Diagnosing human African trypanosomiasis in Angola using a card agglutination test: observational study of active and passive case finding strategies

The comprehensive epidemiological status of human African trypanosomiasis in Nigeria: meta-analysis and systematic review of the full story (1962-2022)

Human African trypanosomiasis (HAT) in Nigeria is caused primarily by Trypanosoma brucei gambiense (gHAT), which has historically been a major human and animal health problem. This study aims to examine the status of gHAT in Nigeria over the past 60 years. The World Health Organization (WHO) set two targets to eliminate HAT as a public health concern by 2020 and terminate its global transmission by 2030. The former target has been achieved, but accurate monitoring and surveillance are important for maintaining this success and delivering the second target. Although recent cases in Nigeria are rare, accurately estimating the national seroprevalence and actual prevalence of gHATs remains challenging. To address this, a meta-analysis reviewed studies on gHATs in Nigeria from databases such as Embase, Global Health, Ovid Medline, Web of Science, and Google Scholar. Ten studies were included, ranging between 1962 and 2016, covering 52 clusters and 5,671,877 individuals, even though databases were scrutinized up to 2022. The seroprevalence ranged from 1.75 to 17.07%, with an overall estimate of 5.01% (95% CI 1.72-9.93). The actual gHAT prevalence detected by parasitological or PCR methods was 0.001 (95% CI 0.000-0.002), indicating a prevalence of 0.1%. Notably, the seroprevalence was greater in southern Nigeria than in northern Nigeria. These findings suggest that the disease might be spreading unnoticed due to the increased movement of people from endemic areas. This study highlights the paucity of studies in Nigeria over the last 60 years and emphasizes the need for further research, systematic surveillance, and proper reporting methods throughout the country.

Specificity of serological screening tests and reference laboratory tests to diagnose gambiense human African trypanosomiasis: a prospective clinical performance study

BACKGROUND

Serological screening tests play a crucial role to diagnose gambiense human African trypanosomiasis (gHAT). Presently, they preselect individuals for microscopic confirmation, but in future "screen and treat" strategies they will identify individuals for treatment. Variability in reported specificities, the development of new rapid diagnostic tests (RDT) and the hypothesis that malaria infection may decrease RDT specificity led us to evaluate the specificity of 5 gHAT screening tests.

METHODS

During active screening, venous blood samples from 1095 individuals from Côte d'Ivoire and Guinea were tested consecutively with commercial (CATT, HAT Sero-K-SeT, Abbott Bioline HAT 2.0) and prototype (DCN HAT RDT, HAT Sero-K-SeT 2.0) gHAT screening tests and with a malaria RDT. Individuals with ≥ 1 positive gHAT screening test underwent microscopy and further immunological (trypanolysis with T.b. gambiense LiTat 1.3, 1.5 and 1.6; indirect ELISA/T.b. gambiense; T.b. gambiense inhibition ELISA with T.b. gambiense LiTat 1.3 and 1.5 VSG) and molecular reference laboratory tests (PCR TBRN3, 18S and TgsGP; SHERLOCK 18S Tids, 7SL Zoon, and TgsGP; Trypanozoon S2-RT-qPCR 18S2, 177T, GPI-PLC and TgsGP in multiplex; RT-qPCR DT8, DT9 and TgsGP in multiplex). Microscopic trypanosome detection confirmed gHAT, while other individuals were considered gHAT free. Differences in fractions between groups were assessed by Chi square and differences in specificity between 2 tests on the same individuals by McNemar.

RESULTS

One gHAT case was diagnosed. Overall test specificities (n = 1094) were: CATT 98.9% (95% CI: 98.1-99.4%); HAT Sero-K-SeT 86.7% (95% CI: 84.5-88.5%); Bioline HAT 2.0 82.1% (95% CI: 79.7-84.2%); DCN HAT RDT 78.2% (95% CI: 75.7-80.6%); and HAT Sero-K-SeT 2.0 78.4% (95% CI: 75.9-80.8%). In malaria positives, gHAT screening tests appeared less specific, but the difference was significant only in Guinea for Abbott Bioline HAT 2.0 (P = 0.03) and HAT Sero-K-Set 2.0 (P = 0.0006). The specificities of immunological and molecular laboratory tests in gHAT seropositives were 98.7-100% (n = 399) and 93.0-100% (n = 302), respectively. Among 44 reference laboratory test positives, only the confirmed gHAT patient and one screening test seropositive combined immunological and molecular reference laboratory test positivity.

