First Wave Of Parasitemia Research Articles

Patient variability in the blood-stage dynamics of Plasmodium falciparum captured by clustering historical data

BackgroundMathematical models provide an understanding of the dynamics of a Plasmodium falciparum blood-stage infection (within-host models), and can predict the impact of control strategies that affect the blood-stage of malaria. However, the dynamics of P. falciparum blood-stage infections are highly variable between individuals. Within-host models use different techniques to capture this inter-individual variation. This struggle may be unnecessary because patients can be clustered according to similar key within-host dynamics. This study aimed to identify clusters of patients with similar parasitaemia profiles so that future mathematical models can include an improved understanding of within-host variation.MethodsPatients’ parasitaemia data were analyzed to identify (i) clusters of patients (from 35 patients) that have a similar overall parasitaemia profile and (ii) clusters of patients (from 100 patients) that have a similar first wave of parasitaemia. For each cluster analysis, patients were clustered based on key features which previous models used to summarize parasitaemia dynamics. The clustering analyses were performed using a finite mixture model. The centroid values of the clusters were used to parameterize two established within-host models to generate parasitaemia profiles. These profiles (that used the novel centroid parameterization) were compared with profiles that used individual-specific parameterization (as in the original models), as well as profiles that ignored individual variation (using overall means for parameterization).ResultsTo capture the variation of within-host dynamics, when studying the overall parasitaemia profile, two clusters efficiently grouped patients based on their infection length and the height of the first parasitaemia peak. When studying the first wave of parasitaemia, five clusters efficiently grouped patients based on the height of the peak and the speed of the clearance following the peak of parasitaemia. The clusters were based on features that summarize the strength of patient innate and adaptive immune responses. Parameterizing previous within host-models based on cluster centroid values accurately predict individual patient parasitaemia profiles.ConclusionThis study confirms that patients have personalized immune responses, which explains the variation of parasitaemia dynamics. Clustering can guide the optimal inclusion of within-host variation in future studies, and inform the design and parameterization of population-based models.

Approaches to Integrated Parasite Management (IPM) for Theileria orientalis with an Emphasis on Immunity.

Integrated parasite management (IPM) for pests, pathogens and parasites involves reducing or breaking transmission to reduce the impact of infection or infestation. For Theileria orientalis, the critical impact of infection is the first wave of parasitaemia from the virulent genotypes, Ikeda and Chitose, associated with the sequelae from the development of anaemia. Therefore, current control measures for T. orientalis advocate excluding the movement of naïve stock from non-endemic regions into infected areas and controlling the tick Haemaphysalis longicornis, the final host. In Australia, treatment of established infection is limited to supportive therapy. To update and expand these options, this review examines progress towards prevention and therapy for T. orientalis, which are key elements for inclusion in IPM measures to control this parasite.

Merozoites of Theileria orientalis buffeli reduce the parasitaemia of T. orientalis ikeda following tick challenge

Theileria orientalis is a tick-borne protozoal parasite causing anaemia and death in susceptible cattle. This investigation aimed to confirm whether immunisation with the “benign” buffeli genotype of T. orientalis could reduce the parasitaemia of the virulent ikeda genotype. Calves were inoculated intravenously or subcutaneously with bovine blood containing merozoites of T. orientalis buffeli and when recipients became positive by PCR, they and control calves were challenged with unfed nymphs of Haemaphysalis longicornis ticks infected as larvae with T. orientalis ikeda. All calves became positive for the challenge within 12 days after tick application. In the immunised calves, the first wave of parasitaemia with T. orientalis ikeda from 4 to 6 weeks was reduced significantly by >80 % before the parasite burden declined into the carrier state by 9 weeks. The parasitaemias in two calves which exhibited low infections with T. orientalis ikeda shortly after arrival, were also significantly reduced after tick challenge. The results confirm the previous studies on immunity to T. sergenti in Japan, and field experience with theileriosis in endemic zones where the carrier state appears to prevent clinical disease despite repeated, seasonal tick infestations with virulent genotypes of the parasite. This method offers a means to reduce the severity of the first wave of theilerial parasitaemia after tick challenge and possibly recover associated production losses.

