Treatment of Human Babesiosis: Then and Now

Transfection of Babesia duncani: A Genetic Toolbox of this Pathogen to Advance Babesia Biology

Human babesiosis is a tick-borne disease caused by Babesia pathogens. The disease, which presents with malaria-like symptoms, can be life-threatening, especially in individuals with weakened immune systems and the elderly. The worldwide prevalence of human babesiosis has been gradually rising, prompting alarm among public health experts. In other pathogens, genetic techniques have proven to be valuable tools for conducting functional studies to understand the importance of specific genes in development and pathogenesis as well as to validate novel cellular targets for drug discovery. Genetic manipulation methods have been established for several non-human Babesia and Theileria species and, more recently, have begun to be developed for human Babesia parasites. We have previously reported the development of a method for genetic manipulation of the human pathogen Babesia duncani. This method is based on positive selection using the hDHFR gene as a selectable marker, whose expression is regulated by the ef-1aB promoter, along with homology regions that facilitate integration into the gene of interest through homologous recombination. Herein, we provide a detailed description of the steps needed to implement this strategy in B. duncani to study gene function. It is anticipated that the implementation of this method will significantly improve our understanding of babesiosis and facilitate the development of novel and more effective therapeutic strategies for the treatment of human babesiosis. Key features This protocol provides an effective means of transfection of B. duncani, enabling genetic manipulation and editing to gain further insights into its biology and pathogenesis. The protocol outlined here for the electroporation of B. duncani represents an advancement over previous methods used for B. bovis [1]. Improvements include higher volume of culture used during the electroporation step and an enhancement in the number of electroporation pulses. These modifications likely enhance the efficiency of gene editing in B. duncani, allowing for quicker and more effective selection of transgenic parasites.

Properties and predicted functions of large genes and proteins of apicomplexan parasites

Evolutionary constraints greatly favor compact genomes that efficiently encode proteins. However, several eukaryotic organisms, including apicomplexan parasites such as Toxoplasma gondii, Plasmodium falciparum and Babesia duncani, the causative agents of toxoplasmosis, malaria and babesiosis, respectively, encode very large proteins, exceeding 20 times their average protein size. Although these large proteins represent <1% of the total protein pool and are generally expressed at low levels, their persistence throughout evolution raises important questions about their functions and possible evolutionary pressures to maintain them. In this study, we examined the trends in gene and protein size, function and expression patterns within seven apicomplexan pathogens. Our analysis revealed that certain large proteins in apicomplexan parasites harbor domains potentially important for functions such as antigenic variation, erythrocyte invasion and immune evasion. However, these domains are not limited to or strictly conserved within large proteins. While some of these proteins are predicted to engage in conventional metabolic pathways within these parasites, others fulfill specialized functions for pathogen-host interactions, nutrient acquisition and overall survival.

Effectiveness of Two New Endochin-like Quinolones, ELQ-596 and ELQ-650, in Experimental Mouse Models of Human Babesiosis

Endochin-like quinolones (ELQs) define a class of small molecule antimicrobials that target the mitochondrial electron transport chain of various human parasites by inhibiting their cytochrome bc1 complexes. The compounds have shown potent activity against a wide range of protozoan parasites, including the intraerythrocytic parasites Plasmodium and Babesia, the agents of human malaria and babesiosis, respectively. First-generation ELQ compounds were previously found to reduce infection by Babesia microti and Babesia duncani in animal models of human babesiosis but achieved a radical cure only in combination with atovaquone and required further optimization to address pharmacological limitations. Here, we report the identification of two second-generation 3-biaryl ELQ compounds, ELQ-596 and ELQ-650, with potent antibabesial activity in vitro and favorable pharmacological properties. In particular, ELQ-598, a prodrug of ELQ-596, demonstrated high efficacy as an orally administered monotherapy at 10 mg/kg. The compound achieved radical cure in both the chronic model of B. microti-induced babesiosis in immunocompromised mice and the lethal infection model induced by B. duncani in immunocompetent mice. Given its high potency, favorable physicochemical properties, and low toxicity profile, ELQ-596 represents a promising drug for the treatment of human babesiosis.

Tick-borne infections in children in North America

PURPOSE OF REVIEW

Because both incidence and awareness of tick-borne infections is increasing, review of major infections and recent advances related to their diagnosis and management is important.

RECENT FINDINGS

A new algorithm, termed modified two-tier testing, for testing for antibodies to Borrelia burgdorferi , the cause of Lyme disease, has been approved and may replace traditional two-tier testing. In addition, doxycycline is now acceptable to use for treatment of and/or prophylaxis for Lyme disease for up to 21 days in children of any age. Borrelia miyamotoi , a bacterium in the relapsing fever type of Borrelia, is the first of this type of Borrelia that is transmitted by hard-bodied ticks such as Ixodes scapularis.

