There is growing international concern about the circulation of pathological viruses in the world economy. Reviewing recent scholarship on avian flu, SARS, and HIV/AIDS, this article argues that the contemporary world economy is generating not just an ecological footprint, but also an important epidemiological one. Illustrating the complex interdependencies that exist between economic and microbial systems of circulation, the article highlights the difficult challenges that states confront in trying to shield populations against these viruses within the current international order. Finally, the article also considers recent attempts to scale up international responses to these viruses, including their progressive securitization and the coming into force of a new set of international health regulations – opening up a new chapter in the bio-history of humanity