Global plan for insecticide resistance management in malaria vectors

Figure 14: kdr West and kdr East mutations are now present on both sides of AfricaFirst ‘kdr West’ detected inCôte d’IvoireFirst ‘kdr East’detectedin KenyaLatest ‘kdr West’ detected in Ethiopia,Sudan, Uganda and ZambiaLatest ‘kdr East’detected in Angolaand Central AfricanRepublicFrom reference (24), with adjustment from the WHO Global Malaria Programme; does not show latest reports such as kdr East in Angola.This map has been reproduced with the agreement of the original author. It reflects data and boundaries as of 2010 or before and should not be understood to reflect current data and boundaries.Metabolic resistance in An. funestus, which has already beenassociated with control failure in South Africa, appears to havespread over long distances across southern Africa; resistance topyrethroids and carbamates in the An. funestus population wasreported in Malawi, 1500 km north of its previously known locationin southern Mozambique. 1The rapid spread of resistance has been particularly alarming insome countries. For example, Benin has reached the point over thepast 2 years at which no areas have full susceptibility.Use of insecticides in both public health and agriculturecan contribute to the evolution of resistance in malariavectors.Use of insecticides in both agriculture and public health contributesto the evolution of resistance in some cases by placing selectionpressure on the vectors.The role of insecticides used for public health in selecting forinsecticide resistance in malaria vector has been clear since the1940s. In some cases, however, there has been good evidencethat agricultural use of pyrethroids, particularly on rice and cottoncrops, has been the main factor causing insecticide resistance inmalaria vector mosquitoes. For example, when cotton was a major1 As susceptibility tests mirrored the situation of An. funestus in Mozambique and South Africanpopulations but showed a markedly different resistant pattern to An. funestus populations in Uganda(which did not show cross-resistance with carbamates), it has been suggested that resistance inMalawi may have spread from South Africa during the past 10 years.crop in Salvador, seasonal fluctuations in resistance in malariavectors were seen to follow the timing of the cotton-spraying (27).On the other hand, there have also been cases where agriculturalinsecticides have been suspected of being the cause of resistancein malaria vectors, but where further investigation has shownthat the resistance was in fact due to anti-malaria spraying (e.g.malathion resistance in Sudan and Sri Lanka) (28).In Africa, pyrethroids have been in widespread use in agriculturefor decades, and in areas of intensive agriculture in West Africa,agricultural insecticides probably contributed to the initialappearance of knockdown resistance in malaria vectors. However,it is only in the last five to ten years, with massive scaling-upof malaria vector control, that we have seen these resistancegenes spreading throughout the region, and reaching very highfrequencies even in areas with little use of agricultural insecticides.Overall, therefore, the evidence suggests that in Africa, agriculturehas been an important prompt for the initial appearance ofresistance in some localities, but the massive scaling up of LLINsand IRS for malaria control has been the main factor driving therecent increases in the geographic distribution and frequency ofinsecticide resistance genes in malaria vectors.Continued use of the same insecticides in both public healthand agriculture will inevitably increase resistance. Effectivemanagement of insecticide resistance will therefore requireactivities in both public health and agriculture, and sharing of dataand information.39