Imaging African trypanosomes

Animal models of neglected parasitic diseases: In vivo multimodal imaging of experimental trypanosomatid infections

African trypanosomiases and leishmaniases are significant neglected tropical diseases (NTDs) that affect millions globally, with severe health and socio-economic consequences, especially in endemic regions. Understanding the pathogenesis and dissemination of Trypanosoma brucei and Leishmania spp. parasites within their hosts is pivotal for the development of effective interventions. Whole-body bioluminescence and fluorescence imaging systems (BLI and FLI, respectively), are powerful tools to visualize and quantify the progression and distribution of these parasites in real-time within live animal models. By combining this technology with the engineering of stable T. brucei and Leishmania spp. strains expressing luciferase and/or fluorescent proteins, crucial aspects of the infection process including the parasites' homing, the infection dynamics, the tissue tropism, or the efficacy of experimental treatments and vaccines can be deeply investigated. This methodology allows for enhanced sensitivity and resolution, elucidating previously unrecognized infection niches and dynamics. Importantly, whole-body in vivo imaging is non-invasive, enabling for longitudinal studies during the course of an infection in the same animal, thereby aligning with the "3Rs" principle of animal research. Here, we detail a protocol for the generation of dual-reporter T. brucei and L. major, and their use to infect mice and follow the spatiotemporal dynamics of infection by in vivo imaging systems. Additionally, 3D micro-computed tomography (μCT) coupled to BLI in T. brucei-infected animals is applied to gain insights into the anatomical parasite distribution. This Chapter underscores the potential of these bioimaging modalities as indispensable tools in parasitology, paving the way for novel therapeutic strategies and deeper insights into host-parasite interactions.

Neurocognitive domains and neuropathological changes in experimental infection with Trypanosoma brucei brucei in Wistar rats

Trypanosoma brucei brucei causes animal trypanosomiasis in several vertebrates and human African trypanosomiasis. Previous studies have only explored the incidence, clinical symptoms, haematology and biochemical changes associated with the disease. The behavioral manipulation hypothesis posits that parasites alter the behavior of host to increase the reproductive abilities of such parasites. Hence, the present study was carried out to investigate changes in behavior and cognition following experimental infection of T. brucei brucei in rat model.

This study involved two groups of animals (uninfected control and T. brucei infected) with 8 rats per group. After confirmation of parasitaemia in the infected rats both groups were assessed to investigate if infection led to behavioral alterations and neuropathological changes using the open field, social interaction and forelimb suspension tests. Immunohistochemistry was performed on brain tissues using glial fibrillary acidic protein and anticalbindin-D28k, antibodies.

We demonstrated that T. brucei infection triggered a significant decrease in exploratory activity, anxiety-like behavior, altered recognition of social novelty and reduced hanging latency in the hanging wire test. Immunohistochemistry revealed significant astrocytosis, loss of dendritic spines and reduction of Purkinje cell layer of the cerebellum.

These results demonstrate that T. brucei infection induce signs of anxiety, impaired motor co-ordination with degeneration and loss of Purkinje cells.

Small animal in vivo imaging of parasitic infections: A systematic review

Non-invasive small animal in vivo imaging is an essential tool in a broad variety of biomedical sciences and enables continuous monitoring of disease progression in order to develop and improve diagnostic, therapeutic and preventive measures. Imaging parasites non-invasively in live animals allows efficient parasite distribution evaluation in the host organism and objective evaluation of parasitic diseases' burden and progression in individual animals. The aim of this systematic review was to summarize recent trends in small animal in vivo imaging and compare and discuss imaging of single-cell and multicellular eukaryotic parasites. A literature survey was performed using Web of Science and PubMed databases in research articles published between 1990 and 2018. The inclusion criteria were using any imaging method to visualize a range of protozoan and helminth parasites in laboratory animals in vivo. A total of 92 studies met our inclusion criteria. Protozoans and helminths were imaged in 88% and 12% of 92 studies, respectively. The most common parasite genus studied was the protozoan Plasmodium followed by Trypanosoma and Leishmania. The most frequent imaging method was bioluminescence. Among the helminths, Schistosoma and Echinococcus were the most studied organisms. In vivo imaging is applicable in both protozoans and helminths. In helminths, however, the use of in vivo imaging methods is limited to some extent. Imaging parasites in small animal models is a powerful tool in preclinical research aiming to develop novel therapeutic and preventive strategies for parasitic diseases of interest both in human and veterinary medicine.

