Ecological Dynamics of Vector-Borne Diseases in Changing Environments.

Abstract

One of the major threats for the current functioning of the world we know is the uncertainty about the effects of global climate change. This dissertation aims to understand the effects of a changing environment on the ecological dynamics of vector-borne diseases, one of the major burdens for human populations worldwide. Vector-borne diseases are expected to be highly sensitive to the effects of climatic change, because of the natural history of both the vectors and parasites, which are highly sensitive to small changes in precipitation and temperature. This dissertation investigates several aspects of the effects of changing environments in vector-borne diseases: (i) The plausibility of early warning systems to predict the future dynamics of a disease based on its association to climatic forces, using a time series for cutaneous leishmaniasis cases from Costa Rica,1991-2001 (ii) The mechanisms regulating co-infections of malaria parasites in the island of Santo, Vanuatu, 1983-1997, and (iii) Abrupt dynamical changes in diseases along smoothly changing environments, temporally for malaria in the archipelago of Vanuatu,1983-1999, and spatio-temporally for cutaneous leishmaniasis in Costa Rica, 1996-2000. Methods involved a suite of qualitative and quantitative techniques in order to robustly assess the reliability of results. Frequency, time and time-frequency domain statistical techniques for time series analysis were used to study the association between disease dynamics and climate, time models predictive ability for early warning systems was tested with “out-of-fit” data. Signed digraph loop analyses and quantitative discrete time models were used to discern working hypothesis about parasite species co-infection regulation. Statistical techniques for breakpoints were used to study abrupt dynamical changes. In addition, spatial clustering techniques were used as guidance to establish transmission risk factors. Results show that early warning systems are feasible goals, that malaria parasites and their interactions seem to be regulated in a bottom-up fashion, and that abrupt changes on the sensitivity to the effects of climate change are dependent on the context of transmission. Finally, all the results confirm the importance of considering the whole environmental context in which vector-borne diseases are transmitted and the need for abstraction to understand and manage the underlying complexity.