Academic journal article Bulletin of the World Health Organization

Climate Change and Vector-Borne Diseases: A Regional Analysis

Academic journal article Bulletin of the World Health Organization

Climate Change and Vector-Borne Diseases: A Regional Analysis

Article excerpt

Voir page 1143 le resume en francais. En la pagina 1144 figura un resumen en espanol.

Introduction

Human life is dependent on the dynamics of the Earth's climate system. The interactions of the atmosphere, oceans, terrestrial and marine biospheres, cryosphere and land surface determine the Earth's surface climate (1). Atmospheric concentrations of greenhouse gases, which include carbon dioxide, methane, and nitrous oxide are increasing, mainly due to human activities, such as use of fossil fuel, land use change and agriculture (2). An increase in greenhouse gases leads to increased warming of the atmosphere and the Earth's surface.

In this article, evidence for the past and current impacts of inter-annual and inter-decadal climate variability on vector-borne diseases is assessed on a continental basis with the aim of shedding light on possible future trends, particularly in view of the increased likelihood of climate change.

It is estimated that average global temperatures will have risen by 1.0-3.5 [degrees] C by 2100 (3), increasing the likelihood of many vector-borne diseases. The temporal and spatial changes in temperature, precipitation and humidity that are expected to occur under different climate change scenarios will affect the biology and ecology of vectors and intermediate hosts and consequently the risk of disease transmission. The risk increases because, although arthropods can regulate their internal temperature by changing their behaviour, they cannot do so physiologically and are thus critically dependent on climate for their survival and development (4). Climate, vector ecology and social economics vary from one continent to the other and therefore there is a need for a regional analysis.

The greatest effect of climate change on transmission is likely to be observed at the extremes of the range of temperatures at which transmission occurs. For many diseases these lie in the range 14-18 [degrees] C at the lower end and ca. 35-40 [degrees] C at the upper end. Warming in the lower range has a significant and non-linear impact on the extrinsic incubation period (5), and consequently disease transmission, while, at the upper end, transmission could cease. However, at around 30-32 [degrees] C, vectorial capacity can increase substantially owing to a reduction in the extrinsic incubation period, despite a reduction in the vector's survival rate. Mosquito species such as the Anopheles gambiae complex, A. funestus, A. darlingi, Culex quinquefasciatus and Medes aegypti are responsible for transmission of most vector-borne diseases, and are sensitive to temperature changes as immature stages in the aquatic environment and as adults. If water temperature rises, the larvae take a shorter time to mature (6) and consequently there is a greater capacity to produce more offspring during the transmission period. In warmer climates, adult female mosquitoes digest blood faster and feed more frequently (7), thus increasing transmission intensity. Similarly, malaria parasites and viruses complete extrinsic incubation within the female mosquito in a shorter time as temperature rises (8), thereby increasing the proportion of infective vectors. Warming above 34 [degrees] C generally has a negative impact on the survival of vectors and parasites (6).

In addition to the direct influence of temperature on the biology of vectors and parasites, changing precipitation patterns can also have short- and long-term effects on vector habitats. Increased precipitation has the potential to increase the number and quality of breeding sites for vectors such as mosquitoes, ticks and snails, and the density of vegetation, affecting the availability of resting sites. Disease reservoirs in rodents can increase when favourable shelter and food availability lead to population increases, in turn leading to disease outbreaks. Human settlement patterns also influence disease trends. In South America, more than 70% of the population is urbanized and therefore only a small proportion is exposed to rural infections. …

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