Abstract
The age distribution of female mosquitoes in the field is a critical component of vectorial capacity because of the extrinsic incubation period of mosquito-borne pathogens. However this parameter has not been well characterized in malaria vectors because of methodological difficulties; transcriptional profiling provides a potential new approach for age determination. In Anopheles gambiae, microarrays were used to examine global gene expression over adult life. Nine genes were selected from the 2714 gene transcripts that displayed age-related transcription patterns, and quantitative reverse transcription PCR used to select the four best performing genes. The resulting age estimation assay was able to predict female age from lab-reared samples with sufficient accuracy to provide a potentially useful tool for studies of malaria epidemiology and control.
Highlights
One of the most sensitive parameters contributing to the vectorial capacity of malaria-transmitting Anopheles mosquitoes is the age distribution of wild females
We consider the data presented to provide the baseline for an assay that would be a very useful addition to the field as the confidence intervals in individual age predictions are acceptable for making population-level comparisons
The assay was less successful for males, but the requirement for age prediction methodologies is in any case much smaller in males, which do not blood feed or transmit malaria
Summary
Despite the critical importance of estimating Anopheles age in field-caught specimens to the understanding of malaria transmission dynamics and epidemiology, and the impact of control interventions, age remains one of the least understood components of vectorial capacity. The ability to estimate the age structure of natural Anopheles populations before and after interventions has acquired considerable importance, and there is a need to develop additional methodologies with which to do so. Expression changes were measured by quantitative reverse transcription PCR (qRT-PCR) on caged mosquitoes of known age and used to build a multivariate calibration model to predict the age of field caught specimens from the same locality. This technique has been used successfully to predict age of Ae. aegypti from Cairns, Australia (Cook et al, 2006, Hugo et al, 2010). We used the An. gambiae genome database (Holt et al, 2002) to design and employ a microarray to examine global gene transcription profiles up to 30 days posteclosion; a previous array study had examined transcription up to 15 days post-eclosion (Marinotti et al, 2006) but it was necessary to extend this period in order to capture expression profiles in older insects
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