Preventing the transmission of artemisinin resistant falciparum malaria Malaria is a disease of devastating impact causing 584,000 deaths in 2013. Artemisinin combination therapies (ACTs) are the frontline treatment for malaria and remain safe and effective throughout most of the world. However, in recent years, resistance to artemisinin has arisen in Southeast Asia, causing slower recovery and malaria treatment failures. It is greatly feared that resistance will spread throughout the region and from there, worldwide. If this happens, in the absence of effective new drugs (that are at best several years from reaching clinical approval), malaria may become untreatable and all the gains made in recent years will be reversed. Malaria is caused by the parasitic organism Plasmodium and transmitted through the bite of Anopheles mosquitoes. Malarial symptoms are caused by successive rounds of parasite invasion of host red blood cells (RBCs), replication, and then re-invasion of further RBCs - termed the asexual cycle. With each cycle, a small proportion of the parasites undergo an alternative developmental pathway forming the sexual stages, or male and female gametocytes. Gametocytes are responsible for onward transmission to the mosquito therefore are essential for the parasite to complete its life cycle. Very few gametocytes are ingested in a mosquito blood meal making this parasite "population bottleneck" an attractive target for therapies that prevent the spread of malaria. Only two approved antimalarial drugs are effective against this gametocyte population - primaquine (PQ) and methylene blue (MB). Given the immediate need to halt the spread of artemisinin resistance in Southeast Asia, every tool in our armoury needs to be deployed - including the aforementioned transmission-blocking drugs. To this end, it's of critical importance to identify whether artemisinin-resistant parasites will respond to PQ and MB (and any other up and coming antimalarial drugs) before embarking on widespread transmission-blocking campaigns. Our project proposes to take already established and characterised Thai isolates of P. falciparum, some showing sensitivity and some resistance to artemisinin, and test them in an existing lab-based assay (the P. falciparum dual gamete formation assay - Pf DGFA) widely regarded as an accurate indicator of transmission-blocking. This will enable us to compare head-to-head the effectiveness of PQ and MB (and their metabolites) under standardised laboratory conditions and rank their effectiveness against artemisinin sensitive and resistant parasites. Additionally, using cutting edge genetic modification techniques (CRISPR), we will generate our own artemisinin resistant parasites by introducing successive mutations in genes known to be important for resistance. By this, we can gain an insight into how each contributes to overall resistance. The second aspect of our project is derived from our recent understanding that the lesser population of male gametocytes are more drug-sensitive than female gametocytes. As it is so expensive and technically challenging to measure malaria transmission directly to the mosquito on a larger scale required for clinical trials, measurements of gametocyte clearance from the infected human are currently used as surrogates. These crude measurements do not measure the viability of the gametocyte, nor take into consideration differences in male and female gametocytes. We propose taking the lab-based Pf DGFA and adapting it for the field to enable an accurate assessment of transmission-blocking during clinical trials. The benefits of our project are twofold. By understanding the effectiveness of current and future transmission-blocking drugs against artemisinin-resistant parasites we will be able to make evidence-based recommendations to the community for future trials. Then, by designing and implementing a new and more informative transmission-blocking assay, we will be giving the community the tools to accurately evaluate said transmission-blocking trials. The Newton Fund builds research and innovation partnerships with developing countries across the world to promote the economic development and social welfare of the partner countries.