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Sleeping sickness
Need for better diagnosticsSleeping sickness presents in two stages. During the first stage, when treatment has the greatest chance of success, infection produces few specific signs and symptoms and is rarely detected. Drugs to treat the first stage are relatively safe, but inefficient in the second stage. The second stage, which starts when parasites invade the central nervous system (CNS), is difficult to treat and the drugs used are highly toxic, with 2% to 10% mortality during or shortly after treatment.
Early diagnosis and treatment of African trypanosomiasis is critical since treatment of late stage disease is associated with high mortality. What's more, early treatment interrupts the parasite’s transmission cycle. Typically, diagnosis is based on visualization of parasites in the blood, lymph node fluid, or cerebrospinal fluid (CSF) by microscopy but sensitivity using this method is limited (Figure 3). Early detection with improved diagnostic tools will help avoid exposing patients to dangerous and expensive drugs. Improved diagnostics and safer drugs are urgently needed Control of HAT depends primarily on a combination of active and passive case detection and curative treatment to reduce or remove human reservoirs of infection from the population. At present, diagnosis and subsequent treatment cannot be properly applied because existing tools are difficult to implement in remote, impoverished settings where the impact of the disease is greatest. As a result, diagnosis of sleeping sickness remains a major and neglected problem. In addition, most of the available drugs used to treat sleeping sickness are not only toxic but also difficult to administer. To address this challenge, better drugs, including possible oral regimens, are urgently needed. Since early-stage sleeping sickness is difficult to recognize clinically, and late-stage disease often leads to the death of patients, the disease control strategy recommended by the WHO relies on systematic screening of at-risk populations using the card agglutination test for trypanosomiasis (CATT), and confirmation of the presence of parasites by microscopy. CATT is a method developed for the detection of specific antibodies against T.b. gambiense, and though quite effective, has some problems of sensitivity and specificity. No similar test is available for T.b. rhodesiense. Since microscopy is both laborious and insensitive, many patients go undiagnosed. In addition, the molecular-based tests that have been developed are impractical and difficult to maintain in the endemic rural areas due to absence of a developed infrastructure. Individuals in whom infection is detected must go on to have their cerebrospinal fluid (CSF) examined to determine whether specific treatment for late stage disease is required. This can only be done by means of a lumbar puncture, which is an additional complication in that it is invasive and painful. Actual tests on CSF also suffer from limited sensitivity and specificity, resulting in inadequate treatment of some patients. Better diagnostic tests that are simple, accurate and robust would revolutionize HAT control, making mass screening in remote, rural areas a realistic goal. Addressing the diagnostic challenge FIND is developing rapid, accurate and affordable first point-of-care diagnostic tests for HAT and other poverty-related diseases that are endemic in the developing world. Since its launch in early 2006, FIND’s HAT diagnostics programme, implemented jointly with the WHO, has established linkages with industry, academic and research institutions in developed and endemic countries. Projects that will enable the development of user-friendly diagnostic tests have been progressing well. The areas of emphasis include improvement in parasite separation from blood and CSF, serological and molecular tests, and staging of the disease.
© Foundation for Innovative New Diagnostics 2008. Click here to see the copyright notice |
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