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Trypanosomiasis, african
Diagnosis

Diagnostic methods

Parasitological diagnosis
Diagnosis may be achieved by microscopic detection of trypanosomes in blood, in chancre aspirates, in lymph or cerebrospinal fluids. However, sensitivity is limited even when parasite concentration techniques (micro-haematocrit or the mini-anion exchange centrifugation technique) are used. Sensitivity is less a problem in acute T.b. rhodesiense infections, where trypanosomes are numerous. Multiple specimens should be collected because parasite numbers fluctuate!
Caution when handling specimens of infected patients, which are highly infectious!

Molecular diagnosis
Nested PCR tests have been developed to differentiate trypanosome species in domestic and wild animals for epidemiological studies. A recent paper describes a multiplex PCR that discriminates between T.b. brucei and zoonotic T.b. rhodesiense.

Antigen detection
An ELISA method is available to detect antigen in serum and cerebrospinal fluid. A simple rapid test, the card indirect agglutination test (CIATT), is available for field surveys.

Antibody detection
Specific antibodies may be demonstrated by ELISA, IFAT and the card agglutination test (CATT). Serology is important in chronic sleeping sickness due to T.b. gambiense.
For serological screening of T. b. gambiense, the feasibility to detect antibodies in human saliva has been proven.
High levels of mainly non-specific IgM are common in African trypanosomiasis due to polyclonal activation of lymphocytes.

 

Diagnostic strategies 

  1. For screening a population in an endemic area
    Rapid antigen detection tests are most convenient to assess endemicity.
     
  2. For diagnosing an individual case
    As a first attempt, one tries to demonstrate trypanosomes in the blood directly or by using concentration methods. As additional methods, antigen – and antibody – detection could be used if blood examinations are negative.
     
  3. For evaluating control measures
    Be aware that in view of the potentially low prevalence after an intervention, you have to select a diagnostic strategy assuring a high predictive value for positive results. This means you should choose a single method (or eventually a combination of methods) with a high specificity!
    To get an exact value for the relative risk in a placebo-controlled intervention study (e.g. a vaccine trial), the specificity should ideally be 100%.
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