A longitudinal study of infection with genotypes of Theileria orientalis in calves and introduced cattle at Dorrigo, New South Wales, and the effect on weight gains

BackgroundIn regions with endemic Theileria orientalis, recovered cattle are carriers, leaving newborn calves and introduced stock as the most susceptible groups to develop clinical disease after tick infestation with parasite transmission. MethodsTo gain information on the kinetics of infection and development and effects of theileriosis caused by virulent ikeda and chitose genotypes and the “benign” buffeli genotype of T.orientalis, this study sampled a total of 134 calves from 3 farms in Dorrigo, Australia, a region with multiple genotypes of the parasite. In addition, 30 introduced beef weaners were bled and weighed for 6 months after arrival. ResultsIn both cohorts, parasitaemia with the ikeda and chitose (genotypes 1 & 2) of T.orientalis was detectable by PCR within 3–4 weeks in >95 % of the groups, with maximal gene copies generated around 5–7 weeks after birth or introduction, before declining. In contrast, parasitaemias of T.orientalis buffeli (genotype 3), increased slowly, with around 80 % of the population testing positive by PCR after 4 months. The parasitaemias of the buffeli genotype did not exceed 40,000 gene copies /ul and were similar to those exhibited by ikeda and chitose genotypes following the “first wave of parasitaemia” as cattle entered the carrier state. In the 30 introduced weaners, the early infection with T.orientalis ikeda and chitose also caused significant reductions in packed cell volume (PCV) and incurred an estimated 20Kg loss in weight gain; the latter had not been recovered by 6 months after introduction. ConclusionsThe results support previous findings in other endemic regions of theileriosis, and imply that amelioration of the early high levels of parasitosis by the virulent genotypes could reduce the initial impact of theileriosis on production, which appears much less affected once animals enter the carrier state.

Myeloid-Derived Suppressor Cells Contribute to Susceptibility to Trypanosoma congolense Infection by Suppressing CD4+ T Cell Proliferation and IFN-γ Production.

Myeloid-derived suppressor cells (MDSCs) are a heterogeneous population of bone marrow-derived myeloid cells that have immune-suppressive activities. These cells have been reported to suppress T cell immunity against tumors as well as in some parasitic and bacterial infections. However, their role during Trypanosoma congolense infection has not been studied. Given that immunosuppression is a hallmark of African trypanosomiasis, we investigated the role of MDSCs in immunity to T. congolense infection. We found increased numbers of MDSCs in the spleen and liver of infected mice, which correlated with increased parasitemia. Depletion of MDSCs significantly increased the percentage of proliferating and IFN-γ-producing CD4+ T cells from the spleen of T. congolense-infected mice. Furthermore, MDSCs from T. congolense-infected mice directly suppressed CD4+ T cell proliferation in a coculture setting. This suppressive effect was abolished by the arginase-1 inhibitor, Nω-hydroxy-nor-l-arginine (nor-NOHA), indicating that MDSCs suppress CD4+ T cell proliferation and function in an arginase-1-dependent manner. Indeed, depletion of MDSCs during infection led to control of the first wave of parasitemia and prolonged survival of infected mice. This was also associated with increased CD4+ T cell proliferation and IFN-γ production. Taken together, our findings identify an important role of MDSCs in the pathogenesis of experimental T. congolense infection via suppression of T cell proliferative and effector cytokine responses in an arginase-1-dependent manner.

