Comparative genomic analysis and phylogenetic position of Theileria equi

Distribution of Rhipicephalus sanguineus and Heamaphysalis elliptica dog ticks and pathogens they are carrying: A systematic review

The role of ixodid ticks especially Rhipicephalus sanguineus and Heamaphysalis elliptica in the epidemiology of several diseases of veterinary and public health importance have been documented. This study conducted a systematic review focusing on the distribution of R. sanguineus and H. elliptica, as well as the common tick-borne pathogens they harbour. The Scopus, ScienceDirect, PubMed, and Web of Science databases were used to search for English journal articles published between January 1990 and June 2021. The articles were assessed by following the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) guidelines. This systematic review was registered on PROSPERO [(ID no: CRD42022327372). Of the studies included in the systematic review, 247 and 19 articles had identified R. sanguineus and H. elliptica respectively, whereas 15 articles had identified both tick species. There is a reported worldwide distribution of R. sanguineus from 64 countries, whereas H. elliptica was only reported in the African continent from 6 countries. In total, 120 articles that were included in this systematic review reported detection of tick-borne pathogens from R. sanguineus (n = 118 articles) and/or H. elliptica (n = 2 articles) ticks. According to the studies tick-borne pathogens harboured by R. sanguineus included protozoa such as Babesia spp., Hepatozoon spp., Leishmania spp., and Theileria spp., as well as bacteria such as Acinetobacter spp. Anaplasma spp., Bacillus spp., Borrelia spp., Brucella spp., Coxiella spp., and Staphylococcus spp. The H. elliptica was reported to be harbouring Babesia spp., Ehrlichia spp. and Rickettsia spp. Most of the studies (50%) used the conventional polymerase chain reaction (PCR) technique for the detection of tick-borne pathogens, followed by real-time PCR (qPCR) (n = 26), and nested PCR (n = 22). This systematic review has shed light on the distribution of two common dog ticks as well as the tick-borne pathogens of veterinary and zoonotic importance they are harbouring. This data will enable surveillance studies that can report whether the distribution of these ticks and their associated tick-borne pathogens is expanding or shrinking or is stable.

The Hypervariable Tpr Multigene Family of Theileria Parasites, Defined by a Conserved, Membrane-Associated, C-Terminal Domain, Includes Several Copies with Defined Orthology Between Species

Multigene families often play an important role in host-parasite interactions. One of the largest multigene families in Theileria parva, the causative agent of East Coast fever, is the T. parva repeat (Tpr) gene family. The function of the putative Tpr proteins remains unknown. The initial publication of the T. parva reference genome identified 39 Tpr family open reading frames (ORFs) sharing a conserved C-terminal domain. Twenty-eight of these are clustered in a central region of chromosome 3, termed the "Tpr locus", while others are dispersed throughout all four nuclear chromosomes. The Tpr locus contains three of the four assembly gaps remaining in the genome, suggesting the presence of additional, as yet uncharacterized, Tpr gene copies. Here, we describe the use of long-read sequencing to attempt to close the gaps in the reference assembly of T. parva (located among multigene families clusters), characterize the full complement of Tpr family ORFs in the T. parva reference genome, and evaluate their evolutionary relationship with Tpr homologs in other Theileria species. We identify three new Tpr family genes in the T. parva reference genome and show that sequence similarity among paralogs in the Tpr locus is significantly higher than between genes outside the Tpr locus. We also identify sequences homologous to the conserved C-terminal domain in five additional Theileria species. Using these sequences, we show that the evolution of this gene family involves conservation of a few orthologs across species, combined with gene gains/losses, and species-specific expansions.

Evaluation of the Inhibitory Effect of Moringa oleifera Leaves Methanolic Extract against In Vitro Growth of Several Babesia Species and Theileria equi and the In Vivo Growth of Babesia microti

The current study evaluated the inhibitory effect of Moringa oleifera leaves methanolic extract (MOL) against the in vitro growth of Babesia bovis (B. bovis), B. caballi, B. bigemina, and Theileria equi (T. equi), as well as in vivo growth of B. microti in mice. Active principles of MOL extract were determined using liquid chromatography mass spectrometry (LC-MS). MOL's anti-piroplasm efficacy was assessed both in vitro and in vivo using the SYBR Green I fluorescence assay. Every 96 hours, the hematological parameters, including red blood cell count (RBCs; 104/UL), hemoglobin content (HGB; g/dl), and hematocrit percent (HCT; %), in the treated mice were monitored using a Celltac MEK6450 automated hematological analyzer. LC-MS of MOL revealed that the most abundant polyphenolic catechism found in the MOL extract was isoquercetin and rutin. MOL inhibited B. bovis, B. caballi, B. bigemina, and T. equi in vitro growth in a dose-dependent way, with IC50 values of 45.29 ± 6.14, 19.16 ± 0.45, 137.49 ± 16.07, and 9.29 ± 0.014 μg/ml, respectively. MOL's in vitro antibabesial activity was enhanced when administrated simultaneously with either diminazene aceturate (DA) or MMV665875 compound from malaria box. In mice infected by B. microti, a combination of MOL and a low dose of DA (12.5 mg·kg-1) resulted in a significant (P < 0.05) reduction in B. microti growth. These findings suggest that MOL is an effective herbal anti-piroplasm therapy, especially when combined with a low dosage of either DA or MMV665875.

A case of equine piroplasmosis in the Tokyo 2020 Olympic Games

Equine piroplasmosis is an infectious disease caused by Babesia caballi and Theileria equi. A competition horse that had been imported to the Equestrian Park for the Tokyo 2020 Olympic Games and had a fever over 40°C and severe anemia was diagnosed with equine piroplasmosis by blood smear and direct polymerase chain reaction (PCR) tests for Theileria equi. Treatment with protozoan anthelmintics and whole blood transfusion diminished the fever, improved the anemia, and allowed the horse to return home safely. Preparation for routine cases of this infection should include the development of a system that allows accurate and prompt international dissemination of information and implementation of quarantine measures.

Genomic Characterization of Theileria luwenshuni Strain Cheeloo

Theileria, a tick-borne intracellular protozoan, can cause infections of various livestock and wildlife around the world, posing a threat to veterinary health. Although more and more Theileria species have been identified, genomes have been available only from four Theileria species to date. Here, we assembled a whole genome of Theileria luwenshuni, an emerging Theileria, through next-generation sequencing of purified erythrocytes from the blood of a naturally infected goat. We designated it T. luwenshuni str. Cheeloo because its genome was assembled by the researchers at Cheeloo College of Medicine, Shandong University, China. The genome of T. lunwenshuni str. Cheeloo was the smallest in comparison with the other four Theileria species. T. luwenshuni str. Cheeloo possessed the fewest gene gains and gene family expansion. The protein count of each category was always comparable between T. luwenshuni str. Cheeloo and T. orientalis str. Shintoku in the Eukaryote Orthologs annotation, though there were remarkable differences in genome size. T. luwenshuni str. Cheeloo had lower counts than the other four Theileria species in most categories at level 3 of Gene Ontology annotation. Kyoto Encyclopedia of Genes and Genomes annotation revealed a loss of the c-Myb in T. luwenshuni str. Cheeloo. The infection rate of T. luwenshuni str. Cheeloo was up to 81.5% in a total of 54 goats from three flocks. The phylogenetic analyses based on both 18S rRNA and cox1 genes indicated that T. luwenshuni had relatively low diversity. The first characterization of the T. luwenshuni genome will promote better understanding of the emerging Theileria. IMPORTANCE Theileria has led to substantial economic losses in animal husbandry. Whole-genome sequencing data of the genus Theileria are currently limited, which has prohibited us from further understanding their molecular features. This work depicted whole-genome sequences of T. luwenshuni str. Cheeloo, an emerging Theileria species, and reported a high prevalence of T. luwenshuni str. Cheeloo infection in goats. The first assembly and characterization of T. luwenshuni genome will benefit exploring the infective and pathogenic mechanisms of the emerging Theileria to provide scientific basis for future control strategies of theileriosis.

