Identification and Characterization of the RouenBd1987 Babesia divergens Rhopty-Associated Protein 1

Human babesiosis is caused by one of several babesial species transmitted by ixodid ticks that have distinct geographical distributions based on the presence of competent animal hosts. The pathology of babesiosis, like malaria, is a consequence of the parasitaemia which develops through the cyclical replication of Babesia parasites in a patient''s red blood cells, though symptoms typically are nonspecific. We have identified the gene encoding Rhoptry-Associated Protein −1 (RAP-1) from a human isolate of B. divergens, Rouen1987 and characterized its protein product at the molecular and cellular level. Consistent with other Babesia RAP-1 homologues, BdRAP-1 is expressed as a 46 kDa protein in the parasite rhoptries, suggesting a possible role in red cell invasion. Native BdRAP-1 binds to an unidentified red cell receptor(s) that appears to be non-sialylated and non-proteinacious in nature, but we do not find significant reduction in growth with anti-rRAP1 antibodies in vitro, highlighting the possibility the B. divergens is able to use alternative pathways for invasion, or there is an alternative, complementary, role for BdRAP-1 during the invasion process. As it is the parasite''s ability to recognize and then invade host cells which is central to clinical disease, characterising and understanding the role of Babesia-derived proteins involved in these steps are of great interest for the development of an effective prophylaxis.     

Artemisone inhibits in vitro and in vivo propagation of Babesia bovis and B. bigemina parasites

Artemisone was evaluated, in in vitro and in vivo, for control of bovine babesiosis caused by Babesia bigemina and Babesiabovis parasites. In vitro, artemisone reduced parasitemia in a dose-dependent manner: the inhibitory effects increased gradually, reaching a maximum inhibition of 99.6% and 86.4% for B. bigemina and B. bovis, respectively 72 h after initiation of treatment with initial parasitemia of 0.5%. In calves infected with either B. bigemina or B. bovis artemisone treatment was well tolerated and prevented development of acute babesiosis in all animals except for one B. bovis-infected calf. The treatment did not eliminate all blood parasites, and recovered animals carried a persistent low-level infection. Treatment with artemisone may be useful as an alternative drug for preventing the pathology that results from babesiosis, without interfering with acquired immune protection following recovery from an acute babesiosis infection or vaccination.     

Human babesiosis

Babesiosis is a worldwide emerging tick-borne disease that is increasing in frequency and geographic range. It imposes a significant health burden, especially on those who are immunocompromised and those who acquire the infection through blood transfusion. Death from babesiosis occurs in up to 20 percent of these groups. Diagnosis is confirmed with identification of typical intraerythrocytic parasites on a thin blood smear or Babesia DNA using PCR. Treatment consists of atovaquone and azithromycin or clindamycin and quinine, and exchange transfusion in severe cases. Personal and communal protective measures can limit the burden of infection but it is important to recognize that none of these measures are likely to prevent the continued expansion of Babesia into non-endemic areas.     

Investigating disease severity in an animal model of concurrent babesiosis and Lyme disease

The incidence of babesiosis, Lyme disease and other tick-borne diseases has increased steadily in Europe and North America during the last five decades. Babesia microti is transmitted by species of Ixodes, the same ticks that transmit the Lyme disease-causing spirochete, Borrelia burgdorferi. B. microti can also be transmitted through transfusion of blood products and is the most common transfusion-transmitted infection in the U.S.A. Ixodes ticks are commonly infected with both B. microti and B. burgdorferi, and are competent vectors for transmitting them together into hosts. Few studies have examined the effects of coinfections on humans and they had somewhat contradictory results. One study linked coinfection with B. microti to a greater number of symptoms of overall disease in patients, while another report indicated that B. burgdorferi infection either did not affect babesiosis symptoms or decreased its severity. Mouse models of infection that manifest pathological effects similar to those observed in human babesiosis and Lyme disease offer a unique opportunity to thoroughly investigate the effects of coinfection on the host. Lyme disease has been studied using the susceptible C3H mouse infection model, which can also be used to examine B. microti infection to understand pathological mechanisms of human diseases, both during a single infection and during coinfections. We observed that high B. microti parasitaemia leads to low haemoglobin levels in infected mice, reflecting the anaemia observed in human babesiosis. Similar to humans, B. microti coinfection appears to enhance the severity of Lyme disease-like symptoms in mice. Coinfected mice have lower peak B. microti parasitaemia compared to mice infected with B. microti alone, which may reflect attenuation of babesiosis symptoms reported in some human coinfections. These findings suggest that B. burgdorferi coinfection attenuates parasite growth while B. microti presence exacerbates Lyme disease-like symptoms in mice.     

