The brain as a source of relapsing Trypanosoma brucei infection in mice after chemotherapy

Treatment of cutaneous Balamuthia mandrillaris infection with diminazene aceturate: a report of 4 cases

Four cases of cutaneous Balamuthia mandrillaris infection were treated with diminazene aceturate. One patient was cured with mainly monotherapy, 2 patients were cured with diminazene aceturate and excision, and 1 patient died of drug induced liver damage. This is the first report of Balamuthia mandrillaris infection treated with diminazene aceturate.

Angiotensin-converting enzyme 2 activator, DIZE in the basolateral amygdala attenuates the tachycardic response to acute stress by modulating glutamatergic tone

The basolateral amygdala (BLA) is critical in the control of the sympathetic output during stress. Studies demonstrated the involvement of the renin-angiotensin system components in the BLA. Angiotensin-(1-7) [Ang-(1-7)], acting through Mas receptors, reduces stress effects. Considering that angiotensin-converting enzyme 2 (ACE2) is the principal enzyme for the production of Ang-(1-7), here we evaluate the cardiovascular reactivity to acute stress after administration of the ACE2 activator, diminazene aceturate (DIZE) into the BLA. We also tested whether systemic treatment with DIZE could modify synaptic activity in the BLA and its effect directly on the expression of the N-methyl-d-aspartate receptors (NMDARs) in NG108 neurons in-vitro. Administration of DIZE into the BLA (200 pmol/100 nL) attenuated the tachycardia to stress (ΔHR, bpm: vehicle = 103 ± 17 vs DIZE = 49 ± 7 p = 0.018); this effect was inhibited by Ang-(1-7) antagonist, A-779 (ΔHR, bpm: DIZE = 49 ± 7 vs A-779 + DIZE = 100 ± 15 p = 0.04). Systemic treatment with DIZE attenuated the excitatory synaptic activity in the BLA (Frequency (Hz): vehicle = 2.9 ± 0.4 vs. DIZE =1.8 ± 0.3 p < 0.04). NG108 cells treated with DIZE demonstrated decreased expression of l subunit NMDAR-NR1 (NR1 expression (a.u): control = 0.534 ± 0.0593 vs. DIZE = 0.254 ± 0.0260) of NMDAR and increases of Mas receptors expression. These data demonstrate that DIZE attenuates the tachycardia evoked by acute stress. This effect results from a central action in the BLA involving activation of Mas receptors. The ACE2 activation via DIZE treatment attenuated the frequency of excitatory synaptic activity in the basolateral amygdala and this effect can be related with the decreases of the NMDAR-NR1 receptor expression.

Molecular detection of 7SL-derived small RNA is a promising alternative for trypanosomosis diagnosis

Equine trypanosomosis comprises different parasitic diseases caused by protozoa of the subgenus Trypanozoon: Trypanosoma equiperdum (causative agent of dourine), Trypanosoma brucei (nagana) and Trypanosoma evansi (surra). Due to the absence of a vaccine and the lack of efficacy of the few available drugs, these diseases represent a major health and economic problem for international equine trade. Development of affordable, sensitive and specific diagnostic tests is therefore crucial to ensure the control of these diseases. Recently, it has been shown that a small RNA derived from the 7SL gene (7SL-sRNA) is produced in high concentrations in sera of cattle infected with Trypanosoma congolense, Trypanosoma vivax and Trypanosoma brucei. Our objective was to determine whether 7SL-sRNA could serve as a marker of active infection in equids experimentally infected with Trypanosoma equiperdum by analysing the sensitivity, specificity and stability of the 7SL-sRNA. Using a two-step RT-qPCR, we were able to detect the presence of 7SL-sRNA between 2 and 7 days post-infection, whereas seroconversion was detected by complement fixation test between 5 and 14 days post-infection. There was a rapid loss of 7SL-sRNA signal from the blood of infected animals one day post-trypanocide treatment. The 7SL-sRNA RT-qPCR allowed an early detection of a treatment failure revealed by glucocorticoid-induced immunosuppression. In addition, the 7SL-sRNA remains detectable in positive sera after 7 days of storage at either 4°C, room temperature or 30°C, suggesting that there is no need to refrigerate serum samples before analysis. Our findings demonstrate continual detection of 7SL-sRNA over an extended period of experimental infection, with signals detected more than six weeks after inoculation. The detection of a strong and consistent 7SL-sRNA signal even during subpatent parasitemia and the early detection of treatment failure highlight the very promising nature of this new diagnostic method.

Tissue tropism in parasitic diseases

Parasitic diseases, such as sleeping sickness, Chagas disease and malaria, remain a major cause of morbidity and mortality worldwide, but particularly in tropical, developing countries. Controlling these diseases requires a better understanding of host-parasite interactions, including a deep appreciation of parasite distribution in the host. The preferred accumulation of parasites in some tissues of the host has been known for many years, but recent technical advances have allowed a more systematic analysis and quantifications of such tissue tropisms. The functional consequences of tissue tropism remain poorly studied, although it has been associated with important aspects of disease, including transmission enhancement, treatment failure, relapse and clinical outcome. Here, we discuss current knowledge of tissue tropism in Trypanosoma infections in mammals, describe potential mechanisms of tissue entry, comparatively discuss relevant findings from other parasitology fields where tissue tropism has been extensively investigated, and reflect on new questions raised by recent discoveries and their potential impact on clinical treatment and disease control strategies.

Validation of a new experimental model for assessing drug efficacy against infection with Trypanosoma equiperdum in horses

Trypanosoma equiperdum, the causative agent of dourine, may affect the central nervous system, leading to neurological signs in infected horses. This location protects the parasite from most (if not all) existing chemotherapies. In this context, the OIE terrestrial code considers dourine as a non-treatable disease and imposes a stamping-out policy for affected animals before a country may achieve its dourine-free status. The use of practices as drastic as euthanasia remains controversial, but the lack of a suitable tool for studying a treatment's efficacy against dourine hampers the development of an alternative strategy for dourine infection management. The present study reports on the development of an experimental infection model for assessing drug efficacy against the nervous form of dourine. The model combines the infection of horses by Trypanosoma equiperdum and the search for trypanosomes in the cerebrospinal fluid (CSF) through an ultrasound-guided cervical sampling protocol. After a development phase involving four horses, we established an infection model that consists of inoculating 5 × 10⁴T. equiperdum OVI parasites intravenously into adult Welsh mares (Equus caballus). To evaluate its efficacy, eight horses were infected according to this model. In all these animals, parasites were observed in the blood at 2 days post-inoculation (p.i.) and in CSF (12.5 ± 1.6 days p.i.) and seroconversion was detected (8.25 ± 0.5 days p.i.). All eight animals also developed fever (rectal temperature > 39 °C), low hematocrit (< 27%), and ventral edema (7.9 ± 2.0 days p.i.), together with other inconstant clinical signs such as edema of the vulva (six out of eight horses) or cutaneous plaques (three out of eight horses). This model provides a robust infection protocol that induces an acute trypanosome infection and that allows parasites to be detected in the CSF of infected horses within a period of time compatible with animal experimentation constraints. We conclude that this model constitutes a suitable tool for analyzing the efficacy of anti-Trypanosoma drugs and vaccines.

Human African trypanosomiasis: How do the parasites enter and cause dysfunctions of the nervous system in murine models?

In this review we describe how Trypanosoma brucei brucei, a rodent pathogenic strain of African trypanosomes, can invade the nervous system, first by localization to the choroid plexus, the circumventricular organs (CVOs) and peripheral ganglia, which have fenestrated vessels, followed by crossing of the blood-brain barrier (BBB) into the white matter, hypothalamus, thalamus and basal ganglia. White blood cells (WBCs) pave the way for the trypanosome neuroinvasion. Experiments with immune deficient mice show that the invasion of WBCs is initiated by the toll-like receptor 9, followed by an augmentation phase that depends on the cytokine IFN-γ and the chemokine CXCL10. Nitric oxide (NO) derived from iNOS then prevents a break-down of the BBB and non-regulated passage of cells. This chain of events is relevant for design of better diagnostic tools to distinguish the different stages of the disease as well as for better understanding of the pathogenesis of the nervous system dysfunctions, which include circadian rhythm changes with sleep pattern disruption, pain syndromes, movement disorders and mental disturbances including dementia.