The complement receptor CRIg dominates clearance of intravascular parasites during African trypanosome infection

Abstract Kupffer cells (KCs), the liver resident macrophages, play a prominent role in clearance of blood-borne pathogens. The mechanisms by which KCs engulf circulating parasites such as African trypanosomes have yet to be determined. Here we show that depletion of KCs resulted in uncontrolled parasitemia in mice infected with Trypanosoma congolense, indicating the essential role of KCs in clearance of intravascular parasites. By using intravital microscopy, we further investigated the dynamics of interactions of KCs with circulating T. congolense in real-time. The results demonstrate that KCs catch circulating parasites in the presence of specific IgM and IgG antibodies, but fail to do so in the absence of specific antibodies. Complement C3 is critically involved in the capture of the parasites mediated by both IgM and IgG. We further demonstrate that complement receptor CRIg, but not CR3, is crucial for KCs to catch the parasites. In support of the findings gained by in vivo imaging, mice deficient of C3 or CRIg, but not CR3, could not control the first wave of parasitemia, and had a dramatic reduced survival time compared to wild-type mice following infection with T. congolense (10 days vs over 100 days). Collectively, our data demonstrate that CRIg play a dominant role in the clearance of circulating parasites by KCs in an antibody dependent manner.

The B cell adaptor molecule Bam32 is critically important for optimal antibody response and resistance to Trypanosoma congolense infection in mice.

BackgroundBam32, a 32 kDa adaptor molecule, plays important role in B cell receptor signalling, T cell receptor signalling and antibody affinity maturation in germinal centres. Since antibodies against trypanosome variant surface glycoproteins (VSG) are critically important for control of parasitemia, we hypothesized that Bam32 deficient (Bam32-/-) mice would be susceptible to T. congolense infection.Methodology/Principal FindingsWe found that T. congolense-infected Bam32-/- mice successfully control the first wave of parasitemia but then fail to control subsequent waves and ultimately succumb to their infection unlike wild type (WT) C57BL6 mice which are relatively resistant. Although infected Bam32-/- mice had significantly higher hepatomegaly and splenomegaly, their serum AST and ALT levels were not different, suggesting that increased liver pathology may not be responsible for the increased susceptibility of Bam32-/- mice to T. congolense. Using direct ex vivo flow cytometry and ELISA, we show that CD4+ T cells from infected Bam32-/- mice produced significantly increased amounts of disease-exacerbating proinflammatory cytokines (including IFN-γ, TNF-α and IL-6). However, the percentages of regulatory T cells and IL-10-producing CD4+ cells were similar in infected WT and Bam32-/- mice. While serum levels of parasite-specific IgM antibodies were normal, the levels of parasite-specific IgG, (particularly IgG1 and IgG2a) were significantly lower in Bam32-/- mice throughout infection. This was associated with impaired germinal centre response in Bam32-/- mice despite increased numbers of T follicular helper (Tfh) cells. Adoptive transfer studies indicate that intrinsic B cell defect was responsible for the enhanced susceptibility of Bam32-/- mice to T. congolense infection.Conclusions/SignificanceCollectively, our data show that Bam32 is important for optimal anti-trypanosome IgG antibody response and suppression of disease-promoting proinflammatory cytokines and its deficiency leads to inability to control T. congolense infection in mice.

A Trypanosoma brucei Kinesin Heavy Chain Promotes Parasite Growth by Triggering Host Arginase Activity

BackgroundIn order to promote infection, the blood-borne parasite Trypanosoma brucei releases factors that upregulate arginase expression and activity in myeloid cells.Methodology/Principal findingsBy screening a cDNA library of T. brucei with an antibody neutralizing the arginase-inducing activity of parasite released factors, we identified a Kinesin Heavy Chain isoform, termed TbKHC1, as responsible for this effect. Following interaction with mouse myeloid cells, natural or recombinant TbKHC1 triggered SIGN-R1 receptor-dependent induction of IL-10 production, resulting in arginase-1 activation concomitant with reduction of nitric oxide (NO) synthase activity. This TbKHC1 activity was IL-4Rα-independent and did not mirror M2 activation of myeloid cells. As compared to wild-type T. brucei, infection by TbKHC1 KO parasites was characterized by strongly reduced parasitaemia and prolonged host survival time. By treating infected mice with ornithine or with NO synthase inhibitor, we observed that during the first wave of parasitaemia the parasite growth-promoting effect of TbKHC1-mediated arginase activation resulted more from increased polyamine production than from reduction of NO synthesis. In late stage infection, TbKHC1-mediated reduction of NO synthesis appeared to contribute to liver damage linked to shortening of host survival time.ConclusionA kinesin heavy chain released by T. brucei induces IL-10 and arginase-1 through SIGN-R1 signaling in myeloid cells, which promotes early trypanosome growth and favors parasite settlement in the host. Moreover, in the late stage of infection, the inhibition of NO synthesis by TbKHC1 contributes to liver pathogenicity.

