Insecticide Resistance and the Future of Malaria Control in Zambia

Abstract

BackgroundIn line with the Global trend to improve malaria control efforts a major campaign of insecticide treated net distribution was initiated in 1999 and indoor residual spraying with DDT or pyrethroids was reintroduced in 2000 in Zambia. In 2006, these efforts were strengthened by the President's Malaria Initiative. This manuscript reports on the monitoring and evaluation of these activities and the potential impact of emerging insecticide resistance on disease transmission.MethodsMosquitoes were captured daily through a series of 108 window exit traps located at 18 sentinel sites. Specimens were identified to species and analyzed for sporozoites. Adult Anopheles mosquitoes were collected resting indoors and larva collected in breeding sites were reared to F1 and F0 generations in the lab and tested for insecticide resistance following the standard WHO susceptibility assay protocol. Annual cross sectional household parasite surveys were carried out to monitor the impact of the control programme on prevalence of Plasmodium falciparum in children aged 1 to 14 years.ResultsA total of 619 Anopheles gambiae s.l. and 228 Anopheles funestus s.l. were captured from window exit traps throughout the period, of which 203 were An. gambiae malaria vectors and 14 An. funestus s.s.. In 2010 resistance to DDT and the pyrethroids deltamethrin, lambda-cyhalothrin and permethrin was detected in both An. gambiae s.s. and An. funestus s.s.. No sporozoites were detected in either species. Prevalence of P. falciparum in the sentinel sites remained below 10% throughout the study period.ConclusionBoth An. gambiae s.s. and An. funestus s.s. were controlled effectively with the ITN and IRS programme in Zambia, maintaining a reduced disease transmission and burden. However, the discovery of DDT and pyrethroid resistance in the country threatens the sustainability of the vector control programme.

Review of the malaria epidemiology and trends in Zambia

“…funestus predominate in the wetter northern part of the country, whilst An. arabiensis predominates in the drier southern region [18] . The presence of potential secondary vectors Anopheles rufipes, Anopheles squamosus and Anopheles coustani has been reported [18] .…”

“…arabiensis predominates in the drier southern region [18] . The presence of potential secondary vectors Anopheles rufipes, Anopheles squamosus and Anopheles coustani has been reported [18] . More recent studies have described the presence of Anopheles nili, Anopheles funestus-like, Anopheles rivulorum within the An.…”

“…More recent studies have described the presence of Anopheles nili, Anopheles funestus-like, Anopheles rivulorum within the An. funestus group [18] .…”

“…Vector susceptibility studies conducted in 2000 in three provinces (Copperbelt, Luapula and Lusaka provinces) showed 100% malaria vector susceptibility to dichlorodiphenyl-trichloroethane (DDT), deltamethrin, malathion and propoxur based on a WHO 1992 protocol [18] . However, 10 years after scaling-up vector control interventions, insecticide resistance to pyrethroids (deltamethrin, lambdacyhalothrin and permethrin) and DDT were detected in An.…”

“…funestus s.s. and other malaria vectors. More resistance has been reported from areas with IRS than those with LLINs [18] . Resistance mutation has been detected in areas showing cross resistance between pyrethroids and DDT [18] .…”