Anopheles funestus resistant to pyrethroid insecticides in South Africa

Abstract

Northern Kwazulu/Natal (KZN) Province of South Africa borders on southern Mozambique, between Swaziland and the Indian Ocean. To control malaria vectors in KZN, houses were sprayed annually with residual DDT 2 g/ m2 until 1996 when the treatment changed to deltamethrin 20-25 mg/m2. At Ndumu (27 degrees 02'S, 32 degrees 19'E) the recorded malaria incidence increased more than six-fold between 1995 and 1999. Entomological surveys during late 1999 found mosquitoes of the Anopheles funestus group (Diptera: Culicidae) resting in sprayed houses in some sectors of Ndumu area. This very endophilic-vector of malaria had been eliminated from South Africa by DDT spraying in the 1950s, leaving the less endophilic An. arabiensis Patton as the only vector of known importance in KZN. Deltamethrin-sprayed houses at Ndumu were checked for insecticide efficacy by bioassay using susceptible An. arabiensis (laboratory-reared) that demonstrated 100% mortality. Members of the An. funestus group from Ndumu houses (29 males, 116 females) were identified by the rDNA PCR method and four species were found: 74 An. funestus Giles sensu stricto, 34 An. parensis Gillies, seven An. rivulorum Leeson and one An. leesoni Evans. Among An. funestus s.s. females, 5.4% (4/74) were positive for Plasmodium falciparum by ELISA and PCR tests. To test for pyrethroid resistance, mosquito adults were exposed to permethrin discriminating dosage and mortality scored 24h post-exposure: survival rates of wild-caught healthy males were 5/10 An. funestus, 1/9 An. rivulorum and 0/2 An. parensis; survival rates of laboratory-reared adult progeny from 19 An. funestus females averaged 14% (after 1h exposure to 1% permethrin 25:75cis:trans on papers in WHO test kits) and 27% (after 30 min in a bottle with 25 microg permethrin 40:60cis:trans). Anopheles funestus families showing >20% survival in these two resistance test procedures numbered 5/19 and 12/19, respectively. Progeny from 15 of the families were tested on 4% DDT impregnated papers and gave 100% mortality. Finding these proportions of pyrethroid-resistant An. funestus, associated with a malaria upsurge at Ndumu, has serious implications for malaria vector control operations in southern Africa.

Electrostatic coating enhances bioavailability of insecticides and breaks pyrethroid resistance in mosquitoes

“…Insecticide exposures were conducted on multiple strains of pyrethroid-resistant mosquitoes, including the major malaria vectors Anopheles arabiensis (27)(28)(29), Anopheles funestus (30,31), and Anopheles gambiae s.s. (32, 33) with well-defined mechanisms and levels of resistance, using standard WHO resistance assays with 0.05% deltamethrin papers (Fig. S1).…”

Impact of pyrethroid resistance on operational malaria control in Malawi

“…An early indicator of the selection of resistance in South Africa was the presence of An. funestus resting inside sprayed houses (16). Over the course of 2009-2010 in Malawi it became easier to find An.…”

Habitat Partitioning of Malaria Vectors in Nchelenge District, Zambia

“…1 Anopheles gambiae tends to oviposit in temporary breeding sites such as puddles and animal foot prints, which are abundant during the rainy season. [2][3][4] In contrast, An. funestus prefers more permanent breeding sites and populations tend to peak toward the end of the rainy season and into the first part of the dry season.…”