Using detergent-enhanced LAMP for African trypanosome detection in human cerebrospinal fluid and implications for disease staging

Objective

Where human African trypanosomiasis (HAT) patients are seen, failure to microscopically diagnose infections by Trypanosoma brucei gambiense in blood smears and/or cerebrospinal fluid (CSF) in the critical early stages of the disease is the single most important factor in treatment failure, a result of delayed treatment onset or its absence. We hypothesized that the enhanced sensitivity of detergent-enhanced loop-mediated isothermal amplification (LAMP) will allow for point of care (POC) detection of African trypanosomes in the CSF of HAT patients where the probability for detecting a single parasite or parasite DNA molecule in 1 μL of CSF sample is negligible by current methods.

Methodology

We used LAMP targeting the multicopy pan-T. brucei repetitive insertion mobile element (RIME LAMP) and the Trypanosoma brucei gambiense 5.8S rRNA-internal transcribed spacer 2 gene (TBG1 LAMP). We tested 1 μL out of 20 μL sham or Triton X-100 treated CSFs from 73 stage-1 and 77 stage-2 HAT patients from the Central African Republic and 100 CSF negative controls.

Results

Under sham conditions, parasite DNA was detected by RIME and TBG1 LAMP in 1.4% of the stage-1 and stage-2 gambiense HAT CSF samples tested. After sample incubation with detergent, the number of LAMP parasite positive stage-2 CSF’s increased to 26%, a value which included the 2 of the 4 CSF samples where trypanosomes were identified microscopically. Unexpected was the 41% increase in parasite positive stage-1 CSF’s detected by LAMP. Cohen’s kappa coefficients for RIME versus TBG1 LAMP of 0.92 (95%CI: 0.82–1.00) for stage-1 and 0.90 (95%CI: 0.80–1.00) for stage-2 reflected a high level of agreement between the data sets indicating that the results were not due to amplicon contamination, data confirmed in χ² tests (p<0.001) and Fisher’s exact probability test (p = 4.7e^-13).

Conclusion

This study detected genomic trypanosome DNA in the CSF independent of the HAT stage and may be consistent with early CNS entry and other scenarios that identify critical knowledge gaps for future studies. Detergent-enhanced LAMP could be applicable for non-invasive African trypanosome detection in human skin and saliva or as an epidemiologic tool for the determination of human (or animal) African trypanosome prevalence in areas where chronically low parasitemias are present.

Human African trypanosomiasis is a fatal disease (if untreated) spread by bloodsucking tsetse flies. These protozoan parasites first enter the lymph and blood to invade many organ systems (early stage sleeping sickness). Weeks to months later, the parasites invade the brain causing a wide variety of neurological symptoms (late stage sleeping sickness). In rural clinical settings, diagnosis still relies on the detection of these microbes in blood and cerebrospinal fluid (CSF) by microscopy. LAMP, or loop-mediated isothermal amplification of DNA, is a technique that can specifically detect very small amounts of DNA from an organism. We previously showed that by simply adding detergent during sample preparation, the analytical sensitivity of LAMP targeting many gene copies is greatly improved, presumably because DNA is released from the pathogen cells and dispersed through the sample. We demonstrated proof of principle using pathogenic trypanosomes in different human body fluids (CSF or blood) and showed that this simple modification should be applicable for diagnosis of other microbial infections where cells are sensitive to detergent lysis. After completion of the above published study, we tested a collection of clinical CSF samples from African patients diagnosed with early or late stage sleeping sickness based on current World Health Organization (WHO) guidelines. For proof-of-concept we tested only a single microliter of detergent-treated CSF to test for late stage disease. We predicted that a significant number of the late stage samples would be LAMP positive, while the early stage CSFs would yield predominantly negative results. Instead, our study detected trypanosome DNA in patient CSF independent of African sleeping sickness stage, results that may be consistent with early brain entry and other scenarios that identify critical knowledge gaps for future studies.