CONCLUSIONS

Although a minor effect of malaria cannot be excluded, gHAT RDT specificities are far below the 95% minimal specificity stipulated by the WHO target product profile for a simple diagnostic tool to identify individuals eligible for treatment. Unless specificity is improved, an RDT-based "screen and treat" strategy would result in massive overtreatment. In view of their inconsistent results, additional comparative evaluations of the diagnostic performance of reference laboratory tests are indicated for better identifying, among screening test positives, those at increased suspicion for gHAT.

TRIAL REGISTRATION

The trial was retrospectively registered under NCT05466630 in clinicaltrials.gov on July 15 2022.

Neglected tropical disease (NTD) diagnostics: current development and operations to advance control

Neglected tropical diseases (NTDs) have become important public health threats that require multi-faceted control interventions. As late treatment and management of NTDs contribute significantly to the associated burdens, early diagnosis becomes an important component for surveillance and planning effective interventions. This review identifies common NTDs and highlights the progress in the development of diagnostics for these NTDs. Leveraging existing technologies to improve NTD diagnosis and improving current operational approaches for deployment of developed diagnostics are crucial to achieving the 2030 NTD elimination target. Point-of-care NTD (POC-NTD) diagnostic tools are recommended preferred diagnostic options in resource-constrained areas for mapping risk zones and monitoring treatment efficacy. However, few are currently available commercially. Technical training of remote health care workers on the use of POC-NTD diagnostics, and training of health workers on the psychosocial consequences of these diagnostics are critical in harnessing POC-NTD diagnostic potential. While the COVID-19 pandemic has challenged the possibility of achieving NTD elimination in 2030 due to the disruption of healthcare services and dwindling financial support for NTDs, the possible contribution of NTDs in exacerbating COVID-19 pandemic should motivate NTD health system strengthening.

Human African Trypanosomiasis (Sleeping Sickness)-Epidemiology, Clinical Manifestations, Diagnosis, Treatment, and Prevention

Purpose of Review

Human African Trypanosomiasis (HAT), also known as sleeping sickness, is a vector-borne parasitic neglected tropical disease (NTD) endemic in sub-Saharan Africa. This review aims to enhance our understanding of HAT and provide valuable insights to combat this significant public health issue by synthesizing the latest research and evidence.

Recent Findings

HAT has reached a historical < 1000 cases in 2018. In patients without neurologic symptoms and signs, the likelihood of a severe meningoencephalitic stage is deemed low, obviating the need for a lumbar puncture to guide treatment decisions using fexinidazole.

Summary

Both forms of the disease, gambiense HAT (gHAT) and rhodesiense HAT (rHAT), have specific epidemiology, risk factors, diagnosis, and treatment. Disease management still requires a high index of suspicion, infectious disease expertise, and specialized medical care. Essential stakeholders in health policy are critical to accomplishing the elimination goals of the NTD roadmap for 2021-2030.

Performance of the SD Bioline rapid diagnostic test as a good alternative to the detection of human African trypanosomiasis in Cameroon

BACKGROUND

Case detection is essential for the management of human African trypanosomiasis (HAT), which is caused by Trypanosoma brucei gambiense. Prior to parasitological confirmation, routine screening using the card agglutination test for trypanosomiasis (CATT) is essential. Recently, individual rapid diagnostic tests (RDTs) for the serodiagnosis of HAT have been developed.

OBJECTIVE

The purpose of this study was to evaluate the contribution of SD Bioline HAT to the serological screening of human African trypanosomiasis in Cameroonian foci.Methods. Between June 2014 and January 2015, blood samples were collected during surveys in the foci of Campo, Yokadouma, and Fontem. The sensitivity (Se) and specificity (Sp) of SD Bioline HAT were determined using the CATT as the gold standard for the detection of specific antibodies against Trypanosoma brucei gambiense.

RESULTS

A total of 88 samples were tested: 59.1% (n=52) in Campo, 31.8% (n=28) in Yokadouma, and 9.1% (n=8) in Fontem. There were 61.4% (n=54) males and 38.4% (n=34) females, and the average age was 35.4 19.0 years. In probed foci, the overall seroprevalence was 11.4% (95% confidence interval: 6.3-19.7) with the CATT method and 18.2% (95% confidence interval: 11.5-27.2%) with the SD Bioline HAT RDT method. The SD Bioline HAT's Se and Sp were 80.0% and 89.7%, respectively.

CONCLUSIONS

This study demonstrated that the overall performance of the SD Bioline HAT was comparable to that of the CATT, with high specificity in the serological detection of HAT.

