To survive in a host, a pathogen must avoid detection by the host immune system or stay one step ahead of it. One way that HIV avoids detection and clearance is by establishing a latent reservoir in resting memory CD4+ T cells. Several aspects of the mechanisms of reactivation from latency are understood, but less is known about the mechanisms by which the virus remains latent. On page 798, José Alcamí and colleagues describe the cellular and viral factors that HIV uses to establish and maintain the latent reservoir.

Many viruses and bacteria that do not have a latent phase subvert key host cell processes using effectors that mimic the structure or function of host proteins. In order to survive, the host needs to overcome the effects of these mimics, setting up a race between the pathogen and the host. This molecular mimicry and its implications for the evolution of the host and the pathogen are described by Malik and Elde on page 787.

Humans aren't the only travellers on this planet; many pathogens also travel long distances, usually aided by humans. Keim and Wagner, on page 813, describe the ecological and evolutionary forces at work and the role of humans in the spread of bacteria across the globe, using the examples of Bacillus anthracis, Francisella tularensis and Yersinia pestis. The clonal nature of these organisms allows their dissemination and spread to be traced over a long period.

In order to grow, bacteria need to coordinate the replication of DNA and cell division with the availability of nutrients. On page 822, Wang and Levin describe the intricate sensing mechanisms in bacteria that ensure that cell division takes place only when the cell is large enough, the chromosome has been replicated and the conditions are favourable.