Intravital imaging of a massive lymphocyte response in the cortical dura of mice after peripheral infection by trypanosomes

Peripheral infection by Trypanosoma brucei, the protozoan responsible for sleeping sickness, activates lymphocytes, and, at later stages, causes meningoencephalitis. We have videoed the cortical meninges and superficial parenchyma of C56BL/6 reporter mice infected with T.b.brucei. By use of a two-photon microscope to image through the thinned skull, the integrity of the tissues was maintained. We observed a 47-fold increase in CD2+ T cells in the meninges by 12 days post infection (dpi). CD11c+ dendritic cells also increased, and extravascular trypanosomes, made visible either by expression of a fluorescent protein, or by intravenous injection of furamidine, appeared. The likelihood that invasion will spread from the meninges to the parenchyma will depend strongly on whether the trypanosomes are below the arachnoid membrane, or above it, in the dura. Making use of optical signals from the skull bone, blood vessels and dural cells, we conclude that up to 40 dpi, the extravascular trypanosomes were essentially confined to the dura, as were the great majority of the T cells. Inhibition of T cell activation by intraperitoneal injection of abatacept reduced the numbers of meningeal T cells at 12 dpi and their mean speed fell from 11.64 ± 0.34 μm/min (mean ± SEM) to 5.2 ± 1.2 μm/min (p = 0.007). The T cells occasionally made contact lasting tens of minutes with dendritic cells, indicative of antigen presentation. The population and motility of the trypanosomes tended to decline after about 30 dpi. We suggest that the lymphocyte infiltration of the meninges may later contribute to encephalitis, but have no evidence that the dural trypanosomes invade the parenchyma.

African trypanosomes are motile parasites that cause sleeping sickness. They multiply first in the blood then cause death mainly by effects on the brain: immune system cells, including T cells and dendritic cells, play major roles in this. Thinking we might see the attack on the brain, we infected mice with trypanosomes and used a two-photon microscope, which allowed us to image the superficial brain and the delicate tissue between the skull and the brain called the meninges without making a hole in the skull. The mice (which were anesthetized) had been genetically modified so that T cells and dendritic cells were fluorescent, as were the trypanosomes. We did not notice much happening in the brain itself, but in the meninges, in a compartment called the dura, huge numbers of T cells and dendritic cells appeared. Trypanosomes also moved from the blood into this compartment. Since T cells, dendritic cells and trypanosomes had not been videoed in the meninges before, we began by observing them carefully: their numbers, their movements and their interactions. The accumulation of lymphocytes is a sign of meningitis, a feature of infection by a wide range of pathogens and our results suggest interesting future work.

A panel of Trypanosoma brucei strains tagged with blue and red-shifted luciferases for bioluminescent imaging in murine infection models

Background

Genetic engineering with luciferase reporter genes allows monitoring Trypanosoma brucei (T.b.) infections in mice by in vivo bioluminescence imaging (BLI). Until recently, luminescent T.b. models were based on Renilla luciferase (RLuc) activity. Our study aimed at evaluating red-shifted luciferases for in vivo BLI in a set of diverse T.b. strains of all three subspecies, including some recently isolated from human patients.

Methodology/Principal findings

We transfected T.b. brucei, T.b. rhodesiense and T.b. gambiense strains with either RLuc, click beetle red (CBR) or Photinus pyralis RE9 (PpyRE9) luciferase and characterised their in vitro luciferase activity, growth profile and drug sensitivity, and their potential for in vivo BLI. Compared to RLuc, the red-shifted luciferases, CBR and PpyRE9, allow tracking of T.b. brucei AnTaR 1 trypanosomes with higher details on tissue distribution, and PpyRE9 allows detection of the parasites with a sensitivity of at least one order of magnitude higher than CBR luciferase. With CBR-tagged T.b. gambiense LiTaR1, T.b. rhodesiense RUMPHI and T.b. gambiense 348 BT in an acute, subacute and chronic infection model respectively, we observed differences in parasite tropism for murine tissues during in vivo BLI. Ex vivo BLI on the brain confirmed central nervous system infection by all luminescent strains of T.b. brucei AnTaR 1, T.b. rhodesiense RUMPHI and T.b. gambiense 348 BT.

Conclusions/Significance

We established a genetically and phenotypically diverse collection of bioluminescent T.b. brucei, T.b. gambiense and T.b. rhodesiense strains, including drug resistant strains. For in vivo BLI monitoring of murine infections, we recommend trypanosome strains transfected with red-shifted luciferase reporter genes, such as CBR and PpyRE9. Red-shifted luciferases can be detected with a higher sensitivity in vivo and at the same time they improve the spatial resolution of the parasites in the entire body due to the better kinetics of their substrate D-luciferin.

Research on African trypanosomes heavily relies on rodent infection models. One way to reduce the number of laboratory rodents used in each experiment and effectively follow the progression of the infection in the same animals is to use genetically modified trypanosomes that allow monitoring of the infection over time with bioluminescence technology, without having to sacrifice the animals at multiple time points. In this study, we were able to establish a collection of bioluminescent strains of all three subspecies of Trypanosoma brucei (T.b.), including T.b. gambiense and T.b. rhodesiense that cause human African trypanosomiasis (HAT) or sleeping sickness. Making use of bioluminescence assays, we demonstrate the diversity of our collection in terms of in vitro and in vivo growth, drug sensitivity and in vivo parasite distribution, including central nervous system tropism. Growth characteristics and drug sensitivity are not affected by the genetic modification with luciferase reporter genes. Trypanosome strains transfected with red-shifted luciferase reporter genes have several advantages compared to the corresponding blue luciferase modified strains. Red light is less absorbed in the blood than blue light, which should lead to higher sensitivity of detection. Furthermore, the substrates that drive the light reaction are better distributed through the body for the red luciferase than for the blue luciferase, which greatly improves spatial resolution of the infection.

Motility and more: the flagellum of Trypanosoma brucei

Trypanosoma brucei is a pathogenic unicellular eukaryote that infects humans and other mammals in sub-Saharan Africa. A central feature of trypanosome biology is the single flagellum of the parasite, which is an essential and multifunctional organelle that facilitates cell propulsion, controls cell morphogenesis and directs cytokinesis. Moreover, the flagellar membrane is a specialized subdomain of the cell surface that mediates attachment to host tissues and harbours multiple virulence factors. In this Review, we discuss the structure, assembly and function of the trypanosome flagellum, including canonical roles in cell motility as well as novel and emerging roles in cell morphogenesis and host-parasite interactions.

Tryps and trips: cell trafficking across the 100-year-old blood-brain barrier

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The blood–brain barrier (BBB) was discovered one century ago by the use of trypan dyes.

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The discovery initiated the targeted brain delivery of drugs.

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Trypan dyes were developed to kill African trypanosomes that cause sleeping sickness.

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Trypanosomes disclose cell trafficking in and out of the BBB.

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Disturbed gating at the BBB may cause neurodegeneration.

One hundred years ago, Edwin E. Goldmann discovered the blood–brain barrier (BBB) using trypan dyes. These dyes were developed and named by Paul Ehrlich during his search for drugs to kill African trypanosomes (extracellular parasites that cause sleeping sickness) while sparing host cells. For Ehrlich, this was the first strategy based on the ‘chemotherapy’ concept he had introduced. The discovery of the BBB revealed, however, the difficulties in drug delivery to the brain. Mechanisms by which parasites enter, dwell, and exit the brain currently provide novel views on cell trafficking across the BBB. These mechanisms also highlight the role of pericytes and endocytosis regulation in BBB functioning and in disrupted BBB gating, which may be involved in the pathogenesis of neurodegeneration.