Gambian human African trypanosomiasis in North West Uganda. Are we on course for the 2020 target?

In 1994, combined active and passive screening reported 1469 cases from the historic Gambian Human African Trypanosomiasis (gHAT) foci of West Nile, Uganda. Since 2011 systematic active screening has stopped and there has been reliance on passive screening. During 2014, passive screening alone detected just nine cases. In the same year a tsetse control intervention was expanded to cover the main gHAT foci in West Nile to curtail transmission of gHAT contributing to the elimination of gHAT as a public health problem in the area. It is known that sole reliance on passive screening is slow to detect cases and can underestimate the actual true number. We therefore undertook an active screening programme designed to test the efficacy of these interventions against gHAT transmission and clarify disease status. Screening was conducted in 28 randomly selected villages throughout the study area, aiming to sample all residents. Whole blood from 10,963 participants was analysed using CATT and 97 CATT suspects (0.9%) were evaluated with microscopy and trypanolysis. No confirmed cases were found providing evidence that the gHAT prevention programmes in West Nile have been effective. Results confirm gHAT prevalence in the study area of West Nile is below the elimination threshold (1 new case / 10,000 population), making elimination on course across this study area if status is maintained. The findings of this study can be used to guide future HAT and tsetse management in other gHAT foci, where reduced caseloads necessitate a shift from active to passive screening.

The number of gHAT cases across West Nile, Uganda has declined in the last 20 years. This decline is due to the impact of programmes of active and passive case detection and treatment which have recently been combined with tsetse control operations (post 2011). We carried out an active survey of gHAT to evaluate the prevalence in areas where vector control has been introduced. Our results confirm that the overall prevalence of gHAT is below 1 case per 10,000 people at risk in the historical foci and shows that results from passive screening are providing an accurate picture of gHAT prevalence in the area.

The impact of passive case detection on the transmission dynamics of gambiense Human African Trypanosomiasis

Gambiense Human African Trypanosomiasis (HAT), or sleeping sickness, is a vector-borne disease affecting largely rural populations in Western and Central Africa. The main method for detecting and treating cases of gambiense HAT are active screening through mobile teams and passive detection through self-referral of patients to dedicated treatment centres or hospitals. Strategies based on active case finding and treatment have drastically reduced the global incidence of the disease over recent decades. However, little is known about the coverage and transmission impact of passive case detection. We used a mathematical model to analyse data from the period between active screening sessions in hundreds of villages that were monitored as part of three HAT control projects run by Médecins Sans Frontières in Southern Sudan and Uganda in the late 1990s and early 2000s. We found heterogeneity in incidence across villages, with a small minority of villages found to have much higher transmission rates and burdens than the majority. We further found that only a minority of prevalent cases in the first, haemo-lymphatic stage of the disease were detected passively (maximum likelihood estimate <30% in all three settings), whereas around 50% of patients in the second, meningo-encephalitic were detected. We estimated that passive case detection reduced transmission in affected areas by between 30 and 50%, suggesting that there is great potential value in improving rates of passive case detection. As gambiense HAT is driven towards elimination, it will be important to establish good systems of passive screening, and estimates such as the ones here will be of value in assessing the expected impact of moving from a primarily active to a more passive screening regime.

Gambiense Human African Trypanosomiasis, or sleeping sickness, is transmitted by the tsetse fly and affects rural populations in Western and Central Africa. It is a deadly disease if untreated, and it is therefore important to find people in the early stages of disease so that appropriate care and medication can be provided. Because of this, much emphasis is put on mobile teams going from village to village and actively finding as many potential patients as possible. This does not reach all infected people, though, and some are only detected passively, that is they report themselves to a health provider, often in advanced stages of disease. It is not clear what proportion of cases of sleeping sickness are detected in this way, or how much onwards transmission is prevented. Here we used a mathematical model to analyse data from a sleeping sickness control programme in Uganda and South Sudan, in order to identify which proportion of people infected with the disease are identified through passive case detection. We found that only a minority of patients are identified in this way in the early stages of disease, but around half are identified if they are in the later stages. We further found that passive screening reduced transmission in affected areas by between 30 and 50%. This suggests that there is great potential value in improving the rates of passive case detection, and we recommend that more emphasis is put on tackling potential barriers that prevent people being detected.

