ARE student François M. Castonguay presented his research on treatment policies against environmentally transmitted diseases (ETDs). This work is a collaboration with Jim Sanchirico. In the research, François and Jim investigate the cost-effectiveness of different treatment policies in the fight against environmentally transmitted diseases (ETDs). They consider the following treatment scenarios: mass drug administration (MDA) to children, MDA to the whole community, a water, sanitation, and hygiene (WASH) measure, as well as various combinations of the above. The use of optimal control techniques enables them to show relative trade-offs between different types of treatment and to shed light on how to optimally treat ETDs. They show how optimal treatment changes if the pathogen living in the environment leads to loss of ecosystem services, or if they were to account for damages caused by the ETD after treatment stops.