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Transmission intensity and drug resistance in malaria population dynamics: implications for climate change.

Artzy-Randrup Y, Alonso D, Pascual M - PLoS ONE (2010)

Bottom Line: We then address the implications of warmer temperatures in an East African highland, where, as in other similar regions at the altitudinal edge of malaria's distribution, there has been a pronounced increase of cases from the 1970s to the 1990s.Climate change and drug resistance can interact and need not be considered as alternative explanations for trends in disease incidence in this region.Non-monotonic patterns of treatment failure with transmission intensity similar to those described as the 'valley phenomenon' for Uganda can result from epidemiological dynamics but under poorly understood assumptions.

View Article: PubMed Central - PubMed

Affiliation: Howard Hughes Medical Institute, Department of Ecology and Evolutionary Biology, University of Michigan, Ann Arbor, Michigan, United States of America. YArtzy@umich.edu

ABSTRACT
Although the spread of drug resistance and the influence of climate change on malaria are most often considered separately, these factors have the potential to interact through altered levels of transmission intensity. The influence of transmission intensity on the evolution of drug resistance has been addressed in theoretical studies from a population genetics' perspective; less is known however on how epidemiological dynamics at the population level modulates this influence. We ask from a theoretical perspective, whether population dynamics can explain non-trivial, non-monotonic, patterns of treatment failure with transmission intensity, and, if so, under what conditions. We then address the implications of warmer temperatures in an East African highland, where, as in other similar regions at the altitudinal edge of malaria's distribution, there has been a pronounced increase of cases from the 1970s to the 1990s. Our theoretical analyses, with a transmission model that includes different levels of immunity, demonstrate that an increase in transmission beyond a threshold can lead to a decrease in drug resistance, as previously shown, but that a second threshold may occur and lead to the re-establishment of drug resistance. Estimates of the increase in transmission intensity from the 1970s to the 1990s for the Kenyan time series, obtained by fitting the two-stage version of the model with an explicit representation of vector dynamics, suggest that warmer temperatures are likely to have moved the system towards the first threshold, and in so doing, to have promoted the faster spread of drug resistance. Climate change and drug resistance can interact and need not be considered as alternative explanations for trends in disease incidence in this region. Non-monotonic patterns of treatment failure with transmission intensity similar to those described as the 'valley phenomenon' for Uganda can result from epidemiological dynamics but under poorly understood assumptions.

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Related in: MedlinePlus

In the first quadrant, where A and B are both positive, when the fraction of clinically immune are below the threshold (), resistance dominates, and above the threshold, the wild type dominates.Reversely, in the third quadrant, when the fraction of clinically immune is low, wild type dominates, and past the threshold, resistance dominates. In the second and forth quadrants, there is no threshold, and the wild type and resistant parasites always dominate, respectively.
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getmorefigures.php?uid=PMC2965653&req=5

pone-0013588-g006: In the first quadrant, where A and B are both positive, when the fraction of clinically immune are below the threshold (), resistance dominates, and above the threshold, the wild type dominates.Reversely, in the third quadrant, when the fraction of clinically immune is low, wild type dominates, and past the threshold, resistance dominates. In the second and forth quadrants, there is no threshold, and the wild type and resistant parasites always dominate, respectively.

Mentions: However, if A and B are not both positive we find that (see Figure 6):


Transmission intensity and drug resistance in malaria population dynamics: implications for climate change.

Artzy-Randrup Y, Alonso D, Pascual M - PLoS ONE (2010)

In the first quadrant, where A and B are both positive, when the fraction of clinically immune are below the threshold (), resistance dominates, and above the threshold, the wild type dominates.Reversely, in the third quadrant, when the fraction of clinically immune is low, wild type dominates, and past the threshold, resistance dominates. In the second and forth quadrants, there is no threshold, and the wild type and resistant parasites always dominate, respectively.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2965653&req=5

pone-0013588-g006: In the first quadrant, where A and B are both positive, when the fraction of clinically immune are below the threshold (), resistance dominates, and above the threshold, the wild type dominates.Reversely, in the third quadrant, when the fraction of clinically immune is low, wild type dominates, and past the threshold, resistance dominates. In the second and forth quadrants, there is no threshold, and the wild type and resistant parasites always dominate, respectively.
Mentions: However, if A and B are not both positive we find that (see Figure 6):

Bottom Line: We then address the implications of warmer temperatures in an East African highland, where, as in other similar regions at the altitudinal edge of malaria's distribution, there has been a pronounced increase of cases from the 1970s to the 1990s.Climate change and drug resistance can interact and need not be considered as alternative explanations for trends in disease incidence in this region.Non-monotonic patterns of treatment failure with transmission intensity similar to those described as the 'valley phenomenon' for Uganda can result from epidemiological dynamics but under poorly understood assumptions.

View Article: PubMed Central - PubMed

Affiliation: Howard Hughes Medical Institute, Department of Ecology and Evolutionary Biology, University of Michigan, Ann Arbor, Michigan, United States of America. YArtzy@umich.edu

ABSTRACT
Although the spread of drug resistance and the influence of climate change on malaria are most often considered separately, these factors have the potential to interact through altered levels of transmission intensity. The influence of transmission intensity on the evolution of drug resistance has been addressed in theoretical studies from a population genetics' perspective; less is known however on how epidemiological dynamics at the population level modulates this influence. We ask from a theoretical perspective, whether population dynamics can explain non-trivial, non-monotonic, patterns of treatment failure with transmission intensity, and, if so, under what conditions. We then address the implications of warmer temperatures in an East African highland, where, as in other similar regions at the altitudinal edge of malaria's distribution, there has been a pronounced increase of cases from the 1970s to the 1990s. Our theoretical analyses, with a transmission model that includes different levels of immunity, demonstrate that an increase in transmission beyond a threshold can lead to a decrease in drug resistance, as previously shown, but that a second threshold may occur and lead to the re-establishment of drug resistance. Estimates of the increase in transmission intensity from the 1970s to the 1990s for the Kenyan time series, obtained by fitting the two-stage version of the model with an explicit representation of vector dynamics, suggest that warmer temperatures are likely to have moved the system towards the first threshold, and in so doing, to have promoted the faster spread of drug resistance. Climate change and drug resistance can interact and need not be considered as alternative explanations for trends in disease incidence in this region. Non-monotonic patterns of treatment failure with transmission intensity similar to those described as the 'valley phenomenon' for Uganda can result from epidemiological dynamics but under poorly understood assumptions.

Show MeSH
Related in: MedlinePlus