Land-use change and pathogen emergence: Differential implication of factors driving emergence across land-use gradients

Background/Question/Methods

Approximately 23% of past Emerging Infectious Disease (EID) events can be linked to land-use change. These EIDs include outbreaks of Ebola virus, Marburg virus, rabies, HIV-AIDS, avian influenza and Yellow Fever.  Increasing human land use is likely leading to biodiversity loss, and facilitating infectious disease spillover events that can lead to disease emergence, and potentially create a future pandemic.

Changes in land-use can alter the distribution, abundance, and diversity of pathogen reservoirs, and create novel opportunities for human contact with these reservoirs, including: new human settlements; movement of agricultural workers into previously undisturbed ecosystems; loss of the protective benefits of biodiversity; increasing utilization of wildlife of human-altered habitats; increase in human-wildlife conflict including direct interactions. All of which has the potential to facilitate the processes of cross-species transmission, amplification, and evolutionary adaptation that constitute an emergence event. Additonally, the suite of events involved in land-use change can disrupt of the complex network of ecosystem relationships that may modulate the dynamics of pathogen circulation.

We hypothesize that the increased contact rates between humans, livestock, and wildlife due to land use change, and agricultural intensification, foster a higher probability of disease emergence events. Consequently, a quantitative analysis of the impacts of land use change, biodiversity, and pathogen emergence are needed, grounded both in empirical evidence and theoretical analyses.

Results/Conclusions

We present the theoretical basis for our approach to understanding the effects of land-use change on pathogen emergence, and make the argument that several factors are involved that may counteract and interact with each other.  We hypothesize that it will be intermediate, and relatively recent, land-use change that may be most important for disease emergence, that different intensities and histories of land-use change may create different risk-profiles, and that different factors may be the largest drivers of emergence across these histories and intensities.  Thus land-use cannot be seen as a statically measured factor, but must consider the complexities of history and context.

We will then briefly cover our work to as part of the USAID Emerging Pandemic Threats PREDICT project Deep Forest, which intends to capture the volume and diversity of pathogens circulating in key wildlife reservoirs as a function of defined ecosystems along a spectrum from pristine/undisturbed to semi-disturbed to disturbed/urban. Data from Latin America, Africa, and Asia will be available to test in the theoretical framework presented here.