify four genotypes of small subunit ribosomal RNA gene (SSUrDNA) of Babesia microti (Kobe-, Otsu-, Nagano- and US-types). In this assay, four genotype-specific pairs of primers targeted on internal transcribed spacer (ITS) 1 or 2 sequences were used and amplicons by each pair of primers were quantitatively detected by fluorescent SYBR Green I. The four genotype-specific pairs of primers displayed the high specificity for homologous genotype DNA. The standard curves of cycle threshold (Ct) values versus amount of target DNA per reaction (log) for all four genotypes were linear and the correlation coefficient (Rsq) values for the curves were from 0.970 to 0.997. The standard curves were almost identical even in the presence of heterologous genotype DNA. This assay could detect 10-30 fg purified DNA (equivalent to the amount of 1-5 parasite DNA) of each genotype B. microti. This assay could also detect each genotype B. microti infection in blood with 3×10(-6)%-1×10(-5)% parasitemia. This assay was applicable to field rodent and tick samples to reveal mixed infection in several samples, for which a single genotype of B. microti had been detected by direct sequencing analyses in our previous studies. This assay also seemed to be applicable to clinical human samples, showing Kobe-type positive results for the first Japanese babesiosis patient and the asymptomatic donor, both infected with Kobe-type B. microti.

Transfusion-transmitted Babesia spp.: bull's-eye on Babesia microti

Babesia spp. are intraerythrocytic protozoan parasites of animals and humans that cause babesiosis, a zoonotic disease transmitted primarily by tick vectors. Although a variety of species or types of Babesia have been described in the literature as causing infection in humans, the rodent parasite Babesia microti has emerged as the focal point of human disease, especially in the United States. Not only has B. microti become established as a public health concern, this agent is increasingly being transmitted by blood transfusion: estimates suggest that between 70 and 100 cases of transfusion-transmitted Babesia (TTB) have occurred over the last 30 years. A recent upsurge in TTB cases attributable to B. microti, coupled with at least 12 fatalities in transfusion recipients diagnosed with babesiosis, has elevated TTB to a key policy issue in transfusion medicine. Despite clarity on a need to mitigate transmission risk, few options are currently available to prevent the transmission of B. microti by blood transfusion. Future mitigation efforts may stress serological screening of blood donors in regionalized areas of endemicity, with adjunct nucleic acid testing during the summer months, when acute infections are prevalent. However, several hurdles remain, including the absence of a licensed blood screening assay and a thorough cost-benefit analysis of proposed interventions. Despite current obstacles, continued discussion of TTB without proactive intervention is no longer a viable alternative.

Importance of nonenteric protozoan infections in immunocompromised people

There are many neglected nonenteric protozoa able to cause serious morbidity and mortality in humans, particularly in the developing world. Diseases caused by certain protozoa are often more severe in the presence of HIV. While information regarding neglected tropical diseases caused by trypanosomatids and Plasmodium is abundant, these protozoa are often not a first consideration in Western countries where they are not endemic. As such, diagnostics may not be available in these regions. Due to global travel and immigration, this has become an increasing problem. Inversely, in certain parts of the world (particularly sub-Saharan Africa), the HIV problem is so severe that diseases like microsporidiosis and toxoplasmosis are common. In Western countries, due to the availability of highly active antiretroviral therapy (HAART), these diseases are infrequently encountered. While free-living amoebae are rarely encountered in a clinical setting, when infections do occur, they are often fatal. Rapid diagnosis and treatment are essential to the survival of patients infected with these organisms. This paper reviews information on the diagnosis and treatment of nonenteric protozoal diseases in immunocompromised people, with a focus on patients infected with HIV. The nonenteric microsporidia, some trypanosomatids, Toxoplasma spp., Neospora spp., some free-living amoebae, Plasmodium spp., and Babesia spp. are discussed.