Knowledge and prevalence of Human African Trypanosomiasis among residents of Kachia grazing reserve, Kachia local government area, Kaduna state, Nigeria, 2012

INTRODUCTION

Human African Trypanosomiasis (HAT) is a vector borne parasitic disease transmitted to humans by infected tse-tse flies cause morbidity including delayed child mental development. Reports of nuisance and bites from tse-tse flies by residents of Kachia grazing led to the study to determine the knowledge, practices and prevalence of HAT among residents of the grazing reserve.

METHODS

We conducted active case search in a cross-sectional study using multi-stage sampling with probability proportionate to size. We administered structured questionnaire on Knowledge, practices relating to HAT prevention and screened for HAT using card agglutination test for Trypanosomiasis (CATT). Knowledge of HAT was scored 0-5 and categorized good (3-5) and poor (0-2) based on score, predisposition to risk of HAT as exposure to ≥two risk factors and, a case of HAT as any respondent that tested positive on CATT. We analysed data using Epi-info and MS-excel.

RESULTS

Of the 300 respondents, mean age 39(±17years) interviewed, 56.3% were males, 12.0% had good knowledge of HAT and 76.3% were exposed to HAT risk factors. Prevention practices included clearing of overgrown bushes around houses (99%), use of insecticidal treated nets (75.7%) and protective clothing (41.0%). Males {Odds Ratio [OR] 5.0; 95% Confidence Interval (CI) 1.8 - 13.6}, age above 40 years {OR 5.0; 95% CI 1.1 - 24.4} and family history of HAT {OR 8.7; 95% CI 2.4 - 32.1} were significantly associated with HAT knowledge. None tested positive on CATT.

CONCLUSION

Despite poor knowledge of HAT, residents practiced HAT preventive measures and zero HAT prevalence was recorded.

Overview of the Diagnostic Methods Used in the Field for Human African Trypanosomiasis: What Could Change in the Next Years?

Sleeping sickness is a parasitic infection caused by two species of trypanosomes (Trypanosoma brucei gambiense and rhodesiense), transmitted by the tsetse fly. The disease eventually affects the central nervous system, resulting in severe neurological symptoms. Without treatment, death is inevitable. During the first stage of the disease, infected patients are mildly symptomatic and early detection of infection allows safer treatment (administered on an outpatient basis) which can avoid death; routine screening of the exposed population is necessary, especially in areas of high endemicity. The current therapeutic treatment of this disease, especially in stage 2, can cause complications and requires a clinical surveillance for several days. A good stage diagnosis of the disease is the cornerstone for delivering the adequate treatment. The task faced by the medical personnel is further complicated by the lack of support from local health infrastructure, which is at best weak, but often nonexistent. Therefore it is crucial to look for new more efficient technics for the diagnosis of stage which are also best suited to use in the field, in areas not possessing high-level health facilities. This review, after an overview of the disease, summarizes the current diagnosis procedures and presents the advances in the field.

Loop Mediated Isothermal Amplification for Detection of Trypanosoma brucei gambiense in Urine and Saliva Samples in Nonhuman Primate Model

Human African trypanosomiasis (HAT) is a vector-borne parasitic zoonotic disease. The disease caused by Trypanosoma brucei gambiense is the most prevalent in Africa. Early diagnosis is hampered by lack of sensitive diagnostic techniques. This study explored the potential of loop mediated isothermal amplification (LAMP) and polymerase chain reaction (PCR) in the detection of T. b. gambiense infection in a vervet monkey HAT model. Six vervet monkeys were experimentally infected with T. b. gambiense IL3253 and monitored for 180 days after infection. Parasitaemia was scored daily. Blood, cerebrospinal fluid (CSF), saliva, and urine samples were collected weekly. PCR and LAMP were performed on serum, CSF, saliva, and urine samples. The detection by LAMP was significantly higher than that of parasitological methods and PCR in all the samples. The performance of LAMP varied between the samples and was better in serum followed by saliva and then urine samples. In the saliva samples, LAMP had 100% detection between 21 and 77 dpi, whereas in urine the detection it was slightly lower, but there was over 80% detection between 28 and 91 dpi. However, LAMP could not detect trypanosomes in either saliva or urine after 140 and 126 dpi, respectively. The findings of this study emphasize the importance of LAMP in diagnosis of HAT using saliva and urine samples.

Diagnostics for the control and elimination of neglected tropical diseases

Practical diagnostic tools of sufficient sensitivity to detect levels of infection that can lead to transmission have been identified as a critical component of successful disease elimination programmes. In this review we describe the diagnostic tests currently available for six neglected tropical diseases that have been targeted for elimination; assess their performance in the light of the requirements for surveillance, certification of elimination and post-elimination surveillance; consider the unmet need for diagnostic tests for these diseases; and review recent technical developments that could meet these needs.