Vaccination against babesiosis using recombinant GPI-anchored proteins

The increase in human babesiosis is of major concern to health authorities. In the USA, most of these cases are due to infections with Babesia microti, whereas in Europe B. divergens is the major cause of clinical disease in humans. Here we review the immunological and biological literature of glycosylphosphatidylinositol (GPI)-anchored merozoite proteins of human Babesia parasites with emphasis on their role in immunity, and provide some new bioinformatical information on B. microti GPI-Anchored Proteins (GPI-AP). Cattle can be vaccinated with soluble parasite antigens (SPA) of Babesia divergens that are released by the parasite during proliferation. The major component in SPA preparations appeared to be a 37?kDa merozoite surface protein that is anchored in the merozoite membrane by a GPI anchor. Animals could be protected by vaccination with the recombinant 37?kDa protein expressed in Escherichia coli, provided the protein had a hydrophobic terminal sequence. Based on this knowledge, a recombinant vaccine was developed against Babesia canis infection in dogs, successfully. In order to identify similar GPI-AP in B. microti, the genome was analysed. Here it is shown that B. microti encodes all proteins necessary for GPI assembly and its subsequent protein transfer. In addition, in total 21 genes encoding for GPI-AP were detected, some of which reacted particularly strongly with sera from B. microti-infected human patients. Reactivity of antibodies with GPI-anchored merozoite proteins appears to be dependent on the structural conformation of the molecule. It is suggested that the three-dimensional structure of the protein that is anchored in the membrane is different from that of the protein that has been shed from the merozoite surface. The significance of this protein’s dynamics in parasite biology and immune evasion is discussed. Finally, we discuss developments in tick and Babesia vaccine research, and the role such vaccines could play in the control of human babesiosis.     

Excessive Pro-Inflammatory Serum Cytokine Concentrations in Virulent Canine Babesiosis

Babesia rossi infection causes a severe inflammatory response in the dog, which is the result of the balance between pro- and anti-inflammatory cytokine secretion. The aim of this study was to determine whether changes in cytokine concentrations were present in dogs with babesiosis and whether it was associated with disease outcome. Ninety-seven dogs naturally infected with B. rossi were studied and fifteen healthy dogs were included as controls. Diagnosis of babesiosis was confirmed by polymerase chain reaction and reverse line blot. Blood samples were collected from the jugular vein at admission, prior to any treatment. Cytokine concentrations were assessed using a canine-specific multiplex assay on an automated analyser. Serum concentrations of interleukin (IL)-2, IL-6, IL-8, IL-10, IL-18, granulocyte-macrophage colony stimulating factor (GM-CSF) and monocyte chemotactic protein-1 (MCP-1) were measured. Twelve of the Babesia-infected dogs died (12%) and 85 survived (88%). Babesia-infected dogs were also divided into those that presented within 48 hours from displaying clinical signs, and those that presented more than 48 hours after displaying clinical signs. Cytokine concentrations were compared between the different groups using the Mann-Whitney U test. IL-10 and MCP-1 concentrations were significantly elevated for the Babesia-infected dogs compared to the healthy controls. In contrast, the IL-8 concentration was significantly decreased in the Babesia-infected dogs compared to the controls. Concentrations of IL-6 and MCP-1 were significantly increased in the non-survivors compared to the survivors. Concentrations for IL-2, IL-6, IL-18 and GM-CSF were significantly higher in those cases that presented during the more acute stage of the disease. These findings suggest that a mixed cytokine response is present in dogs with babesiosis caused by B. rossi, and that an excessive pro-inflammatory response may result in a poor outcome.     

