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Pyrethroid resistance/susceptibility and differential urban/rural distribution of Anopheles arabiensis and An. gambiae s.s. malaria vectors in Nigeria and Ghana.
- Source :
- Medical & Veterinary Entomology; Sep2003, Vol. 17 Issue 3, p326, 7p
- Publication Year :
- 2003
-
Abstract
- 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. [ABSTRACT FROM AUTHOR]
- Subjects :
- MALARIA
ANOPHELES
PYRETHROIDS
Subjects
Details
- Language :
- English
- ISSN :
- 0269283X
- Volume :
- 17
- Issue :
- 3
- Database :
- Complementary Index
- Journal :
- Medical & Veterinary Entomology
- Publication Type :
- Academic Journal
- Accession number :
- 10691767
- Full Text :
- https://doi.org/10.1046/j.1365-2915.2003.00449.x