(last updated 8/8/2013)
Equatorial Guinea has been the target of extensive malaria vector control efforts undertaken under the Bioko Island Malaria Control Program and the Equatorial Guinea Malaria Control initiative in support of the National Malaria Control Program of Equatorial Guinea. On Bioko Island indoor residual spraying with pyrethroids and carbamate insecticides has been in effect since in 2004. In addition, insecticide treated nets have been distributed on the island. On the mainland, the two western provinces have been subjected to IRS, and insecticide treated bed nets were distributed in the two eastern provinces starting in 2007.
Both control methods have had a demonstrable impact on malaria transmission throughout sub-Saharan Africa. At least some of this seems to be the result of reduction in mosquito abundance, rather than reduced contact between vectors and humans. However, estimates of the changes in mosquito abundance can be imprecise due to a variety of limitations associated with various trapping approaches. Previous
attempts to investigate this issue by examining the impact of vector control on the genetic size of malaria vector populations have been inconclusive.
Therefore, we have generated a large data set that is comprised of the genotypes for 13 to 17 microsatellite loci for over 1,500 individuals, and used a recently develop coalescent-based approach (Approximate Bayesian Computation) to determine to which extent IRS and ITN distribution have impacted mosquito effective population sizes during the recent malaria vector control efforts in Equatorial Guinea. Our samples represent multiple time points from seven populations of three species of malaria vectors; An. gambiae (M+S), An. melas and An. moucheti.
An. gambiae and An. melas are by far the two most dominant vectors on Bioko Island, where An moucheti is absent. All three species can be found on the Equatorial Guinea mainland.
Our results show a large impact of both IRS a and ITNs on the effective population size of the three species of malaria mosquito, for all but one location.
A paper describing the results of this study has been published in PLoS Genetics.
We have also used the ABC method to examine short-term fluctuations in the An. gambiae population in Punta Europa, Bioko Island in response to IRS spray rounds. We have analyzed samples from six timepoints during 2009 and 2010 and found that this An. gambiae population fluctuates dramatically between IRS
spray rounds. Specifically, it decreases dramatically after IRS spray rounds, but rebounds within 3-5 months. This indicates that an increase in spray frequency can dramatically improve the impact of IRS programs on mosquito populations.
A paper describing the results of this study has been published in Evolutionary Applications.
We are currently applying this approach to understand the impact of mosquito control on Culex quinquefasciatus mosquitoes in the Houston area.
Publications from this work:
The Effective Population Size of Malaria Mosquitoes: Large Impact of Vector Control. (2012) Athrey G, TK Hodges, MR Reddy, HJ Overgaard, A Matias, FC Ridl, I Kleinschmidt, A Caccone, MA Slotman. PLoS Genetics 8(12): e1003097.
Large fluctuations in the effective population size of the malaria mosquito Anopheles gambiae during vector control (2013) Hodges TK, G Athrey, KC Deitz, HJ Overgaard, A Matias, MA Slotman. Evolutionary Applications 6: 1171-1183