Limits...
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.

Show MeSH

Related in: MedlinePlus

Mosquitoes captured by CDC light traps in Banizoumbou (top) and Zindarou (bottom) in 2006.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC3750695&req=5

Figure 3: Mosquitoes captured by CDC light traps in Banizoumbou (top) and Zindarou (bottom) in 2006.

Mentions: Mosquito collections were conducted as described in Bomblies et al. [2] and Bomblies et al. [1]. Six CDC light traps were deployed overnight in each village once a month from December – May (dry season), and weekly from June – November (wet season). Female Anopheles gambiae s.l. and Anopheles funestus specimens, the important malaria vectors in this region, were identified by microscopy and counted. While the mosquito captures began in 2005, we focus here on 2006, which is the year for which complete climate information was available. As shown in Figure 3, the observed number of anophelines followed a distinct seasonal cycle, increasing after the onset of monsoon rains in June, peaking in September, and returning to low levels by late October. No An. funestus were found in Banizoumbou, but a small number were found in Zindarou. The anopheline population in Zindarou did not persist beyond the end of the rainy season despite the continued availability of water pools for breeding. Bomblies et al. [1] hypothesized that the observed drop in mosquito population, despite continued availability of breeding sites was due to the lack of nutrient availability for larvae, as the decline in population coincided with the end of millet pollination. Here, we investigate whether the seasonal drop in humidity at the end of the rainy season could play a role in limiting mosquito populations.


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)

Mosquitoes captured by CDC light traps in Banizoumbou (top) and Zindarou (bottom) in 2006.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 3: Mosquitoes captured by CDC light traps in Banizoumbou (top) and Zindarou (bottom) in 2006.
Mentions: Mosquito collections were conducted as described in Bomblies et al. [2] and Bomblies et al. [1]. Six CDC light traps were deployed overnight in each village once a month from December – May (dry season), and weekly from June – November (wet season). Female Anopheles gambiae s.l. and Anopheles funestus specimens, the important malaria vectors in this region, were identified by microscopy and counted. While the mosquito captures began in 2005, we focus here on 2006, which is the year for which complete climate information was available. As shown in Figure 3, the observed number of anophelines followed a distinct seasonal cycle, increasing after the onset of monsoon rains in June, peaking in September, and returning to low levels by late October. No An. funestus were found in Banizoumbou, but a small number were found in Zindarou. The anopheline population in Zindarou did not persist beyond the end of the rainy season despite the continued availability of water pools for breeding. Bomblies et al. [1] hypothesized that the observed drop in mosquito population, despite continued availability of breeding sites was due to the lack of nutrient availability for larvae, as the decline in population coincided with the end of millet pollination. Here, we investigate whether the seasonal drop in humidity at the end of the rainy season could play a role in limiting mosquito populations.

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