A Microfluidic-Based Microscopy Platform for Continuous Interrogation of Trypanosoma brucei during Environmental Perturbation

The African trypanosome, Trypanosoma brucei, is the causative agent of human African trypanosomiasis (HAT). African trypanosomes are extracellular parasites that possess a single flagellum that imparts a high degree of motility to the microorganisms. In addition, African trypanosomes show significant metabolic and structural adaptation to environmental conditions. Analysis of the ways that environmental cues affect these organisms generally requires rapid perfusion experiments in combination with single-cell imaging, which are difficult to apply under conditions of rapid motion. Microfluidic devices have been used previously as a strategy for trapping small motile cells in a variety of organisms, including trypanosomes; however, in the past, such devices required individual fabrication in a cleanroom, limiting their application. Here we demonstrate that a commercial microfluidic device, typically used for bacterial trapping, can trap bloodstream and procyclic form trypanosomes, allowing for rapid buffer exchange via perfusion. As a result, time-lapse single-cell microscopy images of these highly motile parasites were acquired during environmental variations. Using these devices, we have been able to perform and analyze perfusion-based single-cell tracking experiments of the responses of the parasite to changes in glucose availability, which is a major step in resolving the mechanisms of adaptation of kinetoplasts to their individual biological niches; we demonstrate utility of this tool for making measurements of procyclic form trypanosome intracellular glucose levels as a function of changes in extracellular glucose concentrations. These experiments demonstrate that cytosolic glucose equilibrates with external conditions as fast as, or faster than, the rate of solution exchange in the instrument.

Gene expression in reproductive organs of tsetse females - initial data in an approach to reduce fecundity

BACKGROUND

Tsetse flies are vectors of African trypanosomes, and their vectorial capacity results in a major public health emergency and vast economic losses in sub-Saharan Africa. Given the limited ability of trypanosome prevention and eradication, tsetse vectors remain major targets of control efforts. Larvae of all three instars are developed in mothers' uteri, nourished through milk, and 'larviposited' shortly before pupation. The past few years have witnessed the emergence of approaches based on knockdown of genes involved in milk production, resulting in a significant reduction of fecundity.

RESULTS

In order to identify further genes applicable in the control of tsetse flies, we determined the expression of protein-coding genes in ovaries and uteri from both virgin and heavily pregnant Glossina morsitans morsitans females. Comparison of expression profiles allowed us to identify candidate genes with increased expression in pregnant individuals. Lists with the highest increases include genes involved in oocyte and embryonic development, or nourishment. Maximum ovarian fold change does not exceed 700, while the highest uterine fold change reaches to more than 4000. Relatively high fold changes of two neuropeptide receptors (for corazonin and myosuppressin) propose the corresponding genes alternative targets.

CONCLUSIONS

Given the higher fold changes in the uterus, targeting gene expression in this tissue may result in a more evident reduction of fecundity. However, ovaries should not be neglected, as manifested by several genes with top fold changes involved in early developmental stages. Apart from focusing on the highest fold changes, neuropeptide receptors with moderate increases in expression should be also verified as targets, given their roles in mediating the tissue control. However, this data needs to be considered initial, and the potential of these genes in affecting female fecundity needs to be verified experimentally.

A new chimeric triple reporter fusion protein as a tool for in vitro and in vivo multimodal imaging to monitor the development of African trypanosomes and Leishmania parasites

Trypanosomiases and leishmaniases, caused by a group of related protist parasites, are Neglected Tropical Diseases currently threatening >500 million people worldwide. Reporter proteins have revolutionised the research on infectious diseases and have opened up new advances in the understanding of trypanosomatid-borne diseases in terms of both biology, pathogenesis and drug development. Here, we describe the generation and some applications of a new chimeric triple reporter fusion protein combining the red-shifted firefly luciferase PpyREH9 and the tdTomato red fluorescent protein, fused by the TY1 tag. Expressed in both Trypanosoma brucei brucei and Leishmania major transgenic parasites, this construct was successfully assessed on different state-of-the-art imaging technologies, at different scales ranging from whole organism to cellular level, both in vitro and in vivo in murine models. For T. b. brucei, the usefulness of this triple marker to monitor the entire parasite cycle in both tsetse flies and mice was further demonstrated. This stable reporter allows to qualitatively and quantitatively scrutinize in real-time several crucial aspects of the parasite's development, including the development of African trypanosomes in the dermis of the mammalian host. We briefly discuss developments in bio-imaging technologies and highlight how we could improve our understanding of parasitism by combining the genetic engineering of parasites to the one of the hosting organisms in which they complete their developmental program.

