Making diagnostic tests for tropical diseases

Barrie Rooney looks at the challenges of treating sleeping sickness.

Along the upper reaches of the Congo River a 30-strong Médecins Sans Frontières (MSF) team move from village to village towing a floating laboratory. Our team is searching for Trypanosoma brucei gambiense, the parasite that causes sleeping sickness (SS). This fatal disease affects people living in remote areas of central Africa’s rainforest where the insect vector thrives.

Transmitted by the bite of the bloodsucking tsetse fly, SS can be a slow killer; taking up to two years to produce the full neurological symptoms, coma and inevitable death.

Everyone in the village must be screened because non-symptomatic carriers act as reservoirs. These carriers must be found and treated in order to break the cycle of transmission for this Neglected Tropical Disease (NTD). Among the designated NTDs, SS is one of three caused by members of the protozoan group Kinetidoplastidia. Chagas and Leishmaniasis are the other two and together they threaten the lives of over 90 million people.

Tsetse fly

Diagnostic challenges

Following an infective insect bite, the SS patient will suffer peaks of parasitaemia as the host mounts a humoral immune response to the changing surface antigens on the SS parasite. Diagnosis is complex and requires a combination of serological and microscopic examination of tissue and blood samples.

A positive result requires an immediate lumbar puncture to assess the disease stage and therefore the type of treatment required. To make screening more accessible to remote populations, recent efforts have focused on simplifying and reducing the cost of point-of-care (POC) diagnostic tests.

diagnostic

Rapid Test Design (RDT) for Human African Trypanosomiasis (HAT)

A widely accepted format for these POC serodiagnostic lateral flow tests (RDTs) is the dipstick design of the common pregnancy test (Figure 1). The key to high sensitivity and specificity is the choice of parasitic antigen (or monoclonal antibody) printed on the test line (T). First generation SS-RDTs use purified extracts from laboratory-derived native parasites which are recognized by serum from infected individuals.

More recently, recombinant bioengineered antigenic proteins have been favoured as they are cheaper to make and more reproducible. However, making biosimilar antigens for parasitic surface proteins can be difficult as they may require complex post-translational modifications. Success has been found by engineering the related species, Leishmania tarentolae, and by modifying the glycosylation pathway of the yeast Pichia.

Trypanosome brucei gambiense

Trypanosome brucei gambiense

Innovator of the Year

The recently awarded BBSRC Innovator of the Year award to the author displays the success of multinational collaborations in translating basic research results into POC tests that stand up to the demands of tropical usage.

Access to a WHO SS biobank of characterized serum samples allowed rigorous testing of prototypes before the chosen test was scaled up for manufacture. Commercial companies were persuaded to waive intellectual property rights and made the tests at cost.

It is currently undergoing an EU-funded, multicentred field trial in Guinea, DR Congo, Burkina Faso and Cote d’Ivoire.

The detection of human and animal reservoirs for these SS and other Kinetidoplast parasites is crucial to the control of these debilitating diseases in neglected populations. Following WHO guidelines on POC tests, we continue to search for new biomarkers and build international consortia to transform them into user-friendly RDTs.

Barrie Rooney is a Research Fellow at the University of Kent and founder of Charity TROZON 

Acknowledgements

BBSRC for funding, CORIS Bioconcept and Jena Bioscience for manufacture, Institute of Tropical Medicine and WHO for access to serum samples, IRD Marseille for field trials and MSF for photographs.

Further reading

  • Neglected tropical diseases
  •    Rooney B, Piening T, Büscher P, Rogé S, and Smales CM (2015). Expression of Trypanosoma brucei gambiense antigens in Leishmania tarentolae. Potential for use in rapid serodiagnostic tests (RDTs). PLoS Neglected Tropical Diseases, 9(12), e0004271
  • Sleeping sickness
  • Wu G, and Zaman MH (2012). Low-cost tools for diagnosing and monitoring HIV infection in low-resource settings. Bull World Health Org 90, 914–920

 

 

 



Categories: Feature Articles

Leave a Reply

%d bloggers like this: