Field evaluation of the CATT/Trypanosoma brucei gambiense on blood‐impregnated filter papers for diagnosis of human African trypanosomiasis in southern Sudan

Abstract

Summary Most Human African Trypanosomiasis (HAT) control programmes in areas endemic for Trypanosoma brucei gambiense rely on a strategy of active mass screening with the Card Agglutination Test for Trypanosomiasis (CATT)/T. b. gambiense. We evaluated the performance, stability and reproducibility of the CATT/T. b. gambiense on blood‐impregnated filter papers (CATT‐FP) in Kajo‐Keji County, South‐Sudan, where some areas are inaccessible to mobile teams. The CATT‐FP was performed with a group of 100 people with a positive CATT on whole blood including 17 confirmed HAT patients and the results were compared with the CATT on plasma (CATT‐P). The CATT‐FP was repeated on impregnated filter papers stored at ambient and refrigerated temperature for 1, 3, 7 and 14 days. Another 82 patients with HAT, including 78 with a positive parasitology, were tested with the CATT‐FP and duplicate filter paper samples were sent to a reference laboratory to assess reproducibility. The CATT‐FP was positive in 90 of 99 patients with HAT (sensitivity: 91%). It was less sensitive than the CATT‐P (mean dilution difference: −2.5). There was no significant loss of sensitivity after storage for up to 14 days both at ambient and cool temperature. Reproducibility of the CATT‐FP was found to be excellent (kappa: 0.84). The CATT‐FP can therefore be recommended as a screening test for HAT in areas where the use of CATT‐P is not possible. Further studies on larger population samples in different endemic foci are still needed before the CATT‐FP can be recommended for universal use.

An Overview of the Clinical Use of Filter Paper in the Diagnosis of Tropical Diseases

“…Nucleic acid testing was evaluated for DBS versus microscopy for Brugian filariasis and Loa loa and seems sensitive, particularly for the latter at 96% 68–70. African and American trypanosomiases have both been successfully diagnosed on DBS with high sensitivity and specificity,71–74 but the sample size for Trypanosoma cruzi was relatively small 73. Strict control of humidity by storing DBS in sealed plastic bags with silica gel immediately after drying may have been a key factor, resulting in the higher sensitivity reported in the work by Chappuis and others71 compared with the work by Truc and others 72…”

Human African Trypanosomiasis Diagnosis in First-Line Health Services of Endemic Countries, a Systematic Review

“…It is a direct agglutination test based on a freeze-dried purified, formaldehyde-fixed and Coomassie-blue-stained bloodstream-form of T. b. gambiense variable antigen type LiTat 1.3. Three CATT formats are available: the classical CATT test on whole blood [5], the CATT on filter paper [12]–[17] and the CATT-D10 [18]. The CATT is a fast and simple agglutination assay for detection of T. b. gambiense -specific antibodies in the blood, plasma, or serum of HAT patients.…”

Options for Field Diagnosis of Human African Trypanosomiasis

“…A recently modified method, the macro-CATT, was developed for testing blood-impregnated FP by using a standard amount of antigen and a higher volume of FP eluate. The macro-CATT was evaluated in southern Sudan and showed a sensitivity of 91% and excellent stability when FP were stored for up to 2 weeks at ambient temperature (25 to 34°C) (23).…”