Rethinking host range in Pneumocystis

Revisiting the Pneumocystis host specificity paradigm and transmission ecology in wild Southeast Asian rodents

“…Our findings stress the importance and necessity of using extensive sampling of closely related mammal host species and genera to fully assess the exact host range and host specificity of Pneumocystis species and detect the rarer lineages whose prevalence are lower than the most common lineages. This study also confirms that the proverbial monoxenism and co-evolution of Pneumocystis and their hosts often presented in the literature could be a sampling artifact rather than a biological reality as recently suggested by Babb-Biernacki et al (2020). Future exhaustive studies of Pneumocystis diversity in taxa other than rodents will help determine whether the relaxed stenoxenism of Pneumocystis in murine rodents observed in this study is an exception or the rule among mammalian hosts.…”

“…Our previous study also demonstrated that most Pneumocystis lineages identified in Southeast Asian murid rodents infected several closely related host species, suggesting that the Pneumocystis host specificity in rodents is mostly limited to the generic level (stenoxenism) rather than the species level (monoxenism) (Latinne et al, 2018). These results contradict the apparent strict host specificity observed in other mammals (Akbar et al, 2012;Demanche et al, 2001;Hugot et al, 2003) but some authors recently suggested that the inferred monoxenism of Pneumocystis in some of these studies was due to the inclusion of only distantly related species and the lack of extensive host intrageneric sampling (Babb-Biernacki et al, 2020).…”

“…Several of these lineages were clearly delineated in phylogenies based on mitochondrial markers, and the level of mitochondrial genetic distance between these lineages and formally recognized species was indicative of phylogenetic species recognition (Latinne et al, 2018). The use of nuclear markers, notoriously difficult to amplify in samples from wild hosts characterized by low Pneumocystis loads (Babb-Biernacki et al, 2020;Demanche et al, 2019), would further confirm their specific taxonomic status. This large diversity of Pneumocystis observed in rodents arose from a complex host-parasite evolutionary history, involving a long-lasting process of co-evolution but also several host switches (Latinne et al, 2018;Petružela et al, 2019).…”

“…Several molecular studies investigating the diversity and host specificity of these fungal parasites in a wide range of mammalian species showed that the Pneumocystis genus is highly diversified and includes numerous divergent taxonomic entities characterized by strong host specificity and apparently restricted to a single host species (Akbar et al, 2012;Danesi et al, 2016;Demanche et al, 2001;Hugot et al, 2003;Petružela et al, 2019). However recent studies called this long-standing Pneumocystis strict host specificity paradigm into question as the biology, evolution, epidemiology and transmission of these airborne-transmitted organisms in natural host populations remain poorly understood (Babb-Biernacki et al, 2020;Cissé and Hauser, 2018;Latinne et al, 2018;Ma et al, 2018).…”

Predicting Species Boundaries and Assessing Undescribed Diversity in Pneumocystis, an Obligate Lung Symbiont

“…However, the true degree of host specificity in this genus has not been sufficiently tested, and evidence suggests some Pneumocystis species may be shared by closely related hosts, such as within mammalian genera [ 17 , 18 , 19 , 20 ]. This evidence has led researchers to reassess assumptions of single host specificity [ 21 , 22 , 23 ]. Unfortunately, we still have little direct evidence.…”