Interacting parasites

Parasitism is the most popular life-style on Earth, and many vertebrates host more than one kind of parasite at a time. A common assumption is that parasite species rarely interact, because they often exploit different tissues in a host, and this use of discrete resources limits competition (1). On page 243 of this issue, however, Telfer et al. (2) provide a convincing case of a highly interactive parasite community in voles, and show how infection with one parasite can affect susceptibility to others. If some human parasites are equally interactive, our current, disease-by-disease approach to modeling and treating infectious diseases is inadequate (3).

Telfer et al.'s study—which involved tracking infections of four different parasites by taking blood samples from nearly 6000 wild voles (Microtus agrestis) over 5 years—helps highlight our growing understanding of how parasites can interact in complex ways (see the figure). What are some of the take-home messages?