Discussion

African trypanosomiasis is a protozoan disease that affects humans (Human African Trypanosomiasis – HAT) and livestock (Animal African Trypanosomiasis – AAT) in sub-saharan Africa. There is a significant need in both HAT and AAT for improved diagnostics, in particular a specific and sensitive trypanosome-derived marker of active infection. This is particularly the case in AAT, where most diagnosis is currently symptomatic or reliant upon microscopy. Small non-coding RNA (ncRNA) are being utilised as biomarkers in a range of diseases. We have identified a small ncRNA encoded by the trypanosomes that is secreted/excreted at high levels in infected animals. The ncRNA is conserved between T. brucei, T. congolense and T. vivax, albeit with sufficient nucleotide differences to allow design of a diagnostic test that differentiates between species. Using quantitative reverse transcription polymerase chain reaction (qRT-PCR) assay, we show that active infection can be detected with high levels of sensitivity and specificity in cattle infected with all three African trypanosome species, and signal rapidly disappears after successful drug treatment. Strikingly, when parasitaemia is non-detectable by the microscopic means, we are able to detect the small ncRNA at high levels. This detection is lost following drug treatment of infected cattle.   Additionally, we show that this small ncRNA can be detected using serum as the qRT-PCR substrate, increasing potential field applicability. As the biomarker is pathogen expressed, this ncRNA has significant potential utility as a diagnostic marker for active infection of AAT and HAT.