Factors Affecting the Propensity of Tsetse Flies to Enter Houses and Attack Humans Inside: Increased Risk of Sleeping Sickness in Warmer Climates

Background

Sleeping sickness, or human African trypanosomiasis, is caused by two species of Trypanosoma brucei that are transmitted to humans by tsetse flies (Glossina spp.) when these insects take a bloodmeal. It is commonly assumed that humans must enter the normal woodland habitat of the flies to become infected, but recent studies found that tsetse frequently attack humans inside buildings. Factors affecting human/tsetse contact in buildings need identification.

Methodology/Principal Findings

In Zimbabwe, tsetse were allowed access to a house via an open door. Those in the house at sunset, and those alighting on humans in the house during the day, were caught using hand-nets. Total catches were unaffected by: (i) the presence of humans in the house and at the door, (ii) wood smoke from a fire inside the house or just outside, (iii) open windows, and (iv) chemicals simulating the odor of cattle or of humans. Catches increased about 10-fold with rising ambient temperatures, and during the hottest months the proportion of the total catch that was taken from the humans increased from 5% to 13%. Of the tsetse caught from humans, 62% consisted of female G. morsitans morstans and both sexes of G. pallidipes, i.e., the group of tsetse that normally alight little on humans. Some of the tsetse caught were old enough to be effective vectors.

Conclusion/Significance

Present results confirm previous suggestions that buildings provide a distinctive and important venue for transmission of sleeping sickness, especially since the normal repellence of humans and smoke seems poorly effective in such places. The importance of the venue would be increased in warmer climates.     

A Two-Patch Model of Gambian Sleeping Sickness: Application to Vector Control Strategies in a Village and Plantations

A compartmental model is described for the spread of Gambian sleeping sickness in a spatially heterogeneous environment in which vector and human populations migrate between two "patches": the village and the plantations. The number of equilibrium points depends on two "summary parameters": gr the proportion removed among human infectives, and R0, the basic reproduction number. The origin is stable for R0 <1 and unstable for R0 >1. Control strategies are assessed by studying the mix of vector control between the two patches that bring R0 below 1. The results demonstrate the importance of vector control in the plantations. For example if 20 percent of flies are in the village and the blood meal rate in the village is 10 percent, then a 20 percent added vector mortality in the village must be combined with a 9 percent added mortality in the plantations in order to bring R0 below 1. The results are quite insentive to the blood meal rate in the village. Optimal strategies (that minimize the total number of flies trapped in both patches) are briefly discussed.     

Genetic Diversity and Population Structure of Trypanosoma brucei in Uganda: Implications for the Epidemiology of Sleeping Sickness and Nagana

Background

While Human African Trypanosomiasis (HAT) is in decline on the continent of Africa, the disease still remains a major health problem in Uganda. There are recurrent sporadic outbreaks in the traditionally endemic areas in south-east Uganda, and continued spread to new unaffected areas in central Uganda. We evaluated the evolutionary dynamics underpinning the origin of new foci and the impact of host species on parasite genetic diversity in Uganda. We genotyped 269 Trypanosoma brucei isolates collected from different regions in Uganda and southwestern Kenya at 17 microsatellite loci, and checked for the presence of the SRA gene that confers human infectivity to T. b. rhodesiense.

Results

Both Bayesian clustering methods and Discriminant Analysis of Principal Components partition Trypanosoma brucei isolates obtained from Uganda and southwestern Kenya into three distinct genetic clusters. Clusters 1 and 3 include isolates from central and southern Uganda, while cluster 2 contains mostly isolates from southwestern Kenya. These three clusters are not sorted by subspecies designation (T. b. brucei vs T. b. rhodesiense), host or date of collection. The analyses also show evidence of genetic admixture among the three genetic clusters and long-range dispersal, suggesting recent and possibly on-going gene flow between them.

Conclusions

Our results show that the expansion of the disease to the new foci in central Uganda occurred from the northward spread of T. b. rhodesiense (Tbr). They also confirm the emergence of the human infective strains (Tbr) from non-infective T. b. brucei (Tbb) strains of different genetic backgrounds, and the importance of cattle as Tbr reservoir, as confounders that shape the epidemiology of sleeping sickness in the region.     

