The cause of the predilection of Babesia gibsoni for reticulocytes

Antioxidant Status, and Blood Zinc and Copper Concentrations in Dogs with Uncomplicated Babesiosis due to Babesia Canis Infections

INTRODUCTION

The aim of the study was to demonstrate a link between uncomplicated Babesia canis infection in dogs and blood concentrations of zinc and copper and erythrocytic antioxidant defence - activities of glutathione (GSH), superoxide dismutase (SOD) and catalase (CAT).

MATERIAL AND METHODS

The study was based on 15 naturally occurring cases of canine babesiosis with anorexia, pyrexia, depression, pale mucous membrane, splenomegaly and dark red urine. Microscopic examination of Giemsa-stained peripheral blood smears and the results of PCR confirmed B. canis infection. Seven apparently healthy dogs brought in for either a check-up or vaccination were used for comparison.

RESULTS

The levels of the erythrocytic antioxidant enzymes - SOD and CAT - were significantly higher in the infected dogs than in cytologically negative dogs. The levels of blood micronutrients were significantly lower in the infected dogs (0.478 μg of zinc per mL vs 1.241 μg/mL and 0.722 μg of copper per mL vs 1.392 μg/mL).

CONCLUSION

Oxidative stress can be posited as one of the mechanisms leading to anaemia in dogs with babesiosis, and therefore antioxidant biomarker and copper and zinc concentrations could be used as indicators of disease severity and prognostic markers.

A Comparison Between Manual Count, Flow Cytometry and Quantitative Real-Time Polymerase Chain Reaction as a Means of Determining Babesia rossi Parasitaemia in Naturally Infected Dogs

PURPOSE

Light microscopic manual count is the current gold standard for parasite quantification. The ability to determine parasite density in whole blood is crucial to understanding disease pathogenesis and finding a suitable automated method of Babesia rossi parasite quantification would facilitate higher throughput and provide results that are more objective. This study investigated both peripheral capillary and central venous whole blood to estimate the correlations between light microscopy, flow cytometry and quantitative real-time polymerase chain reaction (qPCR).

METHODS

Peripheral capillary and central venous blood were sampled from 40 naturally B. rossi-infected dogs and 10 healthy control dogs. Samples were analysed by reverse line blot hybridization assay to confirm a mono-B. rossi infection. Capillary blood parasite density was detected using light microscopic manual counting and venous blood parasitaemia detected by manual counts, flow cytometry and qPCR.

RESULTS

A significant correlation was found between the venous manual counts and flow cytometry (r_s = 0.465; P < 0.001), as well as qPCR (r_s = - 0.500; P < 0.001). A significant correlation was also observed between the capillary manual counts compared to venous manual counts (r_s = 0.793; P < 0.001), flow cytometry (r_s = 0.399; P = 0.004), and qPCR (r_s = - 0.526; P < 0.001).

CONCLUSIONS

The study results suggest that qPCR is of value as an alternative to the gold standard manual count for detecting B. rossi parasitaemia in canine whole blood and that flow cytometry may be useful with further refinement of issues such as background fluorescence and the influence of reticulocytes.

Evaluation of oxidative stress and antioxidant status, serum trace mineral levels and cholinesterases activity in cattle infected with Anaplasma marginale

