The Effects of Wildlife Loss and Land Use Change on Rodent-Borne Disease Risk in East Africa

Funding Year: 2010

Research Areas: Natural Capital

Regions: Africa

This project explores whether the loss of large wildlife and changes in land use increase the risk of infectious disease in developing tropical countries.

Overview

Recent research suggests that human alteration of natural landscapes (e.g., land use change) and of its constituent biodiversity elements (e.g., removal of large wildlife) can amplify disease risk. This observation raises the possibility that conservation initiatives may act synergistically to promote public health and safeguard the environment. The majority of emerging infectious diseases are zoonotic (transmitted from non-human animals to humans) and vector-borne (transmitted by mosquitoes, fleas etc). Successfully understanding the complexity of the multiplelinkages inherent to vector borne zoonoses necessitates adopting an interdisciplinary research approach. This EVP combines the expertise of researchers in multiple departments and research institutions at Stanford to investigate a situation in East Africa where there may be a clear relationship between environmental alteration and increased risk of rodent-borne zoonotic diseases.

Given the enormous economic and social consequences of increased disease risk, the researchers involved with this EVP intended their work to help align economic incentives and societal improvement with conservation objectives. Outputs generated by this effort will help both government and nonprofit groups to make spatially explicit decisions about how to manage landscapes in a way that would achieve the greatest benefits in terms of improved human health and environmental management.

EVP Goals and Approach

This research aims to address two major societal and environmental challenges: 1) the high disease burden and high risk of emergence (and reemergence) of infectious diseases in developing tropical countries (e.g. East Africa), and 2) the contemporary loss of medium and large vertebrates (defaunation) and land conversion of natural areas in these regions (1). The goal is to explore a novel linkage between these two issues by investigating how loss of large wildlife and land conversion may lead to changes in disease risk.

Researchers gathered empirical data to identify the specific mechanisms by which habitat change affects the dynamics of several rodent-borne diseases (e.g. plague, leishmaniasis). Then, they used this data to develop a predictive framework that will generate expectations of how current and future land use will alter disease risk. This framework can provide governments andnonprofits with a tool to consider unexplored but important relationships between human health and environmental health when making management decisions.

Preliminary Results

The EVP has found strong and exciting support for several of its studys hypotheses linking changes in land use to changes in rodent abundance and thus on potential for borne disease (e.g., rodent abundance all species in agriculturally managed landscapes is more than 2.5 times higher than in conserved landscapes (P< 0.01), rodent diversity is lower in all managed landscapes (P< 0.01)). Among the studys unexpected and exciting early results:

• stronger than anticipated temporal and spatial variability observed in rodent abundances across land use types, which may be tied to small scale variation in management practices.

• identification of two new pathogens of medical significance in rodents in the study site: Bartonella rochalimae and Borellia spp. (species identification pending sequence data).

• preliminary results suggesting that prevalence in hosts of Bartonella spp. and an unidentified Trypanosome (screening underway) is elevated in defaunated landscapes.

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Principal Investigators:

Rodolfo Dirzo, Bing Prof in Environmental Science and Senior Fellow at the Woods Institute for the Environment

Michele Barry, Drs. Ben & A. Jess Shenson Professor, Senior Associate Dean, Global Health, Director, Center for Innovation in Global Health, Professor of Medicine & Senior Fellow at the Woods Institute and at the Freeman Spogli Institute

Eric Lambin, George and Setsuko Ishiyama Provostial Professor and Senior Fellow at the Woods Institute for the Environment