5. Human trypanosomiasis

(a) Surveillance

[See also 27: no. 12662.]

Referring to the paper: Abel, P.M., Kiala, G., Loa, V., Behrend, M., Musolf, J., Fleishmann, H., Theophile, J., Krishna, S. & Stich, A., 2004. Retaking sleeping sickness control in Angola. Tropical Medicine and International Health, 9 (1): 141-148, the present authors state that the expression (Summary, lines 3 and 4) "In the period between 1996 and 2001, 13 426 patients were screened for HAT", should have read "In the period between 1996 and 2001, 13 426 patients were treated for HAT".

Africa is severely affected by a resurgence of human African trypanosomiasis (HAT) at epidemic proportions. We report the results of the first five years of a HAT control programme in northern Angola run by the non-governmental organization ANGOTRIP. In the period between 1996 and 2001, 13 426 patients were screened [i.e. treated: see correction below] for HAT. The mortality rate of patients in stage II who were treated with melarsoprol fell from 7.5 percent to 2.9 percent, possibly as a result of training and the standardization of treatment protocols. A total of 191 578 people in three provinces of Angola were screened for HAT. Vector control activities were initiated using Lancien traps. Our experiences reflect the connection between war and the increasing incidence of disease, but also demonstrate that HAT control is possible by dedicated non-governmental organizations in close cooperation with national institutions even under extremely difficult circumstances.

In the Democratic Republic of Congo, the re-emergence of sleeping sickness is no longer limited to rural areas. Over the course of the past decade, more and more cases have been reported from urban centres such as Kinshasa, Mbuji-mayi, Matadi and Boma. This paper presents a retrospective analysis on the region of Kinshasa over the period 1996-2000, using epidemiological surveillance, individual case files and available entomological data. There are 22 health districts in total; they were classified as urban when the population exceeded 5 000/km². The Human African Trypanosomiasis (HAT) control programme reported 2 451 parasitologically confirmed new cases between 1996 and 2000, in the entire region of Kinshasa. Of the affected people 66 percent were aged 15-49 years. Cases occurred in every health district, and 956 (39 percent) occurred in urban residents. Glossina captures in 1999 established the presence of Trypanosoma spp. Local HAT transmission is plausible but not proven. The high number of urban cases necessitates development of control strategies adapted to cities.

Genetic studies of Trypanosoma brucei have been mainly based on rodent inoculation (RI) for isolation of trypanosome strains. However, Trypanosoma brucei gambiense is difficult to grow in rodents. The development and use of the Kit for In Vitro Isolation (KIVI) of trypanosomes has led to a better isolation success. However, some authors report a genetic monomorphism in T. b. gambiense, and the extensive use of the KIVI was suspected as being responsible for this low genetic diversity. In the present work, trypanosome stocks were isolated from both humans and pigs in an active sleeping sickness focus in Côte d’Ivoire. Two methods were simultaneously used for this purpose: KIVI and rodent inoculation. None of the human stocks grew in rodents. Some of the stocks originating from pigs could be isolated with both methods. Each of these stocks (from the same pig) showed a different isoenzymatic pattern according to the isolation method used. All the human stocks identified belonged to the major zymodeme 3 of T. b. gambiense group 1, whereas the stocks isolated from pigs belonged to a new group of zymodemes even if they were genetically closely related. These observations may have significant implications when analysing the population structure of T. brucei, and also raise again the question of the importance of the animal reservoir in human African trypanosomiasis.

In human African trypanosomiasis two disease stages are defined: the first or haemolymphatic stage, and the second, the meningo-encephalitic stage. Stage determination forms the basis of therapeutic decision and is of prime importance, as the drug used to cure second-stage patients has considerable side-effects; however, the tests currently used for stage determination have low sensitivity or specificity. Two new tests for stage determination in the cerebrospinal fluid were evaluated on 73 patients diagnosed with HAT in Côte d’Ivoire. The polymerase chain reaction (PCR) detecting trypanosome DNA (PCR/CSF) is an indirect test for trypanosome detection whereas the latex agglutination test detecting immunoglobulin M (LATEX/IgM) is an indicator for neuro-inflammation. Both tests were compared with classically used tests, double centrifugation and white blood cell count of the CSF. PCR/CSF appeared to be the more sensitive test (96 percent), and may be of use to improve stage determination. However, its value for therapeutic decision appears limited, as patients whose CSF was positive with PCR were successfully treated with pentamidine. This result confirms those of previous works that showed that some patients with trypanosomes in the CSF could be treated successfully with pentamidine. LATEX/IgM, which, depending on the cut-off, showed lower sensitivity of 76 percent and 88 percent, but higher specificity of 83 percent and 71 percent for LATEX/IgM 16 and LATEX/IgM 8 respectively, appears more appropriate for making decisions regarding therapy.