Babesia microti: molecular and antigenic characterizations of a novel 94-kDa protein (BmP94)

A novel gene, BmP94, encoding 94-kDa protein of Babesia microti was identified by immunoscreening of the cDNA expression library. The full-length of BmP94 was expressed in Escherichia coli (rBmP94), which resulted in insoluble form with low yield, and the truncated hydrophilic C-terminus region of the gene was expressed as a soluble protein (rBmP94/CT) with improved productivity. Antiserum raised against rBmP94/CT recognized the 94-kDa native protein in the parasite extract by Western blot analysis. Next, an ELISA using rBmP94/CT was evaluated for diagnostic use, and it demonstrated high sensitivity and specificity when tested with the sera from mice experimentally infected with B. microti and closely related parasites. Moreover, the immunoprotective property of rBmP94/CT as a subunit vaccine was evaluated in BALB/c mice against a B. microti challenge, but no significant protection was observed. Our data suggest that the immunodominant antigen BmP94 could be a promising candidate for diagnostic use for human babesiosis.

Molecular evidence for the presence of new Babesia species in feral raccoons (Procyon lotor) in Hokkaido, Japan

We recently reported that feral raccoons (Procyon lotor) with splenomegaly native to Japan were carriers of a Babesia microti-like parasite identical to that found in the United States, which was likely introduced to Japan from North America via raccoons imported as pets. Thus, we attempted extensive molecular survey for piroplasma infections of feral raccoon with normal spleen in Hokkaido, Japan using nested PCR that target broadly to 18S ribosomal RNA gene (SSU-rDNA) of all the parasites in the genus Babesia, Theileria, Cytauxzoon and B. microti group. Of the 348 raccoon samples analyzed, 9 gave positive signals. Cloning and phylogenetic analysis on SSU-rDNA sequences revealed that six of nine positives were found to be infected with Babesia and the remaining three with previously unreported Sarcocystis. Babesia sequences were further separated into two distantly related groups, those that reside in a novel phylogenetic group were consisted solely of four parasites found in this study, while those which included one identical sequence found in the three of our specimens were assembled together with both Babesia parasites of tick's in Japan and of raccoon's in U.S. These results may indicate that not only a B. microti-like parasite but also at least two yet undescribed Babesia species are being established in their new life cycles in the feral raccoon populations in Japan.

Detection of Kobe-type Babesia microti associated with Japanese human babesiosis in field rodents in central Taiwan and southeastern mainland China

Field rodent surveys for Babesia infection were performed from 2002 to 2005 in the vicinities of human babesiosis occurrences in Taiwan and mainland China. Babesia microti was identified by microscopical examination and/or PCR in 1 Rattus coxinga and 1 Crocidura horsfieldii in central Taiwan and in 13 Niviventer confucianus and 1 Apodemus agrarius in Zhejiang and Fujian Provinces of southeastern China. Of 15 B. microti samples detected by PCR, all except 1 were shown to be the Kobe-type, the aetiological small subunit rRNA gene-type of the first Japanese patient; the exception was also a Kobe-related type. The Kobe-type had been found in rodents only in a few places including the human infection occurrence place in Japan. The internal transcribed spacer 1 to 2 sequences of the Taiwanese and Chinese Kobe-types were very similar to each other but considerably different (approx. 94% pairwise identities) from that of the Japanese Kobe-type. A Taiwanese Kobe-type strain was serologically differentiated from the Kobe strain originating from the Japanese first patient. The distribution of the Kobe-type in the vicinities of human babesiosis occurrences in Taiwan and China as well as in Japan is suggestive of involvement of the Kobe-type in Asian human babesiosis.

Detection of Anaplasma bovis and Anaplasma phagocytophilum from cattle on Yonaguni Island, Okinawa, Japan

DNA fragments of Anaplasma bovis and Anaplasma phagocytophilum were detected in cattle on Yonaguni Island, Okinawa, Japan. Although the pathogenesis and epidemiology of these pathogens have not yet been clarified, this is the first detection of their presence in cattle from Japan.