This study was undertaken to assess the influence of an Anaplasma marginale infection on oxidative stress and antioxidant status, trace elements and cholinesterase as markers of the inflammatory process and biomarkers of oxidative imbalance. An infected group comprised of 35 crossbred Holstein cattle, about 2-3 years old, naturally infected with Anaplasma marginale, were divided into 4 subgroups according to their parasitemia rates (<1%, 1-10%, 10-20%, >20%) and also 10 healthy cattle as control were selected. Blood samples were taken and hematological parameters, activities of antioxidant enzymes including erythrocyte glutathione peroxidase (GSH-Px), superoxide dismutase (SOD), catalase (CAT), glucose-6-phosphate dehydrogenase (G6PD), total antioxidant capacity (TAC), median corpuscularfragility (MCF) as well as acetylcholinesterase (AChE), and serum concentrations of antioxidant trace minerals (copper, iron, zinc, manganese, and selenium) and butyrylcholinesterase (BChE) were determined. In addition, as an index of lipid peroxidation, the level of malondialdehyde (MDA) was measured. The results revealed a significant decrease (P < 0.05) in RBC count, packed cell volume (PCV) and Hb concentration as well as the activities of erythrocyte GSH-Px, SOD, CAT, G6PD, TAC, MCF and AChE and serum concentrations of Cu, Zn, Mn, Se and BchE in the infected cattle. In contrast, significantly increased (P < 0.05) levels of MDA and erythrocyte osmotic fragility as well as serum concentration of iron were recorded in the infected animals. The significant decrease in antioxidant enzyme activities and substantial elevated levels of lipid peroxidation and erythrocyte osmotic fragility associated with the notable increase in parasitemia indicate increased exposure of RBCs to oxidative damage. Furthermore, decrease of cholinesterase in infection by A. marginale can and directly or indirectly lead to increase acetylcholine levels potent anti-inflammatory molecules, thereby inhibiting inflammation.

Evaluation of antioxidant status, oxidative stress and serum trace mineral levels associated with Babesia ovis parasitemia in sheep

Ovine babesiosis is a fatal disease characterized by severe progressive hemolytic anemia. In order to clarify the causal mechanisms implicated in anemia, this study was aimed to assess the antioxidant status and erythrocyte oxidative stress in sheep suffering from ovine babesiosis. Babesia infection was confirmed both with Giemsa's staining blood smears and semi-nested PCR amplified region of 18S rRNA gene. Thirty-eight Iranian sheep, naturally infected with Babesia spp., were considered as the infected group and divided into four subgroups according to parasitemia rates (<1%, 1-2%, 2-3% and >3%), and the same number non-infected animals were selected as the control group. Blood samples were taken and hematological parameters, activities of antioxidant enzymes including erythrocyte glutathione peroxidase (GSH-Px), superoxide dismutase (SOD), catalase (CAT), glucose-6-phosphate dehydrogenase (G6PD), total antioxidant capacity (TAC), median corpuscular fragility (MCF), and serum concentrations of some trace minerals (copper, iron, zinc, manganese, and selenium) were measured. In addition, as an index of lipid peroxidation, the level of malondialdehyde (MDA) was measured. The results revealed a significant decrease (P<0.01) in RBC count, packed cell volume (PCV) and Hb concentration as well as the activities of erythrocyte GSH-Px, SOD, CAT, G6PD, TAC, MCF and serum concentrations of Cu, Zn, Mn and Se in the infected sheep. In contrast, significantly increased (P<0.01) levels of MDA and erythrocyte osmotic fragility as well as serum concentration of iron were recorded in the infected animals. Overall, the observed remarkable decrease in the antioxidant enzyme activities, median corpuscular fragility and substantial elevated levels of lipid peroxidation associated with the notable increase in parasitemia indicate high exposure of RBCs to oxidative damage in Babesia infected sheep. These results indicate that the disturbed antioxidant defense mechanisms in ovine babesiosis can promote the development of anemia.

BCKDH: the missing link in apicomplexan mitochondrial metabolism is required for full virulence of Toxoplasma gondii and Plasmodium berghei

While the apicomplexan parasites Plasmodium falciparum and Toxoplasma gondii are thought to primarily depend on glycolysis for ATP synthesis, recent studies have shown that they can fully catabolize glucose in a canonical TCA cycle. However, these parasites lack a mitochondrial isoform of pyruvate dehydrogenase and the identity of the enzyme that catalyses the conversion of pyruvate to acetyl-CoA remains enigmatic. Here we demonstrate that the mitochondrial branched chain ketoacid dehydrogenase (BCKDH) complex is the missing link, functionally replacing mitochondrial PDH in both T. gondii and P. berghei. Deletion of the E1a subunit of T. gondii and P. berghei BCKDH significantly impacted on intracellular growth and virulence of both parasites. Interestingly, disruption of the P. berghei E1a restricted parasite development to reticulocytes only and completely prevented maturation of oocysts during mosquito transmission. Overall this study highlights the importance of the molecular adaptation of BCKDH in this important class of pathogens.