Malaria Sporozoite Challenge Model Comes of Age

Invited Commentary on ‘Efficacy of preerythrocytic and blood-stage malaria vaccines can be assessed in small sporozoite challenge trials in human volunteers’, Roestenberg et al. Journal of Infectious Diseases 2012. For decades a small group of laboratories have been quietly but steadily testing experimental malaria vaccines in human volunteers and confirming their efficacy by exposing these volunteers to the bite of infected mosquitoes. A few days following the bite of the mosquitoes the volunteers are followed closely for onset of symptoms and for the presence of the parasite in the peripheral blood by preparing blood smears that are examined microscopically. The requirements for a successful challenge that infects 100% of non-immunized volunteers, such as the number of mosquito bites and the length of time the mosquitoes are allowed to feed, were worked out empirically initially.1 The sample size of these sporozoite challenges also was driven by limitations in logistics as well as by ethical concerns about the safety of volunteers.2 Despite these limitations, the cumulative observation through the years has been that the results of these trials accurately predicted success or failure in the field. The advent of quantitative PCR has allowed a more accurate estimation of the parasitemias in these individuals than was ever possible microscopically as well as the calculation of the parasite multiplication rates, making it possible to determine the effect of immunization on these parameters. This is important because pre-erythrocytic vaccines which just target sporozoites and liver stages of the parasite would only have an impact on the first wave of parasitemia coming out of the liver. On the other hand, blood stage vaccines that target merozoites are not predicted to impact the first wave of parasitemia but would affect the multiplication rate in blood. Thus, the addition of quantitative PCR has allowed scientists to determine the effect of a vaccine on the parasite load in the liver and on the multiplication rate in blood. One recent example of the usefulness of this approach was the finding that the AMA-1 vaccine resulted in a reduction of the first wave of parasites.3 A subsequent preliminary trial in Africa also seemed to suggest that this vaccine can offer some protection against vaccine strain parasites.4 With the use of statistical simulation, Roestenberg et al.5 have estimated that with the addition of quantitative PCR sporozoite challenge studies, although small, do have sufficient power to detect clinically relevant differences between immunized volunteers and controls such as 90% or greater inhibition of parastemia or multiplication rate. Some have argued that blood stage vaccines that target the red cell invasive form of the parasite should be tested in the field in order to better observe the effect of vaccine-induced immunity over a period of time. However, the limited published experience and now the analysis by Roestenberg et al.5 seem to argue that the sporozoite challenge model can provide a window into the likelihood that these vaccines can confer protection. The results of Roestenberg and colleagues are welcome news in an era when resources and funding for large field trials are very limited. This is illustrated in the accompanying commentary by Doolan.6 They support the paradigm of subjecting all malaria vaccines to sporozoite challenge trials prior to committing to large field studies.

Genital lesions in male red fronted gazelles (Gazella rufifrons) experimentally infected with Trypanosoma brucei and the effect of melarsamine hydrochloride (Cymelarsan®) and diminazene aceturate (Berenil®) in its treatment