Cyclical appearance of African trypanosomes in the cerebrospinal fluid: new insights in how trypanosomes enter the CNS

It is textbook knowledge that human infective forms of Trypanosoma brucei, the causative agent of sleeping sickness, enter the brain across the blood-brain barrier after an initial phase of weeks (rhodesiense) or months (gambiense) in blood. Based on our results using an animal model, both statements seem questionable. As we and others have shown, the first infection relevant crossing of the blood brain border occurs via the choroid plexus, i.e. via the blood-CSF barrier. In addition, counting trypanosomes in blood-free CSF obtained by an atlanto-occipital access revealed a cyclical infection in CSF that was directly correlated to the trypanosome density in blood infection. We also obtained conclusive evidence of organ infiltration, since parasites were detected in tissues outside the blood vessels in heart, spleen, liver, eye, testis, epididymis, and especially between the cell layers of the pia mater including the Virchow-Robin space. Interestingly, in all organs except pia mater, heart and testis, trypanosomes showed either a more or less degraded appearance of cell integrity by loss of the surface coat (VSG), loss of the microtubular cytoskeleton and loss of the intracellular content, or where taken up by phagocytes and degraded intracellularly within lysosomes. This is also true for trypanosomes placed intrathecally into the brain parenchyma using a stereotactic device. We propose a different model of brain infection that is in accordance with our observations and with well-established facts about the development of sleeping sickness.

Mouse infection and pathogenesis by Trypanosoma brucei motility mutants

The flagellum of Trypanosoma brucei is an essential and multifunctional organelle that drives parasite motility and is receiving increased attention as a potential drug target. In the mammalian host, parasite motility is suspected to contribute to infection and disease pathogenesis. However, it has not been possible to test this hypothesis owing to lack of motility mutants that are viable in the bloodstream life cycle stage that infects the mammalian host. We recently identified a bloodstream-form motility mutant in 427-derived T. brucei in which point mutations in the LC1 dynein subunit disrupt propulsive motility but do not affect viability. These mutants have an actively beating flagellum, but cannot translocate. Here we demonstrate that the LC1 point mutant fails to show enhanced cell motility upon increasing viscosity of the surrounding medium, which is a hallmark of wild type T. brucei, thus indicating that motility of the mutant is fundamentally altered compared with wild type cells. We next used the LC1 point mutant to assess the influence of trypanosome motility on infection in mice. Wesurprisingly found that disrupting parasite motility has no discernible effect on T. brucei bloodstream infection. Infection time-course, maximum parasitaemia, number of waves of parasitaemia, clinical features and disease outcome are indistinguishable between motility mutant and control parasites. Our studies provide an important step toward understanding the contribution of parasite motility to infection and a foundation for future investigations of T. brucei interaction with the mammalian host.

In vivo imaging of trypanosome-brain interactions and development of a rapid screening test for drugs against CNS stage trypanosomiasis

HUMAN AFRICAN TRYPANOSOMIASIS (HAT) MANIFESTS IN TWO STAGES OF DISEASE: firstly, haemolymphatic, and secondly, an encephalitic phase involving the central nervous system (CNS). New drugs to treat the second-stage disease are urgently needed, yet testing of novel drug candidates is a slow process because the established animal model relies on detecting parasitemia in the blood as late as 180 days after treatment. To expedite compound screening, we have modified the GVR35 strain of Trypanosoma brucei brucei to express luciferase, and have monitored parasite distribution in infected mice following treatment with trypanocidal compounds using serial, non-invasive, bioluminescence imaging. Parasites were detected in the brains of infected mice following treatment with diminazene, a drug which cures stage 1 but not stage 2 disease. Intravital multi-photon microscopy revealed that trypanosomes enter the brain meninges as early as day 5 post-infection but can be killed by diminazene, whereas those that cross the blood-brain barrier and enter the parenchyma by day 21 survived treatment and later caused bloodstream recrudescence. In contrast, all bioluminescent parasites were permanently eliminated by treatment with melarsoprol and DB829, compounds known to cure stage 2 disease. We show that this use of imaging reduces by two thirds the time taken to assess drug efficacy and provides a dual-modal imaging platform for monitoring trypanosome infection in different areas of the brain.

Early invasion of brain parenchyma by African trypanosomes

Human African trypanosomiasis or sleeping sickness is a vector-borne parasitic disease that has a major impact on human health and welfare in sub-Saharan countries. Based mostly on data from animal models, it is currently thought that trypanosome entry into the brain occurs by initial infection of the choroid plexus and the circumventricular organs followed days to weeks later by entry into the brain parenchyma. However, Trypanosoma brucei bloodstream forms rapidly cross human brain microvascular endothelial cells in vitro and appear to be able to enter the murine brain without inflicting cerebral injury. Using a murine model and intravital brain imaging, we show that bloodstream forms of T. b. brucei and T. b. rhodesiense enter the brain parenchyma within hours, before a significant level of microvascular inflammation is detectable. Extravascular bloodstream forms were viable as indicated by motility and cell division, and remained detectable for at least 3 days post infection suggesting the potential for parasite survival in the brain parenchyma. Vascular inflammation, as reflected by leukocyte recruitment and emigration from cortical microvessels, became apparent only with increasing parasitemia at later stages of the infection, but was not associated with neurological signs. Extravascular trypanosomes were predominantly associated with postcapillary venules suggesting that early brain infection occurs by parasite passage across the neuroimmunological blood brain barrier. Thus, trypanosomes can invade the murine brain parenchyma during the early stages of the disease before meningoencephalitis is fully established. Whether individual trypanosomes can act alone or require the interaction from a quorum of parasites remains to be shown. The significance of these findings for disease development is now testable.

Towards Point-of-Care Diagnostic and Staging Tools for Human African Trypanosomiaisis

Human African trypanosomiasis is a debilitating disease prevalent in rural sub-Saharan Africa. Control of this disease almost exclusively relies on chemotherapy that should be driven by accurate diagnosis, given the unacceptable toxicity of the few available drugs. Unfortunately, the available diagnostics are characterised by low sensitivities due to the inherent low parasitaemia in natural infections. Demonstration of the trypanosomes in body fluids, which is a prerequisite before treatment, often follows complex algorithms. In this paper, we review the available diagnostics and explore recent advances towards development of novel point-of-care diagnostic tests.

Passage of parasites across the blood-brain barrier

The blood-brain barrier (BBB) is a structural and functional barrier that protects the central nervous system (CNS) from invasion by blood-borne pathogens including parasites. However, some intracellular and extracellular parasites can traverse the BBB during the course of infection and cause neurological disturbances and/or damage which are at times fatal. The means by which parasites cross the BBB and how the immune system controls the parasites within the brain are still unclear. In this review we present the current understanding of the processes utilized by two human neuropathogenic parasites, Trypanosoma brucei spp and Toxoplasma gondii, to go across the BBB and consequences of CNS invasion. We also describe briefly other parasites that can invade the brain and how they interact with or circumvent the BBB. The roles played by parasite-derived and host-derived molecules during parasitic and white blood cell invasion of the brain are discussed.

