Abstract
BackgroundIndoor residual spraying (IRS) was implemented in the department of Ouémé-Plateau, southern Benin, in 2008 and withdrawn in 2011, when long lasting insecticidal nets (LLINs) were distributed to the communities that were previously targeted by IRS. Did the LLIN strategy provide a better level of protection against malaria transmission than IRS?MethodsEntomological surveillance was carried out to assess indicators of transmission risk during the last year of IRS and the first year after the LLIN intervention was put in place (2010–2011). Mosquito biting density was sampled by human landing collection (HLC). Females of Anopheles gambiae s.l. were dissected to estimate the parity rates and the blood meal index. A subsample of the An. gambiae s.l. collection was tested for presence of Plasmodium falciparum sporozoites. In addition, window exit traps and pyrethrum spray catches were performed to assess exophagic behavior of Anopheles vectors.ResultsThere were significant increases in all the indicators following withdrawal of IRS. Vector biting density (p<0.001) and longevity (OR=3.81[3.01-4.82] 95% CI; p<0.001) of the An. gambiae s.l. increased significantly; so too did the blood meal index (OR=1.48 [1.1-1.99] 95% CI; p<0.001). Entomological inoculation rate, after IRS withdrawal at one surveillance site, Adjohoun, rose two fold (9.0 infected bites/person/9 months (Apr-Dec 2011) versus 3.66 infective bites/person during the 9 months preceding IRS (Apr-Dec 2010). A second site, Missérété, experienced a six-fold increase after IRS cessation (15.1 infective bites/person/9 months versus 2.41 during IRS). Exophily after IRS cessation decreased significantly in all areas (p<0.001) suggesting that mosquitoes were more likely to rest in houses with LLINs, than in houses subjected to IRS.ConclusionLLINs did not impact on indicators of transmission to the same levels as did IRS after IRS withdrawal.
Highlights
Indoor residual spraying (IRS) was implemented in the department of Ouémé-Plateau, southern Benin, in 2008 and withdrawn in 2011, when long lasting insecticidal nets (LLINs) were distributed to the communities that were previously targeted by IRS
Malaria vector control is based on two interventions: the long lasting insecticidal net (LLIN) and indoor residual spraying (IRS), both of which have been shown to be effective throughout Africa [2,3]
Human biting rates (HBR) during the IRS campaign versus HBR following IRS withdrawal and distribution of LLINs Mosquito biting rates in three of the districts increased after IRS was withdrawn
Summary
Indoor residual spraying (IRS) was implemented in the department of Ouémé-Plateau, southern Benin, in 2008 and withdrawn in 2011, when long lasting insecticidal nets (LLINs) were distributed to the communities that were previously targeted by IRS. Malaria vector control is based on two interventions: the long lasting insecticidal (mosquito) net (LLIN) and indoor residual spraying (IRS), both of which have been shown to be effective throughout Africa [2,3]. In Zanzibar, the scale-up of insecticide-treated nets (ITN), indoor-residual spraying (IRS) and Artemisinin combination therapy (ACT) combined reduced malaria-related burden at health facilities by over 75% within 5 years [4]. On Bioko Island, Equatorial Guinea, the simultaneous use of IRS, LLINs and Artemisinin Combination Therapy (ACT) resulted in a 90% drop in the presence of P. falciparum circumsporozoite antigen An. gambiae s.l. after 4 years. If a country cannot implement both universal IRS and LLINs at the same time, as is the case for most African countries, and makes a decision to withdraw one of the interventions, what would be the result?
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