The current paper connects anxiety about disease contamination to that about cultural contamination and the exclusionary behavior toward ethnic outgroups that it incites. We suggest that when individuals are exposed to disease fears, an epistemic groundwork is laid for construing outgroups as sources of contamination. We begin with a pilot experiment showing that contagious disease anxiety primes opposition to legalization of illegal aliens. We then analyze historical data about the diffusion of rumor-based ethnic violence, showing that Indian regiments of the East India Company were more likely to mutiny against their British officers if they had been exposed some months earlier to a cholera discourse. (These mutinies were proximally caused by acceptance of a rumor that the Company administration had violated a cultural taboo.) We discuss implications for studying the cognitive antecedents of the diffusion of beliefs and practices in organizations and in cultures.