An optimized in vitro blood-brain barrier model reveals bidirectional transmigration of African trypanosome strains

The transmigration of African trypanosomes across the human blood-brain barrier (BBB) is the critical step during the course of human African trypanosomiasis. The parasites Trypanosoma brucei gambiense and T. b. rhodesiense are transmitted to humans during the bite of tsetse flies. Trypanosomes multiply within the bloodstream and finally invade the central nervous system (CNS), which leads to the death of untreated patients. This project focused on the mechanisms of trypanosomal traversal across the BBB. In order to establish a suitable in vitro BBB model for parasite transmigration, different human cell lines were used, including ECV304, HBMEC and HUVEC, as well as C6 rat astrocytes. Validation of the BBB models with Escherichia coli HB101 and E. coli K1 revealed that a combination of ECV304 cells seeded on Matrigel as a semi-synthetic basement membrane and C6 astrocytes resulted in an optimal BBB model system. The BBB model showed selective permeability for the pathogenic E. coli K1 strain, and African trypanosomes were able to traverse the optimized ECV304-C6 BBB efficiently. Furthermore, coincubation indicated that paracellular macrophage transmigration does not facilitate trypanosomal BBB traversal. An inverse assembly of the BBB model demonstrated that trypanosomes were also able to transmigrate the optimized ECV304-C6 BBB backwards, indicating the relevance of the CNS as a possible reservoir of a relapsing parasitaemia.

Diagnostic accuracy of PCR in gambiense sleeping sickness diagnosis, staging and post-treatment follow-up: a 2-year longitudinal study

Background

The polymerase chain reaction (PCR) has been proposed for diagnosis, staging and post-treatment follow-up of sleeping sickness but no large-scale clinical evaluations of its diagnostic accuracy have taken place yet.

Methodology/Principal Findings

An 18S ribosomal RNA gene targeting PCR was performed on blood and cerebrospinal fluid (CSF) of 360 T. brucei gambiense sleeping sickness patients and on blood of 129 endemic controls from the Democratic Republic of Congo. Sensitivity and specificity (with 95% confidence intervals) of PCR for diagnosis, disease staging and treatment failure over 2 years follow-up post-treatment were determined. Reference standard tests were trypanosome detection for diagnosis and trypanosome detection and/or increased white blood cell concentration in CSF for staging and detection of treatment failure. PCR on blood showed a sensitivity of 88.4% (84.4–92.5%) and a specificity of 99.2% (97.7–100%) for diagnosis, while for disease staging the sensitivity and specificity of PCR on cerebrospinal fluid were 88.4% (84.8–91.9%) and 82.9% (71.2–94.6%), respectively. During follow-up after treatment, PCR on blood had low sensitivity to detect treatment failure. In cerebrospinal fluid, PCR positivity vanished slowly and was observed until the end of the 2 year follow-up in around 20% of successfully treated patients.

Conclusions/Significance

For T.b. gambiense sleeping sickness diagnosis and staging, PCR performed better than, or similar to, the current parasite detection techniques but it cannot be used for post-treatment follow-up. Continued PCR positivity in one out of five cured patients points to persistence of living or dead parasites or their DNA after successful treatment and may necessitate the revision of some paradigms about the pathophysiology of sleeping sickness.

Post-treatment follow-up is crucial for sleeping sickness patient management and still relies on microscopic examination of the cerebrospinal fluid (CSF). Detection of the parasites DNA with the polymerase chain reaction (PCR) is proposed as a promising and possibly non-invasive alternative for monitoring treatment outcome, but has never been evaluated. We performed PCR on blood and CSF of 360 Trypanosoma brucei gambiense sleeping sickness patients, before treatment and during 2 years after treatment, and on blood of 129 controls. We found that performance of PCR to diagnose sleeping sickness and detect brain involvement was better or similar to current diagnostic techniques. However, we observed that PCR was unreliable for monitoring treatment outcome. Continued PCR positivity in cured patients points to persistence of parasites, or their DNA, after successful treatment, challenging the dogma that in sleeping sickness cure equals parasite elimination. In conclusion, we do not recommend PCR for treatment outcome assessment in sleeping sickness.

Efficacy of Cymelarsan and Diminasan against Trypanosoma equiperdum infections in mice and horses

Trypanocidal sensitivity studies were conducted to assess the efficacy of Diminazene diaceturate (Diminasan) and Bis (aminoethylthio) 4-melaminophenylarsine dihydrochloride (Cymelarsan) against Trypanosoma equiperdum (isolated from two mares with chronic cases of dourine) 713/943 and 834/940 Dodola strains in experimentally infected mice and horses. Diminasan at doses from 3.5 mg/kg to 28 mg/kg and Cymelarsan at doses of 0.25 mg/kg and 0.5 mg/kg body weight failed to cure any of the mice, indicating a clear dose dependent relationship in the mean time of relapse observed in mice. Indeed, mice treated with lower doses relapsed after a shorter time than mice treated with higher doses. However, mice treated with Cymelarsan at doses of 1.0 mg/kg and 2.0 mg/kg body weight were cured and no parasitemia was observed for 60 days. The efficacy of Cymelarsan was also tested in horses. Two groups of horses containing two animals each were infected with T. equiperdum 834/940 Dodola strain and treated with Cymelarsan at a dose rate of 0.25 mg/kg and 0.5 mg/kg, respectively. Cymelarsan at 0.25 mg/kg and 0.5 mg/kg body weight cleared parasitemia within 24 h post treatment and none of the animals were found to show relapse throughout the 320 days of observation. The sensitivity of the particular trypanosome strain to Cymelarsan was also supported by the relative improvement in the mean PCV levels of horses following treatment. A statistically significant difference (p<0.01) in the mean PCV levels of horses treated with Cymelarsan was observed between day 20 at peak parasitemia and days 40 as well as 60 of observation. The mean PCV levels of horses in the control group progressively decreased within the first 60 days of post infection. Two of the horses in the control group developed chronic form of dourine manifested by genital as well as nervous signs with progressive loss of body condition within 320 days post infection. The efficacy of Cymelarsan against the chronic form of dourine was confirmed after treatment of one of the control horses with Cymelarsan at a dose rate of 0.25 mg/kg body weight at day 282 post infection. It was noted that the treated horse improved overall body condition and clinical signs such as incoordination of hind legs, weakness and ventral oedema disappeared within 10 days of treatment. Thus, Cymelarsan was found to be quite effective in curing horses in acute as well as chronic form of dourine. The results obtained from the present study will be important for designing effective control measures against dourine.

Kynurenine pathway inhibition reduces central nervous system inflammation in a model of human African trypanosomiasis

Human African trypanosomiasis, or sleeping sickness, is caused by the protozoan parasites Trypanosoma brucei rhodesiense or Trypanosoma brucei gambiense, and is a major cause of systemic and neurological disability throughout sub-Saharan Africa. Following early-stage disease, the trypanosomes cross the blood-brain barrier to invade the central nervous system leading to the encephalitic, or late stage, infection. Treatment of human African trypanosomiasis currently relies on a limited number of highly toxic drugs, but untreated, is invariably fatal. Melarsoprol, a trivalent arsenical, is the only drug that can be used to cure both forms of the infection once the central nervous system has become involved, but unfortunately, this drug induces an extremely severe post-treatment reactive encephalopathy (PTRE) in up to 10% of treated patients, half of whom die from this complication. Since it is unlikely that any new and less toxic drug will be developed for treatment of human African trypanosomiasis in the near future, increasing attention is now being focussed on the potential use of existing compounds, either alone or in combination chemotherapy, for improved efficacy and safety. The kynurenine pathway is the major pathway in the metabolism of tryptophan. A number of the catabolites produced along this pathway show neurotoxic or neuroprotective activities, and their role in the generation of central nervous system inflammation is well documented. In the current study, Ro-61-8048, a high affinity kynurenine-3-monooxygenase inhibitor, was used to determine the effect of manipulating the kynurenine pathway in a highly reproducible mouse model of human African trypanosomiasis. It was found that Ro-61-8048 treatment had no significant effect (P = 0.4445) on the severity of the neuroinflammatory pathology in mice during the early central nervous system stage of the disease when only a low level of inflammation was present. However, a significant (P = 0.0284) reduction in the severity of the neuroinflammatory response was detected when the inhibitor was administered in animals exhibiting the more severe, late central nervous system stage, of the infection. In vitro assays showed that Ro-61-8048 had no direct effect on trypanosome proliferation suggesting that the anti-inflammatory action is due to a direct effect of the inhibitor on the host cells and not a secondary response to parasite destruction. These findings demonstrate that kynurenine pathway catabolites are involved in the generation of the more severe inflammatory reaction associated with the late central nervous system stages of the disease and suggest that Ro-61-8048 or a similar drug may prove to be beneficial in preventing or ameliorating the PTRE when administered as an adjunct to conventional trypanocidal chemotherapy.

