Partnering to develop diagnostic tests for human African trypanosomiasis
29th Meeting of the International Scientific Council for Trypanosomiasis Research and Control
Luanda, Angola, 1-5 October 2007
Diagnosis of human African trypanosomiasis is usually performed in two steps: clinical suspicion or serological screening on one hand and confirmation plus stage determination on the other hand. These two steps are cumbersome, costly and need to be improved. Despite promising results from initial evaluations of other tests, the Card Agglutination Trypanosomiasis Test (CATT) is still the reference serological screening test for Trypanosoma brucei gambiense. There is no equivalent test for screening T.b. rhodesiense which relies on clinical symptoms and signs, indicators that are far from satisfactory.
Moreover, immunofluorescence and ELISA-based serological tests can be performed only in reference centers with highly trained technicians. Their sensitivity is variable. The characteristics of all the existing serological tests are considered as insufficient to ascertain diagnostic results and hence parasitological confirmation by microscope is required before treatment is started.
Parasitological diagnosis is made by microscopic examination of blood or lymph node aspirate. Parasitological diagnosis provides confirmation for trypanosome infection and thus allows a definite diagnosis but requires stage determination by an invasive lumbar puncture and the examination of cerebrospinal fluid. The performance of the different examinations vary according to the technique and parasite concentration but they are all time consuming and leave a lot of patients without diagnosis and therefore without specific treatment.
Screening and diagnostic procedures are mainly performed by national programmes with the punctual aid of specialized, non-governmental organizations or institutions. The expertise developed by the programmes, the interruption of social upheavals and civil strife – permitting access to endemic areas – and efforts to increase screening and treatment of patients have led to a dramatic decrease of incidence of sleeping sickness. Thanks to the technical and financial support of World Health Organization (WHO), these efforts can be maintained and the objective of eliminating sleeping sickness is now realistic but this elimination will be sustainable only if the new diagnostic and treatment tools are made available and properly used in peripheral health settings. On the other hand, the reduction of prevalence reduces at the same time the rank of priority and maintenance of cost-effective specialized teams will be more and more difficult. The decrease of prevalence also alters the predictive value of screening, requiring tests with better characteristics.
In order to improve the performance of the programmes and the sustainability of HAT control, two types of new tests are therefore needed:
- a test for infection with either T.b. gambiense or T.b. rhodesiense that will be simple enough to use at point of care in remote locations and specific enough to direct treatment in screening programs among at-risk populations, and
- a simple staging test to determine whether the central nervous system is affected.
A memorandum of understanding between the WHO and FIND was signed on 24 March 2006. The goal of this initiative is to promote the development of simple and accurate diagnostic tests to improve patient care and disease control and to ensure that these tests are made widely available in sufficient quantities to meet demand in high-burden countries at affordable, or at least preferential, prices.
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