Molecular epidemiological survey of Babesia bovis,Babesia bigemina,and Babesia sp. Mymensingh infections in Mongolian cattle

Bovine babesiosis caused by Babesia species is an economically significant disease of cattle. Severe clinical babesiosis in cattle is caused by Babesia bovis, B. bigemina, and the recently discovered Babesia sp. Mymensingh. Mongolia is an agricultural country with a large cattle inventory. Although previous studies have detected active infections of B. bovis and B. bigemina in Mongolian cattle, only a few provinces were surveyed. Additionally, the endemicity of Babesia sp. Mymensingh in Mongolia remains unknown. We screened blood DNA samples from 725 cattle reared in 16 of the 21 Mongolian provinces using B. bovis-, B. bigemina-, and Babesia. sp. Mymensingh-specific PCR assays. The overall positive rates of B. bovis, B. bigemina, and Babesia sp. Mymensingh were 27.9% (n = 202), 23.6% (n = 171), and 5.4% (n = 39), respectively. B. bovis and B. bigemina were detected in cattle in all surveyed provinces; whereas Babesia sp. Mymensingh was detected in 11 of the 16 surveyed provinces. On a per province basis, the B. bovis- B. bigemina-, and Babesia sp. Mymensingh-positive rates were 5.9–52.0%, 9.1–76.3%, and 0–35.7%, respectively. In conclusion, this is the first report of Babesia sp. Mymensingh in Mongolia. In addition, we found that species of Babesia that are capable of causing bovine clinical babesiosis, including B. bovis, B. bigemina, and Babesia sp. Mymensingh, are widespread throughout the country.     

Babesia sp. BQ1 (Lintan): Molecular evidence of experimental transmission to sheep by Haemaphysalis qinghaiensis and Haemaphysalis longicornis

Ovine babesiosis is an economically important disease induced by tick transmitted haemoparasites throughout the world. In China, several ovine Babesia strains have been isolated from field-collected ticks or sheep blood during the last two decades but little is known about the vector ticks and transmission pattern. Babesia sp. BQ1 (Lintan) is a Babesia strain infective for sheep and goats, isolated from blood of sheep experimentally infested with Haemaphysalis qinghaiensis collected in field. In the present study, we explored the experimental transmission of Babesia sp. BQ1 (Lintan) to sheep by H. qinghaiensis and Haemaphysalis longicornis. Based on the evidence from nested PCR, it suggested that H. qinghaiensis and H. longicornis are the potential vector ticks of Babesia sp. BQ1 (Lintan) and that larvae, nymphs and adults of both tick species were able to transmit Babesia sp. BQ1 (Lintan) to sheep. Parasites could be detected in the blood, by specific nested PCR, for one month post-infestation.     

Genetic diversity of Actinobacillus lignieresii isolates from different hosts

Background

Bovine babesiosis is regarded as a limited health problem for Norwegian cows, and the incidence has decreased markedly since the 1930s. Rare cases of babesiosis in splenectomised humans from infection with Babesia divergens and B.venatorum have been described. The objective of this study was to determine whether birds can introduce Babesia-infected ticks. There are between 30 and 85 million passerine birds that migrate to Norway every spring.

Methods

Passerine birds were examined for ticks at four bird observatories along the southern Norwegian coast during the spring migrations of 2003, 2004 and 2005. The presence of Babesia was detected in the nymphs of Ixodes ricinus by real-time PCR. Positive samples were confirmed using PCR, cloning and phylogenetic analyses.

Results

Of 512 ticks examined, real-time PCR revealed five to be positive (1.0%). Of these, four generated products that indicated the presence of Babesia spp.; each of these were confirmed to be from Babesia venatorum (EU1). Two of the four B. venatorum-positive ticks were caught from birds having an eastern migratory route (P< 0.001).

Conclusions

Birds transport millions of ticks across the North Sea, the Skagerrak and the Kattegat every year. Thus, even with the low prevalence of Babesia-infected ticks, a substantial number of infected ticks will be transported into Norway each year. Therefore, there is a continuous risk for introduction of new Babesia spp. into areas where I. ricinus can survive.     

Three cases of canine babesiosis caused by Babesia odocoilei-like parasites in Japan

Babesia odocoilei-like parasites were first reported in 2003, and their virulence and hosts remain unknown. We report three cases of dogs with canine babesiosis in Iwate Prefecture. Since Iwate Prefecture area is an area of Japan where canine babesiosis is not endemic, we suspected that these cases of canine babesiosis were caused by B. odocoilei-like parasites. In the present study, we tried to identify the Babesia species that caused these cases of canine babesiosis. To classify Babesia parasites, the heat shock protein 70 (HSP70) gene was examined. Accordingly, we cloned and analyzed the HSP70 gene sequences of B. odocoilei-like parasites from three Ixodes ovatus ticks. It was determined that the nucleotide sequence of the HSP70 gene of the B. odocoilei-like parasites was not consistent with that of B. odocoilei, which suggests that these parasites were from a different species than B. odocoilei. Second, we identified the Babesia species that infected the three dogs by using the HSP70 gene and 18S rRNA. A partial HSP70 gene of B. odocoilei-like parasites was detected in the three dogs, but that of B. gibsoni was not detected. Additionally, a partial sequence of 18S rRNA of B. odocoilei-like parasites was detected in two dogs. These results demonstrated that two dogs were certainly infected with B. odocoilei-like parasites and that one dog was probably infected with B. odocoilei-like parasites. Therefore, these dogs were diagnosed with canine babesiosis due to the presence of B. odocoilei-like parasites. As there were only three cases, additional cases are needed to confirm our findings.     