SUMMARY

Awareness of these infections and advances in their diagnosis and treatment is important to assure the best outcomes for affected patients. Table 1 contains a summary of infections discussed.

A Set of Diagnostic Tests for Detection of Active Babesia duncani Infection

Human babesiosis is a rapidly emerging and potentially fatal tick-borne disease caused by intraerythrocytic apicomplexan parasites of the Babesia genus. Among the various species of Babesia that infect humans, B. duncani has been found to cause severe and life-threatening infections. Detection of active B. duncani infection is critical for accurate diagnosis and effective management of the disease. While molecular assays for the detection of B. duncani infection in blood are available, a reliable strategy to detect biomarkers of active infection has not yet been developed. Here, we report the development of the first B. duncani antigen capture assays that rely on the detection of two B. duncani -exported immunodominant antigens, BdV234 and BdV38. The assays were validated using blood samples from cultured parasites in human erythrocytes and B. duncani -infected laboratory mice at different parasitemia levels and following therapy. The assays display high specificity with no cross-reactivity with B. microti , B. divergens , Babesia MO1, or P. falciparum. The assay also demonstrates high sensitivity, detecting as low as 115 infected erythrocytes/µl of blood. Screening of 1,731 blood samples from diverse biorepositories, including previously identified Lyme and/or B. microti positive human samples and new specimens from field mice, showed no evidence of B. duncani infection in these samples. The assays could be useful in diverse diagnostic scenarios, including point-of-care testing for early B. duncani infection detection in patients, field tests for screening reservoir hosts, and high-throughput screening such as blood collected for transfusion.

Short summary

We developed two ELISA-based assays, BdACA38 and BdACA234, for detecting B. duncani , a potentially fatal tick-borne parasite causing human babesiosis. The assays target two immunodominant antigens, BdV234 and BdV38, demonstrating high specificity (no cross-reactivity with other Babesia species or Plasmodium falciparum ) and sensitivity (detecting as low as 115 infected erythrocytes/µl). The assays were validated using in vitro-cultured parasites and infected mice. Screening diverse blood samples showed no evidence of B. duncani active infection among 1,731 human and field mice blood samples collected from the north-eastern, midwestern, and western US. These assays offer potential in diverse diagnostic scenarios, including early patient detection, reservoir animal screening, and transfusion-transmitted babesiosis prevention.

Quercetin as a Promising Antiprotozoan Phytochemical: Current Knowledge and Future Research Avenues

Despite tremendous advances in the prevention and treatment of infectious diseases, only few antiparasitic drugs have been developed to date. Protozoan infections such as malaria, leishmaniasis, and trypanosomiasis continue to exact an enormous toll on public health worldwide, underscoring the need to discover novel antiprotozoan drugs. Recently, there has been an explosion of research into the antiprotozoan properties of quercetin, one of the most abundant flavonoids in the human diet. In this review, we tried to consolidate the current knowledge on the antiprotozoal effects of quercetin and to provide the most fruitful avenues for future research. Quercetin exerts potent antiprotozoan activity against a broad spectrum of pathogens such as Leishmania spp., Trypanosoma spp., Plasmodium spp., Cryptosporidium spp., Trichomonas spp., and Toxoplasma gondii. In addition to its immunomodulatory roles, quercetin disrupts mitochondrial function, induces apoptotic/necrotic cell death, impairs iron uptake, inhibits multiple enzymes involved in fatty acid synthesis and the glycolytic pathways, suppresses the activity of DNA topoisomerases, and downregulates the expression of various heat shock proteins in these pathogens. In vivo studies also show that quercetin is effective in reducing parasitic loads, histopathological damage, and mortality in animals. Future research should focus on designing effective drug delivery systems to increase the oral bioavailability of quercetin. Incorporating quercetin into various nanocarrier systems would be a promising approach to manage localized cutaneous infections. Nevertheless, clinical trials are needed to validate the efficacy of quercetin in treating various protozoan infections.