Degrade to survive: the intricate world of piroplasmid proteases

Piroplasmids of the genera Babesia, Theileria, and Cytauxzoon are tick-transmitted parasites with a high impact on animals and humans. They have complex life cycles in their definitive arthropod and intermediate vertebrate hosts involving numerous processes, including invasion of, and egress from, host cells, parasite growth, transformation, and migration. Like other parasitic protozoa, piroplasmids are equipped with different types of protease to fulfill many of such essential processes. Blockade of some key proteases, using inhibitors or antibodies, hinders piroplasmid growth, highlighting their potential usefulness in drug therapies and vaccine development. A better understanding of the functional significance of these enzymes will contribute to the development of improved control measures for the devastating animal and human diseases caused by these pathogens.

Complete Genome Sequence of Theileria equi NVSL354

We are reporting the nearly complete genome of Theileria equi (Piroplasmida, Apicomplexa), which contains four nuclear chromosomes, a mitochondrial genome, and an apicoplast from the NVSL354 reference isolate. This report includes all six genetic molecules.

Repurposing of the Malaria Box for Babesia microti in mice identifies novel active scaffolds against piroplasmosis

Background

An innovative approach has been introduced for identifying and developing novel potent and safe anti-Babesia and anti-Theileria agents for the control of animal piroplasmosis. In the present study, we evaluated the inhibitory effects of Malaria Box (MBox) compounds (n = 8) against the growth of Babesia microti in mice and conducted bioinformatics analysis between the selected hits and the currently used antibabesial drugs, with far-reaching implications for potent combinations.

Methods

A fluorescence assay was used to evaluate the in vivo inhibitory effects of the selected compounds. Bioinformatics analysis was conducted using hierarchical clustering, distance matrix and molecular weight correlation, and PubChem fingerprint. The compounds with in vivo potential efficacy were selected to search for their target in the piroplasm parasites using quantitative PCR (qPCR).

Results

Screening the MBox against the in vivo growth of the B. microti parasite enabled the discovery of potent new antipiroplasm drugs, including MMV396693 and MMV665875. Interestingly, statistically significant (P < 0.05) downregulation of cysteine protease mRNA levels was observed in MMV665875-treated Theileria equi in vitro culture in comparison with untreated cultures. MMV396693/clofazimine and MMV665875/atovaquone (AV) showed maximum structural similarity (MSS) with each other. The distance matrix results indicate promising antibabesial efficacy of combination therapies consisting of either MMV665875 and AV or MMV396693 and imidocarb dipropionate (ID).

Conclusions

Inhibitory and hematology assay results suggest that MMV396693 and MMV665875 are potent antipiroplasm monotherapies. The structural similarity results indicate that MMV665875 and MMV396693 have a similar mode of action as AV and ID, respectively. Our findings demonstrated that MBox compounds provide a promising lead for the development of new antibabesial therapeutic alternatives.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s13071-022-05430-4.

Complete Genomes of Theileria orientalis Chitose and Buffeli Genotypes Reveal within Species Translocations and Differences in ABC Transporter Content

Theileria orientalis causes losses to cattle producers in Eastern Asia, Oceania and, more recently, North America. One pathogenic genotype (Ikeda) has been sequenced to the chromosomal level, while only draft genomes exist for globally distributed Chitose and Buffeli genotypes. To provide an accurate comparative gene-level analysis and help further understand their pathogenicity, we sequenced isolates of the Chitose and Buffeli genotypes of T. orientalis using long-read sequencing technology. A combination of several long-read assembly methods and short reads produced chromosomal-level assemblies for both Fish Creek (Chitose) and Goon Nure (Buffeli) isolates, including the first complete and circular apicoplast genomes generated for T. orientalis. Comparison with the Shintoku (Ikeda) reference sequence showed both large and small translocations in T. orientalis Buffeli, between chromosomes 2 and 3 and chromosomes 1 and 4, respectively. Ortholog clustering showed expansion of ABC transporter genes in Chitose and Buffeli. However, differences in several genes of unknown function, including DUF529/FAINT-domain-containing proteins, were also identified and these genes were more prevalent in Ikeda and Chitose genotypes. Phylogenetics and similarity measures were consistent with previous short-read genomic analysis. The generation of chromosomal sequences for these highly prevalent T. orientalis genotypes will also support future studies of population genetics and mixed genotype infections.

Serological and molecular detection of Babesia caballi and Theileria equi in Mexico: A prospective study

Equine piroplasmosis is a disease of horses, mules and donkeys, caused by the hemoprotozoans Babesia caballi and Theileria equi and transmitted by ticks of tropical and subtropical regions. Because the clinical signs are not specific, the diagnosis of equine piroplasmosis is difficult. In Mexico, where the environmental factors are conducive to the persistence of these pathogens, there is a lack of molecular studies to evaluate the occurrence of both parasites in horses. In the present study, matching serum and whole blood samples were obtained from 269 horses residing in 24 locations with tropical or subtropical climate and the presence of ticks. Testing of serum samples by ELISA demonstrated 55.7% seroprevalence of B. caballi and 68.4% prevalence of antibodies to T. equi. Blood samples analyzed with nPCR test were 7.8% positive to B. caballi and 78.8% positive to T. equi, while a duplex qPCR showed 15.24% positive samples to B. caballi and 59.11% to T. equi. From these results, 27 samples were sequenced for T. equi and 13 for B. caballi, confirming the presence of both horse parasites that cause equine piroplasmosis and suggesting that they are widespread in Mexico. This is the first study confirming the presence of B. caballi and T. equi in Mexico using both serological and molecular diagnostic methods. This study shows a high incidence of exposure to the etiological agents of equine piroplasmosis in horses in the studied areas.

Insights into equine piroplasmosis in Venezuelan sport horses: Molecular diagnosis, clinical, and cardiovascular findings

Equine piroplasmosis (EP) is a tick-borne infectious disease highly prevalent in tropical and subtropical regions, such as Venezuela. EP affects wild and domestic equids leading to several clinical presentations, from asymptomatic to severely affected animals. In this study, thirty-three (33) sport horses under regular training activities and from endemic regions of north-central Venezuela were submitted to an observational survey, case-control, to describe the presence of clinical signs and natural EP infections. A conventional PCR assay targeting the SSU rRNA gene revealed EP etiologic agents in 13 out of 33 sampled horses (~ 39.4% infections). Nine (9) of these EP-positive samples were confirmed as infected with Babesia caballi (6/9 = 66.7%) or Theileria equi (3/9 = 33.3%) by DNA sequencing and BLASTN analyses. A phylogeny of SSU rRNA gene sequences revealed that these new B. caballi and T. equi sequences clustered within the worldwide distributed phylogenetic genotype A, respectively. No acute EP cases were observed in this study; however, six (6) PCR-positive animals displayed mild clinical signs compatible with EP, including a mild leukocytosis (P < 0.05). The heart rate variability frequency domain analysis in four (4) of these EP-positive infected animals revealed a significant (P < 0.05) higher low-frequency/high-frequency ratio suggesting a sympathovagal imbalance in these chronically infected animals. Other clinical and cardiovascular parameters were similar between the different groups. Sport horses are routinely submitted to intense training programs and sport-related activities that could lead to loss of the host-parasite equilibrium that characterizes enzootic regions, increasing the likelihood of infection reactivation and the risk of transmission. Heart rate variability analysis contributes to evaluate the sympathovagal balance and detecting homeostasis disturbances in sport horses. Molecular diagnostic tests for EP based on the detection of parasite DNA in equine blood samples should be included in the health programs of sport horses in endemic areas.

The Elusive Mitochondrial Genomes of Apicomplexa: Where Are We Now?

Mitochondria are vital organelles of eukaryotic cells, participating in key metabolic pathways such as cellular respiration, thermogenesis, maintenance of cellular redox potential, calcium homeostasis, cell signaling, and cell death. The phylum Apicomplexa is entirely composed of obligate intracellular parasites, causing a plethora of severe diseases in humans, wild and domestic animals. These pathogens include the causative agents of malaria, cryptosporidiosis, neosporosis, East Coast fever and toxoplasmosis, among others. The mitochondria in Apicomplexa has been put forward as a promising source of undiscovered drug targets, and it has been validated as the target of atovaquone, a drug currently used in the clinic to counter malaria. Apicomplexans present a single tubular mitochondria that varies widely both in structure and in genomic content across the phylum. The organelle is characterized by massive gene migrations to the nucleus, sequence rearrangements and drastic functional reductions in some species. Recent third generation sequencing studies have reignited an interest for elucidating the extensive diversity displayed by the mitochondrial genomes of apicomplexans and their intriguing genomic features. The underlying mechanisms of gene transcription and translation are also ill-understood. In this review, we present the state of the art on mitochondrial genome structure, composition and organization in the apicomplexan phylum revisiting topological and biochemical information gathered through classical techniques. We contextualize this in light of the genomic insight gained by second and, more recently, third generation sequencing technologies. We discuss the mitochondrial genomic and mechanistic features found in evolutionarily related alveolates, and discuss the common and distinct origins of the apicomplexan mitochondria peculiarities.