Use of a doxycycline-enrofloxacin-metronidazole combination with/without diminazene diaceturate to treat naturally occurring canine babesiosis caused by <Emphasis Type="Italic">Babesia gibsoni</Emphasis>

Canine babesiosis is an important worldwide, tick-borne disease caused by hemoprotozoan parasites of the genus Babesia. Babesia gibsoni is the predominant species that causes canine babesiosis in Taipei, Taiwan. It is a small pleomorphic intraerythrocytic parasite that can cause erythrocyte destruction and hemolytic anemia. Efficacy of oral administration of a doxycycline-enrofloxacin-metronidazole combination with and without injections of diminazene diaceturate in the management of naturally occurring canine babesiosis caused by B. gibsoni was evaluated retrospectively. The overall efficacy of this combination of doxycycline-enrofloxacin-metronidazole in conjunction with and without administration of diminazene diaceturate was 85.7% and 83.3%, respectively; with a mean recovery time of 24.2 and 23.5 days, respectively. Concomitant use of intramuscular diminazene diaceturate may not improve the efficacy of a doxycycline-enrofloxacin-metronidazole combination in management of canine babesiosis caused by B. gibsoni.     

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

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

Induction of IL-10-Producing CD1dhighCD5+ Regulatory B Cells following Babesia microti-Infection

Background

Understanding the induction of immune regulatory cells upon helminth infection is important for understanding the control of autoimmunity and allergic inflammation in helminth infection. Babesia microti, an intraerythrocytic protozoan of the genus Babesia, is a major cause of the emerging human disease babesiosis, an asymptomatic malaria-like disease. We examined the influence of acute B. microti infection on the development of regulatory B cells together with regulatory T cells.

Principal Findings

Our data demonstrate that B cells stimulated in vitro with B. microti produce interleukin (IL)-10. This cytokine is also secreted by B cells isolated from B. microti-infected mice in response to lipopolysaccharide stimulation. In addition, high levels of IL-10 were detected in the serum of mice after infection with B. microti. The frequency of IL-10-producing CD1d^highCD5⁺ regulatory B cells (Bregs) and CD4⁺CD25⁺FoxP3⁺ T cells increased during the course of B. microti infection. Furthermore, adoptive transfer of IL-10-producing B cells induced by B. microti infection led to increased susceptibility of recipient mice to infection with B. microti. In contrast, experiments with B cell-deficient (µMT) mice demonstrated that lack of B cells enhances susceptibility to B. microti infection.

Conclusions

This study is the first demonstration of the expansion of Bregs following infection by an intraerythrocytic protozoan parasite. These data suggest that B. microti infection in mice provides an excellent model for studying Breg-mediated immune responses and begins to elucidate the mechanism by which helminth infection regulates autoimmunity and allergic inflammation.     

Vertical Transmission of Babesia microti in BALB/c Mice: Preliminary Report

Babesia spp. (Apicomplexa, Piroplasmida) are obligate parasites of many species of mammals, causing a malaria-like infection- babesiosis. Three routes of Babesia infection have been recognized to date. The main route is by a tick bite, the second is via blood transfusion. The third, vertical route of infection is poorly recognized and understood. Our study focused on vertical transmission of B. microti in a well-established mouse model. We assessed the success of this route of infection in BALB/c mice with acute and chronic infections of B. microti. In experimental groups, females were mated on the 1^st day of Babesia infection (Group G0); on the 28^th day post infection (dpi) in the post- acute phase of the parasite infection (G28); and on the 90^th and 150^th dpi (G90 and G150 group, respectively), in the chronic phase of the parasite infection. Pups were obtained from 58% of females mated in the post-acute phase (G28) and from 33% of females in groups G90 and G150. Mice mated in the pre-acute phase of infection (G0) did not deliver pups. Congenital B. microti infections were detected by PCR amplification of Babesia 18S rDNA in almost all pups (96%) from the experimental groups G28, G90 and G150. Parasitaemia in the F1 generation was low and varied between 0.01–0.001%. Vertical transmission of B. microti was demonstrated for the first time in BALB/c mice.     