Molecular survey of Babesia microti, Ehrlichia species and Candidatus neoehrlichia mikurensis in wild rodents from Shimane Prefecture, Japan

A significant number of patients are diagnosed with "fevers of unknown origin" (FUO) in Shimane Prefecture in Japan where tick-borne diseases are endemic. We conducted molecular surveys for Babesia microti, Ehrlichia species, and Candidatus Neoehrlichia mikurensis in 62 FUO cases and 62 wild rodents from Shimane Prefecture, Japan. PCR using primers specific for the Babesia 18S small-subunit rRNA (rDNA) gene and Anaplasmataceae groESL amplified products from 45% (28/62) and 25.8% (16/62) of captured mice, respectively. Of the 28 18S rDNA PCR positives, 23 and five samples were positive for Hobetsu- and Kobe-type B. microti, respectively. In contrast, of the 16 groESL PCR positives, eight, one and seven samples were positive for Ehrlichia muris, Ehrlichia sp. HF565 and Candidatus N. mikurensis, respectively. Inoculation of selected blood samples into Golden Syrian hamsters indicated the presence of Hobetsu- and Kobe-type B. microti in four and one sample, respectively. Isolation of the latter strain was considered important as previous studies suggested that the distribution of this type was so far confined to Awaji Island in Hyogo Prefecture, where the first case of transfusion-associated human babesiosis originated. DNA samples from 62 FUO human cases tested negative for B. microti 18S rDNA gene, Anaplasmataceae groESL gene, Rickettsia japonica 17K genus-common antigen gene and Orientia tsutsugamushi 56K antigen gene by PCRs. We also conducted seroepidemiological surveys on 62 human sera collected in Shimane Prefecture from the FUO patients who were suspected of carrying tick-borne diseases. However, indirect immunofluorescent antibody tests using B. microti- and E. muris-infected cells detected IgG against E. muris in only a single positive sample. This study demonstrates the presence of several potentially important tick-borne pathogens in Shimane Prefecture and suggests the need for further study on the causative agents of FUOs.

First confirmed autochthonous case of human Babesia microti infection in Europe

A 42-year-old female patient with acute myeloid leukemia presented with fever and heavy chest pain after her first cycle of specific chemotherapy. Acute myocardial infarction was excluded, but surprisingly, parasitic inclusions in erythrocytes became obvious in Pappenheim and Giemsa-stained peripheral blood smears. The patient did not remember a tick bite but acknowledged having received several blood transfusions in her recent medical history. Suspicion of malaria was ruled out by use of a dip-stick test. The diagnosis of Babesia microti infection was finally established by specific polymerase chain reaction (PCR). Six weeks after initiation of specific treatment, PCR turned negative and a positive immunoflourescence assay (IFA) with an IgG titer of 1:128 indicated seroconversion. Subsequent screening of donors involved in the transfusion of blood products to the patient demonstrated borderline reactivity for Babesia microti (IgG-titer 1:32) in 1 out of 44 individuals. Neither the patient nor the positively tested blood donor had travelled to North America or Asia. Therefore, this is the first confirmed autochthonous human infection in Europe.

Transfusion-transmitted infections

Although the risk of transfusion-transmitted infections today is lower than ever, the supply of safe blood products remains subject to contamination with known and yet to be identified human pathogens. Only continuous improvement and implementation of donor selection, sensitive screening tests and effective inactivation procedures can ensure the elimination, or at least reduction, of the risk of acquiring transfusion transmitted infections. In addition, ongoing education and up-to-date information regarding infectious agents that are potentially transmitted via blood components is necessary to promote the reporting of adverse events, an important component of transfusion transmitted disease surveillance. Thus, the collaboration of all parties involved in transfusion medicine, including national haemovigilance systems, is crucial for protecting a secure blood product supply from known and emerging blood-borne pathogens.

First case of human babesiosis in Korea: detection and characterization of a novel type of Babesia sp. (KO1) similar to ovine babesia

We report on the first case of human babesiosis in Korea. The intraerythrocytic parasite (KO1) in the patient's blood mainly appeared as paired pyriforms and ring forms; but Maltese cross forms were not seen, and the parasite showed morphological features consistent with those of the genus Babesia sensu stricto. The sequence of the 18S rRNA gene of KO1 was closely related to that of Babesia spp. isolated from sheep in China (similarity, 98%). The present study provides the first evidence of the presence of a hitherto unidentified, new type of Babesia parasite capable of infecting humans.