Sleeping sickness is a lethal African disease caused by parasites of the Trypanosoma brucei subspecies, which is transmitted by tsetse flies. Occasionally, patients are reported outside Africa. Diagnosis of such imported cases can be problematic when the infection is due to Trypanosoma gambiense, the chronic form of sleeping sickness found in west and central Africa. The low number of trypanosomes in the blood and the non-specific, variable symptoms make the diagnosis difficult, particularly when the index of suspicion is low. When the trypanosomes have penetrated into the central nervous system, neuropathological signs become apparent but even at this stage, misdiagnosis is frequent. Rapid and correct diagnosis of sleeping sickness can avoid inappropriate or delayed treatment and even death of the patient. In this article, an overview on the diagnosis of imported cases of T. gambiense sleeping sickness is given, and possible pitfalls in the diagnostic process are highlighted. Bioclinical parameters that should raise the suspicion of sleeping sickness in a patient who has been in west or central Africa are discussed. Techniques for diagnosis are reviewed. A clinician suspecting sleeping sickness should contact a national reference centre for tropical medicine in his or her country, or WHO or the Centers for Disease Control and Prevention (CDC), for clinical consultation and provision of specific diagnostic tests. Appropriate drugs for sleeping sickness treatment are also provided by WHO and the CDC.

A pilot study was carried out on the detection of trypanosome-specific antibodies in saliva for diagnosis of sleeping sickness. All twenty-three saliva samples of parasitologically confirmed Trypanosoma brucei gambiense patients tested positive in an indirect enzyme-linked immunosorbent assay, whereas all 14 saliva samples of a negative control group remained negative. Trypanosome-specific antibody levels in patient saliva correlated with antibody levels in serum, but were about 250-fold lower. Eight of 23 undiluted saliva samples of sleeping sickness patients tested positive in CATT/T. b. gambiense and two of 23 in LATEX/T. b. gambiense. All fourteen saliva samples of the negative control group were also positive in CATT/T. b. gambiense, as were four of 14 in LATEX/T. b. gambiense. CATT and LATEX were thus inappropriate for antibody detection in saliva. These results indicate that trypanosome-specific antibody detection in saliva is possible. This could lead to the development of a simple, non-invasive, reliable saliva field test for diagnosis of sleeping sickness.

Diagnosis of central nervous system (CNS) involvement in human African trypanosomiasis is crucial in determination of therapy. Cerebrospinal fluid (CSF) and serum immunoglobulin concentrations, blood-CSF barrier dysfunction, pattern of intrathecal immunoglobulin synthesis, trypanosome-specific antibody synthesis, and CSF lactate concentrations were analyzed in 272 patients with Trypanosoma brucei gambiense infection. As part of the 2- or 3-class immune response, the predominant intrathecal IgM synthesis was the most sensitive (95 percent) marker for inflammation of the brain. We propose to replace the World Health Organization (WHO) criteria (white blood cell count >5 cells/mlitre and presence of trypanosomes in CSF) with a new approach for stage determination in trypanosomiasis: CNS involvement is diagnosed only in patients with >20 cells/mlitre or with intrathecal IgM synthesis, independent of the presence of trypanosomes in CSF. Compared with the use of these new criteria, the WHO criteria incorrectly classified 49 of 234 patients in the meningoencephalitic stage and 7 of 38 patients in the hemolymphatic disease stage. We also show that trypanosomiasis-related immunoglobulin patterns are of value in differential diagnosis.

In Central Africa, sleeping sickness was brought under control during the 1960s. Since independence, other public health priorities and greatly reduced budgets have resulted in a progressive abandonment of control activities, to the point where during the 1990s the situation once more became critical in several countries. A new dynamism was brought about at the start of the 21st century, but the situation remains serious in 2001: a small renewal of control activities has taken place throughout the region, but it is still too early to see clear results. However, the general feeling today is one of optimism and some spectacular results are being announced.