Bovine babesiosis: Cattle protected in the field with a frozen vaccine containing Babesia bovis and Babesia bigemina cultured in vitro with a serum-free medium

An attenuated live vaccine containing Babesia bovis and B. bigemina cultured in vitro with a serum-free medium was assessed for its clinical protection conferred of naïve cattle, under natural tick-challenge in a high endemicity zone to Babesia spp. Three groups of six animals were treated as follows: group I (GI) received a vaccine derived from parasites cultured with a free-serum medium; group II (GII) were immunized with the standard vaccine, with parasites cultured in a medium supplemented with 40% (v/v) bovine serum; and a control group (GIII) inoculated with non-infected bovine erythrocytes. Inocula were administered by IM route. Experimental animals were kept during 23 days after vaccination in a cattle farm free of ticks and Babesia spp. Thereafter, cattle were moved to a high endemicity farm for natural exposure to Babesia spp. transmitted by Rhipicephalus microplus ticks. Protection against clinical babesiosis was observed in bovines belonging to GI (100%) and GII (83.33%), while the control animals (GIII) were not protected, and showed severe clinical signs, closely related to babesiosis, were observed for at least three consecutive days during the challenge. These were fever, anemia, which were measured simultaneously, and circulating parasites were detected by optic light microscopy. All cattle showed B. bovis and B. bigemina in stained blood films during the challenge; B. bovis antibody titers were higher than those to B. bigemina in GI and GII, and lower titers were determined in GIII. The protective capacity of the vaccine derived from B. bovis and B. bigemina cultured in vitro in a serum-free medium was demonstrated.     

Human Liver Infection in a Dish: Easy-To-Build 3D Liver Models for Studying Microbial Infection

Human liver infection is a major cause of death worldwide, but fundamental studies on infectious diseases affecting humans have been hampered by the lack of robust experimental models that accurately reproduce pathogen-host interactions in an environment relevant for the human disease. In the case of liver infection, one consequence of this absence of relevant models is a lack of understanding of how pathogens cross the sinusoidal endothelial barrier and parenchyma. To fill that gap we elaborated human 3D liver in vitro models, composed of human liver sinusoidal endothelial cells (LSEC) and Huh-7 hepatoma cells as hepatocyte model, layered in a structure mimicking the hepatic sinusoid, which enable studies of key features of early steps of hepatic infection. Built with established cell lines and scaffold, these models provide a reproducible and easy-to-build cell culture approach of reduced complexity compared to animal models, while preserving higher physiological relevance compared to standard 2D systems. For proof-of-principle we challenged the models with two hepatotropic pathogens: the parasitic amoeba Entamoeba histolytica and hepatitis B virus (HBV). We constructed four distinct setups dedicated to investigating specific aspects of hepatic invasion: 1) pathogen 3D migration towards hepatocytes, 2) hepatocyte barrier crossing, 3) LSEC and subsequent hepatocyte crossing, and 4) quantification of human hepatic virus replication (HBV). Our methods comprise automated quantification of E. histolytica migration and hepatic cells layer crossing in the 3D liver models. Moreover, replication of HBV virus occurs in our virus infection 3D liver model, indicating that routine in vitro assays using HBV or others viruses can be performed in this easy-to-build but more physiological hepatic environment. These results illustrate that our new 3D liver infection models are simple but effective, enabling new investigations on infectious disease mechanisms. The better understanding of these mechanisms in a human-relevant environment could aid the discovery of drugs against pathogenic liver infection.     

