One thousand five hundred recruits will be enrolled in the trial. Randomisation will be based on combania (the company, comprising typically 30-50 recruits). Recruits in a combania perform all activities together as a group. The randomisation will be unequal since the investigators expect that the primary comparison requiring the greatest precision is that of adding DEET lotion to PTU. Investigators will randomise 500 recruits for each arm of the primary comparison (PTU plus DEET, PTU uniform only) and 250 recruits to each of DEET only and placebo.