Modeling of spatio-temporal variation in plague incidence in Madagascar from 1980 to 2007

Abstract

Plague is an infectious disease caused by the bacterium Yersinia pestis, which, during the fourteenth century, caused the deaths of an estimated 75 to 200 million people in Europe. Plague epidemics still occur in Africa, Asia and South America. Madagascar is today one of the most endemic countries, reporting nearly one third of the human cases worldwide from 2004 to 2009. The persistence of plague in Madagascar is associated with environmental and climatic conditions. In this paper we present a case study of the spatio-temporal analysis of plague incidence in Madagascar from 1980 to 2007. We study the relationship of plague with temperature and precipitation anomalies, and with elevation. A joint spatio-temporal analysis of the data proves to be computationally intractable. We therefore develop a spatio-temporal log-Gaussian Cox process model, but then carry out marginal temporal and spatial analyses. We also introduce a spatially discrete approximation for Gaussian processes, whose parameters retain a spatially continuous interpretation. We find evidence of a cumulative effect, over time, of temperature anomalies on plague incidence, and of a very high relative risk of plague occurrence for locations above 800 meters in elevation. Our approach provides a useful modelling framework to assess the relationship between exposures and plague risk, irrespective of the spatial resolution at which the latter has been recorded.

Pre-industrial plague transmission is mediated by the synergistic effect of temperature and aridity index

“…On the other hand, evidence from Madagascar shows that the major flea/plague vectors are more adant in colder highland areas at over 800 m a.s.l. [ 22 ], formulating the highly geographically restricted plague endemic regions in highlands [ 68 ]. Fleas in Europe may behave similarly and become more abundant in cold and dry periods, which facilities the transmission of plague.…”

“…Under this approach, scholars employ historical records to reveal the major longitudinal change of plague frequency and reflect the characteristics of the plague-environment relationship. However, except for the influence of climate as afore-stated, the transmission of the disease is closely related to rodent ecology [ 17 – 21 ], flea ecology [ 22 , 23 ], societal factors [ 24 ] and other environmental conditions [ 15 , 25 ]. Given the complexity of plague transmission, the influence of climatic forcing on plague transmission is unlikely to be linear and stationary.…”

Plague risk in the western United States over seven decades of environmental change

“…Elevation has also been previously associated with plague on other continents 42,58,59,60,61,62 , and while the general trend is that there is a lower threshold elevation (and an upper limit, at the extreme altitudes in the Himalayas), that threshold differs substantially between countries. For example, Brazil’s plague reservoirs start at 500 meters above sea level, and are limited by the landscape to no more than 1,000 meters 63 , while Madagascar’s urban plague reservoir in Mahajanga is at sea level 64 , as are the plague reservoirs surrounding the Caspian Sea in Central Asia 65 . Elevation therefore seems to represent the local ecology and distributional limits of fleas and rodents, rather than a global proxy for a bioclimatic or atmospheric variable (e.g.…”

Human plague: An old scourge that needs new answers

“…Similarly, El Niño episodes have been considered an early warning in Peru [45] and Madagascar [54]. Temperature anomalies and altitude have been related to plague occurrence in Madagascar [55]. Temperature and humidity influence the differential development and survival of the 2 main flea vectors (X. cheopis and S. fonquerniei) involved in plague transmission in Madagascar (where plague shows a clear seasonal pattern) [27].…”