Development and validation of serological assays to evaluate malaria transmission

In 2007, the aim to eradicate malaria was revived and reinvigorated, taking into account the experiences and lessons of the earlier efforts initiated in the mid 1950’s. In particular, it was recognised that improvements to diagnosis and surveillance would be essential for directing malaria control and elimination strategies across a highly heterogeneous disease landscape. In response, novel approaches to detecting, measuring and modelling malaria have been developed and implemented leading to elimination successes and significant reductions in disease burden. However, it remains clear that further improvements in this area are needed to tackle malaria where existing efforts have so far failed to break transmission. The work presented in this thesis demonstrates a 'pipeline' of technical and methodological development, aiming to identify, characterise and apply the use of serological biomarkers that may improve our understanding of malaria transmission within endemic settings. The specific studies and work included here describe a linear narrative, from conception to the implementation of serological biomarker approaches, through: 1) the development and optimisation of protein microarray technology to enhance the investigation of malaria parasite antigens as potential serological biomarkers of interest; 2) the evaluation and comparison of two parasite protein production methods in the context of a protein antigen microarray; 3) the utilisation of recently developed assay methods and analysis to investigate sexual stage specific humoral responses as potentially informative biomarkers in the context of malaria transmission; and 4) the application of established methods and known biomarkers to answer specific questions relating to the application of malaria diagnostics in field settings. Key findings include: 1) that the capture of protein antigen specific antibodies using microarray technology can be highly variable depending on specific assay materials and approaches utilised; 2) different protein antigen production methods can impact the capture of specific antibody, even between matched epitopes; 3) antibody responses to known sexual stage parasite antigens were induced in previously malaria naive individuals, developing later than anti-asexual responses; and 4) residual gametocytes after standard artemisinin-based combination therapy do not contribute to circulating levels of the parasite antigen HRP-2, and thus do not impact time to rapid diagnostic test negativity. Together these results demonstrate the complexity of establishing serological assay approaches for use in malaria research and surveillance, but also the potential for the further development and application of such methods to address important knowledge gaps.