A non-stationary relationship between global climate phenomena and human plague incidence in Madagascar.

Katharina S Kreppel,Andy Morse,Lila Rahalison,Sandra Telfer,Cyril Caminade,Matthew Baylis,Matthew Baylis,Minoarison Rajerison

doi:10.1371/journal.pntd.0003155

Abstract

BackgroundPlague, a zoonosis caused by Yersinia pestis, is found in Asia and the Americas, but predominantly in Africa, with the island of Madagascar reporting almost one third of human cases worldwide. Plague's occurrence is affected by local climate factors which in turn are influenced by large-scale climate phenomena such as the El Niño Southern Oscillation (ENSO). The effects of ENSO on regional climate are often enhanced or reduced by a second large-scale climate phenomenon, the Indian Ocean Dipole (IOD). It is known that ENSO and the IOD interact as drivers of disease. Yet the impacts of these phenomena in driving plague dynamics via their effect on regional climate, and specifically contributing to the foci of transmission on Madagascar, are unknown. Here we present the first analysis of the effects of ENSO and IOD on plague in Madagascar.Methodology/principal findingsWe use a forty-eight year monthly time-series of reported human plague cases from 1960 to 2008. Using wavelet analysis, we show that over the last fifty years there have been complex non-stationary associations between ENSO/IOD and the dynamics of plague in Madagascar. We demonstrate that ENSO and IOD influence temperature in Madagascar and that temperature and plague cycles are associated. The effects on plague appear to be mediated more by temperature, but precipitation also undoubtedly influences plague in Madagascar. Our results confirm a relationship between plague anomalies and an increase in the intensity of ENSO events and precipitation.Conclusions/significanceThis work widens the understanding of how climate factors acting over different temporal scales can combine to drive local disease dynamics. Given the association of increasing ENSO strength and plague anomalies in Madagascar it may in future be possible to forecast plague outbreaks in Madagascar. The study gives insight into the complex and changing relationship between climate factors and plague in Madagascar.

Highlights

Plague is a vector-borne, highly virulent zoonotic disease present today in the Americas, Asia and Africa
Our study investigates the effect of global climate drivers on human plague incidence on the island
We found a link between El Nino Southern Oscillation (ENSO), Indian Ocean Dipole (IOD), temperature and precipitation and plague incidence throughout the 48-year time-series it was not constant over time

Summary

Introduction

Plague is a vector-borne, highly virulent zoonotic disease present today in the Americas, Asia and Africa. It is caused by infection with the bacterium Yersinia pestis, which triggers serious illness with up to seventy percent case fatality in human populations if left untreated. Plague is endemic in the highland region of Madagascar and more than one hundred human cases are reported every year, though the true number of cases is likely to be higher. The reasons for such pronounced foci in these areas include extreme poverty and lack of health infrastructure, as well as unique climate features.

Methods

Results

Discussion

Conclusion