The effect of livestock density on Trypanosoma brucei gambiense and T. b. rhodesiense : a causal inference-based approach

Domestic and wild animals are important reservoirs of the rhodesiense form of human African trypanosomiasis (rHAT), however quantification of this effect offers utility for deploying non-medical control activities, and anticipating their success when wildlife are excluded. Further, the uncertain role of animal reservoirs—particularly pigs—threatens elimination of transmission (EOT) targets set for the gambiense form (gHAT). Using a new time series of high-resolution cattle and pig density maps, HAT surveillance data collated by the WHO Atlas of HAT, and methods drawn from causal inference and spatial epidemiology, we conducted a retrospective ecological cohort study in Uganda, Malawi, Democratic Republic of Congo (DRC) and South Sudan to estimate the effect of cattle and pig density on HAT risk.

Trypanosomal variant surface glycoprotein expression in human African trypanosomiasis patients

Trypanosoma brucei gambiense, an extracellular protozoan parasite, is the primary causative agent of human African Trypanosomiasis. T. b. gambiense is endemic to West and Central Africa where it is transmitted by the bite of infected tsetse flies. In the bloodstream of an infected host, the parasite evades antibody recognition by altering the Variant Surface Glycoprotein (VSG) that forms a dense coat on its cell surface through a process known as antigenic variation. Each VSG has a variable N-terminal domain that is exposed to the host and a less variable C-terminal domain that is at least partially hidden from host antibodies. Our lab developed VSG-seq, a targeted RNA-seq method, to study VSG expression in T. brucei. Studies using VSG-seq to characterize antigenic variation in a mouse model have revealed marked diversity in VSG expression within parasite populations, but this finding has not yet been validated in a natural human infection. Here, we used VSG-seq to analyze VSGs expressed in the blood of twelve patients infected with T. b. gambiense. The number of VSGs identified per patient ranged from one to fourteen and, notably, two VSGs were shared by more than one patient. Analysis of expressed VSG N-terminal domain types revealed that 82% of expressed VSGs encoded a type B N-terminus, a bias not seen in datasets from other T. brucei subspecies. C-terminal types in T. b. gambiense infection were also restricted. These results demonstrate a bias either in the underlying VSG repertoire of T. b. gambiense or in the selection of VSGs from the repertoire during infection. This work demonstrates the feasibility of using VSG-seq to study antigenic variation in human infections and highlights the importance of understanding VSG repertoires in the field.Author SummaryHuman African Trypanosomiasis is a neglected tropical disease largely caused by the extracellular parasite known as Trypanosoma brucei gambiense. To avoid elimination by the host, these parasites repeatedly replace their dense surface coat of Variant Surface Glycoprotein (VSG). Despite the important role of VSGs in prolonging infection, VSG expression during natural human infections is poorly understood. A better understanding of natural VSG expression dynamics can clarify the mechanisms which T. brucei uses to alter its VSG coat and improve how trypanosomiasis is diagnosed in humans. We analyzed the expressed VSGs detected in the blood of patients with trypanosomiasis. Our findings indicate that a diverse range of VSGs are expressed in both natural and experimental infections.

Evaluation of improved coloured targets to control riverine tsetse in East Africa: A Bayesian approach

Background Riverine tsetse (Glossina spp.) transmit Trypanosoma brucei gambiense which causes Gambian Human African Trypanosomiasis. Tiny Targets were developed for cost-effective riverine tsetse control, and comprise panels of insecticide-treated blue polyester fabric and black net that attract and kill tsetse. Versus typical blue polyesters, two putatively more attractive fabrics have been developed: Vestergaard ZeroFly blue, and violet. Violet was most attractive to savannah tsetse using large targets, but neither fabric has been tested for riverine tsetse using Tiny Targets. Methods We measured numbers of G. f. fuscipes attracted to electrified Tiny Targets in Kenya and Uganda. We compared violets, Vestergaard blues, and a typical blue polyester, using three replicated Latin squares experiments. We then employed Bayesian statistical analyses to generate expected catches for future target deployments incorporating uncertainty in model parameters, and prior knowledge from previous experiments. Results Expected catches for average future replicates of violet and Vestergaard blue targets were highly likely to exceed those for typical blue. Accounting for catch variability between replicates, it remained moderately probable (70–86% and 59–84%, respectively) that a given replicate of these targets would have a higher expected catch than typical blue on the same day at the same site. Meanwhile, expected catches for average violet replicates were, in general, moderately likely to exceed those for Vestergaard blue. However, the difference in medians was small, and accounting for catch variability, the probability that the expected catch for a violet replicate would exceed a Vestergaard blue equivalent was marginal (46–71%). Conclusion Violet and Vestergaard ZeroFly blue are expected to outperform typical blue polyester in the Tiny Target configuration. Violet is unlikely to greatly outperform Vestergaard blue deployed in this way, but because violet is highly attractive to both riverine and savannah tsetse using different target designs, it may provide the more suitable general-purpose fabric.