Babesia microti Immunoreactive Rhoptry-Associated Protein-1 Paralogs Are Ancestral Members of the Piroplasmid-Confined RAP-1 Family

Babesia, Cytauxzoon and Theileria are tick-borne apicomplexan parasites of the order Piroplasmida, responsible for diseases in humans and animals. Members of the piroplasmid rhoptry-associated protein-1 (pRAP-1) family have a signature cysteine-rich domain and are important for parasite development. We propose that the closely linked B. microti genes annotated as BMR1_03g00947 and BMR1_03g00960 encode two paralogue pRAP-1-like proteins named BmIPA48 and Bm960. The two genes are tandemly arranged head to tail, highly expressed in blood stage parasites, syntenic to rap-1 genes of other piroplasmids, and share large portions of an almost identical ~225 bp sequence located in their 5' putative regulatory regions. BmIPA48 and Bm960 proteins contain a N-terminal signal peptide, share very low sequence identity (<13%) with pRAP-1 from other species, and harbor one or more transmembrane domains. Diversification of the piroplasmid-confined prap-1 family is characterized by amplification of genes, protein domains, and a high sequence polymorphism. This suggests a functional involvement of pRAP-1 at the parasite-host interface, possibly in parasite adhesion, attachment, and/or evasion of the host immune defenses. Both BmIPA48 and Bm960 are recognized by antibodies in sera from humans infected with B. microti and might be promising candidates for developing novel serodiagnosis and vaccines.

Mitochondrial genome of Theileria uilenbergi endemic in sheep and goats in China

Mitochondrial genomes provide new insights that help elucidating biological features, genetic evolution, and classification of protozoans. Theileria uilenbergi (T. uilenbergi), transmitted by Haemaphysalis qinghaiensis and H. longicornis, is considered as highly pathogenic to sheep and goats in China. This study reports and outlines features of its mitochondrial genome. The T. uilenbergi mitochondrial genome is a linear monomeric molecule of 6.0 kb length, which encodes three protein-coding genes named cytochrome c oxidase I (cox1), cytochrome b (cob), and cytochrome c oxidase III (cox3), as well as six large subunit (LSU) rRNA gene fragments, and ends in terminal inverted repeats (TIRs). The array structure and organization of the mitochondrial genome of T. uilenbergi is identical to that of T. parva. Phylogenetic analysis based on the amino acid sequences of cox1, cob, and cox3 genes suggests that T. uilenbergi is distantly related to the group of transforming Theileria species such as T. parva. This study contributes to a comprehensive understanding of the phylogeny and evolution of the mitochondrial genome of piroplasms and provides useful information of diagnostic marker for T. uilenbergi.

Molecular detection and phylogenetic characterization of Theileria equi in horses (Equus caballus) from a peri-urban area of Argentina

To investigate the presence of Theileria equi in an endemic area of equine piroplasmosis 42 horses (Equus caballus) from Corrientes City, Argentina were sampled. Eighty-one percent (34 blood samples) of the analyzed horses were tested positive to the presence of piroplasmid 18S rDNA. All these samples could be identified as T. equi by amplifying the specific EMA-1 (merozoite antigen 1) gene of this species. Phylogenetic analysis of an obtained 18S rDNA complete sequence from one strain resulted in the identification of this sample as T. equi sensu stricto (genotype A). This study presents the first molecular detection and characterization of T. equi by the complete 18S rDNA sequence in Argentina. Based on these results further studies should be carried out to investigate the distribution and heterogeneity of presented genotypes of T. equi in Argentina, which is essential for the diagnosis, prevention and treatment of equine piroplasmosis.

Immune response of adult horses, pregnant mares and foals to an experimental vaccine with recombinant EMA-2 protein of Theileria equi

Equine theileriosis, caused by the Theileria equi protozoan, is a disease of worldwide importance. T. equi expresses surface proteins, of which the EMA-2 protein is a promising antigen for vaccine use. The aim of this study was to evaluate the immune response of adult horses, pregnant mares, and foals to an experimental EMA-2 protein of recombinant T. equi vaccine. A total of 46 horses were used in this study for vaccine trials and challenges. Twelve geldings, 14 pregnant mares, and 14 foals were divided into vaccinated and control groups. Total serum specific anti-rEMA-2 IgG, IgG subclasses, and transcription of cytokines related to the immune response were evaluated. For the vaccine challenge, six six-month-old foals were divided into vaccinated and control groups. For the challenge, blood from a horse with theileriosis was transfused to the foals. Geldings and pregnant mares maintained anti-rEMA-2 IgG levels at 130 and 140 days after vaccination, respectively. The most-detected IgG subclasses in vaccinated were IgG3/5, IgG4/7, and IgG1. IL2, IL10, IL12, IL17, IFN-γ, and TNF-α were the most-transcribed cytokines in PBMCs of vaccinated horses stimulated with rEMA-2. Challenge with T. equi demonstrated that vaccinated foals had an increase of 33% in total IgG four days after blood transfusion, while control foals had no significant response, suggesting that vaccine antibodies may have recognized EMA-2 protein of the native T. equi antigen. T. equi recombinant EMA-2 was shown to be a promising vaccine antigen by inducing humoral and cellular immunity similar to that observed in natural parasite infections.

Theileria equi claudin like apicomplexan microneme protein contains neutralization-sensitive epitopes and interacts with components of the equine erythrocyte membrane skeleton

Theileria equi is a widely distributed apicomplexan parasite that causes severe hemolytic anemia in equid species. There is currently no effective vaccine for control of the parasite and understanding the mechanism that T. equi utilizes to invade host cells may be crucial for vaccine development. Unlike most apicomplexan species studied to date, the role of micronemes in T. equi invasion of host cells is unknown. We therefore assessed the role of the T. equi claudin-like apicomplexan microneme protein (CLAMP) in the invasion of equine erythrocytes as a first step towards understanding the role of this organelle in the parasite. Our findings show that CLAMP is expressed in the merozoite and intra-erythrocytic developmental stages of T. equi and in vitro neutralization experiments suggest that the protein is involved in erythrocyte invasion. Proteomic analyses indicate that CLAMP interacts with the equine erythrocyte α-and β- spectrin chains in the initial stages of T. equi invasion and maintains these interactions while also associating with the anion-exchange protein, tropomyosin 3, band 4.1 and cytoplasmic actin 1 after invasion. Additionally, serological analyses show that T. equi-infected horses mount robust antibody responses against CLAMP indicating that the protein is immunogenic and therefore represents a potential vaccine candidate.

Development of a stable transgenic Theileria equi parasite expressing an enhanced green fluorescent protein/blasticidin S deaminase

Theileria equi, an intraerythrocytic protozoan parasite, causes equine piroplasmosis, a disease which negatively impacts the global horse industry. Genetic manipulation is one of the research tools under development as a control method for protozoan parasites, but this technique needs to be established for T. equi. Herein, we report on the first development of a stable transgenic T. equi line expressing enhanced green fluorescent protein/blasticidin S deaminase (eGFP/BSD). To express the exogenous fusion gene in T. equi, regulatory regions of the elongation factor-1 alpha (ef-1α) gene were identified in T. equi. An eGFP/BSD-expression cassette containing the ef-1α gene promoter and terminator regions was constructed and integrated into the T. equi genome. On day 9 post-transfection, blasticidin-resistant T. equi emerged. In the clonal line of T. equi obtained by limiting dilution, integration of the eGFP/BSD-expression cassette was confirmed in the designated B-locus of the ef-1α gene via PCR and Southern blot analyses. Parasitaemia dynamics between the transgenic and parental T. equi lines were comparable in vitro. The eGFP/BSD-expressing transgenic T. equi and the methodology used to generate it offer new opportunities for better understanding of T. equi biology, with the add-on possibility of discovering effective control methods against equine piroplasmosis.

