Key points
- Definitive diagnosis rests on the observation of trypanosomes by microscopy.
- Rhodesiense human African trypanosomiasis (HAT) is often diagnosed with a blood test.
- Gambiense human African trypanosomiasis (HAT) is more difficult to diagnose.
- You can stage both types of human African trypanosomiasis (HAT) by examining a patient’s cerebrospinal fluid (CSF).
Diagnosis
Rhodesiense HAT
In T. b. rhodesiense infection, the identification of suspected cases relies on the clinical presentation and a history of exposure. The level of parasitemia is relatively high, particularly in the first stage of disease, and trypanosomes can be found in blood. In centrifuged blood, the parasite sediments just above the white blood cells, and examination of the buffy coat will increase sensitivity. Slides stained with Giemsa can be used, but it is easiest to find the parasite by microscopic examination of fresh wet preparations, because the trypanosomes are motile.
Delay between sampling and microscopy should be minimized because trypanosomes will lose motility within a few hours. Parasites can also be found in fluid expressed in trypanosomal chancres and in lymph node aspirates. Serologic testing is not used for the diagnosis of T. b. rhodesiense infection.
Gambiense HAT
Detecting trypanosomes in T. b. gambiense infection is more difficult. The card agglutination test for trypanosomiasis/T. b. gambiense (CATT) is a serologic screening test used for population screening in endemic areas of Africa. It is not available in the United States. The test is insufficiently specific for confirmation of infection but can be helpful in identifying suspect cases.
Parasitologic confirmation rests upon microscopic examination of chancre fluid or lymph node aspirate. The yield in lymph node examination varies from about 40% to 80%. Trypanosomes can also be found in blood; however, the yield is low, and concentration techniques (e.g., centrifugation followed by buffy coat examination, mini-anion exchange centrifugation technique, or microhematocrit centrifugation technique) are helpful. Serial examinations on consecutive days may be needed.
Staging
Staging for HAT infection caused by both T. b. gambiense and T. b. rhodesiense (i.e., assessment of neurological infection) is performed by microscopic examination of CSF collected by lumbar puncture on a wet preparation looking for motile trypomastigotes and WBCs. Patients with five or fewer WBCs per microliter and no trypomastigotes are considered to be in the first stage, and those with more than five WBCs per microliter or trypomastigotes are in the second stage. Other indications of second stage disease include elevated protein and an increase in nonspecific IgM in the CSF.
Diagnostic assistance for HAT is available through DPDx.