Central nervous system involvement in goats undergoing primary infections withTrypanosoma bruceiand relapse infections after chemotherapy

Relapse of infection after trypanocidal drug treatment of trypanosome infections is normally attributed to drug resistance on the part of the parasite, under-dosage of the drug, or reinfection of the host. We have demonstrated relapse infections in goats arising from none of these. Fourteen goats infected withTrypanosoma bruceisuffered severe illness and 3 died within 45 days. Despite treatment with the trypanocidal drug Berenil, a 4th goat died 2 days later. Recovery of the remainder followed chemotherapy, and in 2 goats, necropsiecl 45 days after treatment, no trypanosomes or abnormalities were detected. However 2–3 months after Berenil chemotherapy, despite trypanosomes being undetectable in the blood during the intervening period, infections in 4 of the remaining 8 animals relapsed. At all stages of the primary and relapse infections, trypanosomes isolated from the blood of the goats were completely susceptible to Berenil when tested in mice, as were parasites isolated from cerebrospinal fluid and brain tissue at necropsy. At the time of treatment, only minimal cellular infiltration was found in the central nervous system (CNS), but death from the relapse infection was associated with a very severe meningoencephalitis. We conclude that the relapse infections were caused by the re-emergence of trypanosornes from the CNS, where sequestered parasites were inaccessible to the trypanocidal effects of the drug.

The blood-brain barrier significantly limits eflornithine entry into Trypanosoma brucei brucei infected mouse brain

Drugs to treat African trypanosomiasis are toxic, expensive and subject to parasite resistance. New drugs are urgently being sought. Although the existing drug, eflornithine, is assumed to reach the brain in high concentrations, little is known about how it crosses the healthy and infected blood–brain barrier. This information is essential for the design of drug combinations and new drugs. This study used novel combinations of animal models to address these omissions. Eflornithine crossed the healthy blood–CNS interfaces poorly, but this could be improved by co-administering suramin, but not nifurtimox, pentamidine or melarsoprol. Work using a murine model of sleeping sickness demonstrated that Trypanosoma brucei brucei crossed the blood–CNS interfaces, which remained functional, early in the course of infection. Concentrations of brain parasites increased during the infection and this resulted in detectable blood–brain barrier, but not choroid plexus, dysfunction at day 28 post-infection with resultant increases in eflornithine brain delivery. Barrier integrity was never restored and the animals died at day 37.9 ± 1.2. This study indicates why an intensive treatment regimen of eflornithine is required (poor blood–brain barrier penetration) and suggests a possible remedy (combining eflornithine with suramin). The blood–brain barrier retains functionality until a late, possibly terminal stage, of trypanosoma infection.

Suramin and minocycline treatment of experimental African trypanososmiasis at an early stage of parasite brain invasion

The effect of treatment on relapses of Trypanosoma brucei (T. b.) brucei infections in mice in relation to passage of the parasites across the blood-brain barrier (BBB) as visualized by immunohistochemistry was studied. Three daily intraperitoneal injections of 20mg/kg suramin starting at 15 days post-infection (p.i.), when trypanosomes had begun to traverse the BBB, were curative, but not when starting at 21 days p.i. when parasite brain invasion was more pronounced. Relapses occurred in all mice after one or two daily injections of suramin starting at 15 days p.i., but they were delayed when treatment was supplemented with minocycline, which impedes penetration of T. b. brucei into the brain. This study supports the notion that suramin may be effective even when minor parasite neuroinvasion has appeared in African trypanosomiasis and it shows that minocyline can affect relapses of the disease.

Entry of Trypanosoma brucei gambiense into microvascular endothelial cells of the human blood–brain barrier

Using an in vitro model of the human blood-brain barrier consisting of human brain microvascular endothelial cells we recently demonstrated that Trypanosoma brucei gambiense bloodstream-forms efficiently cross these cells via a paracellular route while Trypanosoma brucei brucei crosses these cells poorly. Using a combination of techniques that include fluorescence activated cell sorting, confocal and electron microscopy, we now show that some T.b. gambiense blood stream form parasites have the capacity to enter human brain microvascular endothelial cells. The intracellular location of the trypanosomes was demonstrated in relation to the endothelial cell plasma membrane and to the actin cytoskeleton. These parasites may be a terminal stage within a lysosomal compartment or they may be viable trypanosomes that will be able to exit the brain microvascular endothelial cells. This process may provide an additional transcellular route by which the parasites cross the blood-brain barrier.

Bovine trypanotolerance: A natural ability to prevent severe anaemia and haemophagocytic syndrome?

Trypanotolerance is the capacity of certain West-African, taurine breeds of cattle to remain productive and gain weight after trypanosome infection. Laboratory studies, comparing Trypanosoma congolense infections in trypanotolerant N'Dama cattle (Bos taurus) and in more susceptible Boran cattle (Bos indicus), confirmed the field observations. Experiments using haemopoietic chimeric twins, composed of a tolerant and a susceptible co-twin, and T cell depletion studies suggested that trypanotolerance is composed of two independent traits. The first is a better capacity to control parasitaemia and is not mediated by haemopoietic cells, T lymphocytes or antibodies. The second is a better capacity to limit anaemia development and is mediated by haemopoietic cells, but not by T lymphocytes or antibodies. Weight gain was linked to the latter mechanism, implying that anaemia control is more important for survival and productivity than parasite control. Anemia is a marker for a more complex pathology which resembles human haemophagocytic syndrome: hepatosplenomegaly, pancytopenia and a large number of hyperactivated phagocytosing macrophages in bone marrow, liver and other tissues. Thus, mortality and morbidity in trypanosome-infected cattle are primarily due to self-inflicted damage by disproportionate immune and/or innate responses. These features of bovine trypanotolerance differ greatly from those in murine models. In mice, resistance is a matter of trypanosome control dependent on acquired immunity. However, a model of anaemia development can be established using C57BL/6J mice. As in cattle, the induction of anaemia was independent of T cells but its development differed with different trypanosome strains. Identification of the molecular pathways that lead to anaemia and haemophagocytosis should allow us to design new strategies to control disease.

A diminazene-resistant strain ofTrypanosoma brucei bruceiisolated from a dog is cross-resistant to pentamidine in experimentally infected albino rats

Trypanosomosis is a major cause of mortality for dogs in Nigeria and treatment with diminazene aceturate has steadily become less effective, either as a result of low quality of the locally available diminazene preparations or of drug resistance. To investigate these alternatives, samples of locally obtained drugs were analysed for diminazene aceturate content and a strain ofTrypanosoma brucei bruceiwas isolated from a diminazene-refractory dog in Nsukka, south-eastern Nigeria, and used to infect albino rats. The quality of diminazene aceturate-based preparations was variable, with two preparations containing less than 95% of the stated active compound. Rats infected withT. bruceiisolated from the dog were treated 7 and 10 days after infection either with 7 mg/kg diminazene aceturate (intraperitoneally, once) or with 4 mg/kg pentamidine isethionate (intramuscularly, 7 consecutive days). Relapse rates were 100% for both trypanocides in the groups of rat treated 10 days post-infection, and 83% and 50% of rats treated 7 days after infection relapsed to diminazene aceturate and pentamidine isethionate, respectively. Careful consideration of physiological parameters showed that pentamidine was only marginally superior to diminazene aceturate as applied in this study. It was concluded that dogs in Nigeria are infected with genuinely diminazene aceturate-resistant trypanosomes that appear to be cross-resistant to pentamidine isethionate.

