Two-Year Follow-Up of Trypanosoma brucei gambiense Serology after Successful Treatment of Human African Trypanosomiasis: Results of Four Different Sero-Diagnostic Tests

Evaluation of the AnTat A/B and LiTat A/B primers for the detection of Trypanosoma bruceigambiense

Elimination of gambiense human African trypanosomiasis (gHAT) as a public health problem has been reached or is in sight in a number of endemic foci and the next step is now to reach the elimination of transmission. The ability to detect Trypanosomabruceigambiense (T.b.gambiense) in both the last human cases and in a suspected animal reservoir becomes increasingly important to reach this goal. We have evaluated here the diagnostic performance of the AnTat A/B and LiTat A/B primers in comparison with the TBR, TgsGP and nested TgsGP PCRs that are currently used for the molecular diagnosis of gHAT. The evaluation was based on serial DNA dilutions from two T.b.gambiense strains for sensitivity, purified reference strains for specificity and field strains isolated from pigs in Côte d'Ivoire for field application. Results showed that the two PCRs (AnTat A/B and LiTat A/B) are not specific for T.b.gambiense, limiting their relevance for studies on suspected animal reservoirs. However, they could represent complementary tools to improve the molecular diagnosis of gHAT in the elimination process even if the detection limit was lowest than for the TgsGP PCR. The results also once more suggest that nested TgsGP PCR should be interpreted with caution as they may lead to an over-estimation of the T.b.gambiense prevalence particularly in animal studies.

Human African trypanosomiasis

Human African trypanosomiasis or sleeping sickness is caused by infection with Trypanosoma brucei gambiense or Trypanosoma brucei rhodesiense parasites, which are transmitted by tsetse flies in sub-Saharan Africa. Control of human African trypanosomiasis is based on case detection, treatment, and vector control. In the past decade, simple rapid diagnostic tests were introduced for gambiense human African trypanosomiasis, facilitating screening in primary health-care facilities. A new oral drug, fexinidazole, became the first-line treatment for gambiense human African trypanosomiasis without severe meningo-encephalitic disease, as well as for rhodesiense human African trypanosomiasis. Medical interventions, in some areas combined with tiny target-based vector control, have substantially reduced human African trypanosomiasis incidence, despite temporary disruptions to health-care systems. The elimination of human African trypanosomiasis as a public health problem has been achieved, and elimination of gambiense human African trypanosomiasis transmission is now targeted for 2030. Improved diagnostics and drugs, continued involvement of populations at risk of disease, health staff, national authorities, and partners and donors all contribute to achieve this goal.

The STROGHAT study protocol: An intervention study to evaluate safety, effectiveness and feasibility of treating gambiense HAT seropositive subjects with acoziborole

Background

Coordinated efforts in the control of gambiense human African trypanosomiasis (gHAT) have significantly reduced its endemicity. WHO targets interruption of transmission by 2030. However, challenges remain, including low sensitivity of the current parasitological confirmation tests, leaving a potential human reservoir untreated. Acoziborole, a single-dose oral treatment, effective in both disease stages with a good safety profile, offers the potential of treatment of parasitologically negative gHAT seropositive subjects, which could improve diagnostic sensitivity. The STROGHAT study aims to evaluate whether this approach can lead to elimination of T.b. gambiense from its human reservoir, and to provide further safety data on acoziborole. It also includes a costing analysis and a prospective evaluation of the performance of the screening and diagnostic tests used.

Methods

STROGHAT is a one-arm epidemiological study, with a nested phase IIIb, one-arm, open label, non-randomized, multicentre clinical trial. It will be implemented over four years in the endemic region of the Equateur North, in the Democratic Republic of Congo. For the first three years, parasitologically negative gHAT seropositive subjects will be treated with acoziborole, while parasitologically confirmed cases will receive standard of care. Individual follow-up needs and accurate prevalence estimate will be based on immunological and molecular tests performed for all gHAT screening test seropositive subjects at a reference laboratory. In the fourth year, standard procedures will resume, and a prevalence survey will assess whether interruption of transmission has been achieved.

Discussion

The manuscript outlines the study background, objectives and methods while discussing its strengths and challenges. If successful, the STROGHAT study will provide critical evidence on the effectiveness, safety and feasibility of the new strategy, and inform future elimination strategies.

Clinical trial registration

NCT06356974. Date of registration: April 4, 2024.

Experimental evidence that immune trypanolysis using the LiTat 1.3 and LiTat 1.5 variant antigen types is not specific to Trypanosoma brucei gambiense in pigs

In the context of the human African trypanosomiasis elimination process, reliable and accurate diagnostic tools are crucial for exploring the role of a potential animal reservoir of Trypanosoma brucei gambiense. The immune trypanolysis test (TL) using the variant antigen types (VAT) LiTat 1.3 and LiTat 1.5, described as a specific serological method to detect people infected by T. b. gambiense, seems to be a promising tool. However, its specificity was recently questioned during field animal surveys. The present study evaluates the performance of TL during experimental T. b. brucei infection in pigs. Eight infected pigs and four uninfected pigs were followed up with blood and plasma collection. Blood was used for parasitological investigation. TL was performed on the plasma with the LiTat 1.3, LiTat 1.5 and LiTat 1.6 VATs. All control pigs remained negative to parasitological investigation and TL. Trypanosomes were detected in all the infected pigs and the first detection was between 10 and 14 days post infection (dpi). TL results showed that infected pigs developed antibodies against the three VATs. The first antibody detections by TL occurred between 14 and 21 dpi for antibodies directed against LiTat 1.6, 21 and 168 dpi for antibodies directed against LiTat 1.5 and 70, and 182 dpi for antibodies directed against LiTat 1.3. This study highlights for the first time that TL using LiTat 1.3 and LiTat 1.5 VATs is not specific to T. b. gambiense. Development of specific diagnostic tools for the detection of T. b. gambiense infections in animals, especially in pigs, is still needed.