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

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Indoor residual spraying (IRS) was implemented in the department of Ouémé-Plateau, southern Benin, in 2008 and withdrawn in 2011, when long lasting insecticidal nets (LLINs) were distributed to the communities that were previously targeted by IRS.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