Human Tick-Borne Diseases and Advances in Anti-Tick Vaccine Approaches: A Comprehensive Review

This comprehensive review explores the field of anti-tick vaccines, addressing their significance in combating tick-borne diseases of public health concern. The main objectives are to provide a brief epidemiology of diseases affecting humans and a thorough understanding of tick biology, traditional tick control methods, the development and mechanisms of anti-tick vaccines, their efficacy in field applications, associated challenges, and future prospects. Tick-borne diseases (TBDs) pose a significant and escalating threat to global health and the livestock industries due to the widespread distribution of ticks and the multitude of pathogens they transmit. Traditional tick control methods, such as acaricides and repellents, have limitations, including environmental concerns and the emergence of tick resistance. Anti-tick vaccines offer a promising alternative by targeting specific tick proteins crucial for feeding and pathogen transmission. Developing vaccines with antigens based on these essential proteins is likely to disrupt these processes. Indeed, anti-tick vaccines have shown efficacy in laboratory and field trials successfully implemented in livestock, reducing the prevalence of TBDs. However, some challenges still remain, including vaccine efficacy on different hosts, polymorphisms in ticks of the same species, and the economic considerations of adopting large-scale vaccine strategies. Emerging technologies and approaches hold promise for improving anti-tick vaccine development and expanding their impact on public health and agriculture.

Tafenoquine-Atovaquone Combination Achieves Radical Cure and Confers Sterile Immunity in Experimental Models of Human Babesiosis

Human babesiosis is a potentially fatal tick-borne disease caused by intraerythrocytic Babesia parasites. The emergence of resistance to recommended therapies highlights the need for new and more effective treatments. Here we demonstrate that the 8-aminoquinoline antimalarial drug tafenoquine inhibits the growth of different Babesia species in vitro, is highly effective against Babesia microti and Babesia duncani in mice and protects animals from lethal infection caused by atovaquone-sensitive and -resistant B. duncani strains. We further show that a combination of tafenoquine and atovaquone achieves cure with no recrudescence in both models of human babesiosis. Interestingly, elimination of B. duncani infection in animals following drug treatment also confers immunity to subsequent challenge. Altogether, the data demonstrate superior efficacy of tafenoquine plus atovaquone combination over current therapies for the treatment of human babesiosis and highlight its potential in providing protective immunity against Babesia following parasite clearance.

Histopathological Aspects of the Influence of Babesia microti on the Placentas of Infected Female Rats

Babesiosis is perceived mainly an animal disease; however, awareness that Babesia spp. parasites that can cause diseases in humans is increasing significantly. Babesiosis is spread by the bite of an infected tick (Ixodes spp.), but it can also be transmitted by transfusion of infected blood and from an infected mother to her child during pregnancy or childbirth. The parasites multiply in the bloodstream and destroy red blood cells. This study aimed to assess the influence of Babesia microti on the histological structure of the placenta. Histopathological material collected from pregnant rats infected with Babesia microti was used in the experiment. Microscopic images of the placentas were assessed by Mallory staining and by using methylene blue-stained semi-thin sections. In addition, FISH was used to detect parasite DNA. The presence of piroplasms in both maternal and fetal vessels was demonstrated. Babesia microti infection caused vacuolization of syncytioblasts and cytotrophoblasts, accumulation of collagen fibers in placental villi, and increased adhesion of erythrocytes to the vascular walls. These results indicate that Babesia may influence the course of pregnancy and invite further research on the mechanism of piroplasm penetration into cells.

Inhibitory effects on bovine babesial infection by iron chelator, 1-(N-acetyl-6-aminohexyl)- 3-hydroxy-2-methylpyridin-4-one (CM1), and antimalarial drugs

BACKGROUND

Babesiosis is an infectious disease caused by protozoa of the apicomplexan phylum, genus Babesia. It is a malaria-like parasitic disease that can be transmitted via tick bites. The apicomplexan phylum of eukaryotic microbial parasites has had detrimental impacts on human and veterinary medicine. There are only a few drugs currently available to treat this disease; however, parasitic strains that are resistant to these commercial drugs are increasing in numbers. Plasmodium and Babesia are closely related as they share similar biological features including mechanisms for host cell invasion and metabolism. Therefore, antimalarial drugs may be useful in the treatment of Babesia infections. In addition to antimalarials, iron chelators also inhibit parasite growth. In this study, we aimed to evaluate the in vitro inhibitory efficacy of iron chelator and different antimalarials in the treatment of Babesia bovis.

METHODS

Cytotoxicity of antimalarial drugs; pyrimethamine, artefenomel, chloroquine, primaquine, dihydroarthemisinine, and the iron chelator, 1-(N-acetyl-6-aminohexyl)- 3-hydroxy-2 methylpyridin-4-one (CM1), were evaluated against Madin Darby Bovine Kidney (MDBK) cells and compared to diminazene aceturate, which is the currently available drug for animal babesiosis using an MTT solution. Afterwards, an evaluation of the in vitro growth-inhibitory effects of antimalarial drug concentrations was performed and monitored using a flow cytometer. Half maximal inhibitory concentrations (IC50) of each antimalarial and iron chelator were determined and compared to the antibabesial drug, diminazine aceturate, by interpolation using a curve-fitting technique. Subsequently, the effect of the drug combination was assessed by constructing an isobologram. Values of the sum of fractional inhibitions at 50% inhibition were then estimated.