The key to egress? Babesia bovis perforin-like protein 1 (PLP1) with hemolytic capacity is required for blood stage replication and is involved in the exit of the parasite from the host cell

Bovine babesiosis is a tick-borne disease caused by apicomplexan parasites of the Babesia genus that represents a major constraint to livestock production worldwide. Currently available vaccines are based on live parasites which have archetypal limitations. Our goal is to identify candidate antigens so that new and effective vaccines against Babesia may be developed. The perforin-like protein (PLP) family has been identified as a key player in cell traversal and egress in related apicomplexans and it was also identified in Babesia, but its function in this parasite remains unknown. The aim of this work was to define the PLP family in Babesia and functionally characterize PLP1, a representative member of the family in Babesia bovis. Bioinformatic analyses demonstrate a variable number of plp genes (four to eight) in the genomes of six different Babesia spp. and conservation of the family members at the secondary and tertiary structure levels. We demonstrate here that Babesia PLPs contain the critical domains present in other apicomplexan PLPs to display the lytic capacity. We then focused on the functional characterization of PLP1 of B. bovis, both in vitro and in vivo. PLP1 is expressed and exposed to the host immune system during infection and has high hemolytic capacity under a wide range of conditions in vitro. A B. bovis plp1 knockout line displayed a decreased growth rate in vitro compared with the wild type strain and a peculiar phenotype consisting of multiple parasites within a single red blood cell, although at low frequency. This phenotype suggests that the lack of PLP1 has a negative impact on the mechanism of egression of the parasite and, therefore, on its capacity to proliferate. It is possible that PLP1 is associated with other proteins in the processes of invasion and egress, which were found to have redundant mechanisms in related apicomplexans. Future work will be focused on unravelling the network of proteins involved in these essential parasite functions.     

In vitro screening of compounds from the Food and Drug Administration-approved library identifies anti-Babesia gibsoni activity of idarubicin hydrochloride and vorinostat

Babesia gibsoni is mainly transmitted by hard ticks of the genus Rhipicephalus (R. sanguineus) and Haemaphysalis (H. longicornis), and causes canine babesiosis. Clinical manifestations of B. gibsoni infection include fever, hemoglobinemia, hemoglobinuria, and progressive anemia. Traditional antibabesial therapy, such as imidocarb dipropionate or diminazene aceturate, can only alleviate severe clinical manifestations and cannot eliminate parasites in the host. Food and Drug Administration (FDA)-approved drugs are a solid starting point for researching novel therapy strategies for canine babesiosis. In this work, we screened 640 FDA-approved drugs against the growth of B. gibsoni in vitro. Among them, 13 compounds (at 10 μM) exhibited high growth inhibition (>60%), and two compounds, namely idarubicin hydrochloride (idamycin) and vorinostat, were chosen for further investigation. The half-maximal inhibitory concentration (IC₅₀) values of idamycin and vorinostat were determined to be 0.044 ± 0.008 μM and 0.591 ± 0.107 μM, respectively. Viability results indicated that a concentration of 4 × IC₅₀ of vorinostat prevented the regrowth of treated B. gibsoni, whereas parasites treated with 4 × IC₅₀ concentration of idamycin remained viable. The B. gibsoni parasites treated with vorinostat exhibited degeneration within erythrocytes and merozoites, in contrast to the oval or signet-ring shape of normal B. gibsoni parasites. In conclusion, FDA-approved drugs offer a valuable platform for drug repositioning in antibabesiosis research. Particularly, vorinostat demonstrated promising inhibitory effects against B. gibsoni in vitro, and further studies on vorinostat are necessary to elucidate its mechanism as a novel treatment in infected animal models.     

Physical and Serologic Properties of an Antigen Prepared from Erythrocytes of Horses with Acute Babesiosis*

SYNOPSIS. By means of precipitation with protamine sulfate, a soluble antigen (PS) was obtained from erythrocytes of horses with acute babesiosis due to Babesia caballi and B. equi. This antigen reacted in gel diffusion tests with sera from horses recovered from acute babesiosis. The PS antigen was found to be muco-protein, susceptible to destruction by trypsin and taka-diastase. Analysis of the antigen by paper electrophoresis revealed 2 components which were not present in similar preparations made from erythrocytes of Babesia-free horses. When the PS antigen was heated in boiling water for 30 minutes, a serologically inactive precipitate was formed; however, the supernate remained serologically active and was termed boiled PS (BPS) antigen. This antigen was polysaccharide in nature; its serologic activity was destroyed by taka-diastase. In gel diffusion tests with sera of recovered horses, the PS antigen formed 2 lines of precipitation which coalesced in a single line formed between these sera and the BPS antigen. Both PS and BPS antigens reacted with sera of horses recovered from acute babesiosis in the gel-diffusion test, but not with sera of dogs and rats recovered from acute infection with Babesia canis and Babesia rodhaini, respectively. The serologic specificity of these antigens suggests that they might have application in the serodiagnosis of inapparent Babesia infections of equine animals.