Trypanosoma brucei gambiense infection in vervet monkeys: a potential model for early-stage disease

BACKGROUND

Non-human primates are important experimental models for human African trypanosomiasis.

METHODS

Six monkeys were intravenously inoculated with 10(5) trypanosomes of Trypanosoma brucei gambiense IL 3253. They were monitored for 180 days for parasitemia, hematology, clinical and biochemical profiles.

RESULTS

The pre-patent period was 2-3 days. From 33 to 123 dpi, the parasitemia was low and only detectable by the hematocrit centrifugation technique. Thereafter, to the end of the experimental period, the parasitemia was undetectable by parasitological methods. Clinical signs observed were lymphadenopathy and splenomegaly. Hematological changes included a decline in hemoglobin occurring between 14 and 56 dpi and a significant decline in platelet counts after infection. The levels of total protein, albumin and globulins increased from 26 dpi for the rest of the experimental period. No parasites were detected in cerebrospinal spinal fluid, and no brain pathology was observed.

CONCLUSION

This vervet monkey model can only be used for early-stage disease Gambian sleeping sickness.

Diagnostic point-of-care tests in resource-limited settings

The aim of diagnostic point-of-care testing is to minimise the time to obtain a test result, thereby allowing clinicians and patients to make a quick clinical decision. Because point-of-care tests are used in resource-limited settings, the benefits need to outweigh the costs. To optimise point-of-care testing in resource-limited settings, diagnostic tests need rigorous assessments focused on relevant clinical outcomes and operational costs, which differ from assessments of conventional diagnostic tests. We reviewed published studies on point-of-care testing in resource-limited settings, and found no clearly defined metric for the clinical usefulness of point-of-care testing. Therefore, we propose a framework for the assessment of point-of-care tests, and suggest and define the term test efficacy to describe the ability of a diagnostic test to support a clinical decision within its operational context. We also propose revised criteria for an ideal diagnostic point-of-care test in resource-limited settings. Through systematic assessments, comparisons between centralised testing and novel point-of-care technologies can be more formalised, and health officials can better establish which point-of-care technologies represent valuable additions to their clinical programmes.

Syndromic algorithms for detection of gambiense human African trypanosomiasis in South Sudan

Background

Active screening by mobile teams is considered the best method for detecting human African trypanosomiasis (HAT) caused by Trypanosoma brucei gambiense but the current funding context in many post-conflict countries limits this approach. As an alternative, non-specialist health care workers (HCWs) in peripheral health facilities could be trained to identify potential cases who need testing based on their symptoms. We explored the predictive value of syndromic referral algorithms to identify symptomatic cases of HAT among a treatment-seeking population in Nimule, South Sudan.

Methodology/Principal Findings

Symptom data from 462 patients (27 cases) presenting for a HAT test via passive screening over a 7 month period were collected to construct and evaluate over 14,000 four item syndromic algorithms considered simple enough to be used by peripheral HCWs. For comparison, algorithms developed in other settings were also tested on our data, and a panel of expert HAT clinicians were asked to make referral decisions based on the symptom dataset. The best performing algorithms consisted of three core symptoms (sleep problems, neurological problems and weight loss), with or without a history of oedema, cervical adenopathy or proximity to livestock. They had a sensitivity of 88.9–92.6%, a negative predictive value of up to 98.8% and a positive predictive value in this context of 8.4–8.7%. In terms of sensitivity, these out-performed more complex algorithms identified in other studies, as well as the expert panel. The best-performing algorithm is predicted to identify about 9/10 treatment-seeking HAT cases, though only 1/10 patients referred would test positive.

Conclusions/Significance

In the absence of regular active screening, improving referrals of HAT patients through other means is essential. Systematic use of syndromic algorithms by peripheral HCWs has the potential to increase case detection and would increase their participation in HAT programmes. The algorithms proposed here, though promising, should be validated elsewhere.