The Dispersal Ecology of Rhodesian Sleeping Sickness Following Its Introduction to a New Area

Tsetse-transmitted human and animal trypanosomiasis are constraints to both human and animal health in sub-Saharan Africa, and although these diseases have been known for over a century, there is little recent evidence demonstrating how the parasites circulate in natural hosts and ecosystems. The spread of Rhodesian sleeping sickness (caused by Trypanosoma brucei rhodesiense) within Uganda over the past 15 years has been linked to the movement of infected, untreated livestock (the predominant reservoir) from endemic areas. However, despite an understanding of the environmental dependencies of sleeping sickness, little research has focused on the environmental factors controlling transmission establishment or the spatially heterogeneous dispersal of disease following a new introduction. In the current study, an annually stratified case-control study of Rhodesian sleeping sickness cases from Serere District, Uganda was used to allow the temporal assessment of correlations between the spatial distribution of sleeping sickness and landscape factors. Significant relationships were detected between Rhodesian sleeping sickness and selected factors, including elevation and the proportion of land which was “seasonally flooding grassland” or “woodlands and dense savannah.” Temporal trends in these relationships were detected, illustrating the dispersal of Rhodesian sleeping sickness into more ‘suitable’ areas over time, with diminishing dependence on the point of introduction in concurrence with an increasing dependence on environmental and landscape factors. These results provide a novel insight into the ecology of Rhodesian sleeping sickness dispersal and may contribute towards the implementation of evidence-based control measures to prevent its further spread.     

Distribution and Density of Tsetse Flies (Glossinidae: Diptera) at the Game/People/Livestock Interface of the Nkhotakota Game Reserve Human Sleeping Sickness Focus in Malawi

In large parts sub-Saharan Africa, tsetse flies, the vectors of African human or animal trypanosomiasis, are, or will in the foreseeable future, be confined to protected areas such as game or national parks. Challenge of people and livestock is likely to occur at the game/livestock/people interface of such infested areas. Since tsetse control in protected areas is difficult, management of trypanosomiasis in people and/or livestock requires a good understanding of tsetse population dynamics along such interfaces. The Nkhotakota Game Reserve, an important focus of human trypanosomiasis in Malawi, is a tsetse-infested protected area surrounded by a virtually tsetse-free zone. The abundance of tsetse (Glossina morsitans morsitans) along the interface, within and outside the game reserve, was monitored over 15 months using epsilon traps. A land cover map described the vegetation surrounding the traps. Few flies were captured outside the reserve. Inside, the abundance of tsetse at the interface was low but increased away from the boundary. This uneven distribution of tsetse inside the reserve is attributed to the uneven distribution of wildlife, the main host of tsetse, being concentrated deeper inside the reserve. Challenge of people and livestock at the interface is thus expected to be low, and cases of trypanosomiasis are likely due to people and/or livestock entering the reserve. Effective control of trypanosomiasis in people and livestock could be achieved by increasing the awareness among people of dangers associated with entering the reserve.     

Hit-to-Lead Development of the Chamigrane Endoperoxide Merulin A for the Treatment of African Sleeping Sickness

Background

Human African trypanosomiasis (HAT) is an infectious disease with a large global health burden occurring primarily in Central and Eastern Africa. Most current treatments have poor blood brain barrier (BBB) penetration, which prevent them from targeting the most lethal stage of the infection. In addition, current therapeutics suffer from a variety of limitations ranging from serious side effects to difficulties with treatment administration. Therefore it is of crucial importance to find new treatments that are safe, affordable, and effective against both sub-species of Trypanosoma brucei.

Methods

Semi-synthetic derivatization of the fungally-derived natural product merulin A (1) has led to the discovery of new development candidates for the protozoan parasite T. brucei, the causative agent of HAT. Creation of an initial SAR library based around the merulin scaffold revealed several key features required for activity, including the endoperoxide bridge, as well as one position suitable for further derivatization. Subsequent synthesis of a 20-membered analogue library, guided by the addition of acyl groups that improve the drug-like properties of the merulin A core, resulted in the development of compound 12 with an IC₅₀ of 60 nM against T. brucei, and a selectivity index greater than 300-fold against HeLa and immortalized glial cells.

Significance

We report the semi-synthetic optimization of the merulin class of endoperoxide natural products as development candidates against T. brucei. We have identified compounds with low nM antiparasitic activities and high selectivity indices against HeLa cells. These compounds can be produced economically in large quantities via a one step derivatization from the microbial fermentation broth isolate, making them encouraging lead candidates for further development.     

