No abstract

The number of microbes on Earth may be 10 30 , exceeding all other diversity. A small number of these can infect people and cause disease. The diversity of parasitic organisms likely correlates with the hosts they live in and the number mammal hosts for zoonotic infections increases with species richness among mammalian orders. Thus, while habitat loss and fragmentation may reduce species diversity, the habitat encroachment by people into species-rich areas may increase the exposure of people to novel infectious agents from wildlife. Here, we present a theoretical framework that exploits the species–area relationship to link the exposure of people to novel infections with habitat biodiversity. We model changes in human exposure to microbes through defined classes of habitat fragmentation and predict that increased habitat division intrinsically increases the hazard from microbes for all modelled biological systems. We apply our model to African tropical forests as an example. Our results suggest that it is possible to identify high-risk areas for the mitigation and surveillance of novel disease emergence and that mitigation measures may reduce this risk while conserving biodiversity.

Bats are reservoirs for several zoonotic pathogens of medical importance; however, infection dynamics of pathogens in wild bat populations remain poorly understood. Here, we examine the influence of host crowding and population age structure on pathogen transmission and diversity in bat populations. Focusing on two pathogen taxa of medical importance, Leptospira bacteria and paramyxoviruses, we monitored host population and pathogen shedding dynamics within a maternity colony of the tropical bat species Mormopterus francoismoutoui, endemic to Réunion Island. Our data reveal astonishingly similar infection dynamics for Leptospira and paramyxoviruses, with infection peaks during late pregnancy and 2 months after the initial birth pulse. Furthermore, although co-infection occurs frequently during the peaks of transmission, the patterns do not suggest any interaction between the two pathogens. Partial sequencing reveals a unique bat-specific Leptospira strain contrasting with the co-circulation of four separate paramyxovirus lineages along the whole breeding period. Patterns of infection highlight the importance of host crowding in pathogen transmission and suggest that most bats developed immune response and stop excreting pathogens. Our results support that bat maternity colonies may represent hot spots of transmission for bacterial and viral infectious agents, and highlight how seasonality can be an important determinant of host-parasite interactions and disease emergence.

Biodiversity hotspots and associated endemism are ideal systems for the study of parasite diversity within host communities. Here, we investigated the ecological and evolutionary forces acting on the diversification of an emerging bacterial pathogen, Leptospira spp., in communities of endemic Malagasy small mammals. We determined the infection rate with pathogenic Leptospira in 20 species of sympatric rodents (subfamily Nesomyinae) and tenrecids (family Tenrecidae) at two eastern humid forest localities. A multilocus genotyping analysis allowed the characterization of bacterial diversity within small mammals and gave insights into their genetic relationships with Leptospira infecting endemic Malagasy bats (family Miniopteridae and Vespertilionidae). We report for the first time the presence of pathogenic Leptospira in Malagasy endemic small mammals, with an overall prevalence of 13%. In addition, these hosts harbour species of Leptospira (L. kirschneri, L. borgpetersenii and L. borgpetersenii group B) which are different from those reported in introduced rats (L. interrogans) on Madagascar. The diversification of Leptospira on Madagascar can be traced millions of years into evolutionary history, resulting in the divergence of endemic lineages and strong host specificity. These observations are discussed in relation to the relative roles of endemic vs. introduced mammal species in the evolution and epidemiology of Leptospira on Madagascar, specifically how biodiversity and biogeographical processes can shape community ecology of an emerging pathogen and lead to its diversification within native animal communities.