Human African trypanosomiasis (HAT or sleeping sickness) is an almost always fatal disease affecting poor people in rural, conflict-affected areas of sub-Saharan Africa. It is difficult to diagnose. Effective treatment exists, but because diagnostic and treatment services are usually based only in hospitals, many HAT patients in rural areas are never detected. Control programmes aim periodically to extend testing services via mobile teams (active screening) but their expense and operational issues severely restrict their use. We explored the predictive value of different combinations of symptoms that were present in a treatment-seeking population to identify people infected with HAT. Through this approach, we identified a simple four-symptom referral algorithm that, if replicable, has the potential to identify one HAT patient for every ten patients referred through subsequent testing. It would identify most symptomatic HAT patients who seek treatment, if systematically applied by non-specialist healthcare workers already working in these areas. As these types of health workers are rarely included in formal HAT control efforts, teaching this algorithm also represents an opportunity to decentralise life-saving knowledge, and contribute to endemic populations' long-term empowerment and ability to help control this disease.

Human african trypanosomiasis diagnosis in first-line health services of endemic countries, a systematic review

While the incidence of Human African Trypanosomiasis (HAT) is decreasing, the control approach is shifting from active population screening by mobile teams to passive case detection in primary care centers. We conducted a systematic review of the literature between 1970 and 2011 to assess which diagnostic tools are most suitable for use in first-line health facilities in endemic countries. Our search retrieved 16 different screening and confirmation tests for HAT. The thermostable format of the Card Agglutination Test for Trypanosomiasis (CATT test) was the most appropriate screening test. Lateral flow antibody detection tests could become alternative screening tests in the near future. Confirmation of HAT diagnosis still depends on visualizing the parasite in direct microscopy. All other currently available confirmation tests are either technically too demanding and/or lack sensitivity and thus rather inappropriate for use at health center level. Novel applications of molecular tests may have potential for use at district hospital level.

Accuracy of five algorithms to diagnose gambiense human African trypanosomiasis

Background

Algorithms to diagnose gambiense human African trypanosomiasis (HAT, sleeping sickness) are often complex due to the unsatisfactory sensitivity and/or specificity of available tests, and typically include a screening (serological), confirmation (parasitological) and staging component. There is insufficient evidence on the relative accuracy of these algorithms. This paper presents estimates of the accuracy of five algorithms used by past Médecins Sans Frontières programmes in the Republic of Congo, Southern Sudan and Uganda.

Methodology and Principal Findings

The sequence of tests in each algorithm was programmed into a probabilistic model, informed by distributions of the sensitivity, specificity and staging accuracy of each test, constructed based on a literature review. The accuracy of algorithms was estimated in a baseline scenario and in a worst-case scenario introducing various near worst-case assumptions. In the baseline scenario, sensitivity was estimated as 85–90% in all but one algorithm, with specificity above 99.9% except for the Republic of Congo, where CATT serology was used as independent confirmation test: here, positive predictive value (PPV) was estimated at <50% in realistic active screening prevalence scenarios. Furthermore, most algorithms misclassified about one third of true stage 1 cases as stage 2, and about 10% of true stage 2 cases as stage 1. In the worst-case scenario, sensitivity was 75–90% and PPV no more than 75% at 1% prevalence, with about half of stage 1 cases misclassified as stage 2.

Conclusions

Published evidence on the accuracy of widely used tests is scanty. Algorithms should carefully weigh the use of serology alone for confirmation, and could enhance sensitivity through serological suspect follow-up and repeat parasitology. Better evidence on the frequency of low-parasitaemia infections is needed. Simulation studies should guide the tailoring of algorithms to specific scenarios of HAT prevalence and availability of control tools.

Gambiense human African trypanosomiasis (HAT, sleeping sickness) usually features low prevalence. The two stages of the disease require different treatments, and stage 2 is fatal if untreated. HAT diagnosis must therefore be highly sensitive (i.e., detect as many true cases as possible) and specific (i.e., minimize false positives). HAT diagnostic algorithms are complex and involve several tests to screen for, confirm and stage infection. We analyzed five algorithms used by Médecins Sans Frontières HAT programmes. We combined published data on the accuracy of each test in the algorithm with a computer program that simulates all possible algorithm branches. We found that all algorithms had reasonable sensitivity (85–90%); specificity was high (>99.9%) except for the Republic of Congo, where confirmation did not rely on microscopic evidence, resulting in frequent false positives (but also higher sensitivity). Algorithms misclassified about one third of stage 1 cases as stage 2, but stage 2 classification was highly accurate. The use of serology alone for confirmation merits caution. HAT diagnosis could be made more sensitively by following up serological suspects and repeating microscopic examinations. Computer simulations can help to adapt algorithms to local conditions in each HAT programme, such as the prevalence of infection and operational constraints.