Secondary Infertility: A Neglected Aspect of Buerger’s Disease

Background:During the gathering of demographic data for the biobank on Buerger’s Disease (BD), we found that, after the clinical manifestation of BD, the patients usually became infertile, and the age of their last child was compatible with the time of disease diagnosis. The aim of this study was to evaluate the underlying cause of secondary infertility in BD patients.Methods:Anti-sperm antibodies (ASA), testosterone, luteinizing hormone (LH), and follicle-stimulating hormone (FSH) in the sera of 39 male BD patients were measured and compared with 39 age-matched Caucasian male controls.Results:Six patients declared that they suffered from impotency. The ASA level was positive in 25.6% of the patients and 2.4% of the controls (p= 0.003, CC= 6.96). The mean levels of testosterone in the patients and controls were 393.12±32.9 ng/dl and 354.37±30.9 ng/dl, respectively. The mean levels of LH in the patients and controls were 0.88±0.12 mIU/r and 0.85±0.1 mIU/r, respectively. The mean levels of FSH in the patients and controls were 4.1± 0.35 mIU/r and 3.56±0.33 mIU/r, respectively. No significant difference in the serum levels of testosterone, LH, or FSH was found between the patients and controls (p> 0.05). The spermograms of three ASA-negative patients demonstrated impaired sperm motility.DiscussionAnti-sperm antibodies, disturbed genital circulation, autonomic dysfunction and sperm motility may be responsible for secondary infertility in Buerger’s Disease.Key Words: Anti-sperm antibody, Buerger’s Disease, Infertility, Thromboangiitis Obliterans     

SVMTriP: A Method to Predict Antigenic Epitopes Using Support Vector Machine to Integrate Tri-Peptide Similarity and Propensity

Identifying protein surface regions preferentially recognizable by antibodies (antigenic epitopes) is at the heart of new immuno-diagnostic reagent discovery and vaccine design, and computational methods for antigenic epitope prediction provide crucial means to serve this purpose. Many linear B-cell epitope prediction methods were developed, such as BepiPred, ABCPred, AAP, BCPred, BayesB, BEOracle/BROracle, and BEST, towards this goal. However, effective immunological research demands more robust performance of the prediction method than what the current algorithms could provide. In this work, a new method to predict linear antigenic epitopes is developed; Support Vector Machine has been utilized by combining the Tri-peptide similarity and Propensity scores (SVMTriP). Applied to non-redundant B-cell linear epitopes extracted from IEDB, SVMTriP achieves a sensitivity of 80.1% and a precision of 55.2% with a five-fold cross-validation. The AUC value is 0.702. The combination of similarity and propensity of tri-peptide subsequences can improve the prediction performance for linear B-cell epitopes. Moreover, SVMTriP is capable of recognizing viral peptides from a human protein sequence background. A web server based on our method is constructed for public use. The server and all datasets used in the current study are available at http://sysbio.unl.edu/SVMTriP.     

Reducing Human-Tsetse Contact Significantly Enhances the Efficacy of Sleeping Sickness Active Screening Campaigns: A Promising Result in the Context of Elimination

Background

Control of gambiense sleeping sickness, a neglected tropical disease targeted for elimination by 2020, relies mainly on mass screening of populations at risk and treatment of cases. This strategy is however challenged by the existence of undetected reservoirs of parasites that contribute to the maintenance of transmission. In this study, performed in the Boffa disease focus of Guinea, we evaluated the value of adding vector control to medical surveys and measured its impact on disease burden.

Methods

The focus was divided into two parts (screen and treat in the western part; screen and treat plus vector control in the eastern part) separated by the Rio Pongo river. Population census and baseline entomological data were collected from the entire focus at the beginning of the study and insecticide impregnated targets were deployed on the eastern bank only. Medical surveys were performed in both areas in 2012 and 2013.

Findings

In the vector control area, there was an 80% decrease in tsetse density, resulting in a significant decrease of human tsetse contacts, and a decrease of disease prevalence (from 0.3% to 0.1%; p=0.01), and an almost nil incidence of new infections (<0.1%). In contrast, incidence was 10 times higher in the area without vector control (>1%, p<0.0001) with a disease prevalence increasing slightly (from 0.5 to 0.7%, p=0.34).

Interpretation

Combining medical and vector control was decisive in reducing T. b. gambiense transmission and in speeding up progress towards elimination. Similar strategies could be applied in other foci.     

Stage Progression and Neurological Symptoms in Trypanosoma brucei rhodesiense Sleeping Sickness: Role of the CNS Inflammatory Response

Background

Human African trypanosomiasis progresses from an early (hemolymphatic) stage, through CNS invasion to the late (meningoencephalitic) stage. In experimental infections disease progression is associated with neuroinflammatory responses and neurological symptoms, but this concept requires evaluation in African trypanosomiasis patients, where correct diagnosis of the disease stage is of critical therapeutic importance.