RESULTS

Results indicate that all drugs tested could safely inhibit babesia parasite growth, as high as 2500 μM were non-toxic to mammalian cells. Although no drugs inhibited B. bovis more effectively than diminazine aceturate in this experiment, in vitro growth inhibition results with IC50 values of pyrimethamine 6.25 ± 2.59 μM, artefenomel 2.56 ± 0.67 μM, chloroquine 2.14 ± 0.76 μM, primaquine 22.61 ± 6.72 μM, dihydroarthemisinine 4.65 ± 0.22 μM, 1-(N-acetyl-6-aminohexyl)- 3-hydroxy-2 methylpyridin-4-one (CM1) 9.73 ± 1.90 μM, and diminazine aceturate 0.42 ± 0.01 μM, confirm that all drugs could inhibit B. bovis and could be used as alternative treatments for bovine babesial infection. Furthermore, the efficacy of a combination of the iron chelator, CM1, in combination with artefenomel dihydroarthemisinin or chloroquine, and artefenomel in combination with the iron chelator, CM1, dihydroarthemisinin or chloroquine, exhibited synergism against B. bovis in vitro.

CONCLUSION

Our evaluation of the inhibitory efficacy of the iron chelator CM1, antimalarial drugs, and a combination of these drugs against B. bovis could be potentially useful in the development and discovery of a novel drug for the treatment of B. bovis in the future.

Babesia BdFE1 esterase is required for the anti-parasitic activity of the ACE inhibitor fosinopril

Effective and safe therapies for the treatment of diseases caused by intraerythrocytic parasites are impeded by the rapid emergence of drug resistance and the lack of novel drug targets. One such disease is human babesiosis, which is a rapidly emerging tick-borne illness caused by Babesia parasites. In this study, we identified fosinopril, a phosphonate-containing, FDA-approved angiotensin converting enzyme (ACE) inhibitor commonly used as a prodrug for hypertension and heart failure, as a potent inhibitor of Babesia duncani parasite development within human erythrocytes. Cell biological and mass spectrometry analyses revealed that the conversion of fosinopril to its active diacid molecule, fosinoprilat, is essential for its antiparasitic activity. We show that this conversion is mediated by a parasite-encoded esterase, BdFE1, which is highly conserved among apicomplexan parasites. Parasites carrying the L238H mutation in the active site of BdFE1 failed to convert the prodrug to its active moiety and became resistant to the drug. Our data set the stage for the development of this class of drugs for the therapy of vector-borne parasitic diseases.

Multiple piroplasm parasites (Apicomplexa: Piroplasmida) in northeastern populations of the invasive Asian longhorned tick, Haemaphysalis longicornis Neumann (Ixodida: Ixodidae), in the United States

Piroplasms, which include the agents of cattle fever and human and dog babesiosis, are a diverse group of blood parasites of significant veterinary and medical importance. The invasive Asian longhorned tick, Haemaphysalis longicornis, is a known vector of piroplasms in its native range in East Asia and invasive range in Australasia. In the USA, H. longicornis has been associated with Theileria orientalis Ikeda outbreaks that caused cattle mortality. To survey invasive populations of H. longicornis for a broad range of piroplasms, 667 questing H. longicornis collected in 2021 from 3 sites in New Jersey, USA, were tested with generalist piroplasm primers targeting the 18S small subunit rRNA (395–515 bp, depending on species) and the cytochrome b oxidase loci (1009 bp). Sequences matching Theileria cervi type F (1 adult, 5 nymphs), an unidentified Theileria species (in 1 nymph), an undescribed Babesia sensu stricto (‘true’ Babesia, 2 adults, 2 nymphs), a Babesia sp. Coco (also a ‘true Babesia’, 1 adult, 1 nymph), as well as Babesia microti S837 (1 adult, 4 nymphs) were recovered. Babesia microti S837 is closely related to the human pathogen B. microti US-type. Additionally, a 132 bp sequence matching the cytochrome b locus of deer, Odocoileus virginanus, was obtained from 2 partially engorged H. longicornis. The diverse assemblage of piroplasms now associated with H. longicornis in the USA spans 3 clades in the piroplasm phylogeny and raises concerns of transmission amplification of veterinary pathogens as well as spillover of pathogens from wildlife to humans.

