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Incorporating the effects of humidity in a mechanistic model of Anopheles gambiae mosquito population dynamics in the Sahel region of Africa.

Yamana TK, Eltahir EA - Parasit Vectors (2013)

Bottom Line: In this case, relative humidity had little effect on the mosquito population.In this case, the decrease in mosquito survival due to relative humidity improved the model's ability to reproduce the seasonal pattern of observed mosquito abundance.Future modeling work should account for these effects of relative humidity.

View Article: PubMed Central - HTML - PubMed

Affiliation: Massachusetts Institute of Technology, 15 Vassar Street, Cambridge, MA 02139, USA. tkcy@mit.edu

ABSTRACT

Background: Low levels of relative humidity are known to decrease the lifespan of mosquitoes. However, most current models of malaria transmission do not account for the effects of relative humidity on mosquito survival. In the Sahel, where relative humidity drops to levels <20% for several months of the year, we expect relative humidity to play a significant role in shaping the seasonal profile of mosquito populations. Here, we present a new formulation for Anopheles gambiae sensu lato (s.l.) mosquito survival as a function of temperature and relative humidity and investigate the effect of humidity on simulated mosquito populations.

Methods: Using existing observations on relationships between temperature, relative humidity and mosquito longevity, we developed a new equation for mosquito survival as a function of temperature and relative humidity. We collected simultaneous field observations on temperature, wind, relative humidity, and anopheline mosquito populations for two villages from the Sahel region of Africa, which are presented in this paper. We apply this equation to the environmental data and conduct numerical simulations of mosquito populations using the Hydrology, Entomology and Malaria Transmission Simulator (HYDREMATS).

Results: Relative humidity drops to levels that are uncomfortable for mosquitoes at the end of the rainy season. In one village, Banizoumbou, water pools dried up and interrupted mosquito breeding shortly after the end of the rainy season. In this case, relative humidity had little effect on the mosquito population. However, in the other village, Zindarou, the relatively shallow water table led to water pools that persisted several months beyond the end of the rainy season. In this case, the decrease in mosquito survival due to relative humidity improved the model's ability to reproduce the seasonal pattern of observed mosquito abundance.

Conclusions: We proposed a new equation to describe Anopheles gambiae s.l. mosquito survival as a function of temperature and relative humidity. We demonstrated that relative humidity can play a significant role in mosquito population and malaria transmission dynamics. Future modeling work should account for these effects of relative humidity.

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Simulated mosquitoes in Banizoumbou (top) and Zindarou (bottom) using the differing values of RHS. Mosquitoes captured by light traps are shown by the dashed line.
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Figure 7: Simulated mosquitoes in Banizoumbou (top) and Zindarou (bottom) using the differing values of RHS. Mosquitoes captured by light traps are shown by the dashed line.

Mentions: The size of the mosquito population in each simulation is shown in Figure 7. In Banizoumbou (Figure 7, top panel), mosquito population levels were closely tied to rainfall. There was little persistence of water pools beyond the end of the rainy season. Since the decrease in rainfall precedes the decrease in humidity, the addition of a stress factor at low levels of RH had minimal effect on mosquito populations. By contrast in Zindarou, where water pools persist for several months after the end of the rainy season, the size of the mosquito population was not limited by water availability. Temperature was also not a limiting factor at the end of the rainy season; in the simulation using the Martens equation for mosquito survival as a function of temperature, the mosquito population remained at high levels for the duration of the simulation (Figure 7, bottom panel, blue line). However, the incorporation of relative humidity into mosquito survival dramatically reduced the number of mosquitoes, beginning in late-October when the RH plummets. The choice of RHS affected the results. In the simulations using RHS = 40% and 42%, the mosquito populations dropped dramatically starting on October 29th. When RHS was set to 35%, there was no change in mosquito populations until November 4th, and the drop was somewhat more gradual than in the in the simulations with higher RHS. There was little difference between simulations with RHC = 5% and RHC = 0% (see Additional file 3).


