In this article, I examine epidemiological research into scrub typhus in British Malaya between 1924 and 1974. Interwar research, I show, explained the incidence of the disease through conjunctions of rats, mites, plantations, lalang grass, and "jungle." In the process, interwar researchers bridged a novel scientific vocabulary centering on disease "reservoirs" with older suspicions of plantations enabling "pests," as well as with a later, explicitly ecological understanding of infectious disease. In exploring this history I thereby help to re-historicize the emergence of ecological notions of disease reservoirs, whilst also pushing at the limit-points of influential notions of "tropicality."