Plasma Blood Levels of Tafenoquine following a Single Oral Dosage in BALBc Mice with Acute Babesia microti Infection That Resulted in Rapid Clearance of Microscopically Detectable Parasitemia

Previous studies of mice infected with Babesia microti have shown that a single dose of tafenoquine administered orally is extremely effective at decreasing microscopically detectable parasitemia. However, a critical limitation of studies to date is the lack of data concerning the plasma levels of tafenoquine that are needed to treat babesiosis. In the current study, we begin to address this gap by examining the plasma levels of tafenoquine associated with the rapid reduction of B. microti patent parasitemia in a mouse model of babesiosis. In the current study, we infected BALB/c mice with 1 × 107B. microti-infected red blood cells. Two days post-infection, mice were treated with 20 mg/kg of tafenoquine succinate or vehicle control administered orally by gavage. Parasitemia and plasma levels of tafenoquine were evaluated every 24 h post-treatment for 96 h. This allowed us to correlate blood plasma levels of tafenoquine with reductions in parasitemia in treated mice. Consistent with previous studies, a single oral dose of 20 mg/kg tafenoquine resulted in a rapid reduction in parasitemia. Plasma levels of tafenoquine 24 h post-administration ranged from 347 to 503 ng/mL and declined thereafter. This blood plasma tafenoquine level is similar to that achieved in humans using the current FDA-approved dose for the prevention of malaria.

A Forty-Year Analysis of the Literature on Babesia Infection (1982-2022): A Systematic Bibliometric Approach

Babesia infection is a tick-borne protozoan disease associated with significant veterinary, economic, and medical importance. This infection affects many hosts, ranging from wild to domestic animals and including man. All vertebrates serve as potential carriers due to the huge diversity of the species. Babesiosis has been associated with severe economic loss in livestock production, especially in cattle farming, and is also a major public health concern in man, which could be fatal. The infection is usually opportunistic, ranging from asymptomatic to symptomatic, usually in immunocompromised subjects or under conditions of stressful management. This study was designed to uncover trends in relation to publication growth and further explore research output regarding babesiosis from data indexed in the WoS. The WoS is the only platform used to map publications on Babesia infection. The search term "babesiosis" or "Babesia infection" was used to extract articles published across the study period from 1982 to 2022. The inclusion criteria were restricted to only articles for the analysis. The results from the search query showed that a total of 3763 articles were published during the study period with an average of 91.70 ± 43.87 articles annually and an average total citation (n = 1874.8). An annual growth rate of 2.5% was recorded during the study period. The year 2021 had the highest number of published articles (n = 193, 5.1%) and citations (n = 7039). The analysis of the most relevant keywords and titles showed that infection (n = 606, 16.1%), babesiosis (n = 444, 11.7%), and Babesia (n = 1302, 16%) were the most relevant keyword plus (ID), author keyword (DE), and title, respectively. The common conceptual framework analysis through K-means clustering showed two clusters comprising 4 and 41 elements, respectively. The United States of America is the top-performing country in terms of article production (n = 707, 20.8%) and the leading funder for babesiosis research, with two of its agencies ranked at the top. These are the Department of Health and Human Services (n = 254, 6.7%) and the National Institute of Health (n= 238,6.3%). Igarashi I. is the top-performing author (n = 231, 6.1%), while Veterinary Parasitology is ranked the top journal (n = 393, 10.4%) in terms of babesiosis publications. Overall, an increase in publications was observed in the study period, with significant output from developed nations.

Babesia duncani multi-omics identifies virulence factors and drug targets

Babesiosis is a malaria-like disease in humans and animals that is caused by Babesia species, which are tick-transmitted apicomplexan pathogens. Babesia duncani causes severe to lethal infection in humans, but despite the risk that this parasite poses as an emerging pathogen, little is known about its biology, metabolic requirements or pathogenesis. Unlike other apicomplexan parasites that infect red blood cells, B. duncani can be continuously cultured in vitro in human erythrocytes and can infect mice resulting in fulminant babesiosis and death. We report comprehensive, detailed molecular, genomic, transcriptomic and epigenetic analyses to gain insights into the biology of B. duncani. We completed the assembly, 3D structure and annotation of its nuclear genome, and analysed its transcriptomic and epigenetics profiles during its asexual life cycle stages in human erythrocytes. We used RNA-seq data to produce an atlas of parasite metabolism during its intraerythrocytic life cycle. Characterization of the B. duncani genome, epigenome and transcriptome identified classes of candidate virulence factors, antigens for diagnosis of active infection and several attractive drug targets. Furthermore, metabolic reconstitutions from genome annotation and in vitro efficacy studies identified antifolates, pyrimethamine and WR-99210 as potent inhibitors of B. duncani to establish a pipeline of small molecules that could be developed as effective therapies for the treatment of human babesiosis.

