African Trypanosomiasis Workup

Updated: Apr 11, 2016
  • Author: Randy O Odero, MB, ChB; Chief Editor: Pranatharthi Haran Chandrasekar, MBBS, MD  more...
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Workup

Approach Considerations

Although general laboratory studies may be helpful in the diagnosis of African trypanosomiasis (sleeping sickness), a definitive diagnosis of T brucei infection requires actual detection of trypanosomes in blood, lymph nodes, cerebrospinal fluid (CSF), skin chancre aspirates, or bone marrow. In areas where diagnostic studies are not readily available, however, symptomatic improvement after empiric treatment is the usual confirmatory test. [7]

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General Blood Studies and Serology

The most significant laboratory abnormalities in African trypanosomiasis include anemia, hypergammaglobulinemia, low complement levels, elevated erythrocyte sedimentation rate (ESR), thrombocytopenia, and hypoalbuminemia (but not eosinophilia or abnormal liver function). In the West African form, the total immunoglobulin M (IgM) level is notably higher in blood and CSF (along with a high CSF protein level).

Serologic antibody detection

Field serology-based diagnosis of African trypanosomiasis has been slow to progress. Although many research tools are available for diagnosis, few are used clinically in endemic areas. [8]

The standard serologic assay for diagnosing West African trypanosomiasis is the card agglutination test for trypanosomiasis (CATT). The CATT can be conducted in the field without electricity, and results are available in only 10 minutes. It is highly sensitive (96%) but less specific because of cross-reactivity with animal trypanosomes. Commercial antibody tests for Eastern African trypanosomiasis are not available.

Antigen detection tests based on enzyme-linked immunosorbent assay (ELISA) technology have been developed. They have shown inconsistent results and are not yet commercially available.

An individual serological rapid diagnostic test for the diagnosis of West African trypanosomiasis was recently developed and commercialized (HAT Sero-K-SeT). Its diagnostic performance was shown to be similar to that of CATT.- [9]

Culture of CSF, blood, bone marrow aspirate, or tissue specimens can be performed in liquid media. Other tests that have been developed but are not frequently used in clinical settings include antibody detection in the CSF and intrathecal space (low sensitivity), polymerase chain reaction (PCR), and serum proteomic tests. Research tools such as isoenzyme analysis and restriction fragment length polymorphism (RFLP) are used for definitive subspecies identification.

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Blood Smear

A wet smear of unstained blood or a Giemsa-stained thick smear (more sensitive; Wright and Leishman stains are inadequate) is examined to look for mobile trypanosomes (see the image below); the organisms remain mobile for only 15-20 minutes. This technique is most sensitive in the early stages of the disease, when the number of circulating parasites is highest (≥5000/mL), particularly in T brucei rhodesiense (East African) trypanosomiasis.

African trypanosomiasis (sleeping sickness). Human African trypanosomiasis (sleeping sickness). Human trypanosomes blood smear.

Better assays are now available, including the hematocrit centrifugation technique for buffy coat examination and the miniature anion-exchange centrifugation technique (mAECT), which filters out the red blood cells (RBCs) but not the trypanosomes. This test can be used to detect serum parasite levels as low as 5 /mL; the test can be repeated on subsequent days to increase the yield when results are negative.

Chancre aspirate can be used as a wet preparation, especially in East African trypanosomiasis, but a blood smear is more sensitive.

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Aspiration of Lymph Node or Bone Marrow

Lymph node aspiration at a high dry magnification (´400) is commonly used as a rapid test for trypanosomes. It requires an immediate search for parasites because, as noted (see above), the organisms are mobile for only 15-20 minutes. This test has more utility in T brucei gambiense (West African) trypanosomiasis.

Bone marrow aspiration may yield positive results in some patients.

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Lumbar Puncture and CSF Assay

Lumbar puncture should be performed whenever trypanosomiasis is suspected. CSF is examined for the purposes of detecting trypanosomes and measuring white blood cell (WBC) counts, protein, and IgM in patients with parasitemia or positive serologies or symptoms. CSF examination helps to diagnose and stage the disease. However, a negative result does not necessarily rule out the diagnosis.

The double centrifugation technique is the most sensitive method for detecting the trypanosomes. Other findings that may be noted on evaluation of the CSF include elevated WBC counts, elevated IgM levels, elevated total protein levels, and raised intracranial pressure. An uncommon characteristic finding is Mott cells, which are thought to be large eosinophilic plasma cells containing IgM that have failed to secrete their antibodies.

Increased intrathecal synthesis of IgM has been found to be the most sensitive indicator of CNS involvement in African trypanosomiasis. CNS disease can manifest early in East African trypanosomiasis.

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Other Studies

Computed tomography (CT) and magnetic resonance imaging (MRI) of the head reveal cerebral edema and white matter enhancement, respectively, in patients with late-stage African trypanosomiasis.

In cases of neurologic involvement, electroencephalography (EEG) usually shows slow wave oscillations (delta waves), a nonspecific finding.

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