African trypanosome interactions with an in vitro model of the human blood-brain barrier

The neurological manifestations of sleeping sickness in man are attributed to the penetration of the blood-brain barrier (BBB) and invasion of the central nervous system by Trypanosoma brucei gambiense and Trypanosoma brucei rhodesiense. However, how African trypanosomes cross the BBB remains an unresolved issue. We have examined the traversal of African trypanosomes across the human BBB using an in vitro BBB model system constructed of human brain microvascular endothelial cells (BMECs) grown on Costar Transwell inserts. Human-infective T. b. gambiense strain IL 1852 was found to cross human BMECs far more readily than the animal-infective Trypanosoma brucei brucei strains 427 and TREU 927. Tsetse fly-infective procyclic trypomastigotes did not cross the human BMECs either alone or when coincubated with bloodstreamform T. b. gambiense. After overnight incubation, the integrity of the human BMEC monolayer measured by transendothelial electrical resistance was maintained on the inserts relative to the controls when the endothelial cells were incubated with T. b. brucei. However, decreases in electrical resistance were observed when the BMEC-coated inserts were incubated with T. b. gambiense. Light and electron microscopy studies revealed that T. b. gambiense initially bind at or near intercellular junctions before crossing the BBB paracellularly. This is the first demonstration of paracellular traversal of African trypanosomes across the BBB. Further studies are required to determine the mechanism of BBB traversal by these parasites at the cellular and molecular level.

Neuronal targeting and functional effects of infectious agents transmitted from animals to man

The nervous system is an «immune-privileged» site and can provide a reservoir to harbor as persistent or latent infections certain microbes that find their way to the brain. From an evolutionary standpoint, such infections are characterized at most times by low levels of the infectious agent in the systemic domain, except when multiplication has just taken place. Hence the ability for transmission of the pathogens from animals to Man will be determined by the availability of microbes to be transferred by a vector (e.g. in trypanosomiasis), or the amount of infective forms of the microbes shed into an environment (e.g. in toxoplasmosis). Using African trypanosomes, toxoplasma,Listeria and influenza A virus as examples, mechanisms by which microbes can spread and be targeted to and within the brain to cause various types of nervous system dysfunctions is reviewed. Newly revealed potentials of certain cytokines to stimulate neurons to control the growth, and even kill, microbes in their cell bodies is also described.

Drug sensitivity of trypanosome populations from cattle in a peri-urban dairy production system in Uganda

Cattle from 50 farms in Mukono County, Uganda, were monitored for trypanosomes every second month over an 18-month period (1995-1996) by mini-anion exchange chromatography and haematocrit centrifugation techniques. Eighteen trypanosome isolates collected from cattle during this period were characterised in cattle, goats and mice for their sensitivity to homidium, isometamidium and diminazene; 10 of the isolates were selected randomly, 8 were from animals that had the highest serum isometamidium concentrations at the time the isolates were collected. All the isolates contained only Trypanosoma brucei and/or T. vivax. In nai;ve Boran (Bos indicus) cattle the isolates exhibited low pathogenicity and were sensitive to diminazene aceturate at 3.5 mg/kg body weight (bw) and isometamidium chloride at 0.5 mg/kg bw. In goats, 5 of 8 isolates were highly pathogenic, producing clinical signs indicative of central nervous system involvement within 60 days of infection; all such isolates contained T. brucei. However, all 8 populations were sensitive in goats to diminazene aceturate at 3.5 mg/kg bw. In contrast, 4 populations were refractory to treatment with isometamidium chloride at 0.5 mg/kg bw in at least 1 out of 3 goats each. Furthermore, 5 populations were refractory to treatment with homidium chloride at 1.0 mg/kg bw in a minimum of 2 out of 3 goats each. In mice, the 50% curative dose values for 11 Mukono isolates that contained T. brucei ranged from 0.30 to 1.89 mg/kg bw for diminazene aceturate, from 0.02 to 0.17 mg/kg bw for isometamidium chloride and from 0.90 to 4.57 mg/kg bw for homidium chloride. Thus, by comparison to reference drug-sensitive populations, all the stabilates were highly sensitive to diminazene and isometamidium, while some expressed low levels of resistance to homidium.

Drug resistance in Trypanosoma brucei spp., the causative agents of sleeping sickness in man and nagana in cattle

Drug resistance in pathogenic trypanosomes threatens successful control of fatal sleeping sickness in man and hinders economic livestock production in sub-Saharan Africa. We report on the occurrence and development of drug resistance, and discuss the genetic basis of such resistance in Trypanosoma brucei. Understanding these mechanisms at the molecular level will enable improved management of existing drugs and provide valuable clues to the development of new trypanocides.

Trypanosoma brucei brucei crosses the blood-brain barrier while tight junction proteins are preserved in a rat chronic disease model

African trypanosomiasis, sleeping sickness in humans, is caused by the systemic infection of the host by the extracellular parasite, the African trypanosome. The pathogenetic mechanisms of the severe symptoms of central nervous system involvement are still not well understood. The present study examined the routes of haematogenous spread of Trypanosoma brucei brucei (Tbb) to the brain, in particular on the question whether parasites can cross the blood-brain barrier, as well as their effect on tight junction proteins. Rats were infected with Tbb and at various times post-infection, the location of the parasite in the central nervous system was examined in relation to the brain vascular endothelium, visualized with an anti-glucose transporter-1 antibody. The tight junction-specific proteins occludin and zonula occludens 1, and the possible activation of the endothelial cell adhesion molecules ICAM-1 and VCAM-1 were also studied. At 12 and 22 days post-infection, the large majority of parasites were confined within blood vessels. At this stage, however, some parasites were also clearly observed in the brain parenchyma. This was accompanied by an upregulation of ICAM-1/VCAM-1. At later stages, 42, 45 and 55 days post-infection, parasites could still be detected within or in association with blood vessels. In addition, the parasite was now frequently found in the brain parenchyma and the extravasation of parasites was more prominent in the white matter than the cerebral cortex. A marked penetration of parasites was seen in the septal nuclei. In spite of this, occludin and zonula occludens 1 staining of the vessels was preserved. The results indicate that the Tbb parasite is able to cross the blood-brain barrier in vivo, without a generalized loss of tight junction proteins.

Infection of organotypic slice cultures from rat central nervous tissue with Trypanosoma brucei brucei

We recently described a new procedure to grow nervous tissue as organotypic culture. The main feature of these slice cultures is to maintain a well preserved, three-dimensional organisation of the central nervous tissue. As these cultures can be kept for several weeks (up to three months), we have used this in vitro approach to study the complex interactions between host tissue and parasites during late stages of cerebral African trypanosomiasis. Light and electron microscopical studies, as well as electrophysiological recordings demonstrate that the structure and function of the nervous tissue is not severely affected even after several weeks of trypanosome infection. The presence of a large number of parasites does not seem to be deleterious to neuronal survival. Secondly, most of the trypanosomes are located around the periphery of the nervous tissue, but many of them also penetrate into the nervous parenchyma. Thirdly, trypanosomes with well-conserved morphology are found within the cytoplasm of glial cells, which in some cases were identified as astrocytes. These "intracellular parasites" seem to actively invade the target cells. Our study demonstrates that the presence of proliferating trypanosomes does not per se interfere with the neural activity of CNS tissues. Secondly, it provides, to the best of our knowledge, the first in vitro demonstration of intracellular forms of African trypanosomes.