The mitochondrial tricarboxylic acid (TCA) cycle is one of the core metabolic pathways of eukaryotic cells, which contributes to cellular energy generation and provision of essential intermediates for macromolecule synthesis. Apicomplexan parasites possess the complete sets of genes coding for the TCA cycle. However, they lack a key mitochondrial enzyme complex that is normally required for production of acetyl-CoA from pyruvate, allowing further oxidation of glycolytic intermediates in the TCA cycle. This study unequivocally resolves how acetyl-CoA is generated in the mitochondrion using a combination of genetic, biochemical and metabolomic approaches. Specifically, we show that T. gondii and P. bergei utilize a second mitochondrial dehydrogenase complex, BCKDH, that is normally involved in branched amino acid catabolism, to convert pyruvate to acetyl-CoA and further catabolize glucose in the TCA cycle. In T. gondii, loss of BCKDH leads to global defects in glucose metabolism, increased gluconeogenesis and a marked attenuation of growth in host cells and virulence in animals. In P. bergei, loss of BCKDH leads to a defect in parasite proliferation in mature red blood cells, although the mutant retains the capacity to proliferate within 'immature' reticulocytes, highlighting the role of host metabolism/physiology on the development of Plasmodium asexual stages.

Detection of anti-Babesia gibsoni heat shock protein 70 antibody and anti-canine heat shock protein 70 antibody in sera from Babesia gibsoni-infected dogs

Antibodies that recognized either Babesia gibsoni or canine red blood cell (RBC) 70-kilodalton (kDa) protein were detected in serum from acutely and chronically B. gibsoni-infected. In those sera, antibodies that reacted with recombinant B. gibsoni and canine heat shock protein 70 (rBgHsp70 and rcHsp70) were detected; therefore, B. gibsoni and canine RBC 70-kDa proteins seemed to be BgHsp70 and cHsp70, respectively. In infected dogs, the amounts of these antibodies increased after infection. Interestingly, polyclonal antibody raised against rBgHsp70 in two rabbits reacted not only with rBgHsp70 but also with rcHsp70 and native cHsp70 from canine RBCs. Because BgHsp70 showed high homology with cHsp70 (70.8%), anti-rBgHsp70 antibody might cross-react with cHsp70. Additionally, the localizations of both BgHsp70 and cHsp70 were observed by indirect fluorescence assay. As a result, cHsp70 was not found on the membrane surface of erythrocytes, suggesting that erythrocytes would not be targets of anti-cHsp70 antibody. Meanwhile, only exoerythrocytic parasites were stained by anti-rBgHsp70 antibody. This result showed that BgHsp70 would be expressed on the surface of parasites during the exoerythrocytic stage. These results indicated that BgHsp70 was a highly immunogenic protein in canine B. gibsoni infection, and that exoerythrocytic parasites might be targets of anti-BgHsp70 antibody.

Clinical management of canine babesiosis

OBJECTIVE

To review and summarize current information regarding epidemiology, pathogenesis, and pathophysiology leading to the various clinical syndromes associated with canine babesiosis. Diagnosis, treatment, preventative strategies, and zoonotic implications are discussed.

ETIOLOGY

Babesiosis is caused by hemoprotozoa of the genus Babesia. Numerous species of Babesia exist worldwide. An increased incidence of babesiosis is described, especially in North America. The babesial organism spends the majority of its life cycle within the erythrocyte of the definitive host, resulting in hemolysis, with or without systemic complications.

DIAGNOSIS

Definitive diagnosis depends on direct visualization of the organism on blood smear or polymerase chain reaction. A positive serologic antibody test indicates exposure with or without active infection.

THERAPY

Antiprotozoal drugs, antimicrobials, and supportive care are the mainstays of babesiosis therapy.

PROGNOSIS

Prognosis depends on the severity of disease, which in turn depends on both organism and host factors. Clinical syndromes associated with a poorer prognosis include red biliary syndrome, acute renal failure, acute respiratory distress syndrome, neurologic dysfunction, acute pancreatitis, cardiac dysfunction, and hypoglycemia.