Methodology/Principal Findings

This was a retrospective study on a cohort of 115 T.b.rhodesiense HAT patients recruited in Eastern Uganda. Paired plasma and CSF samples allowed the measurement of peripheral and CNS immunoglobulin and of CSF cytokine synthesis. Cytokine and immunoglobulin expression were evaluated in relation to disease duration, stage progression and neurological symptoms. Neurological symptoms were not related to stage progression (with the exception of moderate coma). Increases in CNS immunoglobulin, IL-10 and TNF-α synthesis were associated with stage progression and were mirrored by a reduction in TGF-β levels in the CSF. There were no significant associations between CNS immunoglobulin and cytokine production and neurological signs of disease with the exception of moderate coma cases. Within the study group we identified diagnostically early stage cases with no CSF pleocytosis but intrathecal immunoglobulin synthesis and diagnostically late stage cases with marginal CSF pleocytosis and no detectable trypanosomes in the CSF.

Conclusions

Our results demonstrate that there is not a direct linkage between stage progression, neurological signs of infection and neuroinflammatory responses in rhodesiense HAT. Neurological signs are observed in both early and late stages, and while intrathecal immunoglobulin synthesis is associated with neurological signs, these are also observed in cases lacking a CNS inflammatory response. While there is an increase in inflammatory cytokine production with stage progression, this is paralleled by increases in CSF IL-10. As stage diagnostics, the CSF immunoglobulins and cytokines studied do not have sufficient sensitivity to be of clinical value.     

Explaining the Host-Finding Behavior of Blood-Sucking Insects: Computerized Simulation of the Effects of Habitat Geometry on Tsetse Fly Movement

Background

Male and female tsetse flies feed exclusively on vertebrate blood. While doing so they can transmit the diseases of sleeping sickness in humans and nagana in domestic stock. Knowledge of the host-orientated behavior of tsetse is important in designing bait methods of sampling and controlling the flies, and in understanding the epidemiology of the diseases. For this we must explain several puzzling distinctions in the behavior of the different sexes and species of tsetse. For example, why is it that the species occupying savannahs, unlike those of riverine habitats, appear strongly responsive to odor, rely mainly on large hosts, are repelled by humans, and are often shy of alighting on baits?

Methodology/Principal Findings

A deterministic model that simulated fly mobility and host-finding success suggested that the behavioral distinctions between riverine, savannah and forest tsetse are due largely to habitat size and shape, and the extent to which dense bushes limit occupiable space within the habitats. These factors seemed effective primarily because they affect the daily displacement of tsetse, reducing it by up to ∼70%. Sex differences in behavior are explicable by females being larger and more mobile than males.

Conclusion/Significance

Habitat geometry and fly size provide a framework that can unify much of the behavior of all sexes and species of tsetse everywhere. The general expectation is that relatively immobile insects in restricted habitats tend to be less responsive to host odors and more catholic in their diet. This has profound implications for the optimization of bait technology for tsetse, mosquitoes, black flies and tabanids, and for the epidemiology of the diseases they transmit.     

From Health Advice to Taboo: Community Perspectives on the Treatment of Sleeping Sickness in the Democratic Republic of Congo,a Qualitative Study

Background

Socio-cultural and economic factors constitute real barriers for uptake of screening and treatment of Human African Trypanosomiasis (HAT) in the Democratic Republic of Congo (DRC). Better understanding and addressing these barriers may enhance the effectiveness of HAT control.

Methods

We performed a qualitative study consisting of semi-structured interviews and focus group discussions in the Bandundu and Kasaï Oriental provinces, two provinces lagging behind in the HAT elimination effort. Our study population included current and former HAT patients, as well as healthcare providers and program managers of the national HAT control program. All interviews and discussions were voice recorded on a digital device and data were analysed with the ATLAS.ti software.

Findings

Health workers and community members quoted a number of prohibitions that have to be respected for six months after HAT treatment: no work, no sexual intercourse, no hot food, not walking in the sun. Violating these restrictions is believed to cause serious, and sometimes deadly, complications. These strong prohibitions are well-known by the community and lead some people to avoid HAT screening campaigns, for fear of having to observe such taboos in case of diagnosis.

Discussion

The restrictions originally aimed to mitigate the severe adverse effects of the melarsoprol regimen, but are not evidence-based and became obsolete with the new safer drugs. Correct health information regarding HAT treatment is essential. Health providers should address the perspective of the community in a constant dialogue to keep abreast of unintended transformations of meaning.