QSAR-АНАЛІЗ БІБЛІОТЕК 4-ТІАЗОЛІДИНОН-СПОРІДНЕНИХ ГЕТЕРОЦИКЛІВ ДЛЯ ПРОГНОЗУВАННЯ ПРОТИТРИПАНОСОМНИХ ВЛАСТИВОСТЕЙ НОВИХ ПОХІДНИХ

Вступ. Похідні тіазолідинону та споріднених гетероциклів є джерелом нових протипаразитарних агентів, у тому числі молекул із протитрипаносомними властивостями. В актуальних наукових джерелах знайдено ряд досліджень про кількісний взаємозв’язок структура – протитрипаносомна активність, що включає різні підходи комп’ютерної хімії. Більшість досліджень належить до так званих мультитаргетних, коли до вибірки включають результати інших видів протипаразитарних активностей. Розробка нових QSAR-моделей похідних тіазолідинону з протитрипаносомними властивостями дозволить окреслити напрямки спрямованого дизайну нових протипаразитарних агентів на основі циклів тіазолу та тіазолідинону. Мета дослідження – встановити кількісний взаємозв’язок структура – протитрипаносомна активність у межах бібліотек тіазолідинонів та споріднених гетероциклів. Методи дослідження. Побудову математичних моделей на основі QSAR-аналізу здійснювали за допомогою онлайн-платформи Online Chemical Database. Результати й обговорення. Аналіз кількісного взаємозв’язку структура – протитрипаносомна активність проводили із застосуванням математичної моделі асоціативних нейронних мереж (ASNN: Associative Neural Networks) та методу регресії Random Forest (RFR: Random Forest regression) на основі вибірок, що включали похідні ізотіокумарин-3-карбонових кислот, тіопіранотіазолів і 4-тіазолідинон-імідазотіадіазолів із встановленою трипаноцидною активністю щодо Trypanosoma brucei brucei та Trypanosoma brucei gambiense. Кращу прогнозувальну здатність для групи ізотіокумарин-3-карбонових кислот і тіопірано[2,3-d][1,3]тіазол-2-онів обчислено за допомогою алгоритму Random Forest. Модель, обчислена на основі алгоритму Random Forest для групи імідазотіадіазолів, володіє найвищою прогнозувальною здатністю зі значенням R2=0,96. Висновок. На основі методів асоціативних нейронних мереж та регресії Random Forest розроблено прогностичні моделі для прогнозування протипаразитарної активності диверсифікованих похідних ­4-тіазолідинонів і подальшого фокусування напрямків оптимізації нових біологічно активних молекул із трипаноцидними властивостями.

Selenocysteine in Trypanosoma evansi: Identification of the Genes selb, selc, seld, pstk, seltryp and the Selenophosphate Synthetase Protein

Selenoproteins have been described in all three domains of life and their function has been mainly associated with oxidative stress defense. Canonical elements required for selenoprotein production have been identified in members of the kinetoplastid group supporting the existence of a complete selenocysteine synthesis pathway in these organisms. Currently, nothing is known regarding the selenocysteine pathway in Trypanosoma evansi. In this study, we identified the expression of the elements selB, selC, selD, PSTK and selTRYP at the mRNA level in T. evansi. All translated proteins (selD, PSTK, selTRYP and selB) have the domains predicted and higher identity with Trypanosoma brucei. gambiense. The selenophosphate synthetase protein was localized in the cytoplasm. Our results support the existence of an active selenocysteine pathway in T. evansi.

A pilot study demonstrating the identification of Trypanosoma brucei gambiense and T. b. rhodesiense in vectors using a multiplexed high-resolution melt qPCR

Human African Trypanosomiasis (HAT) is a potentially fatal parasitic infection caused by the trypanosome sub-species Trypanosoma brucei gambiense and T. b. rhodesiense transmitted by tsetse flies. Currently, global HAT case numbers are reaching less than 1 case per 10,000 people in many disease foci. As such, there is a need for simple screening tools and strategies to replace active screening of the human population which can be maintained post-elimination for Gambian HAT and long-term for Rhodesian HAT. Here, we describe the proof of principle application of a novel high-resolution melt assay for the xenomonitoring of Trypanosoma brucei gambiense and T. b. rhodesiense in tsetse. Both novel and previously described primers which target species-specific single copy genes were used as part of a multiplex qPCR. An additional primer set was included in the multiplex to determine if samples had sufficient genomic material for detecting genes present in low copy number. The assay was evaluated on 96 wild-caught tsetse previously identified to be positive for T. brucei s. l. of which two were known to be positive for T. b. rhodesiense. The assay was found to be highly specific with no cross-reactivity with non-target trypanosome species and the assay limit of detection was 104 tryps/mL. The qPCR successfully identified three T. b. rhodesiense positive flies, in agreement with the reference species-specific PCRs. This assay provides an alternative to running multiple PCRs when screening for pathogenic sub-species of T. brucei s. l. and produces results in less than 2 hours, avoiding gel electrophoresis and subjective analysis. This method could provide a component of a simple and efficient method of screening large numbers of tsetse flies in known HAT foci or in areas at risk of recrudescence or threatened by the changing distribution of both forms of HAT.

Heme-deficient metabolism and impaired cellular differentiation as an evolutionary trade-off for human infectivity in Trypanosoma brucei gambiense

Resistance to African trypanosomes in humans relies on targeting of a trypanosome lytic factor 1 (TLF1) to trypanosome haptoglobin-hemoglobin receptor (HpHbR). While TLF1 avoidance by the inactivation of the HpHbR contributes to Trypanosoma brucei gambiense human infectivity, the evolutionary trade-off of this adaptation is unknown. Both T. b. gambiense with inactive HpHbR, as well as a genetically engineered T.b.brucei HpHbR knock-out show only trace levels of intracellular heme and lack the downstream hemoprotein activities, thereby providing an extraordinary example of aerobic parasite proliferation in the absence of heme. We further show that HpHbR facilitates the developmental progression by inducing PAD-1 expression that is associated with the formation of cell cycle-arrested stumpy forms in T. b.brucei . Accordingly, T. b. gambiense was found to be poorly competent for slender-to-stumpy differentiation unless a functional HpHbR receptor derived from T. b. brucei was genetically restored.