Known since 1993, the focus of human African trypanosomiasis in Bodo, in southern Chad, is at present the most active in the country. In 2002, it was decided to direct all the activities of the national human African trypanosomiasis control programme (PNLTHA) against this focus. Two preliminary surveys, in February and May, examined 6 958 individuals from 16 different villages and 211 cases of sleeping sickness were detected. In November and December, the PNLTHA team was reinforced by technicians from Cameroon, the Democratic Republic of the Congo and Equatorial Guinea: two survey teams were formed as a result, and in three weeks these teams examined 16 273 inhabitants of 53 villages and three schools in Bodo, and detected 361 new cases of the disease. Moreover, this unprecedented inter-African cooperation over sleeping sickness has provided the opportunity to train doctors, nurses and technicians from Chad and the Sudan who, in their turn, will be able to become involved in sleeping sickness control.

A case of trypanosomiasis was diagnosed in a woman who had never visited Africa, but whose partner had spent some time in Angola and who had symptomless trypanosomiasis. Sexual transmission was suspected. Her 19-month son also had trypanosomiasis (late stage sleeping sickness), and in this case congenital transmission was suspected. All three patients were successfully treated.

(b) Pathology and immunology

Human African trypanosomiasis (HAT), also known as sleeping sickness, is a major cause of mortality and morbidity in sub-Saharan Africa. Current therapy with melarsoprol for CNS HAT has unacceptable side-effects with an overall mortality of 5 percent. This review discusses the issues of diagnosis and staging of CNS disease, its neuropathogenesis, and the possibility of new therapies for treating late-stage disease.

In a clinical trial on efficacy of pentamidine in second stage Trypanosoma brucei gambiense patients with £ 20 cells/ml in cerebrospinal fluid (CSF), 43 percent of treatment failures were observed. We hypothesised that unsuccessful treatment was caused by uncured brain infection. The relationship between treatment outcome and CSF cell count, protein concentration, presence of trypanosomes, the intrathecal immune response, and CSF total IgM and trypanosome specific antibodies detected by LATEX/IgM and LATEX/T. b. gambiense card agglutination tests was examined. Cell counts of 11-20 cells/ml, intrathecal IgM synthesis, CSF end-titres in LATEX/IgM £ 4 and LATEX/T. b. gambiense positive CSF, were associated with treatment failure. Detection of intrathecal IgM synthesis is valuable for assessment of brain involvement and treatment decision.

Quantitative and qualitative techniques for assessment of the intrathecal humoral immune response in human African trypanosomiasis were compared, and their diagnostic potential for detection of the meningo-encephalitic stage of the disease was evaluated. Total and trypanosome specific immunoglobulin G (IgG) and IgM intrathecal synthesis were studied in paired cerebrospinal fluid (CSF) and blood samples of 38 trypanosomiasis patients and in three controls using Reiber’s formulae. The presence of CSF-specific oligoclonal IgG and of trypanosome-specific antibodies was determined using iso-electric focusing followed by immunoblotting and antigen-driven immunoblots. The intrathecal IgG fraction (16 percent positive) and oligoclonal IgG detection (24 percent positive) were insensitive for detection of an intrathecal humoral immune response. Trypanosome-specific IgG synthesis, reflected by the IgG antibody index (AI) (26 percent positive), was confirmed by the presence of oligoclonal specific IgG (47 percent positive), but the latter was more sensitive. Although the detection technique failed for oligoclonal IgM, the intrathecal IgM fraction (42 percent positive) and the IgM AI (32 percent positive) indicated that the meningo-encephalitic stage of the disease is characterized by a dominant intrathecal IgM response, which was higher than the IgG response. The highest combination of diagnostic sensitivity and specificity for the meningo-encephalitic stage of trypanosomiasis was observed for quantitative IgM determinations.

(c) Treatment

[See also 27: nos. 12707, 12723, 12769, 12773.]

Human African trypanosomiasis (HAT), or sleeping sickness, is currently on the rise. HAT develops in two stages, the first involving the hemolymphatic system, and the second, the neurological system. Left untreated, HAT is invariably fatal. There have been no therapeutic advances in more than 40 years. Stage 1 can be treated with pentamidine and suramin, but stage 2 can only be treated with melarsoprol, its toxic arsenic derivative that has a 2-12 percent incidence of fatal side-effects (encephalopathy). Eflornithine has never achieved widespread use because it is difficult to administer under field conditions. Nifurtimox has been used successfully in the treatment of American trypanosomiasis, or Chagas disease, but only in small studies or as a compassionate use treatment. There is little research and development for new drugs in this area: only one prodrug is in the clinical development phase, a pentamidine analogue that offers hope for the replacement of injectable pentamidine with an orally administered drug. Current efforts appear to be focused on reevaluating older drugs. A course of treatment with melarsoprol for 10 days at 2.2 mg/kg/day is now in the multicenter evaluation phase. Orally administered eflornithine is also slated for re-evaluation. In addition, studies of drug combinations are recommended to determine possible combined or synergistic effects and find ways to reduce toxicity.

