Abstract
BackgroundIndoor residual spraying (IRS) is being implemented as one of the malaria prevention methods in the Northern Region of Ghana. Changes in longevity, sporozoite and entomological inoculation rates (EIRs) of major malaria vectors were monitored to assess the impact of IRS in selected districts.MethodsMonthly human landing catches (HLCs) were used to collect mosquitoes from sentinel sites in three adjacent districts between July 2009 and December 2014: Savelugu Nanton (SND) where IRS had been implemented from 2008 to 2014; Tolon Kumbungu (TKD) where IRS had been implemented between 2008 and 2012 and Tamale Metropolis (TML) with no history of IRS. Mosquitoes were morphologically identified to species level and into sibling species, using PCR. Samples of Anopheles gambiae sensu lato (s.l.) were examined for parity and infectivity. EIR was calculated from biting and infectivity rates of malaria vectors.ResultsParity rates of An. gambiae s.l. decreased significantly (p < 0.0001) in SND from 44.8% in 2011 to 28.1% by 2014, and in TKD from 53.3% in 2011 to 46.6% in 2012 (p = 0.001). However 2 years after IRS was discontinued in TKD, the proportion of parous An. gambiae s.l. increased significantly to 68.5% in 2014 (p < 0.0001). Parity rates in the unsprayed district remained high throughout the study period, ranging between 68.6% in 2011 and 72.3% in 2014. The sum of monthly EIRs post-IRS season (July–December) in SND ranged between 2.1 and 6.3 infective bites/person/season (ib/p/s) during the 3 years that the district was sprayed with alphacypermethrin. EIR in SND was reduced to undetectable levels when the insecticide was switched to pirimiphos methyl CS in 2013 and 2014. Two years after IRS was withdrawn from TKD the sum of monthly EIRs (July–December) increased by about fourfold from 41.8 ib/p/s in 2012 to 154.4 ib/p/s in 2014. The EIR in the control area, TML, ranged between 35 ib/p/s in 2009 to 104.71 ib/p/s by 2014.ConclusionsThis study demonstrates that IRS application did have a significant impact on entomological indicators of malaria transmission in the IRS project districts of Northern Ghana. Transmission indicators increased following the withdrawal of IRS from Tolon Kumbungu District.
Highlights
Indoor residual spraying (IRS) is being implemented as one of the malaria prevention methods in the Northern Region of Ghana
Studies have found that the scale up of IRS and insecticidetreated nets (ITNs) contribute to changes in vector behaviour [5, 9], and changes in vector species composition or selection for certain traits that may support rapid evolution of insecticide resistance [10]
The reduction in malaria transmission in the study districts demonstrates the effectiveness of IRS programmes and the potential benefits of their expansion
Summary
Indoor residual spraying (IRS) is being implemented as one of the malaria prevention methods in the Northern Region of Ghana. The use of indoor residual spraying (IRS) and insecticidetreated nets (ITNs) as key vector control interventions. The effectiveness of IRS has been demonstrated through surveys that show a reduction in entomological indices of transmission [4,5,6] or significant reduction in malaria prevalence [4], morbidity and mortality [7, 8]. Studies have found that the scale up of IRS and ITNs contribute to changes in vector behaviour [5, 9], and changes in vector species composition or selection for certain traits that may support rapid evolution of insecticide resistance [10]. New insecticides and formulations tend to be more expensive than the previously used pyrethroids, and have partly contributed to the scale-down of IRS coverage in some countries, including Ghana [2, 11]
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