Insecticide resistance in the malaria vector Anopheles arabiensis (Diptera: Culicidae) and impact of hydropower dam on malaria in Ethiopia
(2012)
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- (en) The study on insecticide resistance illustrates that An. arabiensis populations from parts of Ethiopia are resistant to three-quarters of the insecticide families recommended for malaria vector control. Mosquitoes in our study area were resistance to organochlorine (DDT), pyrethroids (permethrin & deltamethrin) and organophosphates (malathion). In Ethiopia, DDT has been extensively used in IRS in alternation with malathion for over five decades. ITNs use started in 1997 and scaled up since 2005 with the aim of obtaining a high coverage towards an upgraded malaria control. Besides, in 2009 Ethiopia reported using pyrethroids (deltamethrin) for indoor residual spraying against malaria control (WHO, 2011a). The prolonged use of DDT and malathion, the high coverage of ITNs/LLINs and the recent use of pyrethroids for indoor residual spraying are likely to have enhanced the selection pressure for insecticide resistance in An. arabiensis from Ethiopia. The increasing trend in pyrethroids use for indoor residual spraying may not be consistent with the need to preserve the effectiveness of LLINs (WHO, 2011b). Trape et al. (2011) also reported that LLINs may result resistance to insecticides in mosquitoes and the increased pyrethroid resistance of An. gambiae caused the rebound of malaria morbidity in Senegal. In 2011, Ethiopia switched from pyrethroids (deltamethrin) to carbamates (bendiocarb) for IRS because of resistance reported to other classes of insecticides (Van den Berg et al., 2012). The carbamate class is now the only class of insecticides to which the principal malaria vector is susceptible. Unfortunately, evidence of resistance to carbamates (bendocarb) has also emerged in Afro-tropical malaria vectors (Hunt et al., 2011; WHO, 2011a; Hunt et al., 2010; Ranson et al., 2009; Vezenegho et al., 2009). The study at hand provides critical information on mechanisms conferring resistance to a major malaria vector in Ethiopia. We report here for the first time the existence of kdr mutation, i.e., the mechanism which confers cross-resistance to pyrethroids and DDT in An. Arabiensis populations from Ethiopia with the resistant allele being highly spread among the mosquito population. Our data (D. Yewhalaw et al., unpublished) also suggests the presence of other nonspecific detoxifying enzymes in this mosquito population making future malaria vector control in Ethiopia potentially difficult. The observed multiple-resistance coupled with the presence of kdr alleles with high frequency could severely affect malaria vector control programs in Ethiopia. This requires an urgent call for implementing a rational insecticide resistance management (IRM) strategy. The global plan for insecticide resistance management (GPIRM) in malaria vectors suggests that all vector control program should have a resistance management strategy to be implemented pre-emptively without waiting for the appearance of resistance or for evidence of control failure. In areas where genes have already spread, immediate implementation of new vector control strategies is required to preserve the effectiveness of vector control (WHO, 2011a). The options include using insecticides with different modes of action in rotation, as mixed formulations or in mosaic patterns (IRAC, 2011). Integrated vector control interventions should also be considered by the NMCP of Ethiopia as our data suggest the occurrence of multiple-resistance mechanisms. An integrated vector management offers a long-term approach to reduce selection pressure for insecticide resistance, to insure the judicious use of insecticides and to achieve stronger impact (Van den Berg et al., 2012; WHO, 2012). As discussed in chapter 5, hydropower dams provide the cheapest option to meet the increased demand for electricity. Adverse health effects due to environmental changes brought about with the construction of such dams have often been voiced out. The findings of our study indicate that children living close to the dam reservoir shore are at higher risk of malaria infection compared to those living farther away. To avert or mitigate the negative health effects of such water resource schemes, i.e., dams in Ethiopia, sound surveillance and monitoring policies including periodic surveys of potential vectors and periodic medical screening and treatment of cases, should be an integral part of the construction, operational and post-operational phases of dams.
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Gebre, D. Y. (2012). Insecticide resistance in the malaria vector Anopheles arabiensis (Diptera: Culicidae) and impact of hydropower dam on malaria in Ethiopia. https://hdl.handle.net/2078.5/156775