Comparison of PCR-based methods for the detection of Babesia caballi and Theileria equi in field samples collected in Central Italy

Equine piroplasmosis (EP) is a disease of equids caused by Theileria equi and Babesia caballi, members of the order Piroplasmida, transmitted by several species of ticks. As the disease is endemic in many countries, a clinical examination or a serological test are required prior to movement of horses to prove freedom from infection and to avoid the introduction of EP with its sanitary and economic impact, especially in areas where it is absent. Currently, numerous diagnostic PCR protocols are available, some of which are recommended by the World Organisation for Animal Health (OIE). In order to adopt this diagnostic method, the Italian National Reference Centre for Equine Diseases (NRC-ED) conducted a preliminary comparison between an end-point PCR, nested PCR, real-time PCR, and commercial real-time PCR, for the detection of T. equi and B. caballi, respectively. One hundred and three field samples, collected during spring-summer 2013 in Latium and Tuscany regions, were employed for the study, and results discordant between detection assays were confirmed by sequencing. The reference assay was defined as that showing the highest sensitivity, and the relative sensitivity (rSe) and specificity (rSp) of the other methods were estimated referring to this assay. Agreement between methods was estimated by calculating the concordance between each pair of methods. Although no statistical differences were detected among PCR-based methods, the non-commercial real-time PCR assays seemed to be the most suitable for detection of T. equi and B. caballi, respectively. An important advantage of direct PCR detection of the pathogen, in comparison to indirect detection using serological methods, is that it allows specific treatment against the causative pathogen species responsible of the infection as well as for the definition of the infectious status of an animal for international movement.

The repertoire of serine rhomboid proteases of piroplasmids of importance to animal and human health

Babesia, Theileria and Cytauxzoon are tick-borne apicomplexan protozoans of the order Piroplasmida, notorious for the diseases they cause in livestock, pets and humans. Host cell invasion is their Achilles heel, allowing for the development of drug or vaccine-based therapies. In other apicomplexans, cleavage of the transmembrane domain of adhesins by the serine rhomboid proteinase ROM4 is required for successful completion of invasion. In this study, we record and classify the rhomboid repertoire encoded in the genomes of 10 piroplasmid species pertaining to the lineages Babesia sensu stricto (s.s., Clade VI), Theileria sensu stricto (Clade IV), Theileria equi (Clade IV), Cytauxzoon felis (Clade IIIb) and Babesia microti (Clade I), as defined by Schnittger et al. (2012). Fifty-six piroplasmid rhomboid-like proteins were assigned by phylogenetic analysis and bidirectional best hit to the ROM4, ROM6, ROM7 or ROM8 groups, and their crucial motifs for conformation and function were identified. Forty-four of these rhomboids had either been incorrectly classified or misannotated. Babesia s.s. encode five or three ROM4 proteinase paralogs, whereas the remaining piroplasmids encode two ROM4 paralogs. All piroplasmids encode a single ROM6, ROM7 and ROM8. Thus, an increased paralog number of ROM4 is the only feature distinguishing Babesia s.s. from other piroplasmid lineages. Piroplasmid ROM6 is related to the mammalian mitochondrial rhomboid and, accordingly, N-terminal mitochondrial targeting signal sequences was found in some cases. ROM6 is the only rhomboid encoded by piroplasmids that is ubiquitous in other organisms. ROM8 represents a pseudoproteinase that is highly conserved between studied piroplasmids, suggesting that it is important in regulatory functions. ROM4, ROM6, ROM7 and ROM8 are exclusively present in Aconoidasida, which comprises piroplasmids and Plasmodium, suggesting a relevant functional role in erythrocyte invasion. The correct classification and designation of piroplasmid rhomboids presented in this study facilitates an informed choice for future in-depth study of their functions.

N-Glycosylation in Piroplasmids: Diversity within Simplicity

N-glycosylation has remained mostly unexplored in Piroplasmida, an order of tick-transmitted pathogens of veterinary and medical relevance. Analysis of 11 piroplasmid genomes revealed three distinct scenarios regarding N-glycosylation: Babesia sensu stricto (s.s.) species add one or two N-acetylglucosamine (NAcGlc) molecules to proteins; Theileria equi and Cytauxzoon felis add (NAcGlc)2-mannose, while B. microti and Theileria s.s. synthesize dolichol-P-P-NAcGlc and dolichol-P-P-(NAcGlc)2 without subsequent transfer to proteins. All piroplasmids possess the gene complement needed for the synthesis of the N-glycosylation substrates, dolichol-P and sugar nucleotides. The oligosaccharyl transferase of Babesia species, T. equi and C. felis, is predicted to be composed of only two subunits, STT3 and Ost1. Occurrence of short N-glycans in B. bovis merozoites was experimentally demonstrated by fluorescence microscopy using a NAcGlc-specific lectin. In vitro growth of B. bovis was significantly impaired by tunicamycin, an inhibitor of N-glycosylation, indicating a relevant role for N-glycosylation in this pathogen. Finally, genes coding for N-glycosylation enzymes and substrate biosynthesis are transcribed in B. bovis blood and tick stages, suggesting that this pathway is biologically relevant throughout the parasite life cycle. Elucidation of the role/s exerted by N-glycans will increase our understanding of these successful parasites, for which improved control measures are needed.

Rapid protein evolution, organellar reductions, and invasive intronic elements in the marine aerobic parasite dinoflagellate Amoebophrya spp

BACKGROUND

Dinoflagellates are aquatic protists particularly widespread in the oceans worldwide. Some are responsible for toxic blooms while others live in symbiotic relationships, either as mutualistic symbionts in corals or as parasites infecting other protists and animals. Dinoflagellates harbor atypically large genomes (~ 3 to 250 Gb), with gene organization and gene expression patterns very different from closely related apicomplexan parasites. Here we sequenced and analyzed the genomes of two early-diverging and co-occurring parasitic dinoflagellate Amoebophrya strains, to shed light on the emergence of such atypical genomic features, dinoflagellate evolution, and host specialization.

RESULTS

We sequenced, assembled, and annotated high-quality genomes for two Amoebophrya strains (A25 and A120), using a combination of Illumina paired-end short-read and Oxford Nanopore Technology (ONT) MinION long-read sequencing approaches. We found a small number of transposable elements, along with short introns and intergenic regions, and a limited number of gene families, together contribute to the compactness of the Amoebophrya genomes, a feature potentially linked with parasitism. While the majority of Amoebophrya proteins (63.7% of A25 and 59.3% of A120) had no functional assignment, we found many orthologs shared with Dinophyceae. Our analyses revealed a strong tendency for genes encoded by unidirectional clusters and high levels of synteny conservation between the two genomes despite low interspecific protein sequence similarity, suggesting rapid protein evolution. Most strikingly, we identified a large portion of non-canonical introns, including repeated introns, displaying a broad variability of associated splicing motifs never observed among eukaryotes. Those introner elements appear to have the capacity to spread over their respective genomes in a manner similar to transposable elements. Finally, we confirmed the reduction of organelles observed in Amoebophrya spp., i.e., loss of the plastid, potential loss of a mitochondrial genome and functions.

CONCLUSION

These results expand the range of atypical genome features found in basal dinoflagellates and raise questions regarding speciation and the evolutionary mechanisms at play while parastitism was selected for in this particular unicellular lineage.

Molecular tools-advances, opportunities and prospects for the control of parasites of veterinary importance

The recent advancement in genome sequencing facilities, proteomics, transcriptomics, and metabolomics of eukaryotes have opened door for employment of molecular diagnostic techniques for early detection of parasites and determining target molecules for formulating control strategies. It further leads to the introduction of several purified vaccines in the field of veterinary parasitology. Earlier, the conventional diagnostic methods was entirely based upon morphological taxonomy for diagnosis of parasites but nowadays improved molecular techniques help in phylogenetic study and open an another area of molecular taxonomy of parasites with high precision. Control measures based upon targeting endosymbionts in parasites like Dirofilaria immitis is also under exploration in veterinary parasitology. Metagenomics have added an inside story of parasites bionomics which have created havoc in human and animals population since centuries. Omics era is playing a key role in opening the new approaches on parasite biology. Various newer generations of safer vaccines like edible vaccines and subunit vaccines and diagnostic techniques based upon purified immunologically active epitopes have become commercially available against the parasites (helminths, protozoa and arthropod borne diseases). Nowadays, a transgenic and gene knock out studies using RNA interference and CRISPR are also helping in understanding the functions of genes and screening of target genes, which are not available before the advent of molecular tools. Molecular techniques had paramount impact on increasing the sensitivity of diagnostic tools, epidemiological studies and more importantly in controlling these diseases. This review is about the advancements in veterinary parasitology and their impact on the control of these pathogens.