Thirty red fronted gazelles (Gazella rufifrons) were used to assess the genital lesions associated with trypanosomosis and the efficacy of melarsamine hydrochloride (Cymelarsan®) and diminazene aceturate (Berenil®) in the treatment of the condition. The animals were divided into 6 equal groups (A–F). Animals in groups A–E were infected with Trypanosoma brucei, and later treated on day 8 post infection (p.i.) with either melarsamine hydrochloride (Cymelarsan®) at 0.3 mg/kg (Group A) and 0.6 mg/kg (Group B) or diminazene aceturate (Berenil®) at 3.5 mg/kg (Group C) and 7.0 mg/kg (Group D). Animals in group E remained untreated while group F served as healthy controls. Parasitaemia was established by day 8 p.i. in all infected groups and eliminated by day 16 following treatment on day 8 p.i. with melarsamine hydrochloride (Cymelarsan®) (Groups A and B) or diminazene aceturate (Berenil®) (Group D). On the other hand, diminazene aceturate treatment (Berenil®) on day 8 p.i. at 3.5 mg/kg (Group C) caused a temporary disappearance of parasites from the circulation by day 16 p.i. but there was a relapse parasitaemia on day 44 with a peak count of 500 ± 2.79 × 103 parasites/μL of blood by day 52 p.i. In the infected/untreated group (E), parasitaemia fluctuated but attained the same peak as Group C by day 52 p.i. Increase in body temperatures (40.5 ± 3.16 - 42.8 ± 3.25 °C) occurred during the first wave of parasitaemia but declined to pre-infection values from day 28 p.i. in Groups A, B and D. In Groups C and E, there was a second wave of parasitaemia (P < 0.05) with peak counts of 42.4 ± 0.81 × 103/μL and 41.8 ± 0.80 × 103/μL respectively by day 52 p.i. A significant (P < 0.05) decline in packed cell volume was also noted by day 52 p.i. The major clinical signs observed in Groups C and E were pyrexia, inappetance, emaciation, anaemia, dullness, starry hair coat, pallor of buccal and ocular mucous membranes. Similarly, in Groups C and E, the testicles appeared oedematous and painful to touch with degenerative changes, morphological sperm abnormalities and oligospermia with 2.0% and 0% sperm reserves respectively. Sperm reserve was 100% in Groups A, B and D. It is therefore, concluded that trypanosomosis can cause serious infertility in male red fronted gazelles and that early treatments with melarsamine hydrochloride (Cymelarsan®) at 0.3 and 0.6 mg/kg body weight or diminazene aceturate (Berenil®) at 7.0 mg/kg body weight may prevent such effects.

Acute Disruption of Bone Marrow B Lymphopoiesis and Apoptosis of Transitional and Marginal Zone B Cells in the Spleen following a Blood-StagePlasmodium chabaudiInfection in Mice

B cells and antibodies are essential for the protective immune response against a blood-stage Plasmodium infection. Although extensive research has focused on memory as well as plasma B-cell responses during infection, little is known about how malaria affects B-cell development and splenic maturation into marginal zone B (MZB) and follicular B (FoB) cells. In this study, we show that acute Plasmodium chabaudi AS infection in C57Bl/6 mice causes severe disruption of B lymphopoiesis in the bone marrow, affecting in particular pro-, pre-, and immature B cells as well as the expression of the bone marrow B-cell retention chemokine CXCL12. In addition, elevated apoptosis of transitional T2 and marginal zone (MZ) B cells was observed during and subsequent to the control of the first wave of parasitemia. In contrast, Folllicular (Fo) B cells levels were retained in the spleen throughout the infection, suggesting that these are essential for parasite clearance and proper infection control.