Erythrocytic antioxidant defense, lipid peroxides level and blood iron, zinc and copper concentrations in dogs naturally infected with Babesia gibsoni

Babesiosis is a common tick borne disease of dogs in tropical and subtropical regions of the world caused by different species of Babesia. The present study aimed to examine erythrocyte lipid peroxide and erythrocytic antioxidant levels in dogs with clinical babesiosis, caused by Babesia gibsoni, and impact of the disease on blood iron, zinc and copper levels. The study was conducted on 10 naturally occurring cases of canine babesiosis with the history of tick infestation, erratic pyrexia, and prolonged illness. Microscopic examination of Giemsa stained peripheral blood smears confirmed B. gibsoni infection in the erythrocytes. Six apparently healthy dogs of different age, sex and breeds, brought for either health checkup or vaccination were used for comparison. Levels of erythrocytic antioxidant enzymes were significantly (P<0.01) higher in sick dogs than those of cytologically negative dogs (catalase: 0.192+/-0.024 units/mg Hb vs 0.074+/-0.004 units/mg Hb; superoxide dismutase: 0.014+/-0.0009 units/mg Hb vs 0.006+/-0.0008 units/mg Hb and lipid peroxide: 6.01+/-0.30 nmol MDA/mg Hb vs 1.89+/-0.10 nmol MDA/mg Hb). The levels of blood micronutrients were significantly low in these dogs (iron: 89.87+/-8.12 microg/g vs 126.44+/-14.65 microg/g; zinc: 3.67+/-1.85 microg/g vs 5.62+/-1.83 microg/g and copper: 0.55+/-0.63 microg/g vs 0.65+/-0.04 microg/g). The study demonstrated oxidative damage in dogs naturally infected with B. gibsoni. Low level of blood iron, zinc and copper seems to have an additional role in the genesis of anaemia and oxidative stress.

Suppressive effect of culture supernatant of erythrocytes and serum from dogs infected with Babesia gibsoni on the morphological maturation of canine reticulocytes in vitro

The present study evaluated the effects of infected culture supernatant of erythrocytes, fractionation of culture supernatant and serum from dogs infected with Babesia gibsoni (B. gibsoni) on the maturation of canine reticulocytes in vitro. The SDS-PAGE demonstrated that significantly broader bands were generated by both the infected culture supernatant of erythrocytes and the serum from dogs chronically infected with B. gibsoni. The culture supernatant of erythrocytes infected with B. gibsoni strongly suppressed the maturation of reticulocytes. Prior studies showed that chronically infected serum had inhibitory effects on both the maturation of reticulocytes and the canine pyrimidine 5'-nucleotidase subclass I and purine-specific 5'-nucleotidase activity. In addition, serum free infected culture supernatant of erythrocytes had an inhibitory effect on the morphological maturation of reticulocytes. These results suggest that infected serum and culture supernatant of erythrocytes might accumulate excess proteins and/or metabolites as a result of the inhibited maturation of reticulocytes and decreased activity of erythrocyte 5'-nucleotidase. Furthermore, the fractions observed at >150 kDa- and 150-70 kDa- in the infected culture supernatant and serum retarded the maturation of canine reticulocytes in vitro. The results obtained from the in vitro examinations, in the present study, suggested that B. gibsoni itself and/or its metabolites might release certain proteins in the infected culture supernatant and serum from infected dogs and as a result delay morphological maturation of canine reticulocytes.

Babesia microti primarily invades mature erythrocytes in mice

Babesia microti is a tick-borne red blood cell parasite that causes babesiosis in people. Its most common vertebrate reservoir is the white-footed mouse. To determine whether B. microti invades reticulocytes, as does the canine pathogen B. gibsoni, we infected the susceptible inbred mouse strains C.B-17.scid and DBA/2 with a clinical isolate of B. microti. Staining of fixed permeabilized red blood cells with 4',6'-diamidino-2-phenylindole or YOYO-1, a sensitive nucleic acid stain, revealed parasite nuclei as large bright dots. Flow cytometric analysis indicated that parasite DNA is primarily found in mature erythrocytes that expressed Babesia antigens but not the transferrin receptor CD71. In contrast, CD71-positive reticulocytes rarely contained Babesia nuclei and failed to express Babesia antigens. Accordingly, the frequency of YOYO-1-positive, CD71-negative cells strongly correlated with parasitemia, defined as the frequency of infected red blood cells assessed on Giemsa-stained blood smears. Importantly, the absolute numbers generated by the two techniques were similar. Parasitemia was modest and transient in DBA/2 mice but intense and sustained in C.B-17.scid mice. In both strains, parasitemia preceded reticulocytosis, but reticulocytes remained refractory to B. microti. In immunocompetent C.B-17 mice, reticulocytosis developed early, despite a marginal and short-lived parasitemia. Likewise, an early reticulocytosis developed in resistant BALB/cBy and B10.D2 mice. These studies establish that B. microti has a tropism for mature erythrocytes. Although reticulocytes are rarely infected, the delayed reticulocytosis in susceptible strains may result from parasite or host activities to limit renewal of the mature erythrocyte pool, thereby preventing an overwhelming parasitemia.