Whole genome sequencing of Theileria parva using target capture

Protozoan parasite isolation and purification are laborious and time-consuming processes required for high quality genomic DNA used in whole genome sequencing. The objective of this study was to capture whole Theileria parva genomes directly from cell cultures and blood samples using RNA baits. Cell culture material was bait captured or sequenced directly, while blood samples were all captured. Baits had variable success in capturing T. parva genomes from blood samples but were successful in cell cultures. Genome mapping uncovered extensive host contamination in blood samples compared to cell cultures. Captured cell cultures had over 81 fold coverage for the reference genome compared to 0-33 fold for blood samples. Results indicate that baits are specific to T. parva, are a good alternative to conventional methods and thus ideal for genomic studies. This study also reports the first whole genome sequencing of South African T. parva.

Endochin-like quinolone-300 and ELQ-316 inhibit Babesia bovis, B. bigemina, B. caballi and Theileria equi

Background

The most common apicomplexan parasites causing bovine babesiosis are Babesia bovis and B. bigemina, while B. caballi and Theileria equi are responsible for equine piroplasmosis. Treatment and control of these diseases are usually achieved using potentially toxic chemotherapeutics, such as imidocarb diproprionate, but drug-resistant parasites are emerging, and alternative effective and safer drugs are needed. The endochin-like quinolones (ELQ)-300 and ELQ-316 have been proven to be safe and efficacious against related apicomplexans, such as Plasmodium spp., with ELQ-316 also being effective against Babesia microti, without showing toxicity in mammals.

Methods

The inhibitory effects of ELQ-300 and ELQ-316 were assessed on the growth of cultured B. bovis, B. bigemina, B. caballi and T. equi. The percentage of parasitized erythrocytes was measured by flow cytometry, and the effect of the ELQ compounds on the viability of horse and bovine peripheral blood mononuclear cells (PBMC) was assessed by monitoring cell metabolic activity using a colorimetric assay.

Results

We calculated the half maximal inhibitory concentration (IC₅₀) at 72 h, which ranged from 0.04 to 0.37 nM for ELQ-300, and from 0.002 to 0.1 nM for ELQ-316 among all cultured parasites tested at 72 h. None of the parasites tested were able to replicate in cultures in the presence of ELQ-300 and ELQ-316 at the maximal inhibitory concentration (IC₁₀₀), which ranged from 1.3 to 5.7 nM for ELQ-300 and from 1.0 to 6.0 nM for ELQ-316 at 72 h. Neither ELQ-300 nor ELQ-316 altered the viability of equine and bovine PBMC at their IC₁₀₀ in in vitro testing.

Conclusions

The compounds ELQ-300 and ELQ-316 showed significant inhibitory activity on the main parasites responsible for bovine babesiosis and equine piroplasmosis at doses that are tolerable to host cells. These ELQ drugs may be viable candidates for developing alternative protocols for the treatment of bovine babesiosis and equine piroplasmosis.

Twenty Years of Equine Piroplasmosis Research: Global Distribution, Molecular Diagnosis, and Phylogeny

Equine piroplasmosis (EP), caused by the hemoparasites Theileria equi, Theileria haneyi, and Babesia caballi, is an important tick-borne disease of equines that is prevalent in most parts of the world. Infection may affect animal welfare and has economic impacts related to limitations in horse transport between endemic and non-endemic regions, reduced performance of sport horses and treatment costs. Here, we analyzed the epidemiological, serological, and molecular diagnostic data published in the last 20 years, and all DNA sequences submitted to GenBank database, to describe the current global prevalence of these parasites. We demonstrate that EP is endemic in most parts of the world, and that it is spreading into more temperate climates. We emphasize the importance of using DNA sequencing and genotyping to monitor the spread of parasites, and point to the necessity of further studies to improve genotypic characterization of newly recognized parasite species and strains, and their linkage to virulence.

Capture-based enrichment of Theileria parva DNA enables full genome assembly of first buffalo-derived strain and reveals exceptional intra-specific genetic diversity

Theileria parva is an economically important, intracellular, tick-transmitted parasite of cattle. A live vaccine against the parasite is effective against challenge from cattle-transmissible T. parva but not against genotypes originating from the African Cape buffalo, a major wildlife reservoir, prompting the need to characterize genome-wide variation within and between cattle- and buffalo-associated T. parva populations. Here, we describe a capture-based target enrichment approach that enables, for the first time, de novo assembly of nearly complete T. parva genomes derived from infected host cell lines. This approach has exceptionally high specificity and sensitivity and is successful for both cattle- and buffalo-derived T. parva parasites. De novo genome assemblies generated for cattle genotypes differ from the reference by ~54K single nucleotide polymorphisms (SNPs) throughout the 8.31 Mb genome, an average of 6.5 SNPs/kb. We report the first buffalo-derived T. parva genome, which is ~20 kb larger than the genome from the reference, cattle-derived, Muguga strain, and contains 25 new potential genes. The average non-synonymous nucleotide diversity (π_N) per gene, between buffalo-derived T. parva and the Muguga strain, was 1.3%. This remarkably high level of genetic divergence is supported by an average Wright’s fixation index (F_ST), genome-wide, of 0.44, reflecting a degree of genetic differentiation between cattle- and buffalo-derived T. parva parasites more commonly seen between, rather than within, species. These findings present clear implications for vaccine development, further demonstrated by the ability to assemble nearly all known antigens in the buffalo-derived strain, which will be critical in design of next generation vaccines. The DNA capture approach used provides a clear advantage in specificity over alternative T. parva DNA enrichment methods used previously, such as those that utilize schizont purification, is less labor intensive, and enables in-depth comparative genomics in this apicomplexan parasite.

An estimated 50 million cattle in sub-Saharan Africa are at risk of the deadly livestock disease East coast fever (ECF), caused by the parasite Theileria parva, which imposes tremendous economic hardship on smallholder farmers. An existing ECF vaccine protects against strains circulating among cattle, but not against T. parva derived from African Cape buffalo, its main wildlife carrier. Understanding this difference in protective efficacy requires characterization of the genetic diversity in T. parva strains associated with each mammalian host, a goal that has been hindered by the proliferation of T. parva in nucleated host cells, with much larger genomes. Here we adapted a sequence capture approach to target the whole parasite genome, enabling enrichment of parasite DNA over that of the host. Choices in protocol development resulted in nearly 100% parasite genome specificity and sensitivity, making this approach the most successful yet to generate T. parva genome sequence data in a high-throughput manner. The analyses uncovered a degree of genetic differentiation between cattle- and buffalo-derived genotypes that is akin to levels more commonly seen between species. This approach, which will enable an in-depth T. parva population genomics study from cattle and buffalo in the endemic regions, can easily be adapted to other intracellular pathogens.

First report of genetic diversity and risk factor analysis of equine piroplasm infection in equids in Jilin, China

Background

Equine piroplasmosis (EP) is a tick-borne hemoprotozoan disease of equids, caused by Theileria equi and Babesia caballi. Equine piroplasmosis represents a serious challenge to the equine industry due to important economic losses worldwide. The present study aimed to evaluate the prevalence of Theileria equi and Babesia caballi infections in equids from Jilin Province, China.

Methods

A total of 220 blood samples (192 horses and 28 donkeys/mules) were collected from March 2018 to October 2019 in five districts of Jilin Province and analyzed by PCR. Potential risk factors, including the region, sex, management, and host species of the animals were assessed in relation to T. equi infection. Moreover, the V4 hypervariable region of the T. equi 18S rRNA gene was analyzed to identify specific genotypes.

Results

The overall prevalence of T. equi in equids was 27.7%, whereas B. caballi infection was not identified. The district with the highest positive rate was Baicheng (43.3%), followed by Tonghua (28.9%), Yanbian (26.4%), Jilin (23.3%), and Liaoyuan (20.9%). The sex of the animals and farm management were identified as main risk factors, which were significantly associated with the prevalence of Equine piroplasmosis (P < 0.05). The risk factor analysis indicated that the females were at a higher risk (OR: 2.48, 95% CI: 1.17–5.27) of being infected compared to the males, whereas the organized farm was protective factor (OR: 0.42, 95% CI: 0.22–0.80). The phylogenetic analyses revealed that there were two T. equi genotypes (A and E) in Jilin.

