Rethinking host range in Pneumocystis

摘要

Fungi in the genus Pneumocystis are obligate biotrophs and opportunistic pathogens of mammal lungs. They are notable for their high degree of host specificity; it is often argued that Pneumocystis species are restricted to a single host species (i.e., monoxenous) [1, 2]. This monoxenous hypothesis, combined with their ubiquitous presence across mammal diversity, suggests that there may be one Pneumocystis species for each of the 6399 extant mammal species. However, only a small percentage of mammal species have been tested for Pneumocystis, and only five Pneumocystis species have been formally described. Despite our massive knowledge gaps, the notion of monoxenism in Pneumocystis is so pervasive that evidence to the contrary is often described as rare exceptions to a rule [1, 2]. Here, we review the literature on host distribution of Pneumocystis and argue that monoxenism is not supported by the available, albeit limited, data. We emphasize the importance of species discovery and studies of Pneumocystis host range as a prerequisite to the pursuit of other biological questions in these and other medically important fungi.