Response of a T. b. rhodesiense stock with reduced drug susceptibility in vitro to treatment in mice and cattle

In vivo drug susceptibility tests involving treatment of infected mice and cattle were performed on two trypanosome stocks, a T. brucei brucei and a T.b. rhodesiense, isolated in South Eastern Uganda. The T. b. rhodesiense stock had expressed reduced susceptibility to diminazene aceturate and isometamidium chloride in vitro, while the other, a T. b. brucei stock was susceptible. Diminazene aceturate at 14 mg/kg was not sufficient to cure all T. b. rhodesiense infected mice. Similarly, in the case of isometamidium chloride, 33% of infected mice treated with 2.0 mg/kg drug were not cured. In contrast, mice infected with the susceptible T. b. brucei and treated similarly with either drug were all cured. However, when cattle infected with the T. b. rhodesiense stock, or the susceptible T. b. brucei stock, or a 1:1 mixture of the two were treated with 7 mg/kg diminazene aceturate, they were all cured. Use of diagnostic PCR employing T. brucei specific primers confirmed that although the cattle had acquired infection pre-treatment, no trypanosome DNA amplification signal was demonstrated in the samples collected 60 days post-treatment. The reduced susceptibility of this T. b. rhodesiense, which could be demonstrated in mice as well as in culture, may indicate the existing potential for evolution of resistance in South Eastern Uganda.

Trypanosoma brucei brucei: a long-term model of human African trypanosomiasis in mice, meningo-encephalitis, astrocytosis, and neurological disorders

The search for a chronic experimental model for human African trypanosomiasis (HAT) in animals with cerebral lesions and neurological disorders has been difficult. Models with meningo-encephalitis have been proposed using Trypanosoma brucei gambiense or T. b. rhodesiense. Meningo-encephalitis is rare in infection with T. b. brucei. It has been shown that the treatment of mice infected with T. b. brucei with diminazene aceturate (Berenyl) led to development of a rapid meningo-encephalitis. In this study, we report the development of a chronic experimental model of HAT in mice infected with T. b. brucei AnTat 1.1E. To obtain a chronic evolution of the infection, on Day 21 postinfection, mice were treated with a dose of suramin (Moranyl) at 20 mg x kg(-1) body weight, a dose which failed to eliminate trypanosomes in the central nervous system (CNS). This treatment, repeated after each parasitemic relapse in the blood, allowed animals to survive more than 300 days postinfection. After a few weeks of infection, mice displayed neurological signs. Histological studies showed the appearance of increasing inflammatory lesions, from meningitis to meningo-encephalitis, with progression of lesions throughout the perivascular spaces in cerebral and cerebellum parenchyma. No demyelination or neuronal alteration were observed except in the necrotic spaces. Trypanosomes were observed in different structures in CNS. An immunohistochemical study of glial fibrillary acidic protein (GFAP) showed an increasing astrocytosis according to the duration of the infection. This model reproduces neurological and histological pathology observed in the human disease and can be useful for further immunopathological, neurohistological and therapeutic studies on this condition.

Specificity of ethanolamine transport and its further metabolism in Trypanosoma brucei

Ethanolamine is found in trypanosomes as an integral component of the variant surface glycoprotein (VSG) and the membrane phospholipid phosphatidylethanolamine (PE). Steps in the utilization of ethanolamine could represent novel targets for the development of chemotherapeutic drugs and were therefore investigated in detail. Transport of [3H]ethanolamine was studied using structural analogs of ethanolamine. Compounds with substitutions in the amino group or of one of the methylene hydrogens of ethanolamine were the most effective inhibitors. Those analogs studied in detail with respect to their kinetic properties were all found to be competitive inhibitors of ethanolamine transport. Following uptake, ethanolamine is rapidly phosphorylated by an ethanolamine-specific kinase to form phosphoethanolamine. Other acid-soluble intermediates identified by thin layer chromatography were CDP-ethanolamine, dCDP-ethanolamine, and glycerophosphorylethanolamine. The relative amounts of these metabolites varied between slender (dividing) and stumpy (non-dividing) trypanosomes and may reflect special biosynthetic needs of the different morphological forms. Pulse-chase experiments indicated that the acid-soluble metabolites served as precursors for chloroform/methanol-soluble lipids. Radioactive lipids included PE, mono-methyl and dimethyl PE, and lysoPE. Further methylation of dimethylPE to phosphatidylcholine was not observed under the experimental conditions described. These results are consistent with the conclusion that trypanosomes are able to synthesize phospholipids via the Kennedy pathway.

Frequency of diminazene-resistant trypanosomes in populations of Trypanosoma congolense arising in infected animals following treatment with diminazene aceturate

The frequency of trypanosomes resistant to diminazene aceturate at a dose of 25 mg/kg of body weight was investigated for populations of Trypanosoma congolense IL 3274 which reappeared in infected mice after intraperitoneal treatment with diminazene aceturate at the same dosage. At inoculum sizes of 10(2), 10(3), 10(4), 10(5), and 10(6) trypanosomes per mouse, the relapse populations were used to initiate infections in five groups of 100 mice each by the intravenous route. Immediately after infection, 50 mice in each group were treated intraperitoneally with diminazene aceturate at the aforementioned dosage; the other 50 mice functioned as untreated controls. Thereafter, all animals were monitored for 100 days for the presence of trypanosomes. In each group, trypanosomes were detected in 50 of 50 control mice, indicating 100% infectivity for all five inoculum sizes. In contrast, in the groups of 50 mice infected with 10(2), 10(3), 10(4), 10(5) and 10(6) trypanosomes and treated with diminazene aceturate, trypanosomes were detected in 4, 11, 13, 28, and 39 of 50 mice, respectively. By logistic regression, a good fit was found between the number of mice identified as parasitemic and the inoculum sizes. Maximum likelihood estimates for the proportions of trypanosomes resistant to diminazene aceturate at 25 mg/kg of body weight for the inoculum of 10(2), 10(3), 10(4), 10(5), and 10(6) organisms were 8.335 x 10(-4), 2.485 x 10(-4), 3.02 x 10(-5), 8.3 x 10(-6), and 1.6 x 10(-6), respectively. These finding indicate that the majority of the relapse trypanosomes were susceptible the the drug dosage used for selecting the population and that, surprisingly, the calculated proportion of organisms which survived drug exposure varied inversely with the inoculum size. Further experiments with mice indicated that the inverse relationship did not result from alterations in the pharmacokinetics of the drug with different inoculum sizes. The data therefore suggest that parasite inoculum size and drug dosage are important factors in estimating the apparent frequency of diminazene-resistant trypanosomes in populations of T. congolense occurring in vivo.

Apparent rarity of diminazene-resistant trypanosomes in goats infected with a diminazene-resistant population of Trypanosoma congolense

Experiments were carried out in goats to determine the frequency with which diminazene-resistant trypanosomes occur in parasite populations before and after the intramuscular treatment of the goats with diminazene aceturate. Trypanosoma congolense IL 3274, a diminazene-resistant clone, was used to initiate infections in three groups of five goats. The goats in the first group were treated with diminazene aceturate at a dose of 7.0 mg kg-1 bodyweight within 10 seconds of infection; one of the goats was cured. All of the second group, which received no treatment, became parasitaemic. The third group of goats received the same dose of drug as the first group but three days after all of them were first detected parasitaemic; trypanosomes reappeared in all the five goats. When this third group was treated, the frequency of trypanosomes resistant to the drug dosage was estimated to be less than 1 in 10(3). The parasites which reappeared after the treatment of these animals were used to infect two additional groups of five goats intravenously. The goats in one group were treated with the same dose of drug as before, within 10 seconds of infection and were all cured. In contrast, the five goats in the second, untreated, group became parasitaemic. Finally, when the goats in which the infections had relapsed were retreated with diminazene aceturate at the same dose rate, the level of parasitaemia temporarily decreased by at least 10(3) trypanosomes ml-1. These findings suggest that diminazene-resistant T congolense occur at low levels in trypanosome populations despite attempts to select for a population resistant to the dose of drug used.