Characteristics of Human Babesiosis in Europe

One of the Editor's choice articles in 2021 published in Pathogens was a review of human babesiosis in Europe [...].

Epitope profiling of monoclonal antibodies to the immunodominant antigen BmGPI12 of the human pathogen Babesia microti

The significant rise in the number of tick-borne diseases represents a major threat to public health worldwide. One such emerging disease is human babesiosis, which is caused by several protozoan parasites of the Babesia genus of which B. microti is responsible for most clinical cases reported to date. Recent studies have shown that during its intraerythrocytic life cycle, B. microti exports several antigens into the mammalian host using a novel vesicular-mediated secretion mechanism. One of these secreted proteins is the immunodominant antigen BmGPI12, which has been demonstrated to be a reliable biomarker of active B. microti infection. The major immunogenic determinants of this antigen remain unknown. Here we provide a comprehensive molecular and serological characterization of a set of eighteen monoclonal antibodies developed against BmGPI12 and a detailed profile of their binding specificity and suitability in the detection of active B. microti infection. Serological profiling and competition assays using synthetic peptides identified five unique epitopes on the surface of BmGPI12 which are recognized by a set of eight monoclonal antibodies. ELISA-based antigen detection assays identified five antibody combinations that specifically detect the secreted form of BmGPI12 in plasma samples from B. microti-infected mice and humans but not from other Babesia species or P. falciparum.

Babesia duncani in Culture and in Mouse (ICIM) Model for the Advancement of Babesia Biology, Pathogenesis, and Therapy

Babesiosis is a tick-borne disease caused by pathogens belonging to the genus Babesia. In humans, the disease presents as a malaria-like illness and can be fatal in immunocompromised and elderly people. In the past few years, human babesiosis has been a rising concern worldwide. The disease is transmitted through tick bite, blood transfusion, and transplacentally in rare cases, with several species of Babesia causing human infection. Babesia microti, Babesia duncani, and Babesia divergens are of particular interest because of their important health impact and amenability to research inquiries. B. microti, the most commonly reported Babesia pathogen infecting humans, can be propagated in immunocompetent and immunocompromised mice but so far has not been successfully continuously propagated in vitro in human red blood cells (hRBCs). Conversely, B. divergens can be propagated in vitro in human red blood cells but lacks a mouse model to study its virulence. Recent studies have highlighted the uniqueness of B. duncani as an ideal model organism to study intraerythrocytic parasitism in vitro and in vivo. An optimized B. duncani in culture and in mouse (ICIM) model has recently been described, combining long-term continuous in vitro culture of the parasite in hRBCs with an animal model of parasitemia (P) and lethal infection in C3H/HeJ mice. Here, we provide a detailed protocol for the use of the B. duncani ICIM model in research. This model provides a unique and sound foundation to gain further insights into the biology, pathogenesis, and virulence of Babesia and other intraerythrocytic parasites, and has been validated as an efficient system to evaluate novel strategies for the treatment of human babesiosis and possibly other parasitic diseases. This protocol was validated in: J Infect Dis (2022), DOI: 10.1093/infdis/jiac181 Graphical abstract ICIM model [Adapted and modified from Pal et al. (2022)].

Phosphatidylinositol 4-kinase is a viable target for the radical cure of Babesia microti infection in immunocompromised hosts

Human babesiosis is a global emerging tick-borne disease caused by infection with intra-erythrocytic parasites of the genus Babesia. With the rise in human babesiosis cases, the discovery and development of new anti-Babesia drugs are essential. Phosphatidylinositol 4-kinase (PI4K) is a widely present eukaryotic enzyme that phosphorylates lipids to regulate intracellular signaling and trafficking. Previously, we have shown that MMV390048, an inhibitor of PI4K, showed potent inhibition against Babesia species, revealing PI4K as a druggable target for babesiosis. However, twice-administered, 7-day regimens failed to clear Babesia microti parasites from the immunocompromised host. Hence, in this study, we wanted to clarify whether targeting PI4K has the potential for the radical cure of babesiosis. In a B. microti-infected SCID mouse model, a 64-day-consecutive treatment with MMV390048 resulted in the clearance of parasites. Meanwhile, an atovaquone (ATO) resistant parasite line was isolated from the group treated with ATO plus azithromycin. A nonsynonymous variant in the Y272C of the cytochrome b gene was confirmed by sequencing. Likewise, MMV390048 showed potent inhibition against ATO-resistant parasites. These results provide evidence of PI4K as a viable drug target for the radical cure of babesiosis, which will contribute to designing new compounds that can eradicate parasites.