Conclusions

Our findings provided important epidemiological data for the prevention and control of T. equi infection in Jilin, China.

A symbiotic bacterium of shipworms produces a compound with broad spectrum anti-apicomplexan activity

Apicomplexan parasites cause severe disease in both humans and their domesticated animals. Since these parasites readily develop drug resistance, development of new, effective drugs to treat infection caused by these parasites is an ongoing challenge for the medical and veterinary communities. We hypothesized that invertebrate-bacterial symbioses might be a rich source of anti-apicomplexan compounds because invertebrates are susceptible to infections with gregarines, parasites that are ancestral to all apicomplexans. We chose to explore the therapeutic potential of shipworm symbiotic bacteria as they are bona fide symbionts, are easily grown in axenic culture and have genomes rich in secondary metabolite loci [1,2]. Two strains of the shipworm symbiotic bacterium, Teredinibacter turnerae, were screened for activity against Toxoplasma gondii and one strain, T7901, exhibited activity against intracellular stages of the parasite. Bioassay-guided fractionation identified tartrolon E (trtE) as the source of the activity. TrtE has an EC50 of 3 nM against T. gondii, acts directly on the parasite itself and kills the parasites after two hours of treatment. TrtE exhibits nanomolar to picomolar level activity against Cryptosporidium, Plasmodium, Babesia, Theileria, and Sarcocystis; parasites representing all branches of the apicomplexan phylogenetic tree. The compound also proved effective against Cryptosporidium parvum infection in neonatal mice, indicating that trtE may be a potential lead compound for preclinical development. Identification of a promising new compound after such limited screening strongly encourages further mining of invertebrate symbionts for new anti-parasitic therapeutics.

Parasite load and genotype are associated with clinical outcome of piroplasm-infected equines in Israel

Background

Equine piroplasmosis is a highly endemic protozoan disease of horses worldwide, caused by Theileria equi and Babesia caballi. While most horses in endemic areas are subclinically infected, the mechanisms leading to clinical outcome are vastly unknown. Moreover, since clinical signs of disease are not specific, and the prevalence in endemic areas is high, it is difficult to determine if equine piroplasmosis is the cause of disease. To identify possible mechanisms leading to the clinical outcome in an endemic area, we compared parasite loads and genotypes in clinically and subclinically infected horses.

Methods

Blood was collected from horses with clinical signs consistent with equine piroplasmosis, and from apparently healthy horses in Israel. Packed cell volume and total solids were measured. Quantitative and diagnostic polymerase chain reaction were used to identify, quantify and classify equine piroplasmosis infection. Phylogenetic analyses were used to determine the genotype of both parasites.

Results

For both parasites, clinical cases were associated with low mean packed cell volume and high mean parasite load (P < 0.001), enabling the determination of a cut-off value to distinguish between clinically and subclinically infected horses. Samples of Theileria equi from subclinical horses were classified into three different 18S rRNA genotypes, D (n = 23), A (n = 12) and C (n = 5), while samples from all clinical cases (n = 6) were classified as genotype A. The sequences of T. equi equi merozoite antigens 1 (ema-1, n = 9) and 2 (ema-2, n = 11) genes were fairly conserved and did not differ between clinical and subclinical cases. Babesia caballi rhoptry associated protein-1 (rap-1) was classified into sub-genotypes A1 (n = 14) and A2 (n = 5) with no association to clinical outcome. Classification of the 18S rRNA gene (sub-genotypes B1 and B2) agreed with the rap-1 classification.

Conclusions

The results of this study suggest that quantification of parasite loads of infected horses may be used to distinguish between infections resulting in disease and subclinical cases. Although number of clinical cases is limited, we identified T. equi 18S rRNA genotype A to be associated with clinical disease. This finding emphasizes the importance of in-depth genetic characterization of T. equi genotypes to identify possible markers for virulence.

Equid infective Theileria cluster in distinct 18S rRNA gene clades comprising multiple taxa with unusually broad mammalian host ranges

Equine theileriosis, a tick-transmitted disease caused by the hemoprotozoan parasites Theileria equi and Theileria haneyi, affects equids throughout tropical and subtropical regions of the world. It is a significant regulatory concern in non-endemic countries, where testing for equine theileriosis is required prior to horse import to prevent parasite entry. Within endemic areas, infection causes significant morbidity and mortality, leading to economic losses. No vaccine for equine theileriosis is available, and current drug treatment protocols are inconsistent and associated with significant side effects. Recent work has revealed substantial genetic variability among equine theileriosis organisms, and analysis of ribosomal DNA from affected animals around the world indicates that the organisms can be grouped into five distinct clades. As these diverse parasites are capable of infecting a wide range of both tick and mammalian hosts, movement of different equine Theileria species between endemic countries, and eventually into non-endemic countries, is a significant concern. Furthermore, the substantial genetic variability of these organisms will likely render currently utilized importation diagnostic tests unable to detect all equine Theileria spp. To this end, more complete characterization of these diverse parasites is critical to the continued global control of equine theileriosis. This review discusses current knowledge of equine Theileria spp. in this context, and highlights new opportunities and challenges for workers in this field.

Comparative evaluation of two informative markers in the phylogeny of Babesia and Theileria parasites

Piroplasmosis is a serious debilitating and sometimes fatal disease. Phylogenetic relationships within piroplasmida are complex and remain unclear. In the study, we assessed the relative resolution capabilities of the DNA sequences of the nuclear genes 40S ribosomal protein S5 (RPS5) and mitochondrial DNA Cytochrome c oxidase subunit III (cox3) gene in the phylogeny of Babesia and Theileria species isolates. We demonstrated that by using the cox3 gene can recover a better supported species tree for some Theileria species than when using the nuclear RPS5 gene alone, it tends to intra-specific diversity and considerable inter-specific difference. Additionally, the combined DNA sequences of the nuclear RPS5 and cox3 gene improved the inference of evolutionary relationships among Babesia and Theileria species. The mitochondrial cox3 gene outperforms nuclear RPS5 gene and yields better resolution on the intra-specific diversity of Babesia and Theileria species. However, the combined RPS5 nuclear DNA and cox3 DNA tree had more advantage in the phylogeny of Babesia and Theileria species than that of single gene alone.

Serological detection and risk factors for equine piroplasmosis in the semiarid region of Pernambuco, Northeastern Brazil

Equine piroplasmosis, an economically important disease in horses, has so far not been reported in Pernambuco state, Brazil. This study aimed to evaluate the seroprevalence of anti-Babesia caballi and anti-Theileria equi antibodies based on the detection of these agents in equine blood and in ticks on horses in the municipality of Petrolina, Pernambuco, northeastern Brazil. Blood samples were drawn from 393 horses and sera were examined by ELISA. The presence of tick infestations was evaluated, and 101 ticks were subjected to DNA amplification for the detection of Babesia spp. by polymerase chain reaction (PCR). No parasites were detected in the blood smears. Anti-B. caballi and anti-T. equi antibodies were found in 27.2% (107/393) and 34.8% (137/393) horses, respectively. Infestation by Dermacentor nitens was detected in 4.3% (17/393) of the horses. There was no DNA amplification of the agents in ticks. The risk factors for the presence of anti-T. equi antibodies (P < 0.05) were: purebred (P < 0.001), animals older than 156 months (P = 0.014), and the presence of ticks (P = 0.001). No risk factors for B. caballi were identified. This study confirmed the circulation of agents of equine piroplasmosis in the municipality of Petrolina, state of Pernambuco, Brazil.

