Major Surface Antigens in Zoonotic Babesia

1H, 13C and 15N backbone and side-chain resonance assignments of ∆∆BmSA1, the surface antigen of Babesia microti

Human babesiosis is a vector-borne zoonotic infection caused mostly by the Apicomplexan parasite Babesia microti, distributed worldwide. The infection can result in severe symptoms such as hemolytic anemia, especially in immunodeficient patients. Also, asymptomatic patients continue transmission as unscreened blood donors, and represent a risk for Public Health. Early host-parasite interactions are mediated by BmSA1, the major surface antigen of Babesia microti, crucial for invasion and immune escape. Hence, a structural and functional characterization of the BmSA1 protein constitutes a first strategic milestone toward the development of innovative tools to control infection. Knowledge of the 3D structure of such an important antigen is crucial for the development of vaccines or new diagnostic tests. Here, we report the 1H, 15N and 13C NMR resonance assignment of ∆∆BmSA1, a truncated recombinant version of BmSA1 without the N-terminal signal peptide and the hydrophobic C-terminal GPI-anchor. Secondary structure prediction using CSI.3 and TALOS-N demonstrates a high content of alpha-helical structure. This preliminary study provides foundations for further structural characterization of BMSA1.

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

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

What Do We Know about Surface Proteins of Chicken Parasites Eimeria?

Poultry is the first source of animal protein for human consumption. In a changing world, this sector is facing new challenges, such as a projected increase in demand, higher standards of food quality and safety, and reduction of environmental impact. Chicken coccidiosis is a highly widespread enteric disease caused by Eimeria spp. which causes significant economic losses to the poultry industry worldwide; however, the impact on family poultry holders or backyard production-which plays a key role in food security in small communities and involves mainly rural women-has been little explored. Coccidiosis disease is controlled by good husbandry measures, chemoprophylaxis, and/or live vaccination. The first live vaccines against chicken coccidiosis were developed in the 1950s; however, after more than seven decades, none has reached the market. Current limitations on their use have led to research in next-generation vaccines based on recombinant or live-vectored vaccines. Next-generation vaccines are required to control this complex parasitic disease, and for this purpose, protective antigens need to be identified. In this review, we have scrutinised surface proteins identified so far in Eimeria spp. affecting chickens. Most of these surface proteins are anchored to the parasite membrane by a glycosylphosphatidylinositol (GPI) molecule. The biosynthesis of GPIs, as well as the role of currently identified surface proteins and interest as vaccine candidates has been summarised. The potential role of surface proteins in drug resistance and immune escape and how these could limit the efficacy of control strategies was also discussed.

Histopathological Analysis of Selected Organs of Rats with Congenital Babesiosis Caused by Babesia microti

Babesiosis is a tick-borne disease with an increasing number of cases each year. Due to the non-specific symptoms of babesiosis, insightful analyses of the pathogenesis of babesiosis are still very important. Transmission of the disease occurs in a few ways, which makes laboratory diagnosis of piroplasmosis important. Complications associated with the infection can be tragic, especially in patients with immunological disorders. The aim of this study was the histopathological analysis of the spleen and kidney of young Wistar rats infected transplacentally with Babesia microti. Female rats were infected with a reference strain of B. microti (ATCC 30221), and then, birth 3-week-old males were euthanized with isoflurane. Subsequently, the material was collected at autopsy for microscopic and ultrastructural examination. Microscopic and ultrastructural analysis of the spleen and kidney showed degenerative changes within the organ parenchyma and the capsules surrounding the organ. Regenerative and reparative changes through mitotic divisions of parenchymal cells were also evident. Merozoites of B. microti were visible in the section of erythrocytes and the cells building the organ stroma. The results presented in this study proved the negative effects of B. microti on cells and tissues in rats with congenital babesiosis.

Global Metabolomic Profiling of Host Red Blood Cells Infected with Babesia divergens Reveals Novel Antiparasitic Target Pathways