Eflornithine is the only new molecule registered for the treatment of human African trypanosomiasis over the last 50 years. It is the drug used mainly as a back-up for melarsoprol refractory Trypanosoma brucei gambiense cases. The most commonly used dosage regimen for the treatment of T. b. gambiense sleeping sickness consists of 100 mg/kg body weight at intervals of 6 h for 14 days (150 mg/kg body weight in children) of eflornithine given as short infusions. Its efficacy against Trypanosoma brucei rhodesiense is limited due to the innate lack of susceptibility of this parasite based on a higher ornithine decarboxylase turnover. Adverse drug reactions during eflornithine therapy are frequent and the characteristics are similar to other cytotoxic drugs for the treatment of cancer. Their occurrence and intensity increase with the duration of treatment and the severity of the general condition of the patient. Generally, adverse reactions to eflornithine are reversible after the end of treatment. They include convulsions (7 percent), gastrointestinal symptoms like nausea, vomiting and diarrhoea (10-39 percent), bone marrow toxicity leading to anaemia, leucopaenia and thrombo-cytopaenia (25-50 percent), hearing impairment (5 percent in cancer patients) and alopecia (5-10 percent). The drug arrests embryonic development in mice, rats and rabbits but the extent of excretion into breast milk is unknown. The mean half-life is around 3-4 h and the volume of distribution in the range of 0.35 litre/kg. Renal clearance is about 2 ml min/kg (i.v.) and accounts for more than 80 percent of drug elimination. Bioavailability of an orally administered 10 mg/kg dose was estimated at 54 percent. One of the major determinants of successful treatment seems to be the cerebrospinal fluid drug level reached during treatment, and it was shown that levels above 50 mmol/litre must be reached to attain the consistent clearance of parasites. Based on its trypanostatic rather than trypanocidal mode of action, it is a rather slow-acting drug.

Human African trypanosomiasis is a fatal disease caused by Trypanosoma brucei gambiense and Trypanosoma brucei rhodesiense that has re-emerged in recent years. However, very little progress has been made in the development of new drugs against this disease. Most drugs still in use were developed one or more decades ago, and are generally toxic and of limited effectiveness. The most recently introduced compound, eflornithine, is only useful against sleeping sickness caused by T. b. gambiense, and is prohibitively expensive for the African developing countries. We present here an overview of today’s approved and clinically used drugs against this disease.

Three of the four currently approved drugs for the treatment of African trypanosomiasis (sleeping sickness) were developed over 50 years ago. All of the current therapies are unsatisfactory for various reasons, including unacceptable toxicity, poor efficacy, undesirable route of administration, and drug resistance. The possible modes of action of these drugs are briefly reviewed, as are the possible mechanisms of resistance. The intermediate and long-term prospects for the development of safer, effective drugs are discussed.

Drug resistance in African trypanosomes has been studied for almost a hundred years. Beginning with Paul Ehrlich’s work that led to the chemoreceptor hypothesis, reduction of net drug uptake has emerged as the most frequent cause of resistance. This review, therefore, focuses on trypanosomal drug transporter genes. TbAT1 encodes purine permease P2, which mediates influx of melarsoprol and diamidines. Disruption of TbAT1 in Trypanosoma brucei reduced sensitivity to these trypanocides. TbMRPA encodes a putative trypanothione-conjugate efflux pump, and overexpression of TbMRPA in T. brucei causes melarsoprol resistance. It will be important to determine the role of TbAT1 and TbMRPA in sleeping sickness treatment failures.

Human African trypanosomiasis has remained a disease with no effective treatment. Recent progress in HAT research suggests that a vaccine against the disease is far from being successful. Also the emergence of drug-resistant trypanosomes makes further work in this area imperative. So far the treatment for the early stage of HAT involves the drugs pentamidine and suramin which have been very successful. In the second stage of the disease, during which the trypanosomes reside in the cerebrospinal fluid (CSF), treatment is dependent exclusively on the arsenical compound melarsoprol. This is largely due to the inability to find compounds that can cross the blood brain barrier and kill the CSF-residing trypanosomes. This review summarises our current understanding on the treatment of HAT.