Incorporating the effects of humidity in a mechanistic model of Anopheles gambiae mosquito population dynamics in the Sahel region of Africa.

Yamana TK, Eltahir EA - Parasit Vectors (2013)

Simulated mosquitoes in Banizoumbou (top) and Zindarou (bottom) using the differing values of RHS. Mosquitoes captured by light traps are shown by the dashed line.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3750695&req=5

Figure 7: Simulated mosquitoes in Banizoumbou (top) and Zindarou (bottom) using the differing values of RHS. Mosquitoes captured by light traps are shown by the dashed line.
Mentions: The size of the mosquito population in each simulation is shown in Figure 7. In Banizoumbou (Figure 7, top panel), mosquito population levels were closely tied to rainfall. There was little persistence of water pools beyond the end of the rainy season. Since the decrease in rainfall precedes the decrease in humidity, the addition of a stress factor at low levels of RH had minimal effect on mosquito populations. By contrast in Zindarou, where water pools persist for several months after the end of the rainy season, the size of the mosquito population was not limited by water availability. Temperature was also not a limiting factor at the end of the rainy season; in the simulation using the Martens equation for mosquito survival as a function of temperature, the mosquito population remained at high levels for the duration of the simulation (Figure 7, bottom panel, blue line). However, the incorporation of relative humidity into mosquito survival dramatically reduced the number of mosquitoes, beginning in late-October when the RH plummets. The choice of RHS affected the results. In the simulations using RHS = 40% and 42%, the mosquito populations dropped dramatically starting on October 29th. When RHS was set to 35%, there was no change in mosquito populations until November 4th, and the drop was somewhat more gradual than in the in the simulations with higher RHS. There was little difference between simulations with RHC = 5% and RHC = 0% (see Additional file 3).

Bottom Line: In this case, relative humidity had little effect on the mosquito population.In this case, the decrease in mosquito survival due to relative humidity improved the model's ability to reproduce the seasonal pattern of observed mosquito abundance.Future modeling work should account for these effects of relative humidity.

View Article: PubMed Central - HTML - PubMed

Affiliation: Massachusetts Institute of Technology, 15 Vassar Street, Cambridge, MA 02139, USA. tkcy@mit.edu

ABSTRACT

Background: Low levels of relative humidity are known to decrease the lifespan of mosquitoes. However, most current models of malaria transmission do not account for the effects of relative humidity on mosquito survival. In the Sahel, where relative humidity drops to levels <20% for several months of the year, we expect relative humidity to play a significant role in shaping the seasonal profile of mosquito populations. Here, we present a new formulation for Anopheles gambiae sensu lato (s.l.) mosquito survival as a function of temperature and relative humidity and investigate the effect of humidity on simulated mosquito populations.

Methods: Using existing observations on relationships between temperature, relative humidity and mosquito longevity, we developed a new equation for mosquito survival as a function of temperature and relative humidity. We collected simultaneous field observations on temperature, wind, relative humidity, and anopheline mosquito populations for two villages from the Sahel region of Africa, which are presented in this paper. We apply this equation to the environmental data and conduct numerical simulations of mosquito populations using the Hydrology, Entomology and Malaria Transmission Simulator (HYDREMATS).

Results: Relative humidity drops to levels that are uncomfortable for mosquitoes at the end of the rainy season. In one village, Banizoumbou, water pools dried up and interrupted mosquito breeding shortly after the end of the rainy season. In this case, relative humidity had little effect on the mosquito population. However, in the other village, Zindarou, the relatively shallow water table led to water pools that persisted several months beyond the end of the rainy season. In this case, the decrease in mosquito survival due to relative humidity improved the model's ability to reproduce the seasonal pattern of observed mosquito abundance.

Conclusions: We proposed a new equation to describe Anopheles gambiae s.l. mosquito survival as a function of temperature and relative humidity. We demonstrated that relative humidity can play a significant role in mosquito population and malaria transmission dynamics. Future modeling work should account for these effects of relative humidity.

Show MeSH
Related in: MedlinePlus