Identification of sVSG117 as an Immunodiagnostic Antigen and Evaluation of a Dual-Antigen Lateral Flow Test for the Diagnosis of Human African Trypanosomiasis

Introduction Human African Trypanosomiasis (HAT), or African Sleeping Sickness, is caused by two sub-species of Trypanosoma brucei. T. b. gambiense accounts for approximately 95% of HAT infections and occurs across East and Central sub-Saharan Africa. The remaining infections are caused by T. b. rhodesiense in West and Southern Africa. The disease has two stages: Stage 1, where the parasites are limited to the bloodstream, interstitial fluids and lymph of the patient, and stage 2, where parasites are also found in the central nervous system. In recent years, the official number of recorded HAT cases has fallen below 10,000 per year, although possible under-reporting suggests that this is likely a minimum figure [1–3]. Nevertheless, with new therapeutic regimes [4–6] and with a repurposed drug (fexinidazole) [7] and a new chemical entity (an oxaborole) [8] in clinical trials, the potential to eliminate HAT from many regions of sub-Saharan Africa at last exists. However, disease elimination requires excellent and convenient field diagnostics. Currently, the diagnosis of infected individuals relies principally on screening teams that visit at-risk communities and from patients seeking medical help [9,10]. Some patients with T. b gambiense infections remain asymptomatic for years, so early diagnosis of infected individuals benefits not only the patient but also the community where these individuals can act as parasite reservoirs [11]. The most widely used diagnostic for suspected T. b. gambiense infections is the Card Agglutination Test for Trypanosomiasis (CATT). This serological test detects host antibodies to a suspension of fixed and stained T. b. gambiense trypanosomes expressing variant surface glycoprotein (VSG) varia