Mechanisms Controlling Anaemia in Trypanosoma congolense Infected Mice

Background Trypanosoma congolense are extracellular protozoan parasites of the blood stream of artiodactyls and are one of the main constraints on cattle production in Africa. In cattle, anaemia is the key feature of disease and persists after parasitaemia has declined to low or undetectable levels, but treatment to clear the parasites usually resolves the anaemia.Methodology/Principal FindingsThe progress of anaemia after Trypanosoma congolense infection was followed in three mouse strains. Anaemia developed rapidly in all three strains until the peak of the first wave of parasitaemia. This was followed by a second phase, characterized by slower progress to severe anaemia in C57BL/6, by slow recovery in surviving A/J and a rapid recovery in BALB/c. There was no association between parasitaemia and severity of anaemia. Furthermore, functional T lymphocytes are not required for the induction of anaemia, since suppression of T cell activity with Cyclosporin A had neither an effect on the course of infection nor on anaemia. Expression of genes involved in erythropoiesis and iron metabolism was followed in spleen, liver and kidney tissues in the three strains of mice using microarrays. There was no evidence for a response to erythropoietin, consistent with anaemia of chronic disease, which is erythropoietin insensitive. However, the expression of transcription factors and genes involved in erythropoiesis and haemolysis did correlate with the expression of the inflammatory cytokines Il6 and Ifng.Conclusions/SignificanceThe innate immune response appears to be the major contributor to the inflammation associated with anaemia since suppression of T cells with CsA had no observable effect. Several transcription factors regulating haematopoiesis, Tal1, Gata1, Zfpm1 and Klf1 were expressed at consistently lower levels in C57BL/6 mice suggesting that these mice have a lower haematopoietic capacity and therefore less ability to recover from haemolysis induced anaemia after infection.

Development of a rodent model for late stage rhodesian sleeping sickness

A mouse model of Trypanosoma brucei rhodesiense that can be used in pathogenesis and drug studies for Human African Trypanosomosis (HAT) has so far not been developed. In an attempt to develop such a model, a study was undertaken to determine the clinical and pathological changes in mice infected with stock of T. b. rhodesiense (KETRI 2357) and its clone (KETRI 3741). The infections resulted in a mean prepatent period of 3 (range 3-4) days for KETRI 2537 and 4 (range 3-5) days for KETRI 3741. The first wave of parasitaemia for both isolates reached peak (antilog 8.7) between 6-8 DPI and was followed by secondary latency. Thereafter, the parasitaemia increased and remained high, with slight fluctuations. The mean survival period was 36 (range: 7-45) and 50 (18-82) days for the mice infected with KETRI 2537 and KETRI 3741 respectively. At post mortem, the spleens were enlarged and there was generalized congestion in most organs. Histopathological changes were more severe in the parent stock compared to its clone. Meningoencephalitis was observed in mice infected with KETRI 3741 that survived up to 77 days. These studies demonstrate the development of late stage disease in mice infected with T. b. rhodesiense, with potential for use as a model of sleeping sickness.

Experimental Trypanosoma evansi infection in South American coati ( Nasua nasua): hematological, biochemical and histopathological changes

The course of an experimental Trypanosoma evansi infection in coatis ( Nasua nasua, carnivora, Procyonidae) was followed for 262 days. Hematological analysis of the infected coatis revealed a marked decline in hemoglobin, packed-cell volume, and total erythrocyte count. An intense anemia followed the first wave of parasitemia and persisted until the end of the experimental period. Biochemical analysis showed increased serum levels of alanine aminotransferase and aspartate aminotransferase and decreased albumin. The main histopathological features consisted of myocarditis with the presence of degenerate cardiac fibers and meningoencephalitis. This study has shown that coatis infected with T. evansi develop a chronic disease.

Cytokines and antibody responses during Trypanosoma congolense infections in two inbred mouse strains that differ in resistance.

