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Garrod, Gala (2022) Surveillance and monitoring of human African trypanosomiasis in the elimination era, Thesis (Doctoral), Liverpool School of Tropical Medicine.
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G Garrod - PhD Thesis Final.pdf - Accepted Version Download (8MB) | Preview |
Abstract
Human African trypanosomiasis (HAT) is a parasitic disease caused by trypanosomes transmitted by tsetse flies (Glossina spp). Two forms of the disease exist: gambiense HAT (gHAT) and rhodesiense HAT (rHAT) caused by Trypanosoma brucei gambiense and T. b. rhodesiense respectively. A WHO-led programme, centered around case detection, treatment and vector control has driven down the annual number of HAT cases reported globally from a peak of >35,000 cases in the 1990s to 663 in 2020. The WHO aims to eliminate transmission of gHAT by 2030 and eliminate rHAT as a public health problem. As case numbers decline, current surveillance strategies, based largely on case detection, become more difficult and expensive. This thesis examines the utility of a xenomonitoring system to monitor trypanosomes in tsetse being integrated into HAT surveillance.
Towards this aim, two qPCR-based assays were developed to screen for pathogenic trypanosomes in tsetse. One assay allows both human pathogenic subspecies of T. brucei s.l. to be detected simultaneously. The assay was as sensitive as currently available PCR methods whilst reducing the number of assays required from three to one.
A second assay was developed to identify tsetse carrying T. brucei s.l. as well as T. vivax and T. congolense, pathogens of veterinary importance. In laboratory tests, the assay showed high specificity (100%) and sensitivity (96.9%) but sensitivity was much reduced (71.1%) when tested on wild-caught tsetse. Further optimization of the assay will be required for future use as a xenomonitoring method.
Extraction of trypanosome DNA from tsetse is an important but costly and time-consuming precursor to detecting trypanomes using PCR-based methods. Chapter four describes the development of a low-cost and field-friendly alternative using a novel magnetic bead protocol (MagnaExtract). The results indicate that the method could be an effective, cheaper and faster alternative to current commercially-available methods.
Finally, in chapter five the rate of rebound of tsetse following the removal of vector control was simulated using a simulation model (Tsetse Muse) and the model predictions were compared to field data obtained over 36 months from a gHAT focus in Uganda where control of tsetse, using Tiny Targets, has been halted. The simulations predicted that two years after control ceased, tsetse populations would recover by 34-73% according to assumptions regarding habitat quality. In contrast to model predictions, wild populations showed no significant rebound for up to two years after the withdrawal of Tiny Targets. In the context of northern Uganda, limited scaling back of the deployment of Tiny Targets may not lead to the rapid resumption of transmission and hence risk of gHAT.
The results of each data chapter are discussed in the context of the feasibility and benefit of xenomonitoring being integrated into a HAT surveillance system in the future
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