My doctoral thesis explores the history of epidemics in Northern Italy under French domination (1796-1805). It is rooted in the social history of medicine and science and technology studies, and focuses on contested epidemics, that is to say epidemics whose origin, nature and even reality were largely debated, such as intermittent fevers, mal du pays, hospital fever and the fever of Livorno. The scope of my study encompasses two different yet complementary types of “medical wars”: the instrumentalisation of medical knowledge and actors to support French military expansion; and the political and commercial wars waged against states accused of lying about the epidemiological situation of their population. Because it was politically divided, traversed by foreign armies, hit by numerous epidemics, the importance of which some civil and military authorities tried to minimise or even deny, Italy between 1796 and 1805 is a privileged observatory to study the politics of knowledge production and agnotology as far as epidemics are concerned. I show that if epidemic diseases deeply affected Italian societies, medical discourse and public health measures were driven by economic interests and geopolitics more than sanitary reasoning. The examination of the role played by health issues during the campaigns of Italy thus offers a fresh perspective on a military endeavour that laid the foundation of Bonaparte’s political career. It also reveals that not only did military doctors help French imperialism by curing sick and wounded soldiers, but also by publishing treaties defining diseases as endemic instead of epidemic or denying their very existence, which was aimed at fighting the discourse of the municipal authorities accusing the French army of spreading epidemics on Italian soil. Such politics of knowledge and the production of ignorance are also crucial to my analysis of the fever that struck Livorno in 1804. Thanks to a microhistorical approach, I highlight the crucial role played by lay actors in day-to-day epidemiological monitoring, and I demonstrate that informal sources were paradoxically held to be more trustworthy evidence than formal documents signed by doctors and officials. I also analyse the processes of trust-building among foreign health magistrates, showing that local and national public health measures are loosely linked to domestic issues, and in reality often based on the effects they are expected to have on the governments of neighbouring states.