Emerging and reemerging neglected tropical diseases: a review of key characteristics, risk factors, and the policy and innovation environment

In global health, critical challenges have arisen from infectious diseases, including the emergence and reemergence of old and new infectious diseases. Emergence and reemergence are accelerated by rapid human development, including numerous changes in demographics, populations, and the environment. This has also led to zoonoses in the changing human-animal ecosystem, which are impacted by a growing globalized society where pathogens do not recognize geopolitical borders. Within this context, neglected tropical infectious diseases have historically lacked adequate attention in international public health efforts, leading to insufficient prevention and treatment options. This subset of 17 infectious tropical diseases disproportionately impacts the world's poorest, represents a significant and underappreciated global disease burden, and is a major barrier to development efforts to alleviate poverty and improve human health. Neglected tropical diseases that are also categorized as emerging or reemerging infectious diseases are an even more serious threat and have not been adequately examined or discussed in terms of their unique risk characteristics. This review sets out to identify emerging and reemerging neglected tropical diseases and explore the policy and innovation environment that could hamper or enable control efforts. Through this examination, we hope to raise awareness and guide potential approaches to addressing this global health concern.

Establishment of ATP-based luciferase viability assay in 96-well plate for Trypanosoma congolense

Animal African trypanosomosis (AAT), caused by Trypanosoma congolense, is widespread throughout sub-Saharan Africa. There are significant concerns related to the current drugs available for the treatment of AAT due to their limited effectiveness across species and their adverse effects. Moreover, drug resistant trypanosomes have recently been reported in the field. High throughput screening (HTS) of large chemical compound library collections is a promising approach for identifying novel drug candidates. While HTS for Trypanozoon trypanosomes, T. brucei sspp. and T. evansi is well established, no assays have been developed for T. congolense. In the present study, the authors developed an ATP-based luciferase viability assay for T. congolense in a 96-well plate format. The calculated 50% inhibitory concentration (IC50) values for pentamidine and diminazene were 10-100 times higher in T. congolense than in T. brucei. This result suggests that the transporters for the 2 tested compounds differ between T. congolense and T. brucei. This assay could further be applied to screen novel chemical compounds for the treatment of AAT caused by T. congolense.

African Trypanosome-Induced Blood-Brain Barrier Dysfunction under Shear Stress May Not Require ERK Activation

African trypanosomes are tsetse fly transmitted protozoan parasites responsible for human African trypanosomiasis, a disease characterized by a plethora of neurological symptoms and death. How the parasites under microvascular shear stress (SS) flow conditions in the brain cross the blood-brain barrier (BBB) is not known. In vitro studies using static models comprised of human brain microvascular endothelial cells (BMEC) show that BBB activation and crossing by trypanosomes requires the orchestration of parasite cysteine proteases and host calcium-mediated cell signaling. Here, we examine BMEC barrier function and the activation of extracellular signal-regulated kinase (ERK)1/2 and ERK5, mitogen-activated protein kinase family regulators of microvascular permeability, under static and laminar SS flow and in the context of trypanosome infection. Confluent human BMEC were cultured in electric cell-substrate impedance sensing (ECIS) and parallel-plate glass slide chambers. The human BMEC were exposed to 2 or 14 dyn/cm(2) SS in the presence or absence of trypanosomes. Real-time changes in transendothelial electrical resistance (TEER) were monitored and phosphorylation of ERK1/2 and ERK5 analyzed by immunoblot assay. After reaching confluence under static conditions human BMEC TEER was found to rapidly increase when exposed to 2 dyn/cm(2) SS, a condition that mimics SS in brain postcapillary venules. Addition of African trypanosomes caused a rapid drop in human BMEC TEER. Increasing SS to 14 dyn/cm(2), a condition mimicking SS in brain capillaries, led to a transient increase in TEER in both control and infected human BMEC. However, no differences in ERK1/2 and ERK5 activation were found under any condition tested. African trypanosomiasis alters BBB permeability under low shear conditions through an ERK1/2 and ERK5 independent pathway.

'Seeing is Believing'; the use of novel imaging approaches towards creating a greater understanding of parasite: host interactions

This editorial highlights some of the key points made in the six invited reviews in this special issue of Parasite Immunology on the use of contemporary imaging technologies to investigate the parasite: host interface. Three of the reviews deal with the protozoa Trypanosoma, Leishmania, and Plasmodium, whilst the remainder focus on helminth parasites particularly Schistosoma. The reviews cover aspects related to how the development of transgenic parasites has vastly advanced our understanding of how parasites interact with host cells, particularly as a cause of pathology. Imaging technologies have also been exploited in revealing parasite localisation within host tissues and identifying novel therapeutic targets. Combined the reviews show how 'state of the art' imaging technologies have resulted in a seismic advance in our understanding of parasite biology and how this has the potential to develop new, and improved, strategies to combat disease caused by parasite infections.