Pharmacokinetics of melarsoprol in uninfected vervet monkeys

The level of the trypanocidal drug melarsoprol was determined in serum and cerebrospinal fluid (CSF) of six healthy vervet monkeys after intravenous application of the drug following a standard treatment schedule and a recently suggested alternative protocol. The maximum serum levels measured were about 3 micrograms/ml. A three-compartment model was used to analyze the serum data. The mean residence time calculated for melarsoprol in serum was 18 h, the volume of distribution was 3.6 l/kg and the clearance was 3.5 ml/min*kg. In the CSF the drug levels were generally very low, not exceeding 55 ng/ml, and the adaptation of the drug levels was found to be very low. The comparison of the drug concentrations required to eliminate trypanosomes in vitro and the drug concentrations reached in the CSF during treatment revealed that the latter might be insufficient in some cases to eliminate all trypanosomes from this site. The peak serum levels during alternative application of the drug were lower compared to those during empirical treatment. No evidence for drug cumulation in the body was found. The results of this study are compared with recent pharmacokinetic data from human patients, and discussed in the context of the problem of relapses and reactive encephalopathy occurring after treatment of sleeping sickness.

Pharmacokinetics of diminazene in plasma and cerebrospinal fluid of goats

The pharmacokinetics of diminazene in the cerebrospinal fluid (CSF) and plasma of five uninfected goats treated with single intramuscular doses of 3.5 mg diminazene base kg-1 bodyweight was investigated. The concentrations of the drug were determined by high performance liquid chromatography, and were three to four times lower in CSF than in plasma. The kinetics of the drug in CSF and plasma differed significantly with respect to Cmax, tmax, AUC0-48h, AUMC0-48h, Cl and Vd(ss).

A comparison of the antigen detection ELISA and parasite detection for diagnosis of Trypanosoma evansi infections in camels

Two herds of 60 camels each, living in Trypanosoma evansi endemic areas, were selected and studied for a period of 18 months. Animals in one herd were treated prophylactically with quinapyramine prosalt (May and Baker, Dagenham, UK), while those in the other herd were treated individually with quinapyramine dimethylsulphate (May and Baker, Dagenham, UK) when proven parasitaemic. The herd on prophylaxis was sampled for antigen and patent infection monthly. The other herd was sampled weekly for patent infection and fortnightly for antigen. The results obtained could be divided into four categories. The first category comprised cases (52 out of 61) in which the presence of trypanosome antigens could be correlated with parasitological diagnosis. In 80% of these animals the antigens disappeared from the circulation within a period of 30 days following chemotherapy. The second category comprised those animals with parasitologically proven infections but which did not have antigens in their sera. This was observed in nine camels, seven of which were from the herd that was being examined weekly for the presence of trypanosomes. These were considered to be animals in early infection, as the subsequent sera were also negative for anti-trypanosome antibodies and immune complexes. The third category comprised camels which were antigen-positive but aparasitaemic. Sera from these animals were also positive for anti-trypanosome antibodies, indicating that antigen-positivity was a true reflection of trypanosome infections in these animals. The last category comprised pre-weaned camel calves which appeared to have some form of protection against trypanosomiasis, as evidenced by the absence of trypanosomes, antigens and antibodies throughout the early period of their lives. Only occasional antigenaemia was found in a few calves. It is concluded that trypanosome antigen detection may give a more accurate idea of the prevalence of T. evansi infections than does whole parasite detection.

Pharmacology of diminazene: a review

Chemotherapy for trypanosomiasis in domestic livestock depends on only a few compounds, of which several are chemically closely related. Of these compounds, the most widely used therapeutic agent in cattle, sheep and goats is diminazene aceturate. Diminazene was first described in 1955. Subsequently, a substantial body of data has been generated on various pharmacological aspects of the compound. In this review, we consider the current status of knowledge concerning the therapeutic spectrum of diminazene, resistance to diminazene in trypanosomes, and combination therapeutic regimens in which diminazene has been administered together with other compounds. Analytical techniques for diminazene, the pharmacokinetics of diminazene, data concerning diminazene's toxicity, and the different molecular mechanisms by which diminazene may exhibit trypanocidal action are also considered.

Time-dose-response of Trypanosoma brucei brucei to diminazene aceturate (Berenil) and in vitro simulation of drug-concentration-time profiles in cattle plasma

Bloodstream form Trypanosoma brucei brucei of axenically growing populations were incubated in the presence of 10.0, 1.0 or 0.1 micrograms/ml diminazene aceturate (Berenil) at 37 degrees C for various periods and, subsequently, either inoculated into mice or further propagated in vitro in drug-free medium. Growth was monitored for 10 days. The ability of trypanosomes of drug-sensitive CP 2137 (clone 1) to grow in vitro was irreversibly damaged after short incubation (< 1 min) with 10.0 micrograms/ml or after 15 min with 1.0 micrograms/ml diminazene aceturate. In contrast, drug-resistant CP 2469 (clone 1) trypanosomes tolerated incubation with 10 micrograms/ml of drug for up to 6 h and 1.0 micrograms/ml of drug for up to 24 h. Differences in drug susceptibility were also detected regarding infectivity to mice and changes in trypanosome cell volume. The results demonstrated that less than 1 min exposure to diminazene aceturate at concentrations as seen in bovine plasma at the initial peak after diminazene aceturate treatment is enough to irreversibly damage drug-sensitive trypanosomes. However, these concentrations were not sufficient to completely eliminate drug-resistant trypanosomes after exposure for 1-6 h; trypanosomes continued to grow for 48 h before the majority of them died and only a few organisms survived to revive the cultures. When drug-sensitive trypanosomes were exposed in vitro for 24 h to diminazene aceturate at the level of concentrations found in cattle after treatment with 3.5 mg/kg, most of the trypanosomes died and none of the surviving parasites could be propagated in vitro in the absence of drug for more than 2 days. However, a small population of drug-resistant trypanosomes was not irreversibly damaged and a few surviving trypanosomes were able to establish growing cultures. The addition of feeder layer cells did not change the outcome of these experiments.

Comparative pharmacokinetics of diminazene in noninfected Boran (Bos indicus) cattle and Boran cattle infected with Trypanosoma congolense

The pharmacokinetics of diminazene in five female Boran (Bos indicus) cattle before and then during acute and chronic phases of experimental infections with Trypanosoma congolense were investigated. A 7.0% (wt/vol) solution of diminazene aceturate (Berenil) was used in all three phases of the study and administered as a single intramuscular dose of 3.5 mg of diminazene base per kg of body weight. There were no significant differences between the values of pharmacokinetic parameters for the noninfected cattle and the values for cattle with a chronic T. congolense infection. However, the maximum concentration of the drug in plasma during the acute phase of infection (8.25 +/- 1.72 micrograms/ml) was significantly (P < 0.01) greater than that during chronic infection (5.04 +/- 0.26 micrograms/ml) and that in the noninfected state (4.76 +/- 0.76 micrograms/ml). Similarly, the time to maximum concentration of the drug in plasma when diminazene was administered during the acute phase of infection (18.00 +/- 6.71 min) was significantly (P < 0.02) shorter than that for noninfected cattle (36.00 +/- 8.22 min) and that during chronic infection (33.75 +/- 7.50 min). The volume of distribution at steady state during acute infection (1.01 +/- 0.31 liter/kg) was significantly (P < 0.01) smaller than that in the noninfected state (1.37 +/- 0.17 liter/kg) and that in chronic infection (1.51 +/- 0.24 liter/kg). Eight hours after the drug had been administered, the concentration-time data profiles for each of the three study phases were very similar. Mean concentrations of diminazene in plasma 48 h after administration of the drug were 0.43 +/- 0.07 microgram/ml in noninfected cattle, 0.43 +/- 0.11 microgram/ml during the acute phase of trypanosome infection, and 0.44 +/- 0.09 microgram/ml during the chronic phase of the infection. Results of the present study indicate that the area under the concentration-time curve for diminazene in trypanosome-infected cattle did not differ significantly for noninfected cattle. It, therefore, appears that the total amount of diminazene attained and maintained in the plasma of cattle is not significantly altered during infection with T. congolense.