Insecticide Resistance Management in Malaria Vector Control
Insecticide resistance management is not a novel idea, it have been used in agriculture and to address some public health situations over the past century(WHO, 2011b). The renewed attention to IVM enables the integration of several tools to achieve a stronger impact (WHO, 2016a). It also encourages effective coordination of the control activities of all sectors that have an impact on vector-borne diseases, including health, water, solid waste and sewage disposal, housing and agriculture (WHO, 2004).
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Integration of several intervention tools, coupled with new prospects of effective malaria vaccines, has led to the new global initiative for the eradication of malaria.
World Health organization recommended four strategies to implement insecticide resistance management. First, rotations of two or more insecticides with different modes of action every year round. Second, combination of two or more insecticide based vector control interventions in houses (e.g. use of LLINs and IRS in a house from different classes of insecticides). Third, mosaic spraying which is the application of insecticides from two different classes in neighboring geographic areas. Fourth, mixtures of two or more compounds of different insecticide classes to make a single product or formulation, so that the mosquito is guaranteed to come into contact with the two classes at the same time. Mixtures are not currently available for malaria vector control, but will become the future of IRM once they are available.
Insecticide resistance monitoring and management (IRMM) strategic plan was developed by the Ethiopian FMoH in collaboration with stakeholders. For this purpose, 25 malaria sentinel sites were selected to generate entomological and epidemiological data used to implement the strategy by 2017/2018 at country level. Based on evidence obtained from the sentinel sites, the implemented strategy would include the rotation of insecticides and, in case of high malaria transmission areas, interventions using LINNs might be added.
Challenges of insecticide resistance management
The WHO has developed the GPIRM to help member states mitigate the development and spread of resistance (WHO., 2012). Though, countries continue to experience substantial limitations for effective implementation of insecticide resistance management. First, there is limited country level technical resource capacity to support entomological intervention monitoring and evaluation.
Second, gaps in availability of reliable routine monitoring data on vector bionomics, spatial distribution, insecticide resistance, underlying resistance mechanisms, including operational cost of insecticide resistance from epidemiologically representative sites, makes decision-making on resistance management difficult. Third, deficiency in local financial support and sustainability that is threatened by donor dependency.
Fourth, timely scale up has been constrained by scarcity in coordinating in-country entomological resources, coupled with scepticism surrounding scientific findings by some key national and international implementing and funding organizations. Fifth, skilled international technical assistance is a scarce resource that is overstretched. Sixth, there is limited data on malaria transmission and its correlation to epidemiological indices to guide the targeting of tools and monitoring of their impact. However, the potential of IVM provides a window of opportunity that could be exploited for enhanced IRM activities.
Future prospects for malaria control
For the success of the malaria elimination program set by WHO by 2030, innovation of vector control tools to counteract the emergence of drug and insecticide resistance is mandatory (WHO, 2016c). For this reason, ivermectin became a potential tool receiving attention to be used as a malaria control tool (Carlos et al., 2013, Chaccour et al., 2015, WHO, 2016b). The residual insecticides in insecticide-treated wall lining (ITWL) are durable and maintain control of insects significantly longer than IRS and may provide an effective alternative or additional vector control tool to ITNs and IRS (Munga et al., 2009).
Since the discovery of the mosquito larvicidal activity of Bti (serotype H-14) in 1977, several formulations of Bti are used against different mosquito species (Mittal, 2003). Moreover, there is a growing interest in the use of very safe IGRs that are emerging as promising vector control compounds for mosquito control with specific action and are relatively safe to non-target organisms (Mulla and Darwazeh, 1979, Morrison et al., 2008)
Transmission blocking vaccines (TBVs) are being assessed as a way to control the spread of malaria (Wu et al., 2015). Genetic engineering of mosquito’s transgenic technology acts as an alternative strategy to the conventional vector control methods(Catteruccia et al., 2000) .
10. Conclusion and recommendations
The development of resistance in the wild population of An. arabiensis to DDT substantially increased after 2006 following the large-scale distribution of LLINs. Even if utilization of DDT for IRS discontinued in 2009, the populations of An. arabiensis remains resistant to DDT in the country. This might be because of cross-resistance between organochlorine and pyrethroids. A large proportion of the An. arabiensis population developed resistance to pyrethirods class insecticides which are used to impregnate nets, and therefore the use of new generation bed nets might be important to enhance the killing effect of nets.
Though the amount of bendiocarb used for vector control is lower than propoxur, a large proportion of the wild An. arabiensis population developed resistance for bendiocarb compared to propoxur. Anopheles arabiensis was susceptible to primiphos–methyl, and hence it may be used for IRS instead of carbamates in the country to limit the resistance from reaching its tipping point. In addition, considering the non-insecticidal vector control method is important to regain vectors susceptibility for carbamate class, like screening of doors and windows and environmental managements.