The impact of abiotic parameters and host community structure on a multi-host pathogen: the case of Mycobacterium ulcerans in Cameroon

Background/Question/Methods

Multi-host pathogens represent a current threat for public health as well as for biodiversity decline. However, the biotic and abiotic factors affecting transmission potential of such pathogens are extremely difficult to discern because of their complex transmission cycles. A striking example is the environmental pathogen Mycobacterium ulcerans (MU), the agent responsible for Buruli Ulcer (BU), a disease with dramatic socioeconomic and health outcomes in tropical and subtropical countries. Multiple aquatic organisms are likely to play a role either as hosts or vectors of the bacilli, and both water characteristics and biotic components of aquatic ecosystems could influence MU propagation within local aquatic communities. However, their respective contribution on MU ecological dynamics in space and time is unknown, jeopardizing public health attempts for its control. The objective of this study was to study the impact of freshwater ecosystem characteristics and aquatic communities on MU ecological dynamics thanks to an extensive environmental survey conducted in two BU endemic regions in Cameroon.  

Results/Conclusions

Our study shows a broad distribution of MU in all ecosystems and taxonomic groups. Despite its high ubiquity, we demonstrate that some ecosystems can be more at risk of carrying the pathogen, and that this risk fluctuates through time. Firstly, stagnant ecosystems with micro-aerobic conditions, low temperature and high pH promote its persistence in the environment. Total abundance of aquatic invertebrates and vertebrates is inversely associated to MU presence, but taxa that are traditionally considered as environmental indicators of poor water conditions such as Oligochaeta, Hirudinea or Diptera, all show positive associations with MU. Furthermore, MU dynamics are subjected to seasonal variations with the highest presence over the high rainy season and a progressive drop during the high dry season. Thanks to this new body of knowledge, we thus explore the plausibility of the different transmission routes to human populations.