First evidence that parasite infecting apparent aparasitemic serological suspects in human African trypanosomiasis are Trypanosoma brucei gambiense and are similar to those found in patients

Thanks to its sensitivity and its ease of use in the field, the card agglutination test for trypanosomiasis (CATT) is widely used for serological screening of Trypanosoma brucei gambiense human African trypanosomiasis (HAT). Positive subjects are then examined by microscopy to confirm the disease. However, the CATT exhibits false-positive results raising the question of whether CATT-positive subjects who are not confirmed by microscopic detection of trypanosomes (SERO) are truly exposed to T.b. gambiense infection. For this purpose, we applied microsatellite genotyping on DNA extracted from blood of both HAT confirmed patients and SERO subjects in Guinea and Côte d'Ivoire since microsatellite genotyping has proved useful for the study of T.b. gambiense genetic diversity. Problems of amplification failures raise the question of the sensitivity of microsatellite markers when applied on biological samples especially from SERO subjects for who low blood parasitaemia are suspected. Nevertheless, we have shown that the trypanosomes from SERO individuals that have been genotyped belong to T.b. gambiense group 1 and were identical to those found in HAT patients. These results constitute the first evidences that at least some SERO are indeed infected by T.b. gambiense group 1 and that they may constitute a human reservoir of parasite in HAT foci. Whether these individuals should undergo treatment remains an open question as long as their role in HAT transmission is unknown. Our results strongly recommend the follow-up of such subjects to improve control strategies.

Detection of Group 1 Trypanosoma brucei gambiense by loop-mediated isothermal amplification

Trypanosoma brucei gambiense group 1 is the major causative agent of the Gambian human African trypanosomiasis (HAT). Accurate diagnosis of Gambian HAT is still challenged by lack of precise diagnostic methods, low and fluctuating parasitemia, and generally poor services in the areas of endemicity. In this study, we designed a rapid loop-mediated isothermal amplification (LAMP) test for T. b. gambiense based on the 3' end of the T. b. gambiense-specific glycoprotein (TgsGP) gene. The test is specific and amplifies DNA from T. b. gambiense isolates and clinical samples at 62°C within 40 min using a normal water bath. The analytical sensitivity of the TgsGP LAMP was equivalent to 10 trypanosomes/ml using purified DNA and ∼1 trypanosome/ml using supernatant prepared from boiled blood, while those of classical PCR tests ranged from 10 to 10(3) trypanosomes/ml. There was 100% agreement in the detection of the LAMP product by real-time gel electrophoresis and the DNA-intercalating dye SYBR green I. The LAMP amplicons were unequivocally confirmed through sequencing and analysis of melting curves. The assay was able to amplify parasite DNA from native cerebrospinal fluid (CSF) and double-centrifuged supernatant prepared from boiled buffy coat and bone marrow aspirate. The robustness, superior sensitivity, and ability to inspect results visually through color change indicate the potential of TgsGP LAMP as a future point-of-care test.

Point-of-care tests for diagnosing infections in the developing world

Infectious diseases continue to cause an enormous burden of death and disability in developing countries. Increasing access to appropriate treatment for infectious diseases could have a major impact on disease burden. Some common infections can be managed syndromically without the need for diagnostic tests, but this is not appropriate for many infectious diseases, in which a positive diagnostic test is needed before treatment can be given. Since many people in developing countries do not have access to laboratory services, diagnosis depends on the availability of point of care (POC) tests. Historically there has been little investment in POC tests for diseases that are common in developing countries, but that is now changing. Lack of regulation of diagnostic tests in many countries has resulted in the widespread use of sub-standard POC tests, especially for malaria, making it difficult for manufacturers of reliable POC tests to compete. In recent years increased investment, technological advances, and greater awareness about the importance of reliable diagnostic tests has resulted in rapid progress. Rapid, reliable and affordable POC tests, requiring no equipment and minimal training, are now available for HIV infection, syphilis and malaria, but POC tests for other infections are urgently needed. Many countries do not have established criteria for licensing and introducing new diagnostic tests, and many clinicians in developing countries have become disillusioned with diagnostic tests and prefer to rely on clinical judgment. Continuing advocacy and training in the use of POC tests are needed, and systems for quality control of POC tests need to be developed if they are to achieve their maximum potential.

