This article introduces the concept of trans-biopolitics to account for complexity in the intermingling of animal and human bodies, with particular attention to diseases capable of crossing the species divide from animals to humans. While zoonotic diseases never disappeared, they had re-emerged as pressing concerns by the 21st century. The concept of trans-biopolitics takes into account the power relations inherent in human and nonhuman lives in contemporary global, industrial, and technological formations. More specifically, trans-biopolitics revolves around practices determining whose lives are possible or legitimate to prolong, whose bodies are sacrificed in order to preserve the vitality of other bodies, and whose bodies are sustained yet ultimately rendered insignificant. To illustrate, we examine connections between bovine spongiform encephalopathy and feline spongiform encephalopathy, to show how certain bodies (humans, livestock) are taken into consideration in terms of health and food regulations, whereas other bodies (pets) remain at the periphery. Acknowledging human-animal relations in contemporary technological and global contexts challenges us to rethink ways in which the politics of health continues to evolve.