Coinfections acquired from ixodes ticks

The pathogens that cause Lyme disease (LD), human anaplasmosis, and babesiosis can coexist in Ixodes ticks and cause human coinfections. Although the risk of human coinfection differs by geographic location, the true prevalence of coinfecting pathogens among Ixodes ticks remains largely unknown for the majority of geographic locations. The prevalence of dually infected Ixodes ticks appears highest among ticks from regions of North America and Europe where LD is endemic, with reported prevalences of < or =28%. In North America and Europe, the majority of tick-borne coinfections occur among humans with diagnosed LD. Humans coinfected with LD and babesiosis appear to have more intense, prolonged symptoms than those with LD alone. Coinfected persons can also manifest diverse, influenza-like symptoms, and abnormal laboratory test results are frequently observed. Coinfecting pathogens might alter the efficiency of transmission, cause cooperative or competitive pathogen interactions, and alter disease severity among hosts. No prospective studies to assess the immunologic effects of coinfection among humans have been conducted, but animal models demonstrate that certain coinfections can modulate the immune response. Clinicians should consider the likelihood of coinfection when pursuing laboratory testing or selecting therapy for patients with tick-borne illness.

Fay and Rausch 1969 revisited: Babesia microti in Alaskan small mammals

The Holarctic distribution of Babesia microti within small rodents implies an ancient association. A seminal report of piroplasms in Alaskan voles suggested to us the possibility that B. microti entered North America within Eurasian microtine rodents dispersing through Beringian corridors. To test this hypothesis, we analyzed samples from Alaskan rodents by polymerase chain reaction for evidence of infection with B. microti; one-third of the rodents were found to be infected. Sequence analysis of the 18S rDNA gene demonstrates that Alaskan B. microti comprises a clade that infects microtines in several sites across North America and is distinct from a clade that is zoonotic.

The global importance of ticks

Ticks and tick-borne diseases affect animal and human health worldwide and are the cause of significant economic losses. Approximately 10% of the currently known 867 tick species act as vectors of a broad range of pathogens of domestic animals and humans and are also responsible for damage directly due to their feeding behaviour. The most important tick species and the effects they cause are listed. The impact on the global economy is considered to be high and although some estimates are given, there is a lack of reliable data. The impact of ticks and tick-borne diseases on animal production and public health and their control are discussed.

Babesiosis and blood transfusion: flying under the radar

Infectious agents of disease continue to plague transfusion medicine as an increasing number of pathogens are described that pose a potential blood safety risk. While the recent focus has been on newly emerged agents, several well‐established pathogens provide timely reminders that other agents continue to pose threats, but invariably ‘fly under the radar’, thereby failing to elicit adequate measures to prevent their transmission by blood transfusion. Perhaps foremost among this group of agents are the Babesia spp., which have been known to cause human disease, in the USA, for close to 40 years. B. microti, B. divergens and several Babesia‐like agents are responsible for a growing number of human babesiosis infections. Concomitantly, in the USA, there has been a sharp rise in the number of transfusion‐transmitted infections of Babesia spp., attributable almost exclusively to B. microti. Despite the obvious public health issues posed by Babesia spp., options for preventing their transmission by blood transfusion remain limited. However, recognition that the Babesia spp. are indeed an ongoing and expanding blood safety threat will probably prove instrumental in the development of viable interventions to limit transmission of these agents.

Identity of the causal agents of human babesiosis in Europe

Most cases of human babesiosis are caused either by Babesia divergens in Europe or Babesia microti in America. B. microti, once regarded as a single species, occurs as a world-wide species complex and although both phenotypic and genotypic features lend support to suggestions that zoonotic B. microti may occur in Europe, convincing medical evidence is lacking. Several B. divergens-like parasites have emerged in the last few years, but 18S rRNA gene analysis suggests that B. divergens 'sensu stricto' is restricted to European (and North African) cattle. Some of the B. divergens-like parasites only differ from the bovine type by a few bases, and it remains to be determined whether this is sufficient to accord them separate species status. Comparative biology should support genetic data in taxonomic studies of both B. divergens and B. microti.