Molecular genotyping and epidemiology of equine piroplasmids in South Africa

Recently reported substantial genetic diversity within Theileria equi 18S rRNA gene sequences has led to the identification of five genotypes A, B, C, D, and E, complicating molecular and serological diagnosis. In addition, T. haneyi has lately been reported as a species closely related to the T. equi 18S rRNA genotype C (Knowles et al., 2018). Theileria spp. of this group have a monophyletic origin and are therefore referred to as Equus group to distinguish them from the remaining Theileria lineages (Jalovecka et al., 2019). In this study, we report on the development of genotype-specific quantitative real-time PCR assays capable of detecting and distinguishing between each parasite genotype. Alignment of complete 18S rRNA sequences available on GenBank allowed for the design of a single primer pair and five TaqMan minor groove binder (MGB™) probes specific for each genotype (A-E). The assays, evaluated as qPCR simplex and two qPCR multiplex formats (Multiplex EP-ABC and Multiplex EP-DE), were shown to be both efficient and specific in the detection of T. equi genotypes. The developed qPCR assays were used to study (i) the intra-specific diversity of parasite genotypes within horse and zebra, (ii) the inter-specific differences in parasite genotype diversity in horses as compared to zebra, and (iii) the geographic distribution of T. equi 18S rRNA genotypes in South Africa. In addition, (iv) the presence of T. haneyi in South Africa was evaluated. An assessment of 342 equine field samples comprising 149 field horses, 55 racehorses, and 138 wild zebra confirmed the previously reported presence of T. equi 18S rRNA genotypes A, B, C, and D, and absence of genotype E in South African equids. Theileria equi genotypes A, B, C, and D, were detected in zebra, whereas only genotypes A, C and D, could be identified in field horses, and only genotypes A and C in racehorses. Genotypes B and D were the dominant genotypes identified in zebra in South Africa, while horses were predominantly infected with T. equi genotypes A and C. The greater diversity of T. equi genotypes in zebra suggests that it is an ancestral host for this piroplasmid lineage. Importantly, evidence is presented that each identified T. equi genotype segregates independently in each of the three studied equid populations reinforcing the notion that they represent individual separate entities corresponding to species. Preliminary investigations of the relationship between T. equi genotype C infections and Theileria haneyi, suggest that in addition to the five currently known T. equi genotypes, South African equids are also infected with T. haneyi.

Antigenicity assessment of the Theileria equi merozoite antigen (EMA-2) expressed in Pichia pastoris in mice and horses

Equine theileriosis is a severe equine disease caused by the protozoan Theileria equi, which is prevalent in tropical and subtropical areas. In this study, a recombinant equi merozoite antigen-2 (rEMA-2) of T. equi was used as an immunogen. Two groups of 10 mice each were divided into control and vaccinated groups. Sixty mares seronegative for theileriosis were divided in two groups, one vaccinated and another group as a control animal. Mice and mares of the vaccinated groups were inoculated with 150 μL of the vaccine containing 50 μg of rEMA-2 and 2 mL of the vaccine containing 200 μg of rEMA-2, respectively, at days 0 and 21. The immunogenicity of rEMA-2 was evaluated by ELISA and fluorescent antibody test (IFAT) using serum from vaccinated mice, mares and antigenicity in naturally infected horse. At every point throughout the ELISA study, there were significant differences between the vaccinated and control groups (p < 0.05). The vaccine induced 3- and 4-fold IgG increases in mice at the 14th and 28th day, respectively, compared to the control group. The horses' IgG dynamics showed a significant (p < 0.05) increase in the total IgG titer as early as day 7, which increased until day 28 at which time a more significant (p < 0.001) IgG titer was observed. In evaluating the isotypes, we observed a trend similar to that of total IgG, where IgG(T) (IgG3-5) were significantly (p < 0.05) more elevated than the other isotypes analyzed, followed by IgGb (IgG4-7) and IgGa (IgG1). Positive fluorescence was detected by IFAT, suggesting that the protein is immunogenic and conserves some epitopes identical to the native T. equi antigens present in the equine blood smear. Thus, our results suggest that rEMA-2 can be a promising vaccinal antigen.

Babesia Life Cycle - When Phylogeny Meets Biology

Although Babesia represents an important worldwide veterinary threat and an emerging risk to humans, this parasite has been poorly studied as compared to Plasmodium, its malaria-causing relative. In fact, Babesia employs highly specific survival strategies during its intraerythrocytic development and its intricate journey through the tick vector. This review introduces a substantially extended molecular phylogeny of the order Piroplasmida, challenging previous taxonomic classifications. The intriguing developmental proficiencies of Babesia are highlighted and compared with those of other haemoparasitic Apicomplexa. Molecular mechanisms associated with distinctive events in the Babesia life cycle are emphasized as potential targets for the development of Babesia-specific treatments.

The first molecular detection and genetic diversity of Babesia caballi and Theileria equi in horses of Gansu province, China

Equine piroplasmosis, caused by Theileria equi and Babesia caballi, is an economically important tick-borne disease worldwide. In the current study, 242 blood samples were randomly collected from horses in Zhangye city of Gansu province, China. The presence and genetic diversity of piroplasms were evaluated with a nested PCR assay, gene sequencing and phylogenetic analysis. The results showed that seventy-five (31.0%) samples were positive for piroplasms. Sequences analysis showed that seventy-three (30.2%) were positive for T. equi, and seven (2.9%) for B. caballi, five of which (2.1%) were infected with T. equi and B. caballi. Phylogenetic analysis revealed two T. equi genotypes (C and E) and one B. caballi genotype (A). The molecular epidemiological and genetic diversity results provide important epidemiological data for control of equine piroplasmosis caused by T. equi and B. caballi in China.

Identification of a putative methyltransferase gene of Babesia bigemina as a novel molecular biomarker uniquely expressed in parasite tick stages

BACKGROUND

Bovine babesiosis is caused by apicomplexan pathogens of the genus Babesia such as B. bigemina and B. bovis. These tick-borne pathogens have a complex life-cycle involving asexual multiplication in vertebrate hosts and sexual reproduction in invertebrate vectors. In the tick midgut, extracellular Babesia parasites transform into gametes that fuse to form zygotes. Understanding the mechanisms that underlie formation of extracellular Babesia tick stages is an important step towards developing control strategies for preventing tick infection and subsequent parasite transmission.

RESULTS

We induced B. bigemina sexual stages in vitro by exposing parasites to Tris 2-carboxyethyl phosphine (TCEP). Subsequently, we identified a novel putative methyltransferase gene (BBBOND_0204030) that is expressed uniquely in all B. bigemina tick stages but not in blood stages. In vitro TCEP-exposed B. bigemina presented diverse morphology including parasites with long projections, round forms and clusters of round forms indicative of sexual stage induction. We confirmed the development of sexual stages by detecting upregulation of previously defined B. bigemina sexual stage marker genes, ccp2 and 3, and their respective protein expression in TCEP-induced B. bigemina cultures. Next, transcription analysis of in vitro TCEP-induced B. bigemina culture based on an in silico derived list of homologs of Plasmodium falciparum gamete-specific genes demonstrated differential expression of the gene BBBOND_0204030 in induced cells. Further examination of ex vivo infected ticks demonstrated that BBBOND_0204030 is transcribed by multiple stages of B. bigemina during parasite development in tick midgut, ovary and hemolymph. Interestingly, ex vivo results confirmed our in vitro observation that blood stages of B. bigemina do not express BBBOND_0204030 and validated the in vitro system of inducing sexual stages.

CONCLUSIONS

Herein we describe the identification of a B. bigemina gene transcribed exclusively by parasites infecting ticks using a novel method of inducing B. bigemina sexual stages in vitro. We propose that this gene can be used as a marker for parasite development within the tick vector. Together, these tools will facilitate our understanding of parasite-tick interactions, the identification of novel vaccine targets and, consequently, the development of additional strategies to control bovine babesiosis.

The Complexity of Piroplasms Life Cycles

Although apicomplexan parasites of the group Piroplasmida represent commonly identified global risks to both animals and humans, detailed knowledge of their life cycles is surprisingly limited. Such a discrepancy results from incomplete literature reports, nomenclature disunity and recently, from large numbers of newly described species. This review intends to collate and summarize current knowledge with respect to piroplasm phylogeny. Moreover, it provides a comprehensive view of developmental events of Babesia, Theileria, and Cytauxzoon representative species, focusing on uniform consensus of three consecutive phases: (i) schizogony and merogony, asexual multiplication in blood cells of the vertebrate host; (ii) gamogony, sexual reproduction inside the tick midgut, later followed by invasion of kinetes into the tick internal tissues; and (iii) sporogony, asexual proliferation in tick salivary glands resulting in the formation of sporozoites. However, many fundamental differences in this general consensus occur and this review identifies variables that should be analyzed prior to further development of specific anti-piroplasm strategies, including the attractive targeting of life cycle stages of Babesia or Theileria tick vectors.