Inhibition of Na,K-ATPase activity reduces Babesia gibsoni infection of canine erythrocytes with inherited high K, low Na concentrations

Babesia gibsoni multiplies well in canine red blood cells (RBCs) containing high concentrations of potassium (HK), reduced glutathione, and free amino acids as a result of an inherited high Na,K-ATPase activity, i.e., HK RBCs. To determine the role of Na,K-ATPase in the multiplication of B. gibsoni, the effect of ouabain on the proliferation of the parasites in HK RBCs was investigated. To determine the direct effect of ouabain on the parasites, the proliferation of the parasites in normal canine RBCs containing low potassium (LK) and high sodium concentrations, i.e., LK RBCs, which completely lack Na,K-ATPase activity, was observed. Ouabain at 0.1 mM significantly suppressed the multiplication of B. gibsoni in HK RBCs in vitro, whereas it had no effect on the parasites in LK RBCs. The results suggest that the multiplication of B. gibsoni in HK RBCs depends mainly on the presence of Na,K-ATPase in the cells. Therefore, the effects of ouabain on the intracellular cation and free amino acid composition of the HK RBCs were examined. In HK RBCs incubated with ouabain, a marked decrease in the concentration of potassium and an increase in sodium were observed, together with a decrease in the number of parasitized cells. These results suggest that the intracellular cation composition maintained by Na,K-ATPase might be advantageous to the parasites. Moreover, the concentrations of some free amino acids, i.e., asparagine, aspartate, glutamate, glutamine, glycine, and histidine, were markedly decreased in HK RBCs incubated with ouabain. Decreased concentrations of the free amino acids induced by inhibition of Na,K-ATPase seemed to affect the multiplication of B. gibsoni in HK RBCs. Based on these results, it is clear that the high Na,K-ATPase activity in HK RBCs contributes to the proliferation of B. gibsoni by maintaining high potassium and low sodium concentrations, as well as high concentrations of some free amino acids in the cells.

Inhibitory effect of pyrimidine and purine nucleotides on the multiplication of Babesia gibsoni: possible cause of low parasitemia and simultaneous reticulocytosis in canine babesiosis

The present study was conducted to determine the cause of low parasitemia and simultaneous reticulocytosis in canine babesiosis. The parasitemia was significantly decreased in in vitro cultures of Babesia gibsoni by the pretreatment of host canine erythrocytes with lead acetate, which is a specific inhibitor of pyrimidine 5'-nucleotidase subclass I (P5N-I). The serum from dogs chronically infected with B. gibsoni did not decrease the activities of hexokinase, glucose-6-phosphate dehydrogenase or 6-phosphogluconate dehydrogenase in canine reticulocytes, although it was previously reported that this serum had inhibitory effects on both the maturation of reticulocytes and the canine P5N-I and purine-specific 5'-nucleotidase activities. Furthermore, the in vitro multiplication of B. gibsoni was significantly inhibited by pyrimidine nucleotides such as cytidine 5'-monophosphate (5'-CMP), which is preferentially catalyzed by P5N-I and also inhibits the morphological maturation of canine reticulocytes. Purine nucleotides such as inosine 5'-monophosphate (5'-IMP) also had an inhibitory effect on the multiplication of this parasite. These results suggest that nucleotides such as 5'-CMP and 5'-IMP might accumulate in young erythrocytes and/or serum in dogs infected with B. gibsoni as a result of the decreased activity of erythrocyte 5'-nucleotidase, and the accumulation of these nucleotides might inhibit the multiplication of this parasite and simultaneously retard the maturation of reticulocytes. The results obtained from the in vitro examinations in the present study may partially clarify the relationship between low parasitemia and simultaneous reticulocytosis in vivo in canine babesiosis.