Isolation of a human erythrocyte-adapted substrain of Babesia rodhaini and analysis of the merozoite surface protein gene sequences

Babesia rodhaini is a rodent hemoparasite closely related to B. microti, the major causative agent of human babesiosis. We tested the infectivity of B. rodhaini for human erythrocytes by using the SCID mouse model in which the circulating erythrocytes were replaced with those of humans. Initially, parasites grew very poorly in the mouse model, but a variant capable of propagating in human erythrocytes emerged after an adaptation period of three weeks. In an attempt to identify parasite proteins involved in the alteration of host cell preference, an expression cDNA library of B. rodhaini was constructed and screened with immune mouse sera. Although we were able to obtain three merozoite surface protein (MSP) genes, sequences of these genes from both the parental strain and human erythrocyte-adapted substrain were identical. Our results suggest that B. rodhaini has potential ability to infect human erythrocytes, but development of this ability may not be brought about by an amino acid change in MSPs.

Babesia microti-like parasites detected in feral raccoons (Procyon lotor) captured in Hokkaido, Japan

Raccoons (Procyon lotor), which have recently become feral in Japan, were examined for the presence of Babesia microti-like parasites. Out of 372 raccoons captured in the west-central part of Hokkaido, 24 animals with splenomegaly were selected and tested by nested PCR targeting the babesial 18S rRNA gene. B. microti-like parasites were detected in two of the 24 individuals, and their DNA sequences were identical to that of the B. microti-like parasite reported from raccoons in the United States, suggesting that the parasites were probably imported into Japan and that the life cycle of the parasite has already been established in the country. The potential risk of this B. microti-like parasite spreading among dogs and foxes in Japan will need to be carefully monitored, as parasitization by phylogenetically very close parasites has been reported from such animals.

Survey of rodents and ticks in human babesiosis emergence area in Japan: first detection of Babesia microti-like parasites in Ixodes ovatus

Babesia microti-like parasites were detected for the first time in Ixodes ovatus in Hyogo Prefecture, Japan, where two reported types of B. microti-like parasites were recognized in many rodents. Of 80 adult I. ovatus ticks collected, 5 possessed the reported type and 1 possessed a new type of B. microti-like parasite.

Risk and prevention of transfusion-transmitted babesiosis and other tick-borne diseases

PURPOSE OF REVIEW

Tick-borne diseases have increasingly been recognized in the United States as public health problems. The importance of tick-borne diseases has been accelerated by increases in animal populations, as well as increased human recreation in wooded environments that are conducive to tick bites. Babesiosis, usually caused by the intraerythrocytic parasite, Babesia microti and transmitted by the same tick as Lyme disease, has important transfusion implications. Although Lyme disease has not been reported from blood transfusion, newly identified tick-borne diseases such as ehrlichiosis raise additional questions about the role of the tick in transfusion-transmitted diseases.

RECENT FINDINGS

The risk of transfusion-transmitted babesiosis is higher than usually appreciated and in endemic areas represents a major threat to the blood supply. Furthermore, the geographic range of B. microti is expanding, other Babesia spp. have been implicated in transfusion transmission in the western United States, and the movement of blood donors and donated blood components may result in the appearance of transfusion babesiosis in areas less familiar with these parasites. Consequently, a higher degree of clinical suspicion will allow early recognition and treatment of this important transfusion complication.

SUMMARY

In endemic areas transfusion-transmitted babesiosis is more prevalent than usually believed. The extension of the geographic range of various Babesia spp. and the movement of donors and blood products around the United States has resulted in the risk extending to non-endemic areas. Clinicians should maintain a high degree of clinical suspicion for transfusion-transmitted babesiosis.