Human African trypanosomiasis

Human African trypanosomiasis (sleeping sickness) occurs in sub-Saharan Africa. It is caused by the protozoan parasite Trypanosoma brucei, transmitted by tsetse flies. Almost all cases are due to Trypanosoma brucei gambiense, which is indigenous to west and central Africa. Prevalence is strongly dependent on control measures, which are often neglected during periods of political instability, thus leading to resurgence. With fewer than 12 000 cases of this disabling and fatal disease reported per year, trypanosomiasis belongs to the most neglected tropical diseases. The clinical presentation is complex, and diagnosis and treatment difficult. The available drugs are old, complicated to administer, and can cause severe adverse reactions. New diagnostic methods and safe and effective drugs are urgently needed. Vector control, to reduce the number of flies in existing foci, needs to be organised on a pan-African basis. WHO has stated that if national control programmes, international organisations, research institutes, and philanthropic partners engage in concerted action, elimination of this disease might even be possible.

Neglected tropical diseases

INTRODUCTION

The neglected tropical diseases (NTDs) are infectious diseases that principally impact the world's poorest people. They have been neglected for decades, initially as part of a general disregard for the developing world, and more recently due to the intensity of focus on HIV/AIDS, tuberculosis and malaria.

SOURCES OF DATA

Primary research and review articles were selected for inclusion using searches of PubMed and our existing collections.

RESULTS

There have been recent notable successes in NTD control. Dracunculiasis is approaching eradication. Leprosy and onchocerciasis are in decline. There are ambitious plans to eliminate trachoma and lymphatic filariasis. Investment in NTD control has high rates of economic return.

CONCLUSION

Although there are proven strategies to control several NTDs, these diseases continue to cause a massive burden of morbidity. There is urgent need for more basic and operational research, drug and vaccine development, and greater prioritization by governments and international agencies.

The natural progression of Gambiense sleeping sickness: what is the evidence?

Gambiense human African trypanosomiasis (HAT, sleeping sickness) is widely assumed to be 100% pathogenic and fatal. However, reports to the contrary exist, and human trypano-tolerance has been postulated. Furthermore, there is uncertainty about the actual duration of both stage 1 and stage 2 infection, particularly with respect to how long a patient remains infectious. Understanding such basic parameters of HAT infection is essential for optimising control strategies based on case detection. We considered the potential existence and relevance of human trypano-tolerance, and explored the duration of infectiousness, through a review of published evidence on the natural progression of gambiense HAT in the absence of treatment, and biological considerations. Published reports indicate that most gambiense HAT cases are fatal if untreated. Self-resolving and asymptomatic chronic infections probably constitute a minority if they do indeed exist. Chronic carriage, however, deserves further study, as it could seed renewed epidemics after control programmes cease.

African trypanosomiasis: sensitive and rapid detection of the sub-genus Trypanozoon by loop-mediated isothermal amplification (LAMP) of parasite DNA

Control of human African trypanosomiasis (HAT) is dependent on accurate diagnosis and treatment of infected patients. However, sensitivities of tests in routine use are unsatisfactory, due to the characteristically low parasitaemias in naturally infected individuals. We have identified a conserved sequence in the repetitive insertion mobile element (RIME) of the sub-genus Trypanozoon and used it to design primers for a highly specific loop-mediated isothermal amplification (LAMP) test. The test was used to analyse Trypanozoon isolates and clinical samples from HAT patients. The RIME LAMP assay was performed at 62 degrees C using real-time PCR and a water bath. DNA amplification was detectable within 25min. All positive samples detected by gel electrophoresis or in real-time using SYTO-9 fluorescence dye could also be detected visually by addition of SYBR Green I to the product. The amplicon was unequivocally confirmed through restriction enzyme NdeI digestion, analysis of melt curves and sequencing. The analytical sensitivity of the RIME LAMP assay was equivalent to 0.001 trypanosomes/ml while that of classical PCR tests ranged from 0.1 to 1000 trypanosomes/ml. LAMP detected all 75 Trypanozoon isolates while TBR1 and two primers (specific for sub-genus Trypanozoon) showed a sensitivity of 86.9%. The SRA gene PCR detected 21 out of 40 Trypanosoma brucei rhodesiense isolates while Trypanosoma gambiense-specific glycoprotein primers (TgsGP) detected 11 out of 13 T. b. gambiense isolates. Using clinical samples, the LAMP test detected parasite DNA in 18 out of 20 samples which included using supernatant prepared from boiled blood, CSF and direct native serum. The sensitivity and reproducibility of the LAMP assay coupled with the ability to detect the results visually without the need for sophisticated equipment indicate that the technique has strong potential for detection of HAT in clinical settings. Since the LAMP test shows a high tolerance to different biological substances, determination of the appropriate protocols for processing the template to make it a user-friendly technique, prior to large scale evaluation, is needed.