Pyrethroid resistance/susceptibility and differential urban/rural distribution of Anopheles arabiensis and An. gambiae s.s. malaria vectors in Nigeria and Ghana

Abstract

Resistance to pyrethroid insecticides and DDT caused by the kdr gene in the malaria vector Anopheles gambiae Giles s.s. (Diptera: Culicidae) has been reported in several West African countries. To test for pyrethroid resistance in two more countries, we sampled populations of the An. gambiae complex from south-western Ghana and from urban and rural localities in Ogun State, south-west Nigeria. Adult mosquitoes, reared from field-collected larvae, were exposed to the WHO-recommended discriminating dosage of exposure for 1 h to DDT 4%, deltamethrin 0.05% or permethrin 0.75% and mortality was recorded 24 h post-exposure. Susceptibility of An. gambiae s.l. to DDT was 94-100% in Ghana and 72-100% in Nigeria, indicating low levels of DDT resistance. Deltamethrin gave the highest mortality rates: 97-100% in Ghana, 95-100% in Nigeria. Ghanaian samples of An. gambiae s.l. were fully susceptible to permethrin, whereas some resistance to permethrin was detected at 4/5 Nigerian localities (percentage mortalities 75, 82, 88, 90 and 100%), with survivors including both An. arabiensis Patton and An. gambiae s.s. identified by PCR assay. Even so, the mean knockdown time was not significantly different from a susceptible reference strain, indicating absence or low frequency of kdr-type resistance. Such low levels of pyrethroid resistance are unlikely to impair the effectiveness of pyrethroid-impregnated bednets against malaria transmission. Among Nigerian samples of An. gambiae s.l., the majority from two urban localities were identified as An. arabiensis, whereas the majority from rural localities were An. gambiae s.s. These findings are consistent with those of M. Coluzzi et al. (1979). Differences of ecological distribution between molecular forms of An. gambiae s.s. were also found, with rural samples almost exclusively of the S-form, whereas the M-form predominated in urban samples. It is suggested that 'urban island' populations of An. arabiensis and of An. gambiae s.s. M-form in the rainforest belt of West Africa might be appropriate targets for elimination of these malaria vectors by the sterile insect technique.

Susceptibility test of female anopheles mosquitoes to ten insecticides for indoor residual spraying (IRS) baseline data collection in Northeastern Nigeria

“…This confirm earlier studies which separately indicates the knockdown effects of impregnated papers against Anopheles mosquitoes in Nigeria (Awolola et al, 2005;Oduola et al, 2010;Olayemi et al, 2011;Oyewole et al, 2011;Ibrahim et al, 2014). The knockdown of Anopheles mosquitoes exposed to insecticidal papers indicates the presence of KDR resistance mechanism (Kristan et al, 2003;Awolola et al, 2007;Ibrahim et al, 2014) operating in the populations of Anopheles mosquitoes in Misau.…”

“…It is established that prior exposure of mosquitoes to insecticides may induced selection pressure (Kerah-Hinzoumbé et al, 2008). Pyrethroids based aerosols and coils are used for control of mosquitoes and domestic pests and it might contribute to the development of resistance as reported elsewhere (Kristan et al, 2003). The farmers in the community also use cypermethrin, lambdacyhalothrin, deltamethrin, dichlovos and primiphos-methyl for agricultural crop protection.…”

Identification and validation of a gene causing cross-resistance between insecticide classes inAnopheles gambiaefrom Ghana

“…Although DDT resistance is widely known in Ghana (25,26), resistance of this magnitude has not been described previously. Such highlevel resistance could render DDT ineffective for IRS-based vector-control programs and understanding the mechanisms underlying resistance is important for resistance management.…”

High Level of DDT Resistance and Reduced Susceptibility to Deltamethrin in <i>Anopheles gambiae</i>, <i>Anopheles coluzzi</i>, and <i>Anopheles arabiensis</i> from Urban Communities in Oyo State, South-West Nigeria

“…Indeed, the gains of these control interventions have not been significant due to challenges of resistance to insecticides in the primary vector Anopheles. However, the malaria vectors in Nigeria have developed resistance to all the four classes of insecticides, much of which have occurred with DDT (Oduola et al, 2010; and pyrethroids (Awolola et al, 2003;Kristan et al, 2003;Adeogun et al, 2012;PMI, 2015). The phenomenon of physiological resistance to insecticides in the primary malaria vector, Anopheles gambiae, was first observed in Northern Nigeria by Elliot and Ramakrishna in 1956 to the insecticide dieldrin.…”