Monitoring and evaluation of human African trypanosomiasis in an elimination era

Lead Research Organisation: Liverpool School of Tropical Medicine
Department Name: Vector Biology

Abstract

As the global number of HAT cases continues to drop, the focus shifts from control to elimination and beyond. As disease transmission reaches pre-elimination levels, HAT monitoring becomes increasingly challenging. Current methods rely on both active and passive screening of people which is costly, time consuming and requires high coverage. Additionally, as HAT cases drop, the cost of detecting new cases increases significantly. As a result, there is an increasing need for an efficient, sensitive and inexpensive monitoring tool that can be implemented by control programmes and carried into the post-elimination era.

Xenomonitoring offers an alternative through the screening of vectors for infection and has proven effective in the monitoring of lymphatic filariasis (1). The collection and testing of vectors rather than people significantly reduces costs. Furthermore, due to the chronic nature of gambiense HAT, passive screening detects infections that potentially occurred months or years previously whilst xenomonitoring can reveal real-time transmission.

A xenomonitoring methodology using loop-mediated isothermal amplification has been developed (2), and is effective in a laboratory setting at detecting Trypanozoon group infection in pools of tsetse flies. Building on this, this project aims to develop a T.b.gambiense specific xenomonitoring system, which can be utilised in HAT endemic countries.

As a result of large-scale vector control, certain areas have dramatically reduced tsetse populations. This reduction in numbers presents an additional challenge to the implementation of xenomonitoring. Due to similar feeding mechanisms and habitats, hematophagous flies such as Stomoxys are potential candidates for infection screening. Stomoxys have previously been shown to be capable of mechanically transmitting Trypansoma species (3). Despite not developing transmissible infections, the detection of T. b gambiense DNA in these flies would indicate the presence of circulating parasites within an area. Therefore, the xenomonitoring tool developed, will be evaluated for screening both tsetse and Stomoxys flies.

Uganda is currently on track to eliminate HAT by 2020. Following this success, vector control is scheduled to be reduced in specified areas starting in 2019. This provides a unique opportunity to monitor the dynamics of tsetse and trypanosome populations within a historic HAT focus. Previous empirical studies suggest that tsetse populations will recover rapidly following removal of control (4). This project will provide data on the long-term effects of reducing control on vector numbers in a historical HAT focus.

The project is composed of three main research questions:

1. Laboratory based development of a T.b.gambiense detection method.
This will involve the identification and incorporation of suitable primers into a PCR based technology, examining the limits of detection and adaptation of protocols for a field environment. Laboratory reared and wild-flies, will be used to develop accuracy data for the resultant xenomonitoring tool.

2. Can non-vector species be used for HAT xenomonitoring?
Laboratory based assay evaluation will follow a similar methodology to the tsetse monitoring system developed in question one, using laboratory reared Stomoxys. The system will be further assessed in the field using wild flies. These will be tested for both human and animal trypanosome infections.

3. What is the future of HAT control post-elimination/vector control removal?
Beginning in 2018, tsetse numbers will be monitored daily, flies stored and screened for infection. This will be conducted throughout the duration of my PhD. The data collected will be combined with diagnostic data provided through a previously established relationship with FIND. Examining cases alongside vector numbers will work towards proving a more complete picture of HAT transmission and potential risk of resurgence.

Publications

10 25 50
 
Description Investigation of Human African Trypanosomiasis rapid diagnostic test positivity rates in North Western Uganda 
Organisation Foundation for Innovative New Diagnostics (FIND)
Country Switzerland 
Sector Charity/Non Profit 
PI Contribution Analysis of Human African Trypanosomiasis rapid diagnostic data with a view to investigate spatial distribution of positive tests in North Western Uganda.
Collaborator Contribution FIND provided rapid diagnostic data from the region over the last 4 years.
Impact FIND were provided with a report of the analysis conducted and resulting findings.
Start Year 2018