We studied IL-4, IL-10 and IFN-gamma secretion by splenocytes and the plasma levels of different isotypes of antibodies against various antigens of Trypanosoma congolense in highly susceptible BALB/c and relatively resistant C57BL/6 mice during the early course of infection with T. congolense. The patterns of appearance of cytokine spotforming cells in the spleens were essentially similar in the two mouse strains although higher numbers were detected in the spleens of BALB/c than C57BL/6 mice on some days post-infection. However, the amount of IL-4, IL-10 and IFN-gamma secreted into the culture fluids was dramatically different. From day 4 forward, splenocytes from BALB/c mice secreted very high levels of these cytokines. In contrast, splenocytes from infected C57BL/6 mice did not secrete detectable levels of IL-4 throughout the period tested. The secretion of IL-10 and IFN-gamma by C57BL/6 splenocytes only became appreciable on day 6 and was down-regulated by day 8, when the first wave of parasitaemia was being controlled. At days 6-8, splenocytes from infected C57BL/6 mice secreted two-fold higher amounts of IL-12 p40 than those from BALB/c mice. Infected BALB/c mice mounted an earlier IgM antibody response to variant surface glycoprotein (VSG), formalin-fixed T. congolense and whole T. congolense lysates than did infected C57BL/6 mice. However, they failed to make any detectable IgG3 and IgG2a antibody responses to these antigens whereas infected C57BL/6 mice made strong IgG3 and IgG2a responses. We speculate that enhanced resistance against T. congolense infections in mice may be mediated by IL-12 dependent synthesis of IgG2 antibodies to VSG and possibly also common trypanosomal antigens.

Cytokines and antibody responses during Trypanosoma congolense infections in two inbred mouse strains that differ in resistance

We studied IL‐4, IL‐10 and IFN‐γ secretion by splenocytes and the plasma levels of different isotypes of antibodies against various antigens of Trypanosoma congolense in highly susceptible BALB/c and relatively resistant C57BL/6 mice during the early course of infection with T. congolense. The patterns of appearance of cytokine spot‐forming cells in the spleens were essentially similar in the two mouse strains although higher numbers were detected in the spleens of BALB/c than C57BL/6 mice on some days post‐infection. However, the amount of IL‐4, IL‐10 and IFN‐γ secreted into the culture fluids was dramatically different. From day 4 forward, splenocytes from BALB/c mice secreted very high levels of these cytokines. In contrast, splenocytes from infected C57BL/6 mice did not secrete detectable levels of IL‐4 throughout the period tested. The secretion of IL‐10 and IFN‐γ by C57BL/6 splenocytes only became appreciable on day 6 and was down‐regulated by day 8, when the first wave of parasitaemia was being controlled. At days 6–8, splenocytes from infected C57BL/6 mice secreted two‐fold higher amounts of IL‐12 p40 than those from BALB/c mice. Infected BALB/c mice mounted an earlier IgM antibody response to variant surface glycoprotein (VSG), formalin‐fixed T. congolense and whole T. congolense lysates than did infected C57BL/6 mice. However, they failed to make any detectable IgG3 and IgG2a antibody responses to these antigens whereas infected C57BL/6 mice made strong IgG3 and IgG2a responses. We speculate that enhanced resistance against T. congolense infections in mice may be mediated by IL‐12 dependent synthesis of IgG2 antibodies to VSG and possibly also common trypanosomal antigens.

Effect of acute Trypanosoma vivax infection on cattle erythrocyte glutathione and susceptibility to in vitro peroxidation

During acute Trypanosoma vivax infection of calves, produced by intravenous inoculation, the mean packed cell volume and red blood cell counts of the infected animals decreased significantly ( P < 0.05) between Days 6 and 13 post-infection (pi). The moderately severe normocytic anaemia started to develop during the first wave of parasitaemia which occurred from Day 2 pi and peaked between Days 4 and 5 pi. The mean erythrocyte glutathione (GSH) concentration of the infected calves decreased significantly ( P < 0.05) from 58 ± 11.4 mg 100ml −1 red blood cells (RBC) on Day 0 pi to 44.5 ± 12.8 mg 100ml −1 RBC on Day 5 pi. As the GSH values recovered on Day 6 pi and increased thereafter, another slight decrease ( P > 0.05) in GSH concentration occurred on Day 12 pi at the second peak of parasitaemia followed by a significant ( P < 0.05) increase to 79.1 ± 14.6 mg 100ml −1 RBC on Day 13 pi. In the uninfected calves, the mean GSH values ranged from 47.7 ± 7.0 to 60.8 ± 6.8 mg 100ml −1 RBC. When washed, erythrocytes of the infected and uninfected calves were separately challenged with hydrogen peroxide. They produced comparable amounts of thiobarbituric acid reactive substances as a measure of by-products of lipid peroxidation. This suggested that the ability of the erythrocytes to prevent peroxidative injury was not reduced, because GSH regeneration was probably enhanced and the antioxidant capacity of the erythrocytes was maintained.