Babesia divergens is an apicomplexan parasite that infects human red blood cells (RBCs), initiating cycles of invasion, replication, and egress, resulting in extensive metabolic modification of the host cells. Babesia is an auxotroph for most of the nutrients required to sustain these cycles. There are currently limited studies on the biochemical pathways that support these critical processes, necessitating the high-resolution global metabolomics approach described here to uncover the metabolic interactions between parasite and host RBC. Our results reveal an extensive parasite-mediated modulation of RBC metabolite levels of all classes, including lipids, amino acids, carbohydrates, and nucleotides, with numerous metabolic species varying in proportion to the level of infection. Many of these molecules are scavenged from the host RBCs. This is in accord with the needs of a rapidly proliferating parasite with limited biosynthetic capabilities. Probing these pathways in depth, we used growth inhibition assays to quantitate parasite susceptibility to drugs targeting these pathways and stimulated emission depletion (STED) microscopy to obtain high-resolution images of drug-treated parasites to correlate changes in morphology with specific metabolic blocks in order to validate the data generated by the untargeted metabolomics platform. Thus, interruption of cholesterol scavenging from the host cell led to premature parasite egress, while chemical targeting of the hydrolysis of acyl glycerides led to the buildup of malformed parasites that could not successfully egress. This is the first report detailing the global metabolomic profile of the B. divergens-infected RBC. Besides deciphering diverse aspects of the host-parasite relationship, our results can be exploited by others to uncover further drug targets in the host-parasite biochemical network. IMPORTANCE Human babesiosis is caused by apicomplexan parasites of the Babesia genus and is associated with transfusion-transmitted illness and relapsing disease in immunosuppressed populations. Through its continuous cycles of invasion, proliferation, and egress, B. divergens radically changes the metabolic environment of the host red blood cell, allowing us opportunities to study potential chemical vulnerabilities that can be targeted by drugs. This is the first global metabolomic profiling of Babesia-infected human red blood cells, and our analysis revealed perturbation in all biomolecular classes at levels proportional to the level of infection. In particular, lipids and energy flux pathways in the host cell were altered by infection. We validated the changes in key metabolic pathways by performing inhibition assays accompanied by high-resolution microscopy. Overall, this global metabolomics analysis of Babesia-infected red blood cells has helped to uncover novel aspects of parasite biology and identified potential biochemical pathways that can be targeted for chemotherapeutic intervention.

FT-GPI, a highly sensitive and accurate predictor of GPI-anchored proteins, reveals the composition and evolution of the GPI proteome in Plasmodium species

BACKGROUND

Protozoan parasites are known to attach specific and diverse group of proteins to their plasma membrane via a GPI anchor. In malaria parasites, GPI-anchored proteins (GPI-APs) have been shown to play an important role in host-pathogen interactions and a key function in host cell invasion and immune evasion. Because of their immunogenic properties, some of these proteins have been considered as malaria vaccine candidates. However, identification of all possible GPI-APs encoded by these parasites remains challenging due to their sequence diversity and limitations of the tools used for their characterization.

METHODS

The FT-GPI software was developed to detect GPI-APs based on the presence of a hydrophobic helix at both ends of the premature peptide. FT-GPI was implemented in C ++and applied to study the GPI-proteome of 46 isolates of the order Haemosporida. Using the GPI proteome of Plasmodium falciparum strain 3D7 and Plasmodium vivax strain Sal-1, a heuristic method was defined to select the most sensitive and specific FT-GPI software parameters.

RESULTS

FT-GPI enabled revision of the GPI-proteome of P. falciparum and P. vivax, including the identification of novel GPI-APs. Orthology- and synteny-based analyses showed that 19 of the 37 GPI-APs found in the order Haemosporida are conserved among Plasmodium species. Our analyses suggest that gene duplication and deletion events may have contributed significantly to the evolution of the GPI proteome, and its composition correlates with speciation.

CONCLUSION

FT-GPI-based prediction is a useful tool for mining GPI-APs and gaining further insights into their evolution and sequence diversity. This resource may also help identify new protein candidates for the development of vaccines for malaria and other parasitic diseases.

Identification and characterization of extracellular vesicles from red cells infected with Babesia divergens and Babesia microti

Babesiosis is a zoonosis and an important blood-borne human parasitic infection that has gained attention because of its growing infection rate in humans by transfer from animal reservoirs. Babesia represents a potential threat to the blood supply because asymptomatic infections in man are common, and blood from such donors can cause severe disease in certain recipients. Extracellular vesicles (EVs) are vesicles released by cells that contain a complex mixture of proteins, lipids, glycans, and genetic information that have been shown to play important roles in disease pathogenesis and susceptibility, as well as cell–cell communication and immune responses. In this article, we report on the identification and characterization of EVs released from red blood cells (RBCs) infected by two major human Babesia species—Babesia divergens from in vitro culture and those from an in vivo B. microti mouse infection. Using nanoparticle tracking analysis, we show that there is a range of vesicle sizes from 30 to 1,000 nm, emanating from the Babesia-infected RBC. The study of these EVs in the context of hemoparasite infection is complicated by the fact that both the parasite and the host RBC make and release vesicles into the extracellular environment. However, the EV frequency is 2- to 10-fold higher in Babesia-infected RBCs than uninfected RBCs, depending on levels of parasitemia. Using parasite-specific markers, we were able to show that ~50%–60% of all EVs contained parasite-specific markers on their surface and thus may represent the specific proportion of EVs released by infected RBCs within the EV population. Western blot analysis on purified EVs from both in vivo and in vitro infections revealed several parasite proteins that were targets of the host immune response. In addition, microRNA analysis showed that infected RBC EVs have different microRNA signature from uninfected RBC EVs, indicating a potential role as disease biomarkers. Finally, EVs were internalized by other RBCs in culture, implicating a potential role for these vesicles in cellular communication. Overall, our study points to the multiple functional implications of EVs in Babesia–host interactions and support the potential that EVs have as agents in disease pathogenesis.