Effects of land use, habitat characteristics, and small mammal community composition on Leptospira prevalence in northeast Madagascar.

James P Herrera,Pablo Tortosa,Steven M Goodman,Charles L Nunn,Natalie R Wickenkamp,Fiona Baudino,Tamby Nasaina Ranaivoson,Voahangy Soarimalala,Magali Turpin

doi:10.1371/journal.pntd.0008946

Abstract

Human activities can increase or decrease risks of acquiring a zoonotic disease, notably by affecting the composition and abundance of hosts. This study investigated the links between land use and infectious disease risk in northeast Madagascar, where human subsistence activities and population growth are encroaching on native habitats and the associated biota. We collected new data on pathogenic Leptospira, which are bacteria maintained in small mammal reservoirs. Transmission can occur through close contact, but most frequently through indirect contact with water contaminated by the urine of infected hosts. The probability of infection and prevalence was compared across a gradient of natural moist evergreen forest, nearby forest fragments, flooded rice and other types of agricultural fields, and in homes in a rural village. Using these data, we tested specific hypotheses for how land use alters ecological communities and influences disease transmission. The relative abundance and proportion of exotic species was highest in the anthropogenic habitats, while the relative abundance of native species was highest in the forested habitats. Prevalence of Leptospira was significantly higher in introduced compared to endemic species. Lastly, the probability of infection with Leptospira was highest in introduced small mammal species, and lower in forest fragments compared to other habitat types. Our results highlight how human land use affects the small mammal community composition and in turn disease dynamics. Introduced species likely transmit Leptospira to native species where they co-occur, and may displace the Leptospira species naturally occurring in Madagascar. The frequent spatial overlap of people and introduced species likely also has consequences for public health.

Highlights

The global biodiversity crisis has far-reaching effects on human well-being, including changes in disease prevalence in wildlife and people [1,2]
We tested how land use gradients in a forest-frontier agricultural system affect the composition of small mammal communities, and in turn the prevalence of Leptospira
Leptospira prevalence and infection risk were highest in introduced species compared to native species and lower in forest fragments

Summary

Introduction

The global biodiversity crisis has far-reaching effects on human well-being, including changes in disease prevalence in wildlife and people [1,2]. In the case of Lyme disease in the USA, for example, decreased mammal diversity due to habitat fragmentation led to higher incidence of the pathogen, Borrelia, in wildlife [3] In this case, habitat fragmentation favored an increased abundance of the reservoir host, the white-footed mouse, Peromyscus leucopus (family Cricetidae), which in turn increased abundance and transmission of the tick vector [3]. Habitat fragmentation favored an increased abundance of the reservoir host, the white-footed mouse, Peromyscus leucopus (family Cricetidae), which in turn increased abundance and transmission of the tick vector [3] This example and others [5] illustrate the important associations between community ecology and disease transmission dynamics. The nuances of the biological system affect the predicted trajectory of disease transmission in ecological communities

Methods

Results

Discussion

Conclusion