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. 2013 Mar 16:6:73.
doi: 10.1186/1756-3305-6-73.

A shift from indoor residual spraying (IRS) with bendiocarb to long-lasting insecticidal (mosquito) nets (LLINs) associated with changes in malaria transmission indicators in pyrethroid resistance areas in Benin

Razaki A Ossè, Rock Aïkpon, Ghélus Louis Gbédjissi, Virgile Gnanguenon, Michel Sèzonlin, Renaud Govoétchan, Arthur Sovi, Olivier Oussou, Frédéric Oké-Agbo, Martin Akogbéto

A shift from indoor residual spraying (IRS) with bendiocarb to long-lasting insecticidal (mosquito) nets (LLINs) associated with changes in malaria transmission indicators in pyrethroid resistance areas in Benin

Razaki A Ossè et al. Parasit Vectors. .

Abstract

Background: Indoor residual spraying (IRS) was implemented in the department of Ouémé-Plateau, southern Benin, in 2008 and withdrawn in 2011, when long lasting insecticidal nets (LLINs) were distributed to the communities that were previously targeted by IRS. Did the LLIN strategy provide a better level of protection against malaria transmission than IRS?

Methods: Entomological 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.

Results: There 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.

Conclusion: LLINs did not impact on indicators of transmission to the same levels as did IRS after IRS withdrawal.

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Figures

Figure 1
Figure 1
Map of the study area showing localities chosen in central and peripheral areas.
Figure 2
Figure 2
Aggressive variation of An. gambiae s.l density depending on rainfall in Adjohoun (A), Sèmè (B) and Dangbo (C).
Figure 3
Figure 3
Exophily rate of An. gambiae observed during IRS campaign and after IRS withdrawal in central area (A) and peripheral area (B) in the various districts. Exophily rate carrying the same letter per district was not significantly different (p> 0.05).
Figure 4
Figure 4
Parity rate of Anopheles gambiae observed during the implementation of IRS and after IRS withdrawal. The rate carrying the same letter per district was not significantly different (p> 0.05).
Figure 5
Figure 5
Blood feeding rate of Anopheles gambiae observed during IRS implementation and after IRS withdrawal. The rate carrying the same letter per district was not significantly different (p> 0.05).
Figure 6
Figure 6
Blood feeding rate of Culicidae observed during IRS implementation and after IRS withdrawal. The rate carrying the same letter per district was not significantly different (p> 0.05).
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