Analysis of Theileria orientalis draft genome sequences reveals potential species-level divergence of the Ikeda, Chitose and Buffeli genotypes

BACKGROUND

Theileria orientalis (Apicomplexa: Piroplasmida) has caused clinical disease in cattle of Eastern Asia for many years and its recent rapid spread throughout Australian and New Zealand herds has caused substantial economic losses to production through cattle deaths, late term abortion and morbidity. Disease outbreaks have been linked to the detection of a pathogenic genotype of T. orientalis, genotype Ikeda, which is also responsible for disease outbreaks in Asia. Here, we sequenced and compared the draft genomes of one pathogenic (Ikeda) and two apathogenic (Chitose, Buffeli) isolates of T. orientalis sourced from Australian herds.

RESULTS

Using de novo assembled sequences and a single nucleotide variant (SNV) analysis pipeline, we found extensive genetic divergence between the T. orientalis genotypes. A genome-wide phylogeny reconstructed to address continued confusion over nomenclature of this species displayed concordance with prior phylogenetic studies based on the major piroplasm surface protein (MPSP) gene. However, average nucleotide identity (ANI) values revealed that the divergence between isolates is comparable to that observed between other theilerias which represent distinct species. Analysis of SNVs revealed putative recombination between the Chitose and Buffeli genotypes and also between Australian and Japanese Ikeda isolates. Finally, to inform future vaccine studies, dN/dS ratios and surface location predictions were analysed. Six predicted surface protein targets were confirmed to be expressed during the piroplasm phase of the parasite by mass spectrometry.

CONCLUSIONS

We used whole genome sequencing to demonstrate that the T. orientalis Ikeda, Chitose and Buffeli variants show substantial genetic divergence. Our data indicates that future researchers could potentially consider disease-associated Ikeda and closely related genotypes as a separate species from non-pathogenic Chitose and Buffeli.

Cysteine Proteinase C1A Paralog Profiles Correspond with Phylogenetic Lineages of Pathogenic Piroplasmids

Piroplasmid parasites comprising of Babesia, Theileria, and Cytauxzoon are transmitted by ticks to farm and pet animals and have a significant impact on livestock industries and animal health in tropical and subtropical regions worldwide. In addition, diverse Babesia spp. infect humans as opportunistic hosts. Molecular phylogeny has demonstrated at least six piroplasmid lineages exemplified by B. microti, B. duncani, C. felis, T. equi, Theileria sensu stricto (T. annulata, T. parva, and T. orientalis) and Babesia sensu stricto (B. bovis, B. bigemina, and B. ovis). C1A cysteine-proteinases (C1A-Cp) are papain-like enzymes implicated in pathogenic and vital steps of the parasite life cycle such as nutrition and host cell egress. An expansion of C1A-Cp of T. annulata and T. parva with respect to B. bovis and B. ovis was previously described. In the present work, C1A-Cp paralogs were identified in available genomes of species pertaining to each piroplasmid lineage. Phylogenetic analysis revealed eight C1A-Cp groups. The profile of C1A-Cp paralogs across these groups corroborates and defines the existence of six piroplasmid lineages. C. felis, T. equi and Theileria s.s. each showed characteristic expansions into extensive families of C1A-Cp paralogs in two of the eight groups. Underlying gene duplications have occurred as independent unique evolutionary events that allow distinguishing these three piroplasmid lineages. We hypothesize that C1A-Cp paralog families may be associated with the advent of the schizont stage. Differences in the invertebrate tick host specificity and/or mode of transmission in piroplasmid lineages might also be associated with the observed C1A-Cp paralog profiles.

Development and validation of a duplex real-time PCR assay for the diagnosis of equine piroplasmosis

Background

Equine piroplasmosis (EP) is an economically significant infection of horses and other equine species caused by the tick-borne protozoa Theileria equi and Babesia caballi. The long-term carrier state in infected animals makes importation of such subclinical cases a major risk factor for the introduction of EP into non-enzootic areas. Regulatory testing for EP relies on screening of equines by serological methods. The definitive diagnosis of EP infection in individual animals will benefit from the availability of sensitive direct detection methods, for example, when used as confirmatory assays for non-negative serological test results. The objectives of this study were to develop a real-time quantitative polymerase chain reaction (qPCR) assay for simultaneous detection of both agents of EP, perform comprehensive evaluation of its performance and assess the assay’s utility for regulatory testing.

Results

We developed a duplex qPCR targeting the ema-1 gene of T. equi and the 18S rRNA gene of B. caballi and demonstrated that the assay has high analytical sensitivities for both piroplasm species. Validation of the duplex qPCR on samples from 362 competitive enzyme-linked immunosorbent assay (cELISA)-negative horses from Canada and the United States yielded no false-positive reactions. The assay’s performance was further evaluated using samples collected from 430 horses of unknown EP status from a highly endemic area in Brazil. This set of samples was also tested by a single-target 18S rRNA qPCR for T. equi developed at the OIE reference laboratory for EP in Japan, and a previously published single-target 18S rRNA qPCR for B. caballi whose oligonucleotides we adopted for use in the duplex qPCR. Matching serum samples were tested for antibodies to these parasites using cELISA. By the duplex qPCR, T. equi-specific 18S rRNA qPCR and cELISA, infections with T. equi were detected in 87.9% (95% confidence interval, CI: 84.5–90.7%), 90.5% (95% CI: 87.3–92.3%) and 87.4% (95% CI: 84.0–90.2%) of the horses, respectively. The B. caballi prevalence estimates were 9.3% (95% CI: 6.9–12.4%) by the duplex qPCR and 7.9% (95% CI: 5.7–10.9%) by the respective single-target qPCR assay. These values were markedly lower compared to the seroprevalence of 58.6% (95% CI: 53.9–63.2%) obtained by B. caballi-specific cELISA. The relative diagnostic sensitivity of the duplex qPCR for T. equi was 95.5%, as 359 of the 376 horses with exposure to T. equi confirmed by cELISA had parasitemia levels above the detection limit of the molecular assay. In contrast, only 39 (15.5%) of the 252 horses with detectable B. caballi-specific antibodies were positive for this piroplasm species by the duplex qPCR.

Conclusions

The duplex qPCR described here performed comparably to the existing single-target qPCR assays for T. equi and B. caballi and will be more cost-effective in terms of results turnaround time and reagent costs when both pathogens are being targeted for disease control and epidemiological investigations. These validation data also support the reliability of the ema-1 gene-specific oligonucleotides developed in this study for confirmatory testing of non-negative serological test results for T. equi by qPCR. However, the B. caballi-specific qPCR cannot be similarly recommended as a confirmatory assay for routine regulatory testing due to the low level of agreement with serological test results demonstrated in this study. Further studies are needed to determine the transmission risk posed by PCR-negative equines with detectable antibodies to B. caballi.

Serological detection and molecular characterization of piroplasmids in equids in Brazil

Equine piroplasmosis is a disease caused by the hemoparasites Babesia caballi and Theileria equi and is considered to be the most important parasitic infection affecting Equidae. The objective of the present study was to carry out an epidemiological molecular and serological survey for the presence of these two protozoal organisms in equids from the northwestern region of the State of Rio Grande do Sul (RS), south Brazil. For this purpose, blood samples were collected from 90 equids in the city of Passo Fundo, RS, Brazil. Those were animals used for sport activities, outdoor recreational riding, and work including cattle herding and mounted patrol. Anti-T. equi and anti-B. caballi IgG antibodies were detected in the sera of those animals by commercial ELISA kits. The molecular diagnosis of equine piroplasmosis due to T. equi or B. caballi (or both) consisted in the amplification of the 18S rRNA gene by nested PCR followed by sequencing of the amplified PCR product and sequence comparison and phylogenetic analysis of the isolates; 17 (18.9%) and 5 (5.55%) out of the 90 serum samples tested in this study were positive for T. equi and B. caballi, respectively. Piroplasmid 18S rRNA gene fragments were detected by PCR in 24.4% (22/90) of the samples analysed and shared 99-100% identity with sequences of T. equi by BLASTn. Samples for the phylogenetic analysis were divided into 2 groups. In group A, there was close phylogenetic relationship between 4 sequences and sequences previously reported along the US-Mexico border, in South Africa, and in Brazil. There was a phylogenetic proximity between 5 samples from group B and samples tested by other authors in the US and Spain. Variation of the 18S rRNA gene allowed the identification of 9 new T. equi genotypes in the geographical region studied.