BABESIA GIBSONI–SPECIFIC ISOENZYMES RELATED TO ENERGY METABOLISM OF THE PARASITE IN INFECTED ERYTHROCYTES

To clarify the cause of the predilection of Babesia gibsoni for reticulocytes and canine HK erythrocytes (containing high concentrations of potassium) with inherited high concentrations of some amino acids, including glutamate, 4 enzymes in B. gibsoni parasites were examined by polyacrylamide gel electrophoresis (PAGE). The enzymes, i.e., hexokinase, glucose phosphate isomerase, lactate dehydrogenase, and glutamate dehydrogenase (GDH), were found to be associated with B. gibsoni parasites. The parasite-specific enzymes were shown to have different mobility patterns in PAGE from those found in normal canine erythrocytes. GDH, which is able to oxidize glutamate to alpha-ketoglutarate, an intermediate in the citric acid cycle in mitochondria, was detected only in the parasites. Electron microscopy of the parasites revealed double-membraned organelles similar to mitochondria in their cytoplasm. The parasites in in vitro culture contained many more mitochondrialike organelles than those in the peripheral blood of infected dogs. In addition, the size of parasites cultured in vitro was significantly larger than that of parasites in the peripheral blood. Based on these results, it is suggested that B. gibsoni may use glucose as an energy source in its own glycolytic pathway. Moreover, the parasite may also be capable of oxidizing glutamate via GDH in the citric acid cycle, which may operate in the mitochondrialike organelles within the parasite. This may explain the predilection of B. gibsoni for canine reticulocytes and HK erythrocytes with a high concentration of glutamate.

Babesia gibsoni: preferential multiplication in reticulocytes is related to the presence of mitochondria and a high concentration of adenosine 5'-triphosphate in the cells

To determine the cause of the predilection of Babesia gibsoni for reticulocytes, the parasites were cultivated with various types of reconstituted erythrocyte ghosts, which were prepared by resealing erythrocyte ghosts together with variously treated erythrocyte lysate, in vitro. The level of parasitemia in the culture with reconstituted reticulocyte ghosts containing untreated reticulocyte lysate was significantly higher than that in the culture with reconstituted normocyte (mature erythrocyte) ghosts containing untreated normocyte lysate. The removal of mitochondria from reconstituted reticulocyte ghosts by filtration or centrifugation resulted in decreased of parasitemia in those cultures. In contrast, when mitochondria from reticulocytes were loaded into reconstituted normocyte ghosts, the parasitemia in the ghosts loaded mitochondria was increased to the same level as that in reconstituted reticulocyte ghosts. Furthermore, the parsitemia in the culture with reconstituted normocyte ghosts was proportional to the concentration of adenosine 5'-triphosphate in the ghosts. These results suggested that mitochondria of reticulocytes might enhance the multiplication of B. gibsoni through the generation of adenosine 5'-triphosphate within the cells.

Increased generation of superoxide in erythrocytes infected with Babesia gibsoni

The present study was conducted to clarify the mechanism underlying the oxidative process in erythrocytes infected with Babesia gibsoni. The parasite B. gibsoni was cultured together with erythrocytes from normal dogs for 7 days. When parasitemia reached 12.0-13.4% at Day 7. the production of superoxide in erythrocytes was significantly higher in the parasitized culture than in the control culture (p<0.005). The concentration of thiobarbituric acid reactive substances (TBARS) in erythrocytes in parasitized culture was also significantly increased compared with the control culture (p<0.005), indicating that lipid peroxidation was greater in infected erythrocytes than in non-infected cells. In addition, the rates of superoxide generation in the blood of B. gibsoni-infected dogs were also significantly higher than in non-infected dogs (p<0.001). These results indicate that superoxide anions are increased in erythrocytes parasitized with B. gibsoni. and suggest that oxidative damage, due to lipid peroxidation, might be caused in host erythrocytes by the parasite.