Babesia duncani as a Model Organism to Study the Development, Virulence, and Drug Susceptibility of Intraerythrocytic Parasites In Vitro and In Vivo

Human babesiosis is a malaria-like illness caused by tick-borne intraerythrocytic Babesia parasites of the Apicomplexa phylum. Whereas several species of Babesia can cause severe disease in humans, the ability to propagate Babesia duncani both in vitro in human erythrocytes and in mice makes it a unique pathogen to study Babesia biology and pathogenesis. Here we report an optimized B. duncani in culture-in mouse (ICIM) model that combines continuous in vitro culture of the parasite with a precise model of lethal infection in mice. We demonstrate that B. duncani-infected erythrocytes as well as free merozoites can cause lethal infection in C3H/HeJ mice. Highly reproducible parasitemia and survival outcomes could be established using specific parasite loads in different mouse genetic backgrounds. Using the ICIM model, we discovered 2 new endochin-like quinolone prodrugs (ELQ-331 and ELQ-468) that alone or in combination with atovaquone are highly efficacious against B. duncani and Babesia microti.

Specific and Sensitive Diagnosis of Babesia microti Active Infection Using Monoclonal Antibodies to the Immunodominant Antigen BmGPI12

The apicomplexan pathogen Babesia microti is responsible for most cases of human babesiosis worldwide. The disease, which presents as a malaria-like illness, is potentially fatal in immunocompromised or elderly patients, making the need for its accurate and early diagnosis an urgent public health concern. B. microti is transmitted primarily by Ixodes ticks but can also be transmitted via blood transfusion. The parasite completes its asexual reproduction in the host red blood cell, where each invading merozoite develops and multiplies to produce four daughter parasites. While various techniques, such as microscopy, PCR, and indirect fluorescence, have been used over the years for babesiosis diagnosis, detection of the secreted B. microti immunodominant antigen BmGPI12 using specific polyclonal antibodies was found to be the most effective method for the diagnosis of active infection and for evaluation of clearance following drug treatment. Here, we report the development of a panel of 16 monoclonal antibodies against BmGPI12. These antibodies detected secreted BmGPI12 in the plasma of infected humans. Antigen capture assays identified a combination of two monoclonal antibodies, 4C8 and 1E11, as a basis for a monoclonal antibody-based BmGPI12 capture assay (mGPAC) to detect active B. microti infection. Using a collection of 105 previously characterized human plasma samples, the mGPAC assay showed 97.1% correlation with RNA-based PCR (transcription-mediated amplification [TMA]) for positive and negative samples. The mGPAC assay also detected BmGPI12 in the plasma of six babesiosis patients at the time of diagnosis but not in three matched posttreatment samples. The mGPAC assay could thus be used alone or in combination with other assays for accurate detection of active B. microti infection.

Babesia, Theileria, Plasmodium and Hemoglobin

The Propagation of Plasmodium spp. and Babesia/Theileria spp. vertebrate blood stages relies on the mediated acquisition of nutrients available within the host’s red blood cell (RBC). The cellular processes of uptake, trafficking and metabolic processing of host RBC proteins are thus crucial for the intraerythrocytic development of these parasites. In contrast to malarial Plasmodia, the molecular mechanisms of uptake and processing of the major RBC cytoplasmic protein hemoglobin remain widely unexplored in intraerythrocytic Babesia/Theileria species. In the paper, we thus provide an updated comparison of the intraerythrocytic stage feeding mechanisms of these two distantly related groups of parasitic Apicomplexa. As the associated metabolic pathways including proteolytic degradation and networks facilitating heme homeostasis represent attractive targets for diverse antimalarials, and alterations in these pathways underpin several mechanisms of malaria drug resistance, our ambition is to highlight some fundamental differences resulting in different implications for parasite management with the potential for novel interventions against Babesia/Theileria infections.

Efficacy of Short-Term High Dose Pulsed Dapsone Combination Therapy in the Treatment of Chronic Lyme Disease/Post-Treatment Lyme Disease Syndrome (PTLDS) and Associated Co-Infections: A Report of Three Cases and Literature Review