The pathophysiology of ovine trypanosomosis: haemotological and blood biochemical changes

The course of Trypanosoma congolense infection in sheep was followed for 96 days. Infected animals developed fluctuating parasitaemia, macrocytic normochromic anaemia and leucocytosis which was principally a lymphocytosis. Following treatment with the trypanocidal drug, diminazene aceturate at 84 days after infection, the haematological values returbed to normal within 12 days. Infected sheep developed hypocholesterolaemia and hypophospholipidaemia leading to a reduction in total serum lipids. This study has shown that sheep infected with T. congolense develop anaemia, the onset of which follows the first wave of parasitaemia. The changes in blood lipids observed in infected sheep appeared to be related to the intensity and duration of parasitaemia.

Parasitémie et manifestations cliniques chez des chiens infectés par &lt;em&gt;Trypanosoma brucei&lt;/em&gt;

Four dogs were infected with Trypanosoma brucei (Mkar strain) while another four were used as uninfected controls. Two of the dogs showed acute disease and died in the first wave of parasitaemia on days 7 and 8 post infection (PI) while the other two died from the sub-acute disease on days 24 and 28 PI corresponding to the second wave of parasitaemia. In the first wave of parasitaemia there was a sharp decrease in the packed cell volume, red blood cell, haemoglobin, total leucocytes, eosinophil, neutrophil and lymphocyte values, but during the period of low parasitaemia there was a slight recovery of the values of total leucocytes and lymphocytes although these and the other values showed a continuous decrease during the second wave of parasitaemia. In contrast, there was a consistent monocytosis in both acute and sub-acute diseases. The general picture was that of loss of condition, anaemia, leucopenia, monocytosis, ocular impairment, elevated temperature, pulse and respiratory rates, the difference between the acute and sub-acute diseases being in the degree of intensity. The degree of anaemia noted and the circulatory disturbances associated with the infection could have caused the death of all the infected dogs.

A light and electron microscopic study of changes in blood and bone marrow in acute hemorrhagic Trypanosoma vivax infection in calves.

Eleven 6-month-old calves were tsetse fly challenged with a stock of Trypanosoma vivax (IL 2337) that causes hemorrhagic infection. The calves were randomly euthanatized every 4 to 6 days; two other calves served as controls. Peripheral blood changes included anemia, thrombocytopenia, and an initial leukopenia. Later in the course of infection, leukocytosis associated with lymphocytosis and neutropenia developed. Moderate reticulocytosis (highest mean count 3.6 +/- 3.7%, maximum count 9.4%) accompanied the first wave of parasitemia, but poor response (highest mean 0.4 +/- 0.0%) occurred during the second wave, despite the persistence of severe anemia. Light microscopic examination of bone marrow samples showed a drop in the myeloid: erythroid ratio with a decrease in granulocytes, particularly metamyelocytes, bands, and segmenters. Increase in lymphocyte counts corresponded with the appearance of lymphoid nodules within the marrow. Megakaryocytic volume increased significantly in infected animals, and some megakaryocytes showed emperipolesis of red cells, neutrophils, and lymphocytes. Transmission electron microscopic examination of the bone marrow revealed that trypanosomes had crossed the sinusoidal endothelium into the hematopoietic compartment as early as the second day of parasitemia. Macrophages proliferated in the bone marrow; and from the second day of parasitemia until the end of the experimental infection, on day 46, the macrophages had phagocytosed normoblasts, eosinophil and neutrophil myelocytes, metamyelocytes, bands, and segmenters, as well as reticulocytes, erythrocytes, and thrombocytes. Therefore, dyserythropoiesis and dysgranulocytopoiesis were responsible, in part, for the observed anemia and granulocytopenia, respectively.