Effects of Microclimatic Changes Caused by Deforestation on the Survivorship and Reproductive Fitness of Anopheles Gambiae in Western Kenya Highlands

Abstract

Land use changes have been suggested as one of the causes for malaria epidemics in the African highlands. This study investigated the effects of deforestation-induced changes in indoor temperature on the survivorship and reproductive fitness of Anopheles gambiae in an epidemic prone area in the western Kenya highlands. We found that the mean indoor temperatures of houses located in the deforested area were 1.2 degrees C higher than in houses located in the forested area during the dry season and 0.7 degrees C higher during the rainy season. The mosquito mortality rate was highly age-dependent regardless of study site or season. Mosquitoes that were placed in houses in the deforested area showed a 64.8-79.5% higher fecundity than those in houses located in the forested area, but the median survival time was reduced by 5-7 days. Female mosquitoes in the deforested area showed a 38.5-40.6% increase in net reproductive rate and an 11.6-42.9% increase in intrinsic growth rate than those in the forested area. Significant increases in net reproductive rate and intrinsic growth rate for mosquitoes in the deforested area suggest that deforestation enhances mosquito reproductive fitness, increasing mosquito population growth potential in the western Kenya highlands. The vectorial capacity of An. gambiae under study was estimated at least 106% and 29% higher in the deforested area than in the forested area in dry and rainy seasons, respectively.

Influence of climate on malaria transmission depends on daily temperature variation

“…stephensi to moderate diurnal temperature variation is unique among malaria parasites and their mosquito vectors. Moreover, the effects will apply whether considering aquatic, terrestrial, indoor, or outdoor environments because all can exhibit variable diurnal temperatures (17,25,28) (Fig. 1).…”

Understanding the link between malaria risk and climate

“…These can differ from outdoor temperatures, both in terms of mean and DTR, depending on altitude (19,37) and the nature of the building structure (38) and surroundings (37). Incorporating this source of temperature variation is not straight forward.…”

Malaria Transmission in the African Highlands in a Changing Climate Situation: Perspective from Kenyan Highlands

“…We found that deforestation increased the indoor mean temperature by 1.8 0 C. Mean maximum and minimum temperatures were increased by 2.3 0 C and 1.5 0 C respectively. Outdoor temperatures were increased by 0.5 0 C. The mean indoor relative humidity in the deforested area was about 22.6% lower than in the forest area during the dry season (79.88% vs. 57.29%) (Afrane et al 2005;Afrane et al 2006;Afrane et al 2008;Afrane et al 2007). Temperature and humidity were measured in houses in study sites that were originally forest but large portions of it have been deforested.…”

“…However, despite the decreased survivorship of the mosquitoes due to the effects of deforestation, mosquitoes still had an enhanced reproductive fitness by 40%. Over the course of their life span, mosquitoes in deforested areas laid far more eggs and thus, had better fecundity than mosquitoes in the forested areas by over 65% (Afrane et al 2006). The reproductive fitness of a mosquito is its ability to reproduce over its entire life span.…”

“…In warmer climates, adult female mosquitoes digest blood faster and feed more frequently (Afrane et al 2005), thus increasing transmission intensity. Increased biting frequency and faster blood meal digestion also means increased fecundity and better reproductive fitness (Afrane et al 2006). Similarly, malaria parasites complete extrinsic incubation within the female mosquito in a shorter time as temperature rises (Afrane et al 2008) thereby increasing the proportion of infective vectors.…”