Lyme disease and associated co-infections are increasing worldwide and approximately 20% of individuals develop chronic Lyme disease (CLD)/Post-Treatment Lyme Disease Syndrome (PTLDS) despite early antibiotics. A seven- to eight-week protocol of double dose dapsone combination therapy (DDDCT) for CLD/PTLDS results in symptom remission in approximately 50% of patients for one year or longer, with published culture studies indicating higher doses of dapsone demonstrate efficacy against resistant biofilm forms of Borrelia burgdorferi. The purpose of this study was, therefore, to evaluate higher doses of dapsone in the treatment of resistant CLD/PTLDS and associated co-infections. A total of 25 patients with a history of Lyme and associated co-infections, most of whom had ongoing symptoms despite several courses of DDDCT, took one or more courses of high dose pulsed dapsone combination therapy (200 mg dapsone × 3–4 days and/or 200 mg BID × 4 days), depending on persistent symptoms. The majority of patients noticed sustained improvement in eight major Lyme symptoms, including fatigue, pain, headaches, neuropathy, insomnia, cognition, and sweating, where dapsone dosage, not just the treatment length, positively affected outcomes. High dose pulsed dapsone combination therapy may represent a novel therapeutic approach for the treatment of resistant CLD/PTLDS, and should be confirmed in randomized, controlled clinical trials.

Splenic artery embolization for spontaneous splenic rupture due to Babesiosis: a case report

Babesiosis incidence in the United States has been increasing with an 11% rise between 2018 and 2019 based on the latest CDC annual summary, reaching its highest ever reported incidence. This primarily tick-borne disease is particularly prevalent in New England. Despite predominantly nonspecific and at times subtle symptoms, life-threatening complications do occur. One such complication is splenic rupture which has been suggested to be more common in younger and otherwise healthy individuals. This is a report on a successful splenic artery embolization in a 65-year-old male from upstate New York who, unlike most prior studies, showed splenic rupture after he was discharged with negative parasitemia and general improvement following several days of targeted antibiotic therapy. Increased incidence and various presentations of Babesiosis call for an attempt to promote clinical awareness for radiologists among other specialties.

An Alternative Culture Medium for Continuous In Vitro Propagation of the Human Pathogen Babesia duncani in Human Erythrocytes

Continuous propagation of Babesia duncani in vitro in human erythrocytes and the availability of a mouse model of B. duncani lethal infection make this parasite an ideal model to study Babesia biology and pathogenesis. Two culture media, HL-1 and Claycomb, with proprietary formulations are the only culture media known to support the parasite growth in human erythrocytes; however, the HL-1 medium has been discontinued and the Claycomb medium is often unavailable leading to major interruptions in the study of this pathogen. To identify alternative media conditions, we evaluated the growth of B. duncani in various culture media with well-defined compositions. We report that the DMEM-F12 culture medium supports the continuous growth of the parasite in human erythrocytes to levels equal to those achieved in the HL-1 and Claycomb media. We generated new clones of B. duncani from the parental WA-1 clinical isolate after three consecutive subcloning events in this medium. All clones showed a multiplication rate in vitro similar to that of the WA-1 parental isolate and cause fatal infection in C3H/HeJ mice. The culture medium, which can be readily reconstituted from its individual components, and the tools and resources developed here will facilitate the study of B. duncani.

Deep Learning for Microscopic Examination of Protozoan Parasites

The infectious and parasitic diseases represent a major threat to public health and are among the main causes of morbidity and mortality. The complex and divergent life cycles of parasites present major difficulties associated with the diagnosis of these organisms by microscopic examination. Deep learning has shown extraordinary performance in biomedical image analysis including various parasites diagnosis in the past few years. Here we summarize advances of deep learning in the field of protozoan parasites microscopic examination, focusing on publicly available microscopic image datasets of protozoan parasites. In the end, we summarize the challenges and future trends, which deep learning faces in protozoan parasite diagnosis.

In Silico Survey and Characterization of Babesia microti Functional and Non-Functional Proteases

Human babesiosis caused by the intraerythrocytic apicomplexan Babesia microti is an expanding tick-borne zoonotic disease that may cause severe symptoms and death in elderly or immunocompromised individuals. In light of an increasing resistance of B. microti to drugs, there is a lack of therapeutic alternatives. Species-specific proteases are essential for parasite survival and possible chemotherapeutic targets. However, the repertoire of proteases in B. microti remains poorly investigated. Herein, we employed several combined bioinformatics tools and strategies to organize and identify genes encoding for the full repertoire of proteases in the B. microti genome. We identified 64 active proteases and 25 nonactive protease homologs. These proteases can be classified into cysteine (n = 28), serine (n = 21), threonine (n = 14), asparagine (n = 7), and metallopeptidases (n = 19), which, in turn, are assigned to a total of 38 peptidase families. Comparative studies between the repertoire of B. bovis and B. microti proteases revealed differences among sensu stricto and sensu lato Babesia parasites that reflect their distinct evolutionary history. Overall, this data may help direct future research towards our understanding of the biology and pathogenicity of Babesia parasites and to explore proteases as targets for developing novel therapeutic interventions.