Article

Understanding the link between malaria risk and climate

Center for Infectious Disease Dynamics, Department of Entomology, Chemical Ecology Laboratory, Pennsylvania State University, University Park, PA 16802, USA.
Proceedings of the National Academy of Sciences (Impact Factor: 9.67). 09/2009; 106(33):13844-9. DOI: 10.1073/pnas.0903423106
Source: PubMed

ABSTRACT

The incubation period for malaria parasites within the mosquito is exquisitely temperature-sensitive, so that temperature is a major determinant of malaria risk. Epidemiological models are increasingly used to guide allocation of disease control resources and to assess the likely impact of climate change on global malaria burdens. Temperature-based malaria transmission is generally incorporated into these models using mean monthly temperatures, yet temperatures fluctuate throughout the diurnal cycle. Here we use a thermodynamic malaria development model to demonstrate that temperature fluctuation can substantially alter the incubation period of the parasite, and hence malaria transmission rates. We find that, in general, temperature fluctuation reduces the impact of increases in mean temperature. Diurnal temperature fluctuation around means >21 degrees C slows parasite development compared with constant temperatures, whereas fluctuation around <21 degrees C speeds development. Consequently, models which ignore diurnal variation overestimate malaria risk in warmer environments and underestimate risk in cooler environments. To illustrate the implications further, we explore the influence of diurnal temperature fluctuation on malaria transmission at a site in the Kenyan Highlands. Based on local meteorological data, we find that the annual epidemics of malaria at this site cannot be explained without invoking the influence of diurnal temperature fluctuation. Moreover, while temperature fluctuation reduces the relative influence of a subtle warming trend apparent over the last 20 years, it nonetheless makes the effects biologically more significant. Such effects of short-term temperature fluctuations have not previously been considered but are central to understanding current malaria transmission and the consequences of climate change.

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Available from: Krijn Paaijmans
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    • "Global warming changes the climate, and climatic factors play important roles in the spatial and temporal distribution of malaria [22,23]. The relationship between climatic variables and malaria transmission has been reported in many countries2122232425. Malaria has been identified as one of the most climate sensitive diseases [26],with studies suggesting significant associations between temperature and malaria incidence [27]. "

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    • "Vector control interventions such as ITNs and IRS, using chemical insecticide or fungal biopesticide sprays, are the primary options available to contain and prevent pathogen transmission, and can cause substantial decreases in malaria transmission when vectorial capacity is high (Guyatt and Snow 2002). A critical factor influencing vectorial capacity is adult mosquito survival through the extrinsic incubation period of the parasite (EIP), ranging from approximately 10 to more than 30 days for malaria, depending on temperature (Patz and Olson 2006, Paaijmans et al. 2009). Only a relatively small fraction of mosquitoes naturally live long enough to infect humans when the EIP is long. "
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    • "For example, if the temperature simultaneously increases the feeding activity of an organism preying on cercariae in transmission, the numbers of parasites attacking the amphipods will become reduced (Thieltges et al., 2008; Studer et al., 2010). Other factors, such as the amplitude of temperature variability, also have the capacity to affect parasite fitness (Paaijmans, Read & Thomas, 2009). Furthermore, parasites themselves may be subjected to hyperparasitism (parasites parasitizing parasites) by other organisms, the occurrence and life-history of which is likely